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rfc:rfc6063

Internet Engineering Task Force (IETF) A. Doherty Request for Comments: 6063 RSA, The Security Division of EMC Category: Standards Track M. Pei ISSN: 2070-1721 VeriSign, Inc.

                                                            S. Machani
                                                      Diversinet Corp.
                                                            M. Nystrom
                                                       Microsoft Corp.
                                                         December 2010
        Dynamic Symmetric Key Provisioning Protocol (DSKPP)

Abstract

 The Dynamic Symmetric Key Provisioning Protocol (DSKPP) is a client-
 server protocol for initialization (and configuration) of symmetric
 keys to locally and remotely accessible cryptographic modules.  The
 protocol can be run with or without private key capabilities in the
 cryptographic modules and with or without an established public key
 infrastructure.
 Two variations of the protocol support multiple usage scenarios.
 With the four-pass variant, keys are mutually generated by the
 provisioning server and cryptographic module; provisioned keys are
 not transferred over-the-wire or over-the-air.  The two-pass variant
 enables secure and efficient download and installation of pre-
 generated symmetric keys to a cryptographic module.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6063.

Doherty, et al. Standards Track [Page 1] RFC 6063 DSKPP December 2010

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
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 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Doherty, et al. Standards Track [Page 2] RFC 6063 DSKPP December 2010

Table of Contents

 1. Introduction ....................................................6
    1.1. Key Words ..................................................6
    1.2. Version Support ............................................6
    1.3. Namespace Identifiers ......................................7
         1.3.1. Defined Identifiers .................................7
         1.3.2. Identifiers Defined in Related Specifications .......7
         1.3.3. Referenced Identifiers ..............................8
 2. Terminology .....................................................8
    2.1. Definitions ................................................8
    2.2. Notation ..................................................10
    2.3. Abbreviations .............................................11
 3. DSKPP Overview .................................................11
    3.1. Protocol Entities .........................................12
    3.2. Basic DSKPP Exchange ......................................12
         3.2.1. User Authentication ................................12
         3.2.2. Protocol Initiated by the DSKPP Client .............14
         3.2.3. Protocol Triggered by the DSKPP Server .............16
         3.2.4. Variants ...........................................17
                3.2.4.1. Criteria for Using the Four-Pass Variant ..17
                3.2.4.2. Criteria for Using the Two-Pass Variant ...18
    3.3. Status Codes ..............................................18
    3.4. Basic Constructs ..........................................20
         3.4.1. User Authentication Data (AD) ......................20
                3.4.1.1. Authentication Code Format ................20
                3.4.1.2. User Authentication Data Calculation ......23
         3.4.2. The DSKPP One-Way Pseudorandom Function,
                DSKPP-PRF ..........................................24
         3.4.3. The DSKPP Message Hash Algorithm ...................24
 4. Four-Pass Protocol Usage .......................................25
    4.1. The Key Agreement Mechanism ...............................25
         4.1.1. Data Flow ..........................................25
         4.1.2. Computation ........................................27
    4.2. Message Flow ..............................................28
         4.2.1. KeyProvTrigger .....................................28
         4.2.2. KeyProvClientHello .................................29
         4.2.3. KeyProvServerHello .................................30
         4.2.4. KeyProvClientNonce .................................32
         4.2.5. KeyProvServerFinished ..............................34
 5. Two-Pass Protocol Usage ........................................35
    5.1. Key Protection Methods ....................................36
         5.1.1. Key Transport ......................................36
         5.1.2. Key Wrap ...........................................37
         5.1.3. Passphrase-Based Key Wrap ..........................37
    5.2. Message Flow ..............................................38
         5.2.1. KeyProvTrigger .....................................38
         5.2.2. KeyProvClientHello .................................39

Doherty, et al. Standards Track [Page 3] RFC 6063 DSKPP December 2010

         5.2.3. KeyProvServerFinished ..............................43
 6. Protocol Extensions ............................................44
    6.1. The ClientInfoType Extension ..............................45
    6.2. The ServerInfoType Extension ..............................45
 7. Protocol Bindings ..............................................45
    7.1. General Requirements ......................................45
    7.2. HTTP/1.1 Binding for DSKPP ................................46
         7.2.1. Identification of DSKPP Messages ...................46
         7.2.2. HTTP Headers .......................................46
         7.2.3. HTTP Operations ....................................47
         7.2.4. HTTP Status Codes ..................................47
         7.2.5. HTTP Authentication ................................47
         7.2.6. Initialization of DSKPP ............................47
         7.2.7. Example Messages ...................................48
 8. DSKPP XML Schema ...............................................49
    8.1. General Processing Requirements ...........................49
    8.2. Schema ....................................................49
 9. Conformance Requirements .......................................58
 10. Security Considerations .......................................59
    10.1. General ..................................................59
    10.2. Active Attacks ...........................................60
         10.2.1. Introduction ......................................60
         10.2.2. Message Modifications .............................60
         10.2.3. Message Deletion ..................................61
         10.2.4. Message Insertion .................................62
         10.2.5. Message Replay ....................................62
         10.2.6. Message Reordering ................................62
         10.2.7. Man in the Middle .................................63
    10.3. Passive Attacks ..........................................63
    10.4. Cryptographic Attacks ....................................63
    10.5. Attacks on the Interaction between DSKPP and User
          Authentication ...........................................64
    10.6. Miscellaneous Considerations .............................65
         10.6.1. Client Contributions to K_TOKEN Entropy ...........65
         10.6.2. Key Confirmation ..................................65
         10.6.3. Server Authentication .............................65
         10.6.4. User Authentication ...............................66
         10.6.5. Key Protection in Two-Pass DSKPP ..................66
         10.6.6. Algorithm Agility .................................67
 11. Internationalization Considerations ...........................68
 12. IANA Considerations ...........................................68
    12.1. URN Sub-Namespace Registration ...........................68
    12.2. XML Schema Registration ..................................69
    12.3. MIME Media Type Registration .............................69
    12.4. Status Code Registration .................................70
    12.5. DSKPP Version Registration ...............................70
    12.6. PRF Algorithm ID Sub-Registry ............................70
         12.6.1. DSKPP-PRF-AES .....................................71

Doherty, et al. Standards Track [Page 4] RFC 6063 DSKPP December 2010

         12.6.2. DSKPP-PRF-SHA256 ..................................71
    12.7. Key Container Registration ...............................72
 13. Intellectual Property Considerations ..........................73
 14. Contributors ..................................................73
 15. Acknowledgements ..............................................73
 16. References ....................................................74
    16.1. Normative References .....................................74
    16.2. Informative References ...................................76
 Appendix A.  Usage Scenarios ......................................78
   A.1.  Single Key Request ........................................78
   A.2.  Multiple Key Requests .....................................78
   A.3.  User Authentication .......................................78
   A.4.  Provisioning Time-Out Policy ............................78
   A.5.  Key Renewal ...............................................79
   A.6.  Pre-Loaded Key Replacement ..............................79
   A.7.  Pre-Shared Manufacturing Key ............................79
   A.8.  End-to-End Protection of Key Material ...................80
 Appendix B.  Examples .............................................80
   B.1.  Trigger Message ...........................................80
   B.2.  Four-Pass Protocol ......................................81
     B.2.1.  <KeyProvClientHello> without a Preceding Trigger ......81
     B.2.2.  <KeyProvClientHello> Assuming a Preceding Trigger .....82
     B.2.3.  <KeyProvServerHello> Without a Preceding Trigger ......83
     B.2.4.  <KeyProvServerHello> Assuming Key Renewal .............84
     B.2.5.  <KeyProvClientNonce> Using Default Encryption .........85
     B.2.6.  <KeyProvServerFinished> Using Default Encryption ......85
   B.3.  Two-Pass Protocol .......................................86
     B.3.1.  Example Using the Key Transport Method ................86
     B.3.2.  Example Using the Key Wrap Method .....................90
     B.3.3.  Example Using the Passphrase-Based Key Wrap Method ..94
 Appendix C.  Integration with PKCS #11 ............................98
   C.1.  The Four-Pass Variant ...................................98
   C.2.  The Two-Pass Variant ....................................98
 Appendix D.  Example of DSKPP-PRF Realizations .................101
   D.1.  Introduction .............................................101
   D.2.  DSKPP-PRF-AES ..........................................101
     D.2.1.  Identification .......................................101
     D.2.2.  Definition ...........................................101
     D.2.3.  Example ..............................................102
   D.3.  DSKPP-PRF-SHA256 .......................................103
     D.3.1.  Identification .......................................103
     D.3.2.  Definition ...........................................103
     D.3.3.  Example ..............................................104

Doherty, et al. Standards Track [Page 5] RFC 6063 DSKPP December 2010

1. Introduction

 Symmetric-key-based cryptographic systems (e.g., those providing
 authentication mechanisms such as one-time passwords and challenge-
 response) offer performance and operational advantages over public
 key schemes.  Such use requires a mechanism for the provisioning of
 symmetric keys providing equivalent functionality to mechanisms such
 as the Certificate Management Protocol (CMP) [RFC4210] and
 Certificate Management over CMS (CMC) [RFC5272] in a Public Key
 Infrastructure.
 Traditionally, cryptographic modules have been provisioned with keys
 during device manufacturing, and the keys have been imported to the
 cryptographic server using, e.g., a CD-ROM disc shipped with the
 devices.  Some vendors also have proprietary provisioning protocols,
 which often have not been publicly documented (the Cryptographic
 Token Key Initialization Protocol (CT-KIP) is one exception
 [RFC4758]).
 This document describes the Dynamic Symmetric Key Provisioning
 Protocol (DSKPP), a client-server protocol for provisioning symmetric
 keys between a cryptographic module (corresponding to DSKPP Client)
 and a key provisioning server (corresponding to DSKPP Server).
 DSKPP provides an open and interoperable mechanism for initializing
 and configuring symmetric keys to cryptographic modules that are
 accessible over the Internet.  The description is based on the
 information contained in [RFC4758], and contains specific
 enhancements, such as user authentication and support for the
 [RFC6030] format for transmission of keying material.
 DSKPP has two principal protocol variants.  The four-pass protocol
 variant permits a symmetric key to be established that includes
 randomness contributed by both the client and the server.  The two-
 pass protocol requires only one round trip instead of two and permits
 a server specified key to be established.

1.1. Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

1.2. Version Support

 There is a provision made in the syntax for an explicit version
 number.  Only version "1.0" is currently specified.

Doherty, et al. Standards Track [Page 6] RFC 6063 DSKPP December 2010

 The purpose for versioning the protocol is to provide a mechanism by
 which changes to required cryptographic algorithms (e.g., SHA-256)
 and attributes (e.g., key size) can be deployed without disrupting
 existing implementations; likewise, outdated implementations can be
 de-commissioned without disrupting operations involving newer
 protocol versions.
 The numbering scheme for DSKPP versions is "<major>.<minor>".  The
 major and minor numbers MUST be treated as separate integers and each
 number MAY be incremented higher than a single digit.  Thus, "DSKPP
 2.4" would be a lower version than "DSKPP 2.13", which in turn would
 be lower than "DSKPP 12.3".  Leading zeros (e.g., "DSKPP 6.01") MUST
 be ignored by recipients and MUST NOT be sent.
 The major version number should be incremented only if the data
 formats or security algorithms have changed so dramatically that an
 older version implementation would not be able to interoperate with a
 newer version (e.g., removing support for a previously mandatory-to-
 implement algorithm now found to be insecure).  The minor version
 number indicates new capabilities (e.g., introducing a new algorithm
 option) and MUST be ignored by an entity with a smaller minor version
 number but be used for informational purposes by the entity with the
 larger minor version number.

1.3. Namespace Identifiers

 This document uses Uniform Resource Identifiers (URIs) [RFC3986] to
 identify resources, algorithms, and semantics.

1.3.1. Defined Identifiers

 The XML namespace [XMLNS] URI for Version 1.0 of DSKPP is:
 "urn:ietf:params:xml:ns:keyprov:dskpp"
 References to qualified elements in the DSKPP schema defined herein
 use the prefix "dskpp", but any prefix is allowed.

1.3.2. Identifiers Defined in Related Specifications

 This document relies on qualified elements already defined in the
 Portable Symmetric Key Container [RFC6030] namespace, which is
 represented by the prefix "pskc" and declared as:
 xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"

Doherty, et al. Standards Track [Page 7] RFC 6063 DSKPP December 2010

1.3.3. Referenced Identifiers

 Finally, the DSKPP syntax presented in this document relies on
 algorithm identifiers defined in the XML Signature [XMLDSIG]
 namespace:
 xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
 References to algorithm identifiers in the XML Signature namespace
 are represented by the prefix "ds".

2. Terminology

2.1. Definitions

 Terms are defined below as they are used in this document.  The same
 terms may be defined differently in other documents.
 Authentication Code (AC):  User Authentication Code comprised of a
    string of hexadecimal characters known to the device and the
    server and containing at a minimum a client identifier and a
    password.  This ClientID/password combination is used only once
    and may have a time limit, and then discarded.
 Authentication Data (AD):  User Authentication Data that is derived
    from the Authentication Code (AC)
 Client ID:  An identifier that the DSKPP Server uses to locate the
    real username or account identifier on the server.  It can be a
    short random identifier that is unrelated to any real usernames.
 Cryptographic Module:  A component of an application, which enables
    symmetric key cryptographic functionality
 Device:  A physical piece of hardware, or a software framework, that
    hosts symmetric key cryptographic modules
 Device ID (DeviceID):  A unique identifier for the device that houses
    the cryptographic module, e.g., a mobile phone
 DSKPP Client:  Manages communication between the symmetric key
    cryptographic module and the DSKPP Server
 DSKPP Server:  The symmetric key provisioning server that
    participates in the DSKPP run

Doherty, et al. Standards Track [Page 8] RFC 6063 DSKPP December 2010

 DSKPP Server ID (ServerID):  The unique identifier of a DSKPP Server
 Key Agreement:  A key establishment protocol whereby two or more
    parties can agree on a key in such a way that both influence the
    outcome
 Key Confirmation:  The assurance of the rightful participants in a
    key-establishment protocol that the intended recipient of the
    shared key actually possesses the shared key
 Key Issuer:  An organization that issues symmetric keys to end-users
 Key Package (KP):  An object that encapsulates a symmetric key and
    its configuration data
 Key ID (KeyID):  A unique identifier for the symmetric key
 Key Protection Method (KPM):  The key transport method used during
    two-pass DSKPP
 Key Protection Method List (KPML):  The list of key protection
    methods supported by a cryptographic module
 Key Provisioning Server:  A lifecycle management system that provides
    a key issuer with the ability to provision keys to cryptographic
    modules hosted on end-users' devices
 Key Transport:  A key establishment procedure whereby the DSKPP
    Server selects and encrypts the keying material and then sends the
    material to the DSKPP Client [NIST-SP800-57]
 Key Transport Key:  The private key that resides on the cryptographic
    module.  This key is paired with the DSKPP Client's public key,
    which the DSKPP Server uses to encrypt keying material during key
    transport [NIST-SP800-57]
 Key Type:  The type of symmetric key cryptographic methods for which
    the key will be used (e.g., Open AUTHentication HMAC-Based One-
    Time Password (OATH HOTP) or RSA SecurID authentication, AES
    encryption, etc.)
 Key Wrapping:  A method of encrypting keys for key transport
    [NIST-SP800-57]

Doherty, et al. Standards Track [Page 9] RFC 6063 DSKPP December 2010

 Key Wrapping Key:  A symmetric key encrypting key used for key
    wrapping [NIST-SP800-57]
 Keying Material:  The data necessary (e.g., keys and key
    configuration data) necessary to establish and maintain
    cryptographic keying relationships [NIST-SP800-57]
 Manufacturer's Key:  A unique master key pre-issued to a hardware
    device, e.g., a smart card, during the manufacturing process.  If
    present, this key may be used by a cryptographic module to derive
    secret keys
 Protocol Run:  Complete execution of the DSKPP that involves one
    exchange (two-pass) or two exchanges (four-pass)
 Security Attribute List (SAL):  A payload that contains the DSKPP
    version, DSKPP variant (four- or two-pass), key package formats,
    key types, and cryptographic algorithms that the cryptographic
    module is capable of supporting

2.2. Notation

 ||                    String concatenation
 [x]                   Optional element x
 A ^ B                 Exclusive-OR operation on strings A and B
                       (where A and B are of equal length)
 <XMLElement>          A typographical convention used in the body of
                       the text
 DSKPP-PRF(k,s,dsLen)  A keyed pseudorandom function
 E(k,m)                Encryption of m with the key k
 K                     Key used to encrypt R_C (either K_SERVER or
                       K_SHARED), or in MAC or DSKPP_PRF computations
 K_AC                  Secret key that is derived from the
                       Authentication Code and used for user
                       authentication purposes
 K_MAC                 Secret key derived during a DSKPP exchange for
                       use with key confirmation
 K_MAC'                A second secret key used for server
                       authentication
 K_PROV                A provisioning master key from which two keys
                       are derived: K_TOKEN and K_MAC
 K_SERVER              Public key of the DSKPP Server; used for
                       encrypting R_C in the four-pass protocol
                       variant

Doherty, et al. Standards Track [Page 10] RFC 6063 DSKPP December 2010

 K_SHARED              Secret key that is pre-shared between the DSKPP
                       Client and the DSKPP Server; used for
                       encrypting R_C in the four-pass protocol
                       variant
 K_TOKEN               Secret key that is established in a
                       cryptographic module using DSKPP
 R                     Pseudorandom value chosen by the DSKPP Client
                       and used for MAC computations
 R_C                   Pseudorandom value chosen by the DSKPP Client
                       and used as input to the generation of K_TOKEN
 R_S                   Pseudorandom value chosen by the DSKPP Server
                       and used as input to the generation of K_TOKEN
 URL_S                 DSKPP Server address, as a URL

2.3. Abbreviations

 AC      Authentication Code
 AD      Authentication Data
 DSKPP   Dynamic Symmetric Key Provisioning Protocol
 HTTP    Hypertext Transfer Protocol
 KP      Key Package
 KPM     Key Protection Method
 KPML    Key Protection Method List
 MAC     Message Authentication Code
 PC      Personal Computer
 PDU     Protocol Data Unit
 PKCS    Public Key Cryptography Standards
 PRF     Pseudorandom Function
 PSKC    Portable Symmetric Key Container
 SAL     Security Attribute List (see Section 2.1)
 TLS     Transport Layer Security
 URL     Uniform Resource Locator
 USB     Universal Serial Bus
 XML     eXtensible Markup Language

3. DSKPP Overview

 The following sub-sections provide a high-level view of protocol
 internals and how they interact with external provisioning
 applications.  Usage scenarios are provided in Appendix A.

Doherty, et al. Standards Track [Page 11] RFC 6063 DSKPP December 2010

3.1. Protocol Entities

 A DSKPP provisioning transaction has three entities:
 Server:   The DSKPP provisioning server.
 Cryptographic Module:  The cryptographic module to which the
    symmetric keys are to be provisioned, e.g., an authentication
    token.
 Client:  The DSKPP Client that manages communication between the
    cryptographic module and the key provisioning server.
 The principal syntax is XML [XML] and it is layered on a transport
 mechanism such as HTTP [RFC2616] and HTTP Over TLS [RFC2818].  While
 it is highly desirable for the entire communication between the DSKPP
 Client and server to be protected by means of a transport providing
 confidentiality and integrity protection such as HTTP over Transport
 Layer Security (TLS), such protection is not sufficient to protect
 the exchange of the symmetric key data between the server and the
 cryptographic module and DSKPP is designed to permit implementations
 that satisfy this requirement.
 The server only communicates to the client.  As far as the server is
 concerned, the client and cryptographic module may be considered to
 be a single entity.
 From a client-side security perspective, however, the client and the
 cryptographic module are separate logical entities and may in some
 implementations be separate physical entities as well.
 It is assumed that a device will host an application layered above
 the cryptographic module, and this application will manage
 communication between the DSKPP Client and cryptographic module.  The
 manner in which the communicating application will transfer DSKPP
 elements to and from the cryptographic module is transparent to the
 DSKPP Server.  One method for this transfer is described in
 [CT-KIP-P11].

3.2. Basic DSKPP Exchange

3.2.1. User Authentication

 In a DSKPP message flow, the user has obtained a new hardware or
 software device embedded with a cryptographic module.  The goal of
 DSKPP is to provision the same symmetric key and related information
 to the cryptographic module and the key management server, and

Doherty, et al. Standards Track [Page 12] RFC 6063 DSKPP December 2010

 associate the key with the correct username (or other account
 identifier) on the server.  To do this, the DSKPP Server MUST
 authenticate the user to be sure he is authorized for the new key.
 User authentication occurs within the protocol itself *after* the
 DSKPP Client initiates the first message.  In this case, the DSKPP
 Client MUST have access to the DSKPP Server URL.
 Alternatively, a DSKPP web service or other form of web application
 can authenticate a user *before* the first message is exchanged.  In
 this case, the DSKPP Server MUST trigger the DSKPP Client to initiate
 the first message in the protocol transaction.

Doherty, et al. Standards Track [Page 13] RFC 6063 DSKPP December 2010

3.2.2. Protocol Initiated by the DSKPP Client

 In the following example, the DSKPP Client first initiates DSKPP, and
 then the user is authenticated using a Client ID and Authentication
 Code.
 Crypto       DSKPP                          DSKPP    Key Provisioning
 Module       Client                         Server        Server
  |             |                              |             |
  |             |                              |     +---------------+
  |             |                              |     |Server creates |
  |             |                              |     |and stores     |
  |             |                              |     |Client ID and  |
  |             |                              |     |Auth. Code and |
  |             |                              |     |delivers them  |
  |             |                              |     |to user out-of-|
  |             |                              |     |band.          |
  |             |                              |     +---------------+
  |             |                              |             |
  |  +----------------------+                  |             |
  |  |User enters Client ID,|                  |             |
  |  |Auth. Code, and URL   |                  |             |
  |  +----------------------+                  |             |
  |             |                              |             |
  |             |<-- 1. TLS handshake with --->|             |
  |             |        server auth.          |             |
  |             |                              |             |
  |             | 2. <KeyProvClientHello> ---->|     User -->|
  |             |                              |     Auth.   |
  |             |<-- [3. <KeyProvServerHello>] |             |
  |             |                              |             |
  |             | [4. <KeyProvClientNonce>] -->|             |
  |             |                              |             |
  |             |<- 5. <KeyProvServerFinished> |             |
  |             |                              |             |
  |             |                              |             |
  |<-- Key      |                              |      Key -->|
  |    Package  |                              |   Package   |
                    Figure 1: Basic DSKPP Exchange

Doherty, et al. Standards Track [Page 14] RFC 6063 DSKPP December 2010

 Before DSKPP begins:
 o  The Authentication Code is generated by the DSKPP Server, and
    delivered to the user via an out-of-band trustworthy channel
    (e.g., a paper slip delivered by IT department staff).
 o  The user typically enters the Client ID and Authentication Code
    manually, possibly on a device with only a numeric keypad.  Thus,
    they are often short numeric values (for example, 8 decimal
    digits).  However, the DSKPP Server is free to generate them in
    any way it wishes.
 o  The DSKPP Client needs the URL [RFC3986] of the DSKPP Server
    (which is not user specific or secret, and may be pre-configured
    somehow), and a set of trust anchors for verifying the server
    certificate.
 o  There must be an account for the user that has an identifier and
    long-term username (or other account identifier) to which the
    token will be associated.  The DSKPP Server will use the Client ID
    to find the corresponding Authentication Code for user
    authentication.
 In Step 1, the client establishes a TLS connection, authenticates the
 server (that is, validates the certificate, and compares the host
 name in the URL with the certificate) as described in Section 3.1 of
 [RFC2818].
 Next, the DSKPP Client and DSKPP Server exchange DSKPP messages
 (which are sent over HTTPS).  In these messages:
 o  The client and server negotiate which cryptographic algorithms
    they want to use, which algorithms are supported for protecting
    DSKPP messages, and other DSKPP details.
 o  The client sends the Client ID to the server, and proves that it
    knows the corresponding Authentication Code.
 o  The client and server agree on a secret key (token key or
    K_TOKEN); depending on the negotiated protocol variant, this is
    either a fresh key derived during the DSKPP run (called "four-pass
    variant", since it involves four DSKPP messages) or is generated
    by (or pre-exists on) the server and transported to the client
    (called "two-pass variant" in the rest of this document, since it
    involves two DSKPP messages).
 o  The server sends a "key package" to the client.  The package only
    includes the key itself in the case of the "two-pass variant";
    with either variant, the key package contains attributes that
    influence how the provisioned key will be later used by the
    cryptographic module and cryptographic server.  The exact contents
    depend on the cryptographic algorithm (e.g., for a one-time
    password algorithm that supports variable-length OTP values, the
    length of the OTP value would be one attribute in the key
    package).

Doherty, et al. Standards Track [Page 15] RFC 6063 DSKPP December 2010

 After the protocol run has been successfully completed, the
 cryptographic modules stores the contents of the key package.
 Likewise, the DSKPP provisioning server stores the contents of the
 key package with the cryptographic server, and associates these with
 the correct username.  The user can now use the their device to
 perform symmetric-key based operations.
 The exact division of work between the cryptographic module and the
 DSKPP Client -- and key Provisioning server and DSKPP Server -- are
 not specified in this document.  The figure above shows one possible
 case, but this is intended for illustrative purposes only.

3.2.3. Protocol Triggered by the DSKPP Server

 In the first message flow (previous section), the Client ID and
 Authentication Code were delivered to the client by some out-of-band
 means (such as paper sent to the user).
 Web           DSKPP                          DSKPP            Web
 Browser       Client                         Server          Server
   |              |                              |               |
   |<-------- HTTPS browsing + some kind of user auth. --------->|
   |              |                              |               |
   | some HTTP request ----------------------------------------->|
   |              |                              |
   |              |                              |<------------->|
   |              |                              |               |
   |<----------------------- HTTP response with <KeyProvTrigger> |
   |              |                              |               |
   | Trigger ---->|                              |               |
   |              |                              |               |
   |              |<-- 1. TLS handshake with --->|               |
   |              |        server auth.          |               |
   |              |                              |               |
   |              |     ... continues...         |               |
        Figure 2: DSKPP Exchange with Web-Based Authentication
 In the second message flow, the user first authenticates to a web
 server (for example, an IT department's "self-service" Intranet
 page), using an ordinary web browser and some existing credentials.
 The user then requests (by clicking a link or submitting a form)
 provisioning of a new key to the cryptographic module.  The web
 server will reply with a <KeyProvTrigger> message that contains the
 Client ID, Authentication Code, and URL of the DSKPP Server.  This
 information is also needed by the DSKPP Server; how the web server
 and DSKPP Server interact is beyond the scope of this document.

Doherty, et al. Standards Track [Page 16] RFC 6063 DSKPP December 2010

 The <KeyProvTrigger> message is sent in an HTTP response, and it is
 marked with MIME type "application/dskpp+xml".  It is assumed the web
 browser has been configured to recognize this MIME type; the browser
 will start the DSKPP Client and provide it with the <KeyProvTrigger>
 message.
 The DSKPP Client then contacts the DSKPP Server and uses the Client
 ID and Authentication Code (from the <KeyProvTrigger> message) the
 same way as in the first message flow.

3.2.4. Variants

 As noted in the previous section, once the protocol has started, the
 client and server MAY engage in either a two-pass or four-pass
 message exchange.  The four-pass and two-pass protocols are
 appropriate in different deployment scenarios.  The biggest
 differentiator between the two is that the two-pass protocol supports
 transport of an existing key to a cryptographic module, while the
 four-pass involves key generation on-the-fly via key agreement.  In
 either case, both protocol variants support algorithm agility through
 the negotiation of encryption mechanisms and key types at the
 beginning of each protocol run.

3.2.4.1. Criteria for Using the Four-Pass Variant

 The four-pass protocol is needed under one or more of the following
 conditions:
 o  Policy requires that both parties engaged in the protocol jointly
    contribute entropy to the key.  Enforcing this policy mitigates
    the risk of exposing a key during the provisioning process as the
    key is generated through mutual agreement without being
    transferred over-the-air or over-the-wire.  It also mitigates risk
    of exposure after the key is provisioned, as the key will not be
    vulnerable to a single point of attack in the system.
 o  A cryptographic module does not have private key capabilities.
 o  The cryptographic module is hosted by a device that neither was
    pre-issued with a manufacturer's key or other form of pre-shared
    key (as might be the case with a smart card or Subscriber Identity
    Module (SIM) card) nor has a keypad that can be used for entering
    a passphrase (such as present on a mobile phone).

Doherty, et al. Standards Track [Page 17] RFC 6063 DSKPP December 2010

3.2.4.2. Criteria for Using the Two-Pass Variant

 The two-pass protocol is needed under one or more of the following
 conditions:
 o  Pre-existing (i.e., legacy) keys must be provisioned via transport
    to the cryptographic module.
 o  The cryptographic module is hosted on a device that was pre-issued
    with a manufacturer's key (such as may exist on a smart card), or
    other form of pre-shared key (such as may exist on a SIM-card),
    and is capable of performing private key operations.
 o  The cryptographic module is hosted by a device that has a built-in
    keypad with which a user may enter a passphrase, useful for
    deriving a key wrapping key for distribution of keying material.

3.3. Status Codes

 Upon transmission or receipt of a message for which the Status
 attribute's value is not "Success" or "Continue", the default
 behavior, unless explicitly stated otherwise below, is that both the
 DSKPP Server and the DSKPP Client MUST immediately terminate the
 DSKPP run.  DSKPP Servers and DSKPP Clients MUST delete any secret
 values generated as a result of failed runs of DSKPP.  Session
 identifiers MAY be retained from successful or failed protocol runs
 for replay detection purposes, but such retained identifiers MUST NOT
 be reused for subsequent runs of the protocol.
 When possible, the DSKPP Client SHOULD present an appropriate error
 message to the user.
 These status codes are valid in all DSKPP Response messages unless
 explicitly stated otherwise:
 Continue:  The DSKPP Server is ready for a subsequent request from
    the DSKPP Client.  It cannot be sent in the server's final
    message.
 Success:  Successful completion of the DSKPP session.  It can only be
    sent in the server's final message.
 Abort:  The DSKPP Server rejected the DSKPP Client's request for
    unspecified reasons.
 AccessDenied:  The DSKPP Client is not authorized to contact this
    DSKPP Server.

Doherty, et al. Standards Track [Page 18] RFC 6063 DSKPP December 2010

 MalformedRequest:  The DSKPP Server failed to parse the DSKPP
    Client's request.
 UnknownRequest:  The DSKPP Client made a request that is unknown to
    the DSKPP Server.
 UnknownCriticalExtension:  A DSKPP extension marked as "Critical"
    could not be interpreted by the receiving party.
 UnsupportedVersion:  The DSKPP Client used a DSKPP version not
    supported by the DSKPP Server.  This error is only valid in the
    DSKPP Server's first response message.
 NoSupportedKeyTypes:  "NoSupportedKeyTypes" indicates that the DSKPP
    Client only suggested key types that are not supported by the
    DSKPP Server.  This error is only valid in the DSKPP Server's
    first response message.
 NoSupportedEncryptionAlgorithms:  The DSKPP Client only suggested
    encryption algorithms that are not supported by the DSKPP Server.
    This error is only valid in the DSKPP Server's first response
    message.
 NoSupportedMacAlgorithms:  The DSKPP Client only suggested MAC
    algorithms that are not supported by the DSKPP Server.  This error
    is only valid in the DSKPP Server's first response message.
 NoProtocolVariants:  The DSKPP Client did not suggest a required
    protocol variant (either two-pass or four-pass).  This error is
    only valid in the DSKPP Server's first response message.
 NoSupportedKeyPackages:  The DSKPP Client only suggested key package
    formats that are not supported by the DSKPP Server.  This error is
    only valid in the DSKPP Server's first response message.
 AuthenticationDataMissing:  The DSKPP Client didn't provide
    Authentication Data that the DSKPP Server required.
 AuthenticationDataInvalid:  The DSKPP Client supplied User
    Authentication Data that the DSKPP Server failed to validate.
 InitializationFailed:  The DSKPP Server could not generate a valid
    key given the provided data.  When this status code is received,
    the DSKPP Client SHOULD try to restart DSKPP, as it is possible
    that a new run will succeed.

Doherty, et al. Standards Track [Page 19] RFC 6063 DSKPP December 2010

 ProvisioningPeriodExpired:  The provisioning period set by the DSKPP
    Server has expired.  When the status code is received, the DSKPP
    Client SHOULD report the reason for key initialization failure to
    the user and the user MUST register with the DSKPP Server to
    initialize a new key.

3.4. Basic Constructs

 The following calculations are used in both DSKPP variants.

3.4.1. User Authentication Data (AD)

 User Authentication Data (AD) is derived from a Client ID and
 Authentication Code that the user enters before the first DSKPP
 message is sent.
 Note: The user will typically enter the Client ID and Authentication
 Code manually, possibly on a device with only numeric keypad.  Thus,
 they are often short numeric values (for example, 8 decimal digits).
 However, the DSKPP Server is free to generate them in any way it
 wishes.

3.4.1.1. Authentication Code Format

 AC is encoded in Type-Length-Value (TLV) format.  The format consists
 of a minimum of two TLVs and a variable number of additional TLVs,
 depending on implementation.
 The TLV fields are defined as follows:
 Type (1 character)        A hexadecimal character identifying the
                           type of information contained in the Value
                           field.
 Length (2 characters)     Two hexadecimal characters indicating the
                           length of the Value field to follow.  The
                           field value MAY be up to 255 characters.
                           The Length value 00 MAY be used to specify
                           custom tags without any field values.
 Value (variable length)   A variable-length string of hexadecimal
                           characters containing the instance-specific
                           information for this TLV.

Doherty, et al. Standards Track [Page 20] RFC 6063 DSKPP December 2010

 The following table summarizes the TLVs defined in this document.
 Optional TLVs are allowed for vendor-specific extensions with the
 constraint that the high bit MUST be set to indicate a vendor-
 specific type.  Other TLVs are left for later revisions of this
 protocol.
 +------+------------+-------------------------------------------+
 | Type | TLV Name   | Conformance | Example Usage               |
 +------+------------+-------------------------------------------+
 |  1   | Client ID  | Mandatory   | { "AC00000A" }              |
 +------+------------+-------------+-----------------------------+
 |  2   | Password   | Mandatory   | { "3582AF0C3E" }            |
 +------+------------+-------------+-----------------------------+
 |  3   | Checksum   | Optional    | { "4D5" }                   |
 +------+------------+-------------+-----------------------------+
 The Client ID is a mandatory TLV that represents the requester's
 identifier of maximum length 255.  The value is represented as a
 string of hexadecimal characters that identifies the key request.
 For example, suppose Client ID is set to "AC00000A", the Client ID
 TLV in the AC will be represented as "108AC00000A".
 The Password is a mandatory TLV the contains a one-time use shared
 secret known by the user and the Provisioning Server.  The Password
 value is unique and SHOULD be a random string to make AC more
 difficult to guess.  The string MUST contain hexadecimal characters
 only.  For example, suppose password is set to "3582AF0C3E", then the
 Password TLV would be "20A3582AF0C3E".
 The Checksum is an OPTIONAL TLV, which is generated by the issuing
 server and sent to the user as part of the AC.  If the TLV is
 provided, the checksum value MUST be computed using the CRC16
 algorithm [ISO3309].  When the user enters the AC, the typed AC
 string of characters is verified with the checksum to ensure it is
 correctly entered by the user.  For example, suppose the AC with
 combined Client ID tag and Password tag is set to
 "108AC00000A20A3582AF0C3E", then the CRC16 calculation would generate
 a checksum of 0x356, resulting in a Checksum TLV of "334D5".  The
 complete AC string in this example would be
 "108AC00000A20A3582AF0C3E3034D5".
 Although this specification recommends using hexadecimal characters
 only for the AC at the application's user interface layer and making
 the TLV triples non-transparent to the user as described in the
 example above; implementations MAY additionally choose to use other
 printable Unicode characters [UNICODE] at the application's user
 interface layer in order to meet specific local, context or usability
 requirements.  When non-hexadecimal characters are desired at the

Doherty, et al. Standards Track [Page 21] RFC 6063 DSKPP December 2010

 user interface layer such as when other printable US-ASCII characters
 or international characters are used, SASLprep [RFC4013] MUST be used
 to normalize user input before converting it to a string of
 hexadecimal characters.  For example, if a given application allows
 the use of any printable US-ASCII characters and extended ASCII
 characters for Client ID and Password fields, and the Client ID is
 set to "myclient!D" and the associated Password is set to
 "mYpas&#rD", the user enters through the keyboard or other means a
 Client ID of "myclient!D" and a Password of "mYpas&#rD" in separate
 form fields or as instructed by the provider.  The application's
 layer processing user input MUST then convert the values entered by
 the user to the following string for use in the protocol:
 "1146D79636C69656E7421442126D5970617326237244" (note that in this
 example the Checksum TLV is not added).
 The example is explained further below in detail:
 Assume that the raw Client ID value or the value entered by the use
 is: myclient!ID
 The Client ID value as characters names is:
    U+006D LATIN SMALL LETTER M character
    U+0079 LATIN SMALL LETTER Y character
    U+0063 LATIN SMALL LETTER C character
    U+006C LATIN SMALL LETTER L character
    U+0069 LATIN SMALL LETTER I character
    U+0065 LATIN SMALL LETTER E character
    U+006E LATIN SMALL LETTER N character
    U+0074 LATIN SMALL LETTER T character
    U+0021 EXCLAMATION MARK character (!)
    U+0044 LATIN CAPITAL LETTER D character
 The UTF-8 conversion of the Client ID value is: 6D 79 63 6C 69 65 6E
 74 21 44
 The length of the Client ID value in hexadecimal characters is: 14
 The TLV presentation of the Client ID field is:
 1146D79636C69656E742144
 The raw Password value or the value entered by the user is: mYpas&#rD
 The Password value as character names is:
    U+006D LATIN SMALL LETTER M character
    U+0059 LATIN LARGE LETTER Y character
    U+0070 LATIN SMALL LETTER P character

Doherty, et al. Standards Track [Page 22] RFC 6063 DSKPP December 2010

    U+0061 LATIN SMALL LETTER A character
    U+0073 LATIN SMALL LETTER S character
    U+0026 AMPERSAND character (&)
    U+0023 POUND SIGN character (#)
    U+0072 LATIN SMALL LETTER R character
    U+0044 LATIN LARGE LETTER D character
 The UTF-8 conversion of the password value is: 6D 59 70 61 73 26 23
 72 44
 The length of the password value in hexadecimal characters is: 12
 The TLV presentation of the password field is: 2126D5970617326237244
 The combined Client ID and password fields value or the AC value is:
 1146D79636C69656E7421442126D5970617326237244

3.4.1.2. User Authentication Data Calculation

 The Authentication Data consists of a Client ID (extracted from the
 AC) and a value, which is derived from AC as follows (refer to
 Section 3.4.2 for a description of DSKPP-PRF in general and
 Appendix D for a description of DSKPP-PRF-AES):
 MAC = DSKPP-PRF(K_AC, AC->ClientID||URL_S||R_C||[R_S], 16)
 In four-pass DSKPP, the cryptographic module uses R_C, R_S, and URL_S
 to calculate the MAC, where URL_S is the URL the DSKPP Client uses
 when contacting the DSKPP Server.  In two-pass DSKPP, the
 cryptographic module does not have access to R_S, therefore only R_C
 is used in combination with URL_S to produce the MAC.  In either
 case, K_AC MUST be derived from AC->password as follows [PKCS-5]:
 K_AC = PBKDF2(AC->password, R_C || K, iter_count, 16)
 One of the following values for K MUST be used:
 a.  In four-pass:
     *  The public key of the DSKPP Server (K_SERVER), or (in the pre-
        shared key variant) the pre-shared key between the client and
        the server (K_SHARED).
 b.  In two-pass:
     *  The public key of the DSKPP Client, or the public key of the
        device when a device certificate is available.
     *  The pre-shared key between the client and the server
        (K_SHARED).
     *  A passphrase-derived key.

Doherty, et al. Standards Track [Page 23] RFC 6063 DSKPP December 2010

 The iteration count, iter_count, MUST be set to at least 100,000
 except in the last two two-pass cases (where K is set to K_SHARED or
 a passphrase-derived key), in which case iter_count MUST be set to 1.

3.4.2. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF

 Regardless of the protocol variant employed, there is a requirement
 for a cryptographic primitive that provides a deterministic
 transformation of a secret key k and a varying length octet string s
 to a bit string of specified length dsLen.
 This primitive must meet the same requirements as for a keyed hash
 function: it MUST take an arbitrary length input and generate an
 output that is one way and collision free (for a definition of these
 terms, see, e.g., [FAQ]).  Further, its output MUST be unpredictable
 even if other outputs for the same key are known.
 From the point of view of this specification, DSKPP-PRF is a "black-
 box" function that, given the inputs, generates a pseudorandom value
 and MAY be realized by any appropriate and competent cryptographic
 technique.  Appendix D contains two example realizations of DSKPP-
 PRF.
 DSKPP-PRF(k, s, dsLen)
 Input:
 k     secret key in octet string format
 s     octet string of varying length consisting of variable data
       distinguishing the particular string being derived
 dsLen desired length of the output
 Output:
 DS    pseudorandom string, dsLen octets long
 For the purposes of this document, the secret key k MUST be at least
 16 octets long.

3.4.3. The DSKPP Message Hash Algorithm

 When sending its last message in a protocol run, the DSKPP Server
 generates a MAC that is used by the client for key confirmation.
 Computation of the MAC MUST include a hash of all DSKPP messages sent
 by the client and server during the transaction.  To compute a
 message hash for the MAC given a sequence of DSKPP messages msg_1,
 ..., msg_n, the following operations MUST be carried out:

Doherty, et al. Standards Track [Page 24] RFC 6063 DSKPP December 2010

 a.  The sequence of messages contains all DSKPP Request and Response
     messages up to but not including this message.
 b.  Re-transmitted messages are removed from the sequence of
     messages.
     Note: The resulting sequence of messages MUST be an alternating
     sequence of DSKPP Request and DSKPP Response messages
 c.  The contents of each message is concatenated together.
 d.  The resultant string is hashed using SHA-256 in accordance with
     [FIPS180-SHA].

4. Four-Pass Protocol Usage

 This section describes the methods and message flow that comprise the
 four-pass protocol variant.  Four-pass DSKPP depends on a client-
 server key agreement mechanism.

4.1. The Key Agreement Mechanism

 With four-pass DSKPP, the symmetric key that is the target of
 provisioning, is generated on-the-fly without being transferred
 between the DSKPP Client and DSKPP Server.  The data flow and
 computation are described below.

4.1.1. Data Flow

 A sample data flow showing key generation during the four-pass
 protocol is shown in Figure 3.

Doherty, et al. Standards Track [Page 25] RFC 6063 DSKPP December 2010

 +----------------------+                  +----------------------+
 |    +------------+    |                  |                      |
 |    | Server key |    |                  |                      |
 | +<-|  Public    |------>------------->-------------+---------+ |
 | |  |  Private   |    |                  |          |         | |
 | |  +------------+    |                  |          |         | |
 | |        |           |                  |          |         | |
 | V        V           |                  |          V         V |
 | |   +---------+      |                  |        +---------+ | |
 | |   | Decrypt |<-------<-------------<-----------| Encrypt | | |
 | |   +---------+      |                  |        +---------+ | |
 | |      |  +--------+ |                  |            ^       | |
 | |      |  | Server | |                  |            |       | |
 | |      |  | Random |--->------------->------+  +----------+  | |
 | |      |  +--------+ |                  |   |  | Client   |  | |
 | |      |      |      |                  |   |  | Random   |  | |
 | |      |      |      |                  |   |  +----------+  | |
 | |      |      |      |                  |   |        |       | |
 | |      V      V      |                  |   V        V       | |
 | |   +------------+   |                  | +------------+     | |
 | +-->|  DSKPP PRF |   |                  | |  DSKPP PRF |<----+ |
 |     +------------+   |                  | +------------+       |
 |           |          |                  |       |              |
 |           V          |                  |       V              |
 |       +-------+      |                  |   +-------+          |
 |       |  Key  |      |                  |   |  Key  |          |
 |       +-------+      |                  |   +-------+          |
 |       +-------+      |                  |   +-------+          |
 |       |Key Id |-------->------------->------|Key Id |          |
 |       +-------+      |                  |   +-------+          |
 +----------------------+                  +----------------------+
       DSKPP Server                              DSKPP Client
  Figure 3: Principal Data Flow for DSKPP Key Generation Using Public
                              Server Key
 The inclusion of the two random nonces (R_S and R_C) in the key
 generation provides assurance to both sides (the cryptographic module
 and the DSKPP Server) that they have contributed to the key's
 randomness and that the key is unique.  The inclusion of the
 encryption key (K) ensures that no man in the middle may be present,
 or else the cryptographic module will end up with a key different
 from the one stored by the legitimate DSKPP Server.
 Conceptually, although R_C is one pseudorandom string, it may be
 viewed as consisting of two components, R_C1 and R_C2, where R_C1 is
 generated during the protocol run, and R_C2 can be pre-generated and

Doherty, et al. Standards Track [Page 26] RFC 6063 DSKPP December 2010

 loaded on the cryptographic module before the device is issued to the
 user.  In that case, the latter string, R_C2, SHOULD be unique for
 each cryptographic module.
 A man in the middle (in the form of corrupt client software or a
 mistakenly contacted server) may present his own public key to the
 cryptographic module.  This will enable the attacker to learn the
 client's version of K_TOKEN.  However, the attacker is not able to
 persuade the legitimate server to derive the same value for K_TOKEN,
 since K_TOKEN is a function of the public key involved, and the
 attacker's public key must be different than the correct server's (or
 else the attacker would not be able to decrypt the information
 received from the client).  Therefore, once the attacker is no longer
 "in the middle," the client and server will detect that they are "out
 of sync" when they try to use their keys.  In the case of encrypting
 R_C with K_SERVER, it is therefore important to verify that K_SERVER
 really is the legitimate server's key.  One way to do this is to
 independently validate a newly generated K_TOKEN against some
 validation service at the server (e.g., using a connection
 independent from the one used for the key generation).

4.1.2. Computation

 In four-pass DSKPP, the client and server both generate K_TOKEN and
 K_MAC by deriving them from a provisioning key (K_PROV) using the
 DSKPP-PRF (refer to Section 3.4.2) as follows:
 K_PROV = DSKPP-PRF(k,s,dsLen), where
     k = R_C (i.e., the secret random value chosen by the DSKPP
     Client)
     s = "Key generation" || K || R_S (where K is the key used to
     encrypt R_C and R_S is the random value chosen by the DSKPP
     Server)
     dsLen = (desired length of K_PROV whose first half constitutes
     K_MAC and second half constitutes K_TOKEN)
 Then, K_TOKEN and K_MAC are derived from K_PROV, where
     K_PROV = K_MAC || K_TOKEN
 When computing K_PROV, the derived keys, K_MAC and K_TOKEN, MAY be
 subject to an algorithm-dependent transform before being adopted as a
 key of the selected type.  One example of this is the need for parity
 in DES keys.
 Note that this computation pertains to four-pass DSKPP only.

Doherty, et al. Standards Track [Page 27] RFC 6063 DSKPP December 2010

4.2. Message Flow

 The four-pass protocol flow consists of two message exchanges:
 1:  Pass 1 = <KeyProvClientHello>, Pass 2 = <KeyProvServerHello>
 2:  Pass 3 = <KeyProvClientNonce>, Pass 4 = <KeyProvServerFinished>
 The first pair of messages negotiate cryptographic algorithms and
 exchange nonces.  The second pair of messages establishes a symmetric
 key using mutually authenticated key agreement.
 The purpose and content of each message are described below.  XML
 format and examples are in Section 8 and Appendix B.

4.2.1. KeyProvTrigger

         DSKPP Client                         DSKPP Server
         ------------                         ------------
                              [<---]       AD, [DeviceID],
                                          [KeyID], [URL_S]
 When this message is sent:
    The "trigger" message is optional.  The DSKPP Server sends this
    message after the following out-of-band steps are performed:
    1.  A user directed their browser to a key provisioning web
        application and signs in (i.e., authenticates).
    2.  The user requests a key.
    3.  The web application processes the request and returns an
        Authentication Code to the user, e.g., in response to an
        enrollment request via a secure web session.
    4.  The web application retrieves the Authentication Code from the
        user (possibly by asking the user to enter it using a web
        form, or alternatively by the user selecting a URL in which
        the Authentication Code is embedded).
    5.  The web application derives Authentication Data (AD) from the
        Authentication Code as described in Section 3.4.1.
    6.  The web application passes AD, and possibly a DeviceID
        (identifies a particular device to which the key is to be
        provisioned) and/or KeyID (identifies a key that will be
        replaced) to the DSKPP Server.
 Purpose of this message:
    To start a DSKPP session: The DSKPP Server uses this message to
    trigger a client-side application to send the first DSKPP message.
    To provide a way for the key provisioning system to get the DSKPP
    Server URL to the DSKPP Client.

Doherty, et al. Standards Track [Page 28] RFC 6063 DSKPP December 2010

    So the key provisioning system can point the DSKPP Client to a
    particular cryptographic module that was pre-configured in the
    DSKPP provisioning server.
    In the case of key renewal, to identify the key to be replaced.
 What is contained in this message:
    AD MUST be provided to allow the DSKPP Server to authenticate the
    user before completing the protocol run.
    A DeviceID MAY be included to allow a key provisioning application
    to bind the provisioned key to a specific device.
    A KeyID MAY be included to allow the key provisioning application
    to identify a key to be replaced, e.g., in the case of key
    renewal.
    The Server URL MAY be included to allow the key provisioning
    application to inform the DSKPP Client of which server to contact.

4.2.2. KeyProvClientHello

         DSKPP Client                         DSKPP Server
         ------------                         ------------
         SAL, [AD],
         [DeviceID], [KeyID]     --->
 When this message is sent:
    When a DSKPP Client first connects to a DSKPP Server, it is
    required to send the <KeyProvClientHello> as its first message.
    The client can also send a <KeyProvClientHello> in response to a
    <KeyProvTrigger>.
 What is contained in this message:
    The Security Attribute List (SAL) included with
    <KeyProvClientHello> contains the combinations of DSKPP versions,
    variants, key package formats, key types, and cryptographic
    algorithms that the DSKPP Client supports in order of the client's
    preference (favorite choice first).
    If <KeyProvClientHello> was preceded by a <KeyProvTrigger>, then
    this message MUST also include the Authentication Data (AD),
    DeviceID, and/or KeyID that was provided with the trigger.
    If <KeyProvClientHello> was not preceded by a <KeyProvTrigger>,
    then this message MAY contain a DeviceID that was pre-shared with
    the DSKPP Server, and a key ID associated with a key previously
    provisioned by the DSKPP provisioning server.

Doherty, et al. Standards Track [Page 29] RFC 6063 DSKPP December 2010

 Application note:
    If this message is preceded by trigger message <KeyProvTrigger>,
    then the application will already have AD available (see
    Section 4.2.1).  However, if this message was not preceded by
    <KeyProvTrigger>, then the application MUST retrieve the User
    Authentication Code, possibly by prompting the user to manually
    enter their Authentication Code, e.g., on a device with only a
    numeric keypad.
    The application MUST also derive Authentication Data (AD) from the
    Authentication Code, as described in Section 3.4.1, and save it
    for use in its next message, <KeyProvClientNonce>.
 How the DSKPP Server uses this message:
    The DSKPP Server will look for an acceptable combination of DSKPP
    version, variant (in this case, four-pass), key package format,
    key type, and cryptographic algorithms.  If the DSKPP Client's SAL
    does not match the capabilities of the DSKPP Server, or does not
    comply with key provisioning policy, then the DSKPP Server will
    set the Status attribute to something other than "Continue".
    Otherwise, the Status attribute will be set to "Continue".
    If included in <KeyProvClientHello>, the DSKPP Server will
    validate the Authentication Data (AD), DeviceID, and KeyID.  The
    DSKPP Server MUST NOT accept the DeviceID unless the server sent
    the DeviceID in a preceding trigger message.  Note that it is also
    legitimate for a DSKPP Client to initiate the DSKPP run without
    having received a <KeyProvTrigger> message from a server, but in
    this case any provided DeviceID MUST NOT be accepted by the DSKPP
    Server unless the server has access to a unique key for the
    identified device and that key will be used in the protocol.

4.2.3. KeyProvServerHello

         DSKPP Client                         DSKPP Server
         ------------                         ------------
                               <---    SAL, R_S, [K], [MAC]
 When this message is sent:
    The DSKPP Server will send this message in response to a
    <KeyProvClientHello> message after it looks for an acceptable
    combination of DSKPP version, variant (in this case, four-pass),
    key package format, key type, and set of cryptographic algorithms.
    If it could not find an acceptable combination, then it will still
    send the message, but with a failure status.

Doherty, et al. Standards Track [Page 30] RFC 6063 DSKPP December 2010

 Purpose of this message:
    With this message, the context for the protocol run is set.
    Furthermore, the DSKPP Server uses this message to transmit a
    random nonce, which is required for each side to agree upon the
    same symmetric key (K_TOKEN).
 What is contained in this message:
    A status attribute equivalent to the server's return code to
    <KeyProvClientHello>.  If the server found an acceptable set of
    attributes from the client's SAL, then it sets status to Continue
    and returns an SAL (selected from the SAL that it received in
    <KeyProvClientHello>).  The Server's SAL specifies the DSKPP
    version and variant (in this case, four-pass), key type,
    cryptographic algorithms, and key package format that the DSKPP
    Client MUST use for the remainder of the protocol run.
    A random nonce (R_S) for use in generating a symmetric key through
    key agreement; the length of R_S may depend on the selected key
    type.
    A key (K) for the DSKPP Client to use for encrypting the client
    nonce included with <KeyProvClientNonce>.  K represents the
    server's public key (K_SERVER) or a pre-shared secret key
    (K_SHARED).
    A MAC MUST be present if a key is being renewed so that the DSKPP
    Client can confirm that the replacement key came from a trusted
    server.  This MAC MUST be computed using DSKPP-PRF (see
    Section 3.4.2), where the input parameter k MUST be set to the
    existing MAC key K_MAC' (i.e., the value of the MAC key that
    existed before this protocol run; the implementation MAY specify
    K_MAC' to be the value of the K_TOKEN that is being replaced), and
    input parameter dsLen MUST be set to the length of R_S.
 How the DSKPP Client uses this message:
    When the Status attribute is not set to "Continue", this indicates
    failure and the DSKPP Client MUST abort the protocol.
    If successful execution of the protocol will result in the
    replacement of an existing key with a newly generated one, the
    DSKPP Client MUST verify the MAC provided in <KeyProvServerHello>.
    The DSKPP Client MUST terminate the DSKPP session if the MAC does
    not verify, and MUST delete any nonces, keys, and/or secrets
    associated with the failed run.

Doherty, et al. Standards Track [Page 31] RFC 6063 DSKPP December 2010

    If the Status attribute is set to "Continue", the cryptographic
    module generates a random nonce (R_C) using the cryptographic
    algorithm specified in the SAL.  The length of the nonce R_C will
    depend on the selected key type.
    Encrypt R_C using K and the encryption algorithm included in the
    SAL.
 The method the DSKPP Client MUST use to encrypt R_C:
    If K is equivalent to K_SERVER (i.e., the public key of the DSKPP
    Server), then an RSA encryption scheme from PKCS #1 [PKCS-1] MAY
    be used.  If K is equivalent to K_SERVER, then the cryptographic
    module SHOULD verify the server's certificate before using it to
    encrypt R_C as described in [RFC2818], Section 3.1, and [RFC5280].
    If K is equivalent to K_SHARED, the DSKPP Client MAY use the
    DSKPP-PRF to avoid dependence on other algorithms.  In this case,
    the client uses K_SHARED as input parameter k (K_SHARED SHOULD be
    used solely for this purpose) as follows:
    dsLen = len(R_C), where "len" is the length of R_C
    DS = DSKPP-PRF(K_SHARED, "Encryption" || R_S, dsLen)
    This will produce a pseudorandom string DS of length equal to R_C.
    Encryption of R_C MAY then be achieved by XOR-ing DS with R_C:
    E(DS, R_C) = DS ^ R_C
    The DSKPP Server will then perform the reverse operation to
    extract R_C from E(DS, R_C).

4.2.4. KeyProvClientNonce

         DSKPP Client                         DSKPP Server
         ------------                         ------------
         E(K,R_C), AD          --->
 When this message is sent:
    The DSKPP Client will send this message immediately following a
    <KeyProvServerHello> message whose status was set to "Continue".
 Purpose of this message:
    With this message the DSKPP Client transmits User Authentication
    Data (AD) and a random nonce encrypted with the DSKPP Server's key
    (K).  The client's random nonce is required for each side to agree
    upon the same symmetric key (K_TOKEN).

Doherty, et al. Standards Track [Page 32] RFC 6063 DSKPP December 2010

 What is contained in this message:
    Authentication Data (AD) that was derived from an Authentication
    Code entered by the user before <KeyProvClientHello> was sent
    (refer to Section 3.2).
    The DSKPP Client's random nonce (R_C), which was encrypted as
    described in Section 4.2.3.
 How the DSKPP Server uses this message:
    The DSKPP Server MUST use AD to authenticate the user.  If
    authentication fails, then the DSKPP Server MUST set the return
    code to a failure status.
    If user authentication passes, the DSKPP Server decrypts R_C using
    its key (K).  The decryption method is based on whether K that was
    transmitted to the client in <KeyProvServerHello> was equal to the
    server's public key (K_SERVER) or a pre-shared key (K_SHARED)
    (refer to Section 4.2.3 for a description of how the DSKPP Client
    encrypts R_C).
    After extracting R_C, the DSKPP Server computes K_TOKEN using a
    combination of the two random nonces R_S and R_C and its
    encryption key, K, as described in Section 4.1.2.  The particular
    realization of DSKPP-PRF (e.g., those defined in Appendix D)
    depends on the MAC algorithm contained in the <KeyProvServerHello>
    message.  The DSKPP Server then generates a key package that
    contains key usage attributes such as expiry date and length.  The
    key package MUST NOT include K_TOKEN since in the four-pass
    variant K_TOKEN is never transmitted between the DSKPP Server and
    Client.  The server stores K_TOKEN and the key package with the
    user's account on the cryptographic server.
    Finally, the server generates a key confirmation MAC that the
    client will use to avoid a false "Commit" message that would cause
    the cryptographic module to end up in state in which the server
    does not recognize the stored key.
 The MAC used for key confirmation MUST be calculated as follows:
    msg_hash = SHA-256(msg_1, ..., msg_n)
    dsLen = len(msg_hash)
    MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || msg_hash, dsLen)

Doherty, et al. Standards Track [Page 33] RFC 6063 DSKPP December 2010

    where
    MAC The DSKPP Pseudorandom Function defined in Section 3.4.2 is
        used to compute the MAC.  The particular realization of DSKPP-
        PRF (e.g., those defined in Appendix D) depends on the MAC
        algorithm contained in the <KeyProvServerHello> message.  The
        MAC MUST be computed using the existing MAC key (K_MAC), and a
        string that is formed by concatenating the (ASCII) string "MAC
        1 computation" and a msg_hash.
    K_MAC  The key derived from K_PROV, as described in Section 4.1.2.
    msg_hash  The message hash (defined in Section 3.4.3) of messages
              msg_1, ..., msg_n.

4.2.5. KeyProvServerFinished

         DSKPP Client                         DSKPP Server
         ------------                         ------------
                                <---               KP, MAC
 When this message is sent:
    The DSKPP Server will send this message after authenticating the
    user and, if authentication passed, generating K_TOKEN and a key
    package, and associating them with the user's account on the
    cryptographic server.
 Purpose of this message:
    With this message, the DSKPP Server confirms generation of the key
    (K_TOKEN) and transmits the associated identifier and application-
    specific attributes, but not the key itself, in a key package to
    the client for protocol completion.
 What is contained in this message:
    A status attribute equivalent to the server's return code to
    <KeyProvClientNonce>.  If user authentication passed, and the
    server successfully computed K_TOKEN, generated a key package, and
    associated them with the user's account on the cryptographic
    server, then it sets the Status attribute to "Success".
    If the Status attribute is set to "Success", then this message
    acts as a "Commit" message, instructing the cryptographic module
    to store the generated key (K_TOKEN) and associate the given key
    identifier with this key.  As such, a key package (KP) MUST be
    included in this message, which holds an identifier for the
    generated key (but not the key itself) and additional
    configuration, e.g., the identity of the DSKPP Server, key usage
    attributes, etc.  The default symmetric key package format MUST be

Doherty, et al. Standards Track [Page 34] RFC 6063 DSKPP December 2010

    based on the Portable Symmetric Key Container (PSKC) defined in
    [RFC6030].  Alternative formats MAY include [RFC6031], PKCS #12
    [PKCS-12], or PKCS #5 XML [PKCS-5-XML] format.
    With KP, the server includes a key confirmation MAC that the
    client uses to avoid a false "Commit" message.  The MAC algorithm
    is the same DSKPP-PRF that was sent in the <KeyProvServerHello>
    message.
 How the DSKPP Client uses this message:
    When the Status attribute is not set to "Success", this indicates
    failure and the DSKPP Client MUST abort the protocol.
    After receiving a <KeyProvServerFinished> message with Status =
    "Success", the DSKPP Client MUST verify the key confirmation MAC
    that was transmitted with this message.  The DSKPP Client MUST
    terminate the DSKPP session if the MAC does not verify, and MUST,
    in this case, also delete any nonces, keys, and/or secrets
    associated with the failed run of the protocol.
    If <KeyProvServerFinished> has Status = "Success", and the MAC was
    verified, then the DSKPP Client MUST calculate K_TOKEN from the
    combination of the two random nonces R_S and R_C and the server's
    encryption key, K, as described in Section 4.1.2.  The DSKPP-PRF
    is the same one used for MAC computation.  The DSKPP Client
    associates the key package contained in <KeyProvServerFinished>
    with the generated key, K_TOKEN, and stores this data permanently
    on the cryptographic module.
    After this operation, it MUST NOT be possible to overwrite the key
    unless knowledge of an authorizing key is proven through a MAC on
    a later <KeyProvServerHello> (and <KeyProvServerFinished>)
    message.

5. Two-Pass Protocol Usage

 This section describes the methods and message flow that comprise the
 two-pass protocol variant.  Two-pass DSKPP is essentially a transport
 of keying material from the DSKPP Server to the DSKPP Client.  The
 DSKPP Server transmits keying material in a key package formatted in
 accordance with [RFC6030], [RFC6031], PKCS #12 [PKCS-12], or PKCS #5
 XML [PKCS-5-XML].
 The keying material includes a provisioning master key, K_PROV, from
 which the DSKPP Client derives two keys: the symmetric key to be
 established in the cryptographic module, K_TOKEN, and a key, K_MAC,
 used for key confirmation.  The keying material also includes key
 usage attributes, such as expiry date and length.

Doherty, et al. Standards Track [Page 35] RFC 6063 DSKPP December 2010

 The DSKPP Server encrypts K_PROV to ensure that it is not exposed to
 any other entity than the DSKPP Server and the cryptographic module
 itself.  The DSKPP Server uses any of three key protection methods to
 encrypt K_PROV: Key Transport, Key Wrap, and Passphrase-Based Key
 Wrap Key Protection methods.
 While the DSKPP Client and server may negotiate the key protection
 method to use, the actual key protection is carried out in the
 KeyPackage.  The format of a KeyPackage specifies how a key should be
 protected using the three key protection methods.  The following
 KeyPackage formats are defined for DSKPP:
 o  PSKC Key Container [RFC6030] at
    urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
 o  SKPC Key Container [RFC6031] at
    urn:ietf:params:xml:ns:keyprov:dskpp:skpc-key-container
 o  PKCS12 Key Container [PKCS-12] at
    urn:ietf:params:xml:ns:keyprov:dskpp:pkcs12-key-container
 o  PKCS5-XML Key Container [PKCS-5-XML] at
    urn:ietf:params:xml:ns:keyprov:dskpp:pkcs5-xml-key-container
 Each of the key protection methods is described below.

5.1. Key Protection Methods

 This section introduces three key protection methods for the two-pass
 variant.  Additional methods MAY be defined by external entities or
 through the IETF process.

5.1.1. Key Transport

 Purpose of this method:
    This method is intended for PKI-capable devices.  The DSKPP Server
    encrypts keying material and transports it to the DSKPP Client.
    The server encrypts the keying material using the public key of
    the DSKPP Client, whose private key part resides in the
    cryptographic module.  The DSKPP Client decrypts the keying
    material and uses it to derive the symmetric key, K_TOKEN.
 This method is identified with the following URN:
    urn:ietf:params:xml:schema:keyprov:dskpp:transport
 The DSKPP Server and Client MUST support the following mechanism:
    http://www.w3.org/2001/04/xmlenc#rsa-1_5 encryption mechanism
    defined in [XMLENC].

Doherty, et al. Standards Track [Page 36] RFC 6063 DSKPP December 2010

5.1.2. Key Wrap

 Purpose of this method:
    This method is ideal for pre-keyed devices, e.g., SIM cards.  The
    DSKPP Server encrypts keying material using a pre-shared key
    wrapping key and transports it to the DSKPP Client.  The DSKPP
    Client decrypts the keying material, and uses it to derive the
    symmetric key, K_TOKEN.
 This method is identified with the following URN:
    urn:ietf:params:xml:schema:keyprov:dskpp:wrap
 The DSKPP Server and Client MUST support all of the following key
 wrapping mechanisms:
 AES128 KeyWrap
    Refer to id-aes128-wrap in [RFC3394] and
    http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
 AES128 KeyWrap with Padding
    Refer to id-aes128-wrap-pad in [RFC5649] and
    http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
 AES-CBC-128
    Refer to [FIPS197-AES] and
    http://www.w3.org/2001/04/xmlenc#aes128-cbc in [XMLENC]

5.1.3. Passphrase-Based Key Wrap

 Purpose of this method:
    This method is a variation of the Key Wrap Method that is
    applicable to constrained devices with keypads, e.g., mobile
    phones.  The DSKPP Server encrypts keying material using a
    wrapping key derived from a user-provided passphrase, and
    transports the encrypted material to the DSKPP Client.  The DSKPP
    Client decrypts the keying material, and uses it to derive the
    symmetric key, K_TOKEN.
    To preserve the property of not exposing K_TOKEN to any other
    entity than the DSKPP Server and the cryptographic module itself,
    the method SHOULD be employed only when the device contains
    facilities (e.g., a keypad) for direct entry of the passphrase.
 This method is identified with the following URN:
    urn:ietf:params:xml:schema:keyprov:dskpp:passphrase-wrap

Doherty, et al. Standards Track [Page 37] RFC 6063 DSKPP December 2010

 The DSKPP Server and Client MUST support the following:
  • The PBES2 password-based encryption scheme defined in [PKCS-5]

(and identified as

       http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2 in
       [PKCS-5-XML]).
  • The PBKDF2 passphrase-based key derivation function also

defined in [PKCS-5] (and identified as

       http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbkdf2
       in [PKCS-5-XML]).
  • All of the following key wrapping mechanisms:
       AES128 KeyWrap
          Refer to id-aes128-wrap in [RFC3394] and
          http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
       AES128 KeyWrap with Padding
          Refer to id-aes128-wrap-pad in [RFC5649] and
          http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
       AES-CBC-128
          Refer to [FIPS197-AES] and
          http://www.w3.org/2001/04/xmlenc#aes128-cbc in [XMLENC]

5.2. Message Flow

 The two-pass protocol flow consists of one exchange:
 1:  Pass 1 = <KeyProvClientHello>, Pass 2 = <KeyProvServerFinished>
 Although there is no exchange of the <ServerHello> message or the
 <ClientNonce> message, the DSKPP Client is still able to specify
 algorithm preferences and supported key types in the
 <KeyProvClientHello> message.
 The purpose and content of each message are described below.  XML
 format and examples are in Section 8 and Appendix B.

5.2.1. KeyProvTrigger

 The trigger message is used in exactly the same way for the two-pass
 variant as for the four-pass variant; refer to Section 4.2.1.

Doherty, et al. Standards Track [Page 38] RFC 6063 DSKPP December 2010

5.2.2. KeyProvClientHello

         DSKPP Client                         DSKPP Server
         ------------                         ------------
         SAL, AD, R_C,
         [DeviceID], [KeyID],
         KPML                   --->
 When this message is sent:
    When a DSKPP Client first connects to a DSKPP Server, it is
    required to send the <KeyProvClientHello> as its first message.
    The client can also send <KeyProvClientHello> in response to a
    <KeyProvTrigger> message.
 Purpose of this message:
    With this message, the DSKPP Client specifies its algorithm
    preferences and supported key types as well as which DSKPP
    versions, protocol variants (in this case "two-pass"), key package
    formats, and key protection methods that it supports.
    Furthermore, the DSKPP Client facilitates user authentication by
    transmitting the Authentication Data (AD) that was provided by the
    user before the first DSKPP message was sent.
 Application note:
    This message MUST send User Authentication Data (AD) to the DSKPP
    Server.  If this message is preceded by trigger message
    <KeyProvTrigger>, then the application will already have AD
    available (see Section 4.2.1).  However, if this message was not
    preceded by <KeyProvTrigger>, then the application MUST retrieve
    the User Authentication Code, possibly by prompting the user to
    manually enter their Authentication Code, e.g., on a device with
    only a numeric keypad.  The application MUST also derive
    Authentication Data (AD) from the Authentication Code, as
    described in Section 3.4.1, and save it for use in its next
    message, <KeyProvClientNonce>.
 What is contained in this message:
    The Security Attribute List (SAL) included with
    <KeyProvClientHello> contains the combinations of DSKPP versions,
    variants, key package formats, key types, and cryptographic
    algorithms that the DSKPP Client supports in order of the client's
    preference (favorite choice first).
    Authentication Data (AD) that was either included with
    <KeyProvTrigger>, or generated as described in the "Application
    Note" above.

Doherty, et al. Standards Track [Page 39] RFC 6063 DSKPP December 2010

    The DSKPP Client's random nonce (R_C), which was used by the
    client when generating AD.  By inserting R_C into the DSKPP
    session, the DSKPP Client is able to ensure the DSKPP Server is
    live before committing the key.
    If <KeyProvClientHello> was preceded by a <KeyProvTrigger>, then
    this message MUST also include the DeviceID and/or KeyID that was
    provided with the trigger.  Otherwise, if a trigger message did
    not precede <KeyProvClientHello>, then this message MAY include a
    DeviceID that was pre-shared with the DSKPP Server, and MAY
    contain a key ID associated with a key previously provisioned by
    the DSKPP provisioning server.
    The list of key protection methods (KPML) that the DSKPP Client
    supports.  Each item in the list MAY include an encryption key
    "payload" for the DSKPP Server to use to protect keying material
    that it sends back to the client.  The payload MUST be of type
    <ds:KeyInfoType> ([XMLDSIG]).  For each key protection method, the
    allowable choices for <ds:KeyInfoType> are:
  • Key Transport

Only those choices of <ds:KeyInfoType> that identify a public

       key (i.e., <ds:KeyName>, <ds:KeyValue>, <ds:X509Data>, or <ds:
       PGPData>).  The <ds:X509Certificate> option of the <ds:
       X509Data> alternative is RECOMMENDED when the public key
       corresponding to the private key on the cryptographic module
       has been certified.
  • Key Wrap

Only those choices of <ds:KeyInfoType> that identify a

       symmetric key (i.e., <ds:KeyName> and <ds:KeyValue>).  The <ds:
       KeyName> alternative is RECOMMENDED.
  • Passphrase-Based Key Wrap

The <ds:KeyName> option MUST be used and the key name MUST

       identify the passphrase that will be used by the server to
       generate the key wrapping key.  The identifier and passphrase
       components of <ds:KeyName> MUST be set to the Client ID and
       Authentication Code components of AD (same AD as contained in
       this message).
 How the DSKPP Server uses this message:
    The DSKPP Server will look for an acceptable combination of DSKPP
    version, variant (in this case, two-pass), key package format, key
    type, and cryptographic algorithms.  If the DSKPP Client's SAL
    does not match the capabilities of the DSKPP Server, or does not

Doherty, et al. Standards Track [Page 40] RFC 6063 DSKPP December 2010

    comply with key provisioning policy, then the DSKPP Server will
    set the Status attribute to something other than "Success".
    Otherwise, the Status attribute will be set to "Success".
    The DSKPP Server will validate the DeviceID and KeyID if included
    in <KeyProvClientHello>.  The DSKPP Server MUST NOT accept the
    DeviceID unless the server sent the DeviceID in a preceding
    trigger message.  Note that it is also legitimate for a DSKPP
    Client to initiate the DSKPP run without having received a
    <KeyProvTrigger> message from a server, but in this case any
    provided DeviceID MUST NOT be accepted by the DSKPP Server unless
    the server has access to a unique key for the identified device
    and that key will be used in the protocol.
    The DSKPP Server MUST use AD to authenticate the user.  If
    authentication fails, then the DSKPP Server MUST set the return
    code to a failure status, and MUST, in this case, also delete any
    nonces, keys, and/or secrets associated with the failed run of the
    protocol.
    If user authentication passes, the DSKPP Server generates a key
    K_PROV.  In the two-pass case, wherein the client does not have
    access to R_S, K_PROV is randomly generated solely by the DSKPP
    Server wherein K_PROV MUST consist of two parts of equal length,
    i.e.,
       K_PROV = K_MAC || K_TOKEN
    The length of K_TOKEN (and hence also the length of K_MAC) is
    determined by the type of K_TOKEN, which MUST be one of the key
    types supported by the DSKPP Client.  In cases where the desired
    key length for K_TOKEN is different from the length of K_MAC for
    the underlying MAC algorithm, the greater length of the two MUST
    be chosen to generate K_PROV.  The actual MAC key is truncated
    from the resulting K_MAC when it is used in the MAC algorithm when
    K_MAC is longer than necessary in order to match the desired
    K_TOKEN length.  If K_TOKEN is longer than needed in order to
    match the K_MAC length, the provisioning server and the receiving
    client must determine the actual secret key length from the target
    key algorithm and store only the truncated portion of the K_TOKEN.
    The truncation MUST take the beginning bytes of the desired length
    from K_TOKEN or K_MAC for the actual key.  For example, when a
    provisioning server provisions an event based HOTP secret key with
    length 20 and MAC algorithm DSKPP-PRF-SHA256 (Appendix D), K_PROV
    length will be 64.  The derived K_TOKEN and K_MAC will each
    consist of 32 bytes.  The actual HOTP key should be the first 20
    bytes of the K_TOKEN.

Doherty, et al. Standards Track [Page 41] RFC 6063 DSKPP December 2010

    Once K_PROV is computed, the DSKPP Server selects one of the key
    protection methods from the DSKPP Client's KPML, and uses that
    method and corresponding payload to encrypt K_PROV.  The DSKPP
    Server generates a key package to transport the key encryption
    method information and the encrypted provisioning key (K_PROV).
    The encrypted data format is subject to the choice supported by
    the selected key package.  The key package MUST specify and use
    the selected key protection method and the key information that
    was received in <KeyProvClientHello>.  The key package also
    includes key usage attributes such as expiry date and length.  The
    server stores the key package and K_TOKEN with a user account on
    the cryptographic server.
    The server generates a MAC for key confirmation, which the client
    will use to avoid a false "Commit" message that would cause the
    cryptographic module to end up in state in which the server does
    not recognize the stored key.
    In addition, if an existing key is being renewed, the server
    generates a second MAC that it will return to the client as server
    Authentication Data (AD) so that the DSKPP Client can confirm that
    the replacement key came from a trusted server.
 The method the DSKPP Server MUST use to calculate the key
 confirmation MAC:
    msg_hash = SHA-256(msg_1, ..., msg_n)
    dsLen = len(msg_hash)
    MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || msg_hash ||
    ServerID, dsLen)
    where
    MAC         The MAC MUST be calculated using the already
                established MAC algorithm and MUST be computed on the
                (ASCII) string "MAC 1 computation", msg_hash, and
                ServerID using the existing MAC key K_MAC.
    K_MAC       The key that is derived from K_PROV, which the DSKPP
                Server MUST provide to the cryptographic module.
    msg_hash    The message hash, defined in Section 3.4.3, of
                messages msg_1, ..., msg_n.
    ServerID    The identifier that the DSKPP Server MUST include in
                the <KeyPackage> element of <KeyProvServerFinished>.

Doherty, et al. Standards Track [Page 42] RFC 6063 DSKPP December 2010

    If DSKPP-PRF (defined in Section 3.4.2) is used as the MAC
    algorithm, then the input parameter s MUST consist of the
    concatenation of the (ASCII) string "MAC 1 computation", msg_hash,
    and ServerID, and the parameter dsLen MUST be set to the length of
    msg_hash.
 The method the DSKPP Server MUST use to calculate the server
 authentication MAC:
    The MAC MUST be computed on the (ASCII) string "MAC 2
    computation", the server identifier ServerID, and R, using a pre-
    existing MAC key K_MAC' (the MAC key that existed before this
    protocol run).  Note that the implementation may specify K_MAC' to
    be the value of the K_TOKEN that is being replaced.
    If DSKPP-PRF is used as the MAC algorithm, then the input
    parameter s MUST consist of the concatenation of the (ASCII)
    string "MAC 2 computation" ServerID, and R.  The parameter dsLen
    MUST be set to at least 16 (i.e., the length of the MAC MUST be at
    least 16 octets):
    dsLen >= 16
    MAC = DSKPP-PRF (K_MAC', "MAC 2 computation" || ServerID || R,
    dsLen)
    The MAC algorithm MUST be the same as the algorithm used by the
    DSKPP Server to calculate the key confirmation MAC.

5.2.3. KeyProvServerFinished

        DSKPP Client                         DSKPP Server
         ------------                         ------------
                                <---           KP, MAC, AD
 When this message is sent:
    The DSKPP Server will send this message after authenticating the
    user and, if authentication passed, generating K_TOKEN and a key
    package, and associating them with the user's account on the
    cryptographic server.
 Purpose of this message:
    With this message, the DSKPP Server transports a key package
    containing the encrypted provisioning key (K_PROV) and key usage
    attributes.

Doherty, et al. Standards Track [Page 43] RFC 6063 DSKPP December 2010

 What is contained in this message:
    A Status attribute equivalent to the server's return code to
    <KeyProvClientHello>.  If the server found an acceptable set of
    attributes from the client's SAL, then it sets Status to
    "Success".
    The confirmation message MUST include the Key Package (KP) that
    holds the DSKPP Server's ID, key ID, key type, encrypted
    provisioning key (K_PROV), encryption method, and additional
    configuration information.  The default symmetric key package
    format MUST be based on the Portable Symmetric Key Container
    (PSKC) defined in [RFC6030].  Alternative formats MAY include
    [RFC6031], PKCS #12 [PKCS-12], or PKCS #5 XML [PKCS-5-XML].
    This message MUST include a MAC that the DSKPP Client will use for
    key confirmation.  This key confirmation MAC is calculated using
    the "MAC 1 computation" as described in the previous section.
    Finally, if an existing key is being replaced, then this message
    MUST also include a server authentication MAC (calculated using
    the "MAC 2 computation" as described in the previous section),
    which is passed as AD to the DSKPP Client.
 How the DSKPP Client uses this message:
    After receiving a <KeyProvServerFinished> message with Status =
    "Success", the DSKPP Client MUST verify both MACs (MAC and AD).
    The DSKPP Client MUST terminate the DSKPP run if either MAC does
    not verify, and MUST, in this case, also delete any nonces, keys,
    and/or secrets associated with the failed run of the protocol.
    If <KeyProvServerFinished> has Status = "Success" and the MACs
    were verified, then the DSKPP Client MUST extract K_PROV from the
    provided key package, and derive K_TOKEN.  Finally, the DSKPP
    Client initializes the cryptographic module with K_TOKEN and the
    corresponding key usage attributes.  After this operation, it MUST
    NOT be possible to overwrite the key unless knowledge of an
    authorizing key is proven through a MAC on a later
    <KeyProvServerFinished> message.

6. Protocol Extensions

 DSKPP has been designed to be extensible.  The sub-sections below
 define two extensions that are included with the DSKPP schema.  Since
 it is possible that the use of extensions will harm interoperability,
 protocol designers are advised to carefully consider the use of
 extensions.  For example, if a particular implementation relies on

Doherty, et al. Standards Track [Page 44] RFC 6063 DSKPP December 2010

 the presence of a proprietary extension, then it may not be able to
 interoperate with independent implementations that have no knowledge
 of this extension.
 Extensions may be sent with any DSKPP message using the
 ExtensionsType.  The ExtensionsType type is a list of Extensions
 containing type-value pairs that define optional features supported
 by a DSKPP Client or server.  Each extension MAY be marked as
 Critical by setting the Critical attribute of the Extension to
 "true".  Unless an extension is marked as Critical, a receiving party
 need not be able to interpret it; a receiving party is always free to
 disregard any (non-critical) extensions.

6.1. The ClientInfoType Extension

 The ClientInfoType extension MAY contain any client-specific data
 required of an application.  This extension MAY be present in a
 <KeyProvClientHello> or <KeyProvClientNonce> message.  When present,
 this extension MUST NOT be marked as Critical.
 DSKPP Servers MUST support this extension.  DSKPP Servers MUST NOT
 attempt to interpret the data it carries and, if received, MUST
 include it unmodified in the current protocol run's next server
 response.  DSKPP Servers need not retain the ClientInfoType data.

6.2. The ServerInfoType Extension

 The ServerInfoType extension MAY contain any server-specific data
 required of an application, e.g., state information.  This extension
 is only valid in <KeyProvServerHello> messages for which the Status
 attribute is set to "Continue".  When present, this extension MUST
 NOT be marked as Critical.
 DSKPP Clients MUST support this extension.  DSKPP Clients MUST NOT
 attempt to interpret the data it carries and, if received, MUST
 include it unmodified in the current protocol run's next client
 request (i.e., the <KeyProvClientNonce> message).  DSKPP Clients need
 not retain the ServerInfoType data.

7. Protocol Bindings

7.1. General Requirements

 DSKPP assumes a reliable transport.

Doherty, et al. Standards Track [Page 45] RFC 6063 DSKPP December 2010

7.2. HTTP/1.1 Binding for DSKPP

 This section presents a binding of the previous messages to HTTP/1.1
 [RFC2616].  This HTTP binding is mandatory to implement, although
 newer versions of the specification might define additional bindings
 in the future.  Note that the HTTP client will normally be different
 from the DSKPP Client (i.e., the HTTP client will "proxy" DSKPP
 messages from the DSKPP Client to the DSKPP Server).  Likewise, on
 the HTTP server side, the DSKPP Server MAY receive DSKPP message from
 a "front-end" HTTP server.  The DSKPP Server will be identified by a
 specific URL, which may be pre-configured, or provided to the client
 during initialization.

7.2.1. Identification of DSKPP Messages

 The MIME type for all DSKPP messages MUST be
 application/dskpp+xml

7.2.2. HTTP Headers

 In order to avoid caching of responses carrying DSKPP messages by
 proxies, the following holds:
 o  When using HTTP/1.1, requesters SHOULD:
    *  Include a Cache-Control header field set to "no-cache, no-
       store".
    *  Include a Pragma header field set to "no-cache".
 o  When using HTTP/1.1, responders SHOULD:
    *  Include a Cache-Control header field set to "no-cache, no-must-
       revalidate, private".
    *  Include a Pragma header field set to "no-cache".
    *  NOT include a Validator, such as a Last-Modified or ETag
       header.
 To handle content negotiation, HTTP requests MAY include an HTTP
 Accept header field.  This header field SHOULD should be identified
 using the MIME type specified in Section 7.2.1.  The Accept header
 MAY include additional content types defined by future versions of
 this protocol.
 There are no other restrictions on HTTP headers, besides the
 requirement to set the Content-Type header value to the MIME type
 specified in Section 7.2.1.

Doherty, et al. Standards Track [Page 46] RFC 6063 DSKPP December 2010

7.2.3. HTTP Operations

 Persistent connections as defined in HTTP/1.1 are OPTIONAL.  DSKPP
 requests are mapped to HTTP requests with the POST method.  DSKPP
 responses are mapped to HTTP responses.
 For the four-pass DSKPP, messages within the protocol run are bound
 together.  In particular, <KeyProvServerHello> is bound to the
 preceding <KeyProvClientHello> by being transmitted in the
 corresponding HTTP response. <KeyProvServerHello> MUST have a
 SessionID attribute, and the SessionID attribute of the subsequent
 <KeyProvClientNonce> message MUST be identical.
 <KeyProvServerFinished> is then once again bound to the rest through
 HTTP (and possibly through a SessionID).

7.2.4. HTTP Status Codes

 A DSKPP HTTP responder that refuses to perform a message exchange
 with a DSKPP HTTP requester SHOULD return a 403 (Forbidden) response.
 In this case, the content of the HTTP body is not significant.  In
 the case of an HTTP error while processing a DSKPP request, the HTTP
 server MUST return a 500 (Internal Server Error) response.  This type
 of error SHOULD be returned for HTTP-related errors detected before
 control is passed to the DSKPP processor, or when the DSKPP processor
 reports an internal error (for example, the DSKPP XML namespace is
 incorrect, or the DSKPP schema cannot be located).  If a request is
 received that is not a DSKPP Client message, the DSKPP responder MUST
 return a 400 (Bad request) response.
 In these cases (i.e., when the HTTP response code is 4xx or 5xx), the
 content of the HTTP body is not significant.
 Redirection status codes (3xx) apply as usual.
 Whenever the HTTP POST is successfully invoked, the DSKPP HTTP
 responder MUST use the 200 status code and provide a suitable DSKPP
 message (possibly with DSKPP error information included) in the HTTP
 body.

7.2.5. HTTP Authentication

 No support for HTTP/1.1 authentication is assumed.

7.2.6. Initialization of DSKPP

 If a user requests key initialization in a browsing session, and if
 that request has an appropriate Accept header (e.g., to a specific
 DSKPP Server URL), the DSKPP Server MAY respond by sending a DSKPP

Doherty, et al. Standards Track [Page 47] RFC 6063 DSKPP December 2010

 initialization message in an HTTP response with Content-Type set
 according to Section 7.2.1 and response code set to 200 (OK).  The
 initialization message MAY carry data in its body, such as the URL
 for the DSKPP Client to use when contacting the DSKPP Server.  If the
 message does carry data, the data MUST be a valid instance of a
 <KeyProvTrigger> element.
 Note that if the user's request was directed to some other resource,
 the DSKPP Server MUST NOT respond by combining the DSKPP content type
 with response code 200.  In that case, the DSKPP Server SHOULD
 respond by sending a DSKPP initialization message in an HTTP response
 with Content-Type set according to Section 7.2.1 and response code
 set to 406 (Not Acceptable).

7.2.7. Example Messages

 a.  Initialization from DSKPP Server:
     HTTP/1.1 200 OK
     Cache-Control: no-store
     Content-Type: application/dskpp+xml
     Content-Length: <some value>
     DSKPP initialization data in XML form...
 b.  Initial request from DSKPP Client:
     POST http://example.com/cgi-bin/DSKPP-server HTTP/1.1
     Cache-Control: no-cache, no-store
     Pragma: no-cache
     Host: www.example.com
     Content-Type: application/dskpp+xml
     Content-Length: <some value>
     DSKPP data in XML form (supported version, supported
     algorithms...)
 c.  Initial response from DSKPP Server:
     HTTP/1.1 200 OK
     Cache-Control: no-cache, no-must-revalidate, private
     Pragma: no-cache
     Content-Type: application/dskpp+xml
     Content-Length: <some value>
     DSKPP data in XML form (server random nonce, server public key,
     ...)

Doherty, et al. Standards Track [Page 48] RFC 6063 DSKPP December 2010

8. DSKPP XML Schema

8.1. General Processing Requirements

 Some DSKPP elements rely on the parties being able to compare
 received values with stored values.  Unless otherwise noted, all
 elements that have the XML schema "xs:string" type, or a type derived
 from it, MUST be compared using an exact binary comparison.  In
 particular, DSKPP implementations MUST NOT depend on case-insensitive
 string comparisons, normalization or trimming of white space, or
 conversion of locale-specific formats such as numbers.
 Implementations that compare values that are represented using
 different character encodings MUST use a comparison method that
 returns the same result as converting both values to the Unicode
 character encoding [UNICODE] and then performing an exact binary
 comparison.
 No collation or sorting order for attributes or element values is
 defined.  Therefore, DSKPP implementations MUST NOT depend on
 specific sorting orders for values.

8.2. Schema

  <?xml version="1.0" encoding="utf-8"?>
  <xs:schema
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     targetNamespace="urn:ietf:params:xml:ns:keyprov:dskpp"
     elementFormDefault="qualified" attributeFormDefault="unqualified"
        version="1.0">
     <xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
        schemaLocation=
        "http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/
        xmldsig-core-schema.xsd"/>
     <xs:import namespace="urn:ietf:params:xml:ns:keyprov:pskc"
        schemaLocation="keyprov-pskc-1.0.xsd"/>
     <xs:complexType name="AbstractRequestType" abstract="true">
        <xs:annotation>
           <xs:documentation> Basic types </xs:documentation>
        </xs:annotation>
        <xs:attribute name="Version" type="dskpp:VersionType"
           use="required"/>
     </xs:complexType>

Doherty, et al. Standards Track [Page 49] RFC 6063 DSKPP December 2010

     <xs:complexType name="AbstractResponseType" abstract="true">
        <xs:annotation>
           <xs:documentation> Basic types </xs:documentation>
        </xs:annotation>
        <xs:attribute name="Version" type="dskpp:VersionType"
           use="required"/>
        <xs:attribute name="SessionID" type="dskpp:IdentifierType" />
        <xs:attribute name="Status" type="dskpp:StatusCode"
           use="required"/>
     </xs:complexType>
     <xs:simpleType name="VersionType">
        <xs:restriction base="xs:string">
           <xs:pattern value="\d{1,2}\.\d{1,3}" />
        </xs:restriction>
     </xs:simpleType>
     <xs:simpleType name="IdentifierType">
        <xs:restriction base="xs:string">
           <xs:maxLength value="128" />
        </xs:restriction>
     </xs:simpleType>
     <xs:simpleType name="StatusCode">
        <xs:restriction base="xs:string">
           <xs:enumeration value="Continue" />
           <xs:enumeration value="Success" />
           <xs:enumeration value="Abort" />
           <xs:enumeration value="AccessDenied" />
           <xs:enumeration value="MalformedRequest" />
           <xs:enumeration value="UnknownRequest" />
           <xs:enumeration value="UnknownCriticalExtension" />
           <xs:enumeration value="UnsupportedVersion" />
           <xs:enumeration value="NoSupportedKeyTypes" />
           <xs:enumeration value="NoSupportedEncryptionAlgorithms" />
           <xs:enumeration value="NoSupportedMacAlgorithms" />
           <xs:enumeration value="NoProtocolVariants" />
           <xs:enumeration value="NoSupportedKeyPackages" />
           <xs:enumeration value="AuthenticationDataMissing" />
           <xs:enumeration value="AuthenticationDataInvalid" />
           <xs:enumeration value="InitializationFailed" />
           <xs:enumeration value="ProvisioningPeriodExpired" />
        </xs:restriction>
     </xs:simpleType>

Doherty, et al. Standards Track [Page 50] RFC 6063 DSKPP December 2010

     <xs:complexType name="DeviceIdentifierDataType">
        <xs:choice>
           <xs:element name="DeviceId" type="pskc:DeviceInfoType" />
           <xs:any namespace="##other" processContents="strict" />
        </xs:choice>
     </xs:complexType>
     <xs:simpleType name="PlatformType">
        <xs:restriction base="xs:string">
           <xs:enumeration value="Hardware" />
           <xs:enumeration value="Software" />
           <xs:enumeration value="Unspecified" />
        </xs:restriction>
     </xs:simpleType>
     <xs:complexType name="TokenPlatformInfoType">
        <xs:attribute name="KeyLocation"
           type="dskpp:PlatformType"/>
        <xs:attribute name="AlgorithmLocation"
           type="dskpp:PlatformType"/>
     </xs:complexType>
     <xs:simpleType name="NonceType">
        <xs:restriction base="xs:base64Binary">
           <xs:minLength value="16" />
        </xs:restriction>
     </xs:simpleType>
     <xs:complexType name="AlgorithmsType">
        <xs:sequence maxOccurs="unbounded">
           <xs:element name="Algorithm" type="dskpp:AlgorithmType"/>
        </xs:sequence>
     </xs:complexType>
     <xs:simpleType name="AlgorithmType">
        <xs:restriction base="xs:anyURI" />
     </xs:simpleType>
     <xs:complexType name="ProtocolVariantsType">
        <xs:sequence>
           <xs:element name="FourPass" minOccurs="0" />
           <xs:element name="TwoPass"
              type="dskpp:KeyProtectionDataType" minOccurs="0"/>
        </xs:sequence>
     </xs:complexType>

Doherty, et al. Standards Track [Page 51] RFC 6063 DSKPP December 2010

     <xs:complexType name="KeyProtectionDataType">
        <xs:annotation>
           <xs:documentation xml:lang="en">
              This element is only valid for two-pass DSKPP.
           </xs:documentation>
        </xs:annotation>
        <xs:sequence maxOccurs="unbounded">
          <xs:element name="SupportedKeyProtectionMethod"
             type="xs:anyURI"/>
          <xs:element name="Payload"
             type="dskpp:PayloadType" minOccurs="0"/>
        </xs:sequence>
     </xs:complexType>
     <xs:complexType name="PayloadType">
        <xs:choice>
           <xs:element name="Nonce" type="dskpp:NonceType" />
           <xs:any namespace="##other" processContents="strict"/>
        </xs:choice>
     </xs:complexType>
     <xs:complexType name="KeyPackagesFormatType">
        <xs:sequence maxOccurs="unbounded">
           <xs:element name="KeyPackageFormat"
              type="dskpp:KeyPackageFormatType"/>
        </xs:sequence>
     </xs:complexType>
     <xs:simpleType name="KeyPackageFormatType">
        <xs:restriction base="xs:anyURI" />
     </xs:simpleType>
     <xs:complexType name="AuthenticationDataType">
        <xs:annotation>
           <xs:documentation xml:lang="en">
              Authentication Data contains a MAC.
           </xs:documentation>
        </xs:annotation>
        <xs:sequence>
           <xs:element name="ClientID"
              type="dskpp:IdentifierType" minOccurs="0"/>
           <xs:choice>
              <xs:element name="AuthenticationCodeMac"
                 type="dskpp:AuthenticationMacType"/>
              <xs:any namespace="##other" processContents="strict" />
           </xs:choice>
        </xs:sequence>
     </xs:complexType>

Doherty, et al. Standards Track [Page 52] RFC 6063 DSKPP December 2010

     <xs:complexType name="AuthenticationMacType">
        <xs:sequence>
           <xs:element minOccurs="0" name="Nonce"
              type="dskpp:NonceType"/>
           <xs:element minOccurs="0" name="IterationCount"
              type="xs:int"/>
           <xs:element name="Mac" type="dskpp:MacType" />
        </xs:sequence>
     </xs:complexType>
     <xs:complexType name="MacType">
        <xs:simpleContent>
           <xs:extension base="xs:base64Binary">
              <xs:attribute name="MacAlgorithm" type="xs:anyURI"/>
           </xs:extension>
        </xs:simpleContent>
     </xs:complexType>
     <xs:complexType name="KeyPackageType">
        <xs:sequence>
           <xs:element minOccurs="0" name="ServerID"
              type="xs:anyURI"/>
           <xs:element minOccurs="0" name="KeyProtectionMethod"
              type="xs:anyURI" />
           <xs:choice>
              <xs:element name="KeyContainer"
                 type="pskc:KeyContainerType"/>
              <xs:any namespace="##other" processContents="strict"/>
           </xs:choice>
        </xs:sequence>
     </xs:complexType>
     <xs:complexType name="InitializationTriggerType">
        <xs:sequence>
           <xs:element minOccurs="0" name="DeviceIdentifierData"
              type="dskpp:DeviceIdentifierDataType" />
           <xs:element minOccurs="0" name="KeyID"
              type="xs:base64Binary"/>
           <xs:element minOccurs="0" name="TokenPlatformInfo"
              type="dskpp:TokenPlatformInfoType" />
           <xs:element name="AuthenticationData"
              type="dskpp:AuthenticationDataType" />
           <xs:element minOccurs="0" name="ServerUrl"
              type="xs:anyURI"/>
           <xs:any minOccurs="0" namespace="##other"
              processContents="strict" />
        </xs:sequence>
     </xs:complexType>

Doherty, et al. Standards Track [Page 53] RFC 6063 DSKPP December 2010

     <xs:complexType name="ExtensionsType">
        <xs:annotation>
           <xs:documentation> Extension types </xs:documentation>
        </xs:annotation>
        <xs:sequence maxOccurs="unbounded">
           <xs:element name="Extension"
              type="dskpp:AbstractExtensionType"/>
        </xs:sequence>
     </xs:complexType>
     <xs:complexType name="AbstractExtensionType" abstract="true">
        <xs:attribute name="Critical" type="xs:boolean" />
     </xs:complexType>
     <xs:complexType name="ClientInfoType">
        <xs:complexContent mixed="false">
           <xs:extension base="dskpp:AbstractExtensionType">
              <xs:sequence>
                 <xs:element name="Data" type="xs:base64Binary"/>
              </xs:sequence>
           </xs:extension>
        </xs:complexContent>
     </xs:complexType>
     <xs:complexType name="ServerInfoType">
        <xs:complexContent mixed="false">
           <xs:extension base="dskpp:AbstractExtensionType">
              <xs:sequence>
                 <xs:element name="Data" type="xs:base64Binary"/>
              </xs:sequence>
           </xs:extension>
        </xs:complexContent>
     </xs:complexType>
     <xs:element name="KeyProvTrigger"
        type="dskpp:KeyProvTriggerType">
        <xs:annotation>
           <xs:documentation> DSKPP PDUs </xs:documentation>
        </xs:annotation>
     </xs:element>

Doherty, et al. Standards Track [Page 54] RFC 6063 DSKPP December 2010

     <xs:complexType name="KeyProvTriggerType">
        <xs:annotation>
        <xs:documentation xml:lang="en">
           Message used to trigger the device to initiate a
           DSKPP run.
        </xs:documentation>
        </xs:annotation>
        <xs:sequence>
           <xs:choice>
              <xs:element name="InitializationTrigger"
                 type="dskpp:InitializationTriggerType" />
              <xs:any namespace="##other" processContents="strict"/>
           </xs:choice>
        </xs:sequence>
        <xs:attribute name="Version" type="dskpp:VersionType"/>
     </xs:complexType>
     <xs:element name="KeyProvClientHello"
        type="dskpp:KeyProvClientHelloPDU">
        <xs:annotation>
           <xs:documentation>KeyProvClientHello PDU</xs:documentation>
        </xs:annotation>
     </xs:element>
     <xs:complexType name="KeyProvClientHelloPDU">
        <xs:annotation>
           <xs:documentation xml:lang="en">
              Message sent from DSKPP Client to DSKPP Server to
              initiate a DSKPP session.
           </xs:documentation>
        </xs:annotation>
        <xs:complexContent mixed="false">
           <xs:extension base="dskpp:AbstractRequestType">
              <xs:sequence>
                 <xs:element minOccurs="0" name="DeviceIdentifierData"
                    type="dskpp:DeviceIdentifierDataType" />
                 <xs:element minOccurs="0" name="KeyID"
                    type="xs:base64Binary" />
                 <xs:element minOccurs="0" name="ClientNonce"
                    type="dskpp:NonceType" />
                 <xs:element name="SupportedKeyTypes"
                    type="dskpp:AlgorithmsType" />
                 <xs:element name="SupportedEncryptionAlgorithms"
                    type="dskpp:AlgorithmsType" />
                 <xs:element name="SupportedMacAlgorithms"
                    type="dskpp:AlgorithmsType" />
                 <xs:element minOccurs="0"
                    name="SupportedProtocolVariants"
                    type="dskpp:ProtocolVariantsType" />

Doherty, et al. Standards Track [Page 55] RFC 6063 DSKPP December 2010

                 <xs:element minOccurs="0" name="SupportedKeyPackages"
                    type="dskpp:KeyPackagesFormatType" />
                 <xs:element minOccurs="0" name="AuthenticationData"
                    type="dskpp:AuthenticationDataType" />
                 <xs:element minOccurs="0" name="Extensions"
                    type="dskpp:ExtensionsType" />
              </xs:sequence>
           </xs:extension>
        </xs:complexContent>
     </xs:complexType>
     <xs:element name="KeyProvServerHello"
        type="dskpp:KeyProvServerHelloPDU">
        <xs:annotation>
           <xs:documentation>KeyProvServerHello PDU</xs:documentation>
        </xs:annotation>
     </xs:element>
     <xs:complexType name="KeyProvServerHelloPDU">
        <xs:annotation>
           <xs:documentation xml:lang="en">
              Response message sent from DSKPP Server to DSKPP Client
              in four-pass DSKPP.
           </xs:documentation>
        </xs:annotation>
        <xs:complexContent mixed="false">
           <xs:extension base="dskpp:AbstractResponseType">
              <xs:sequence minOccurs="0">
                 <xs:element name="KeyType"
                    type="dskpp:AlgorithmType"/>
                 <xs:element name="EncryptionAlgorithm"
                    type="dskpp:AlgorithmType" />
                 <xs:element name="MacAlgorithm"
                    type="dskpp:AlgorithmType"/>
                 <xs:element name="EncryptionKey"
                    type="ds:KeyInfoType"/>
                 <xs:element name="KeyPackageFormat"
                    type="dskpp:KeyPackageFormatType" />
                 <xs:element name="Payload" type="dskpp:PayloadType"/>
                 <xs:element minOccurs="0" name="Extensions"
                    type="dskpp:ExtensionsType" />
                 <xs:element minOccurs="0" name="Mac"
                    type="dskpp:MacType"/>
              </xs:sequence>
           </xs:extension>
        </xs:complexContent>
     </xs:complexType>

Doherty, et al. Standards Track [Page 56] RFC 6063 DSKPP December 2010

     <xs:element name="KeyProvClientNonce"
        type="dskpp:KeyProvClientNoncePDU">
        <xs:annotation>
           <xs:documentation>KeyProvClientNonce PDU</xs:documentation>
        </xs:annotation>
     </xs:element>
     <xs:complexType name="KeyProvClientNoncePDU">
        <xs:annotation>
           <xs:documentation xml:lang="en">
              Response message sent from DSKPP Client to
              DSKPP Server in a four-pass DSKPP session.
           </xs:documentation>
        </xs:annotation>
        <xs:complexContent mixed="false">
           <xs:extension base="dskpp:AbstractRequestType">
              <xs:sequence>
                 <xs:element name="EncryptedNonce"
                    type="xs:base64Binary"/>
                 <xs:element minOccurs="0" name="AuthenticationData"
                    type="dskpp:AuthenticationDataType" />
                 <xs:element minOccurs="0" name="Extensions"
                    type="dskpp:ExtensionsType" />
              </xs:sequence>
              <xs:attribute name="SessionID"
                 type="dskpp:IdentifierType" use="required"/>
           </xs:extension>
        </xs:complexContent>
     </xs:complexType>
     <xs:element name="KeyProvServerFinished"
        type="dskpp:KeyProvServerFinishedPDU">
        <xs:annotation>
           <xs:documentation>
              KeyProvServerFinished PDU
           </xs:documentation>
        </xs:annotation>
     </xs:element>
     <xs:complexType name="KeyProvServerFinishedPDU">
        <xs:annotation>
           <xs:documentation xml:lang="en">
              Final message sent from DSKPP Server to DSKPP Client in
              a DSKPP session.  A MAC value serves for key
              confirmation, and optional AuthenticationData serves for
              server authentication.
           </xs:documentation>
        </xs:annotation>
        <xs:complexContent mixed="false">
           <xs:extension base="dskpp:AbstractResponseType">

Doherty, et al. Standards Track [Page 57] RFC 6063 DSKPP December 2010

              <xs:sequence minOccurs="0">
                 <xs:element name="KeyPackage"
                    type="dskpp:KeyPackageType" />
                 <xs:element minOccurs="0" name="Extensions"
                    type="dskpp:ExtensionsType" />
                 <xs:element name="Mac" type="dskpp:MacType" />
                 <xs:element minOccurs="0" name="AuthenticationData"
                    type="dskpp:AuthenticationMacType" />
              </xs:sequence>
           </xs:extension>
        </xs:complexContent>
     </xs:complexType>
   </xs:schema>

9. Conformance Requirements

 In order to assure that all implementations of DSKPP can
 interoperate, the DSKPP Server:
 a.  MUST implement the four-pass variation of the protocol
     (Section 4)
 b.  MUST implement the two-pass variation of the protocol (Section 5)
 c.  MUST support user authentication (Section 3.2.1)
 d.  MUST support the following key derivation functions:
     *  DSKPP-PRF-AES DSKPP-PRF realization (Appendix D)
     *  DSKPP-PRF-SHA256 DSKPP-PRF realization (Appendix D)
 e.  MUST support the following encryption mechanisms for protection
     of the client nonce in the four-pass protocol:
     *  Mechanism described in Section 4.2.4
 f.  MUST support one of the following encryption algorithms for
     symmetric key operations, e.g., key wrap:
     *  KW-AES128 without padding; refer to
        http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
     *  KW-AES128 with padding; refer to
        http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC] and
        [RFC5649]
     *  AES-CBC-128; refer to [FIPS197-AES]
 g.  MUST support the following encryption algorithms for asymmetric
     key operations, e.g., key transport:
     *  RSA Encryption Scheme [PKCS-1]

Doherty, et al. Standards Track [Page 58] RFC 6063 DSKPP December 2010

 h.  MUST support the following integrity/KDF MAC functions:
     *  DSKPP-PRF-AES (Appendix D)
     *  DSKPP-PRF-SHA256 (Appendix D)
 i.  MUST support the PSKC key package [RFC6030]; all three PSKC key
     protection methods (Key Transport, Key Wrap, and Passphrase-Based
     Key Wrap) MUST be implemented
 j.  MAY support the ASN.1 key package as defined in [RFC6031]
 DSKPP Clients MUST support either the two-pass or the four-pass
 variant of the protocol.  DSKPP Clients MUST fulfill all requirements
 listed in item (c) - (j).
 Finally, implementations of DSKPP MUST bind DSKPP messages to
 HTTP/1.1 as described in Section 7.2.
 Of course, DSKPP is a security protocol, and one of its major
 functions is to allow only authorized parties to successfully
 initialize a cryptographic module with a new symmetric key.
 Therefore, a particular implementation may be configured with any of
 a number of restrictions concerning algorithms and trusted
 authorities that will prevent universal interoperability.

10. Security Considerations

10.1. General

 DSKPP is designed to protect generated keying material from exposure.
 No entities other than the DSKPP Server and the cryptographic module
 will have access to a generated K_TOKEN if the cryptographic
 algorithms used are of sufficient strength and, on the DSKPP Client
 side, generation and encryption of R_C and generation of K_TOKEN take
 place as specified in the cryptographic module.  This applies even if
 malicious software is present in the DSKPP Client.  However, as
 discussed in the following sub-sections, DSKPP does not protect
 against certain other threats resulting from man-in-the-middle
 attacks and other forms of attacks.  DSKPP MUST, therefore, be run
 over a transport providing confidentiality and integrity, such as
 HTTP over Transport Layer Security (TLS) with a suitable ciphersuite
 [RFC2818], when such threats are a concern.  Note that TLS
 ciphersuites with anonymous key exchanges are not suitable in those
 situations [RFC5246].

Doherty, et al. Standards Track [Page 59] RFC 6063 DSKPP December 2010

10.2. Active Attacks

10.2.1. Introduction

 An active attacker MAY attempt to modify, delete, insert, replay, or
 reorder messages for a variety of purposes including service denial
 and compromise of generated keying material.

10.2.2. Message Modifications

 Modifications to a <KeyProvTrigger> message will either cause denial
 of service (modifications of any of the identifiers or the
 Authentication Code) or will cause the DSKPP Client to contact the
 wrong DSKPP Server.  The latter is in effect a man-in-the-middle
 attack and is discussed further in Section 10.2.7.
 An attacker may modify a <KeyProvClientHello> message.  This means
 that the attacker could indicate a different key or device than the
 one intended by the DSKPP Client, and could also suggest other
 cryptographic algorithms than the ones preferred by the DSKPP Client,
 e.g., cryptographically weaker ones.  The attacker could also suggest
 earlier versions of DSKPP, in case these versions have been shown to
 have vulnerabilities.  These modifications could lead to an attacker
 succeeding in initializing or modifying another cryptographic module
 than the one intended (i.e., the server assigning the generated key
 to the wrong module) or gaining access to a generated key through the
 use of weak cryptographic algorithms or protocol versions.  DSKPP
 implementations MAY protect against the latter by having strict
 policies about what versions and algorithms they support and accept.
 The former threat (assignment of a generated key to the wrong module)
 is not possible when the shared-key variant of DSKPP is employed
 (assuming existing shared keys are unique per cryptographic module),
 but is possible in the public key variation.  Therefore, DSKPP
 Servers MUST NOT accept unilaterally provided device identifiers in
 the public key variation.  This is also indicated in the protocol
 description.  In the shared-key variation, however, an attacker may
 be able to provide the wrong identifier (possibly also leading to the
 incorrect user being associated with the generated key) if the
 attacker has real-time access to the cryptographic module with the
 identified key.  The result of this attack could be that the
 generated key is associated with the correct cryptographic module but
 the module is associated with the incorrect user.  See Section 10.5
 for a further discussion of this threat and possible countermeasures.
 An attacker may also modify a <KeyProvServerHello> message.  This
 means that the attacker could indicate different key types,
 algorithms, or protocol versions than the legitimate server would,
 e.g., cryptographically weaker ones.  The attacker may also provide a

Doherty, et al. Standards Track [Page 60] RFC 6063 DSKPP December 2010

 different nonce than the one sent by the legitimate server.  Clients
 MAY protect against the former through strict adherence to policies
 regarding permissible algorithms and protocol versions.  The latter
 (wrong nonce) will not constitute a security problem, as a generated
 key will not match the key generated on the legitimate server.  Also,
 whenever the DSKPP run would result in the replacement of an existing
 key, the <Mac> element protects against modifications of R_S.
 Modifications of <KeyProvClientNonce> messages are also possible.  If
 an attacker modifies the SessionID attribute, then, in effect, a
 switch to another session will occur at the server, assuming the new
 SessionID is valid at that time on the server.  It still will not
 allow the attacker to learn a generated K_TOKEN since R_C has been
 wrapped for the legitimate server.  Modifications of the
 <EncryptedNonce> element, e.g., replacing it with a value for which
 the attacker knows an underlying R'C, will not result in the client
 changing its pre-DSKPP state, since the server will be unable to
 provide a valid MAC in its final message to the client.  The server
 MAY, however, end up storing K'TOKEN rather than K_TOKEN.  If the
 cryptographic module has been associated with a particular user, then
 this could constitute a security problem.  For a further discussion
 about this threat, and a possible countermeasure, see Section 10.5
 below.  Note that use of TLS does not protect against this attack if
 the attacker has access to the DSKPP Client (e.g., through malicious
 software, "Trojans") [RFC5246].
 Finally, attackers may also modify the <KeyProvServerFinished>
 message.  Replacing the <Mac> element will only result in denial of
 service.  Replacement of any other element may cause the DSKPP Client
 to associate, e.g., the wrong service with the generated key.  DSKPP
 SHOULD be run over a transport providing confidentiality and
 integrity when this is a concern.

10.2.3. Message Deletion

 Message deletion will not cause any other harm than denial of
 service, since a cryptographic module MUST NOT change its state
 (i.e., "commit" to a generated key) until it receives the final
 message from the DSKPP Server and successfully has processed that
 message, including validation of its MAC.  A deleted
 <KeyProvServerFinished> message will not cause the server to end up
 in an inconsistent state vis-a-vis the cryptographic module if the
 server implements the suggestions in Section 10.5.

Doherty, et al. Standards Track [Page 61] RFC 6063 DSKPP December 2010

10.2.4. Message Insertion

 An active attacker may initiate a DSKPP run at any time, and suggest
 any device identifier.  DSKPP Server implementations MAY receive some
 protection against inadvertently initializing a key or inadvertently
 replacing an existing key or assigning a key to a cryptographic
 module by initializing the DSKPP run by use of the <KeyProvTrigger>.
 The <AuthenticationData> element allows the server to associate a
 DSKPP run e.g., with an earlier user-authenticated session.  The
 security of this method, therefore, depends on the ability to protect
 the <AuthenticationData> element in the DSKPP initialization message.
 If an eavesdropper is able to capture this message, he may race the
 legitimate user for a key initialization.  DSKPP over a transport
 providing confidentiality and integrity, coupled with the
 recommendations in Section 10.5, is RECOMMENDED when this is a
 concern.
 Insertion of other messages into an existing protocol run is seen as
 equivalent to modification of legitimately sent messages.

10.2.5. Message Replay

 During four-pass DSKPP, attempts to replay a previously recorded
 DSKPP message will be detected, as the use of nonces ensures that
 both parties are live.  For example, a DSKPP Client knows that a
 server it is communicating with is "live" since the server MUST
 create a MAC on information sent by the client.
 The same is true for two-pass DSKPP thanks to the requirement that
 the client sends R in the <KeyProvClientHello> message and that the
 server includes R in the MAC computation.

10.2.6. Message Reordering

 An attacker may attempt to re-order four-pass DSKPP messages but this
 will be detected, as each message is of a unique type.  Note: Message
 re-ordering attacks cannot occur in two-pass DSKPP since each party
 sends at most one message each.

Doherty, et al. Standards Track [Page 62] RFC 6063 DSKPP December 2010

10.2.7. Man in the Middle

 In addition to other active attacks, an attacker posing as a man in
 the middle may be able to provide his own public key to the DSKPP
 Client.  This threat and countermeasures to it are discussed in
 Section 4.1.1.  An attacker posing as a man in the middle may also be
 acting as a proxy and, hence, may not interfere with DSKPP runs but
 still learn valuable information; see Section 10.3.

10.3. Passive Attacks

 Passive attackers may eavesdrop on DSKPP runs to learn information
 that later on may be used to impersonate users, mount active attacks,
 etc.
 If DSKPP is not run over a transport providing confidentiality, a
 passive attacker may learn:
 o  What cryptographic modules a particular user possesses
 o  The identifiers of keys on those cryptographic modules and other
    attributes pertaining to those keys, e.g., the lifetime of the
    keys
 o  DSKPP versions and cryptographic algorithms supported by a
    particular DSKPP Client or server
 o  Any value present in an <extension> that is part of
    <KeyProvClientHello>
 Whenever the above is a concern, DSKPP MUST be run over a transport
 providing confidentiality.  If man-in-the-middle attacks for the
 purposes described above are a concern, the transport MUST also offer
 server-side authentication.

10.4. Cryptographic Attacks

 An attacker with unlimited access to an initialized cryptographic
 module may use the module as an "oracle" to pre-compute values that
 later on may be used to impersonate the DSKPP Server.  Section 4.1.1
 contains a discussion of this threat and steps RECOMMENDED to protect
 against it.
 Implementers are advised that cryptographic algorithms become weaker
 with time.  As new cryptographic techniques are developed and
 computing performance improves, the work factor to break a particular
 cryptographic algorithm will reduce.  Therefore, cryptographic

Doherty, et al. Standards Track [Page 63] RFC 6063 DSKPP December 2010

 algorithm implementations SHOULD be modular allowing new algorithms
 to be readily inserted.  That is, implementers SHOULD be prepared to
 regularly update the algorithms in their implementations.

10.5. Attacks on the Interaction between DSKPP and User Authentication

 If keys generated in DSKPP will be associated with a particular user
 at the DSKPP Server (or a server trusted by, and communicating with
 the DSKPP Server), then in order to protect against threats where an
 attacker replaces a client-provided encrypted R_C with his own R'C
 (regardless of whether the public key variation or the shared-secret
 variation of DSKPP is employed to encrypt the client nonce), the
 server SHOULD NOT commit to associate a generated K_TOKEN with the
 given cryptographic module until the user simultaneously has proven
 both possession of the device that hosts the cryptographic module
 containing K_TOKEN and some out-of-band provided authenticating
 information (e.g., an Authentication Code).  For example, if the
 cryptographic module is a one-time password token, the user could be
 required to authenticate with both a one-time password generated by
 the cryptographic module and an out-of-band provided Authentication
 Code in order to have the server "commit" to the generated OTP value
 for the given user.  Preferably, the user SHOULD perform this
 operation from another host than the one used to initialize keys on
 the cryptographic module, in order to minimize the risk of malicious
 software on the client interfering with the process.
 Note: This scenario, wherein the attacker replaces a client-provided
 R_C with his own R'C, does not apply to two-pass DSKPP as the client
 does not provide any entropy to K_TOKEN.  The attack as such (and its
 countermeasures) still applies to two-pass DSKPP, however, as it
 essentially is a man-in-the-middle attack.
 Another threat arises when an attacker is able to trick a user into
 authenticating to the attacker rather than to the legitimate service
 before the DSKPP run.  If successful, the attacker will then be able
 to impersonate the user towards the legitimate service, and
 subsequently receive a valid DSKPP trigger.  If the public key
 variant of DSKPP is used, this may result in the attacker being able
 to (after a successful DSKPP run) impersonate the user.  Ordinary
 precautions MUST, therefore, be in place to ensure that users
 authenticate only to legitimate services.

Doherty, et al. Standards Track [Page 64] RFC 6063 DSKPP December 2010

10.6. Miscellaneous Considerations

10.6.1. Client Contributions to K_TOKEN Entropy

 In four-pass DSKPP, both the client and the server provide
 randomizing material to K_TOKEN, in a manner that allows both parties
 to verify that they did contribute to the resulting key.  In the two-
 pass DSKPP version defined herein, only the server contributes to the
 entropy of K_TOKEN.  This means that a broken or compromised
 (pseudo)random number generator in the server may cause more damage
 than it would in the four-pass variant.  Server implementations
 SHOULD therefore take extreme care to ensure that this situation does
 not occur.

10.6.2. Key Confirmation

 four-pass DSKPP Servers provide key confirmation through the MAC on
 R_C in the <KeyProvServerFinished> message.  In the two-pass DSKPP
 variant described herein, key confirmation is provided by the MAC
 including R, using K_MAC.

10.6.3. Server Authentication

 DSKPP Servers MUST authenticate themselves whenever a successful
 DSKPP two-pass protocol run would result in an existing K_TOKEN being
 replaced by a K_TOKEN', or else a denial-of-service attack where an
 unauthorized DSKPP Server replaces a K_TOKEN with another key would
 be possible.  In two-pass DSKPP, servers authenticate by including
 the AuthenticationDataType extension containing a MAC as described in
 Section 5 for two-pass DSKPP.
 Whenever a successful DSKPP two-pass protocol run would result in an
 existing K_TOKEN being replaced by a K_TOKEN', the DSKPP Client and
 Server MUST do the following to prevent a denial-of-service attack
 where an unauthorized DSKPP Server replaces a K_TOKEN with another
 key:
 o  The DSKPP Server MUST use the AuthenticationDataType extension to
    transmit a second MAC, calculated as described in Section 5.2.2.
 o  The DSKPP Client MUST authenticate the server using the MAC
    contained in the AuthenticationDataType extension received from
    the DSKPP Server to which it is connected.

Doherty, et al. Standards Track [Page 65] RFC 6063 DSKPP December 2010

10.6.4. User Authentication

 A DSKPP Server MUST authenticate a client to ensure that K_TOKEN is
 delivered to the intended device.  The following measures SHOULD be
 considered:
 o  When an Authentication Code is used for client authentication, a
    password dictionary attack on the Authentication Data is possible.
 o  The length of the Authentication Code when used over a non-secure
    channel SHOULD be longer than what is used over a secure channel.
    When a device, e.g., some mobile phones with small screens, cannot
    handle a long Authentication Code in a user-friendly manner, DSKPP
    SHOULD rely on a secure channel for communication.
 o  In the case that a non-secure channel has to be used, the
    Authentication Code SHOULD be sent to the server MAC'd as
    specified in Section 3.4.1.  The Authentication Code and nonce
    value MUST be strong enough to prevent offline brute-force
    recovery of the Authentication Code from the Hashed MAC (HMAC)
    data.  Given that the nonce value is sent in plaintext format over
    a non-secure transport, the cryptographic strength of the
    Authentication Data depends more on the quality of the
    Authentication Code.
 o  When the Authentication Code is sent from the DSKPP Server to the
    device in a DSKPP initialization trigger message, an eavesdropper
    may be able to capture this message and race the legitimate user
    for a key initialization.  To prevent this, the transport layer
    used to send the DSKPP trigger MUST provide confidentiality and
    integrity, e.g. a secure browser session.

10.6.5. Key Protection in Two-Pass DSKPP

 Three key protection methods are defined for the different usages of
 two-pass DSKPP, which MUST be supported by a key package format, such
 as [RFC6030] and [RFC6031].  Therefore, key protection in the two-
 pass DSKPP is dependent upon the security of the key package format
 selected for a protocol run.  Some considerations for the Passphrase-
 Based Key Wrap method follow.
 The Passphrase-Based Key Wrap method SHOULD depend upon the PBKDF2
 function from [PKCS-5] to generate an encryption key from a
 passphrase and salt string.  It is important to note that passphrase-
 based encryption is generally limited in the security that it
 provides despite the use of salt and iteration count in PBKDF2 to
 increase the complexity of attack.  Implementations SHOULD therefore

Doherty, et al. Standards Track [Page 66] RFC 6063 DSKPP December 2010

 take additional measures to strengthen the security of the
 Passphrase-Based Key Wrap method.  The following measures SHOULD be
 considered where applicable:
 o  The passphrase is the same as the one-time password component of
    the Authentication Code (see Section 3.4.1) for a description of
    the AC format).  The passphrase SHOULD be selected well, and usage
    guidelines such as the ones in [NIST-PWD] SHOULD be taken into
    account.
 o  A different passphrase SHOULD be used for every key initialization
    wherever possible (the use of a global passphrase for a batch of
    cryptographic modules SHOULD be avoided, for example).  One way to
    achieve this is to use randomly generated passphrases.
 o  The passphrase SHOULD be protected well if stored on the server
    and/or on the cryptographic module and SHOULD be delivered to the
    device's user using secure methods.
 o  User pre-authentication SHOULD be implemented to ensure that
    K_TOKEN is not delivered to a rogue recipient.
 o  The iteration count in PBKDF2 SHOULD be high to impose more work
    for an attacker using brute-force methods (see [PKCS-5] for
    recommendations).  However, it MUST be noted that the higher the
    count, the more work is required on the legitimate cryptographic
    module to decrypt the newly delivered K_TOKEN.  Servers MAY use
    relatively low iteration counts to accommodate devices with
    limited processing power such as some PDA and cell phones when
    other security measures are implemented and the security of the
    Passphrase-Based Key Wrap method is not weakened.
 o  TLS [RFC5246] SHOULD be used where possible to protect a two-pass
    protocol run.  Transport level security provides a second layer of
    protection for the newly generated K_TOKEN.

10.6.6. Algorithm Agility

 Many protocols need to be algorithm agile.  One reason for this is
 that in the past many protocols had fixed sized fields for
 information such as hash outputs, keys, etc.  This is not the case
 for DSKPP, except for the key size in the computation of DSKPP-PRF.
 Another reason was that protocols did not support algorithm
 negotiation.  This is also not the case for DSKPP, except for the use
 of SHA-256 in the MAC confirmation message.  Updating the key size
 for DSKPP-PRF or the MAC confirmation message algorithm will require
 a new version of the protocol, which is supported with the Version
 attribute.

Doherty, et al. Standards Track [Page 67] RFC 6063 DSKPP December 2010

11. Internationalization Considerations

 DSKPP is meant for machine-to-machine communications; as such, its
 elements are tokens not meant for direct human consumption.  DSKPP
 exchanges information using XML.  All XML processors are required to
 understand UTF-8 [RFC3629] encoding, and therefore all DSKPP Clients
 and servers MUST understand UTF-8 encoded XML.  Additionally, DSKPP
 Servers and clients MUST NOT encode XML with encodings other than
 UTF-8.

12. IANA Considerations

 This document requires several IANA registrations, detailed below.

12.1. URN Sub-Namespace Registration

 This section registers a new XML namespace,
 "urn:ietf:params:xml:ns:keyprov:dskpp" per the guidelines in
 [RFC3688]:
 URI:  urn:ietf:params:xml:ns:keyprov:dskpp
 Registrant Contact:
    IETF, KEYPROV Working Group (keyprov@ietf.org), Andrea Doherty
    (andrea.doherty@rsa.com)
 XML:
    BEGIN
       <?xml version="1.0"?>
       <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
       <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
       <head>
          <title>DSKPP Messages</title>
       </head>
       <body>
          <h1>Namespace for DSKPP Messages</h1>
          <h2>urn:ietf:params:xml:ns:keyprov:dskpp</h2>
          <p>See RFC 6063</p>
       </body>
       </html>
    END

Doherty, et al. Standards Track [Page 68] RFC 6063 DSKPP December 2010

12.2. XML Schema Registration

 This section registers an XML schema as per the guidelines in
 [RFC3688].
 URI:  urn:ietf:params:xml:ns:keyprov:dskpp
 Registrant Contact:
    IETF, KEYPROV Working Group (keyprov@ietf.org), Andrea Doherty
    (andrea.doherty@rsa.com)
 Schema:
    The XML for this schema can be found as the entirety of Section 8
    of this document.

12.3. MIME Media Type Registration

 This section registers the "application/dskpp+xml" MIME type:
 To:  ietf-types@iana.org
 Subject:  Registration of MIME media type application/dskpp+xml
 MIME media type name:  application
 MIME subtype name:  dskpp+xml
 Required parameters:  (none)
 Optional parameters:  charset
    Indicates the character encoding of enclosed XML.
 Encoding considerations:  Uses XML, which can employ 8-bit
    characters, depending on the character encoding used.  See
    [RFC3023], Section 3.2.  Implementations need to support UTF-8
    [RFC3629].
 Security considerations:  This content type is designed to carry
    protocol data related to key management.  Security mechanisms are
    built into the protocol to ensure that various threats are dealt
    with.  Refer to Section 10 of RFC 6063 for more details
 Interoperability considerations:  None
 Published specification:  RFC 6063.
 Applications that use this media type:  Protocol for key exchange.
 Additional information:
    Magic Number(s): (none)
    File extension(s): .xmls
    Macintosh File Type Code(s): (none)
 Person & email address to contact for further information:
    Andrea Doherty (andrea.doherty@rsa.com)
 Intended usage:  LIMITED USE
 Author/Change controller:  The IETF
 Other information:  This media type is a specialization of
    application/xml [RFC3023], and many of the considerations
    described there also apply to application/dskpp+xml.

Doherty, et al. Standards Track [Page 69] RFC 6063 DSKPP December 2010

12.4. Status Code Registration

 This section registers status codes included in each DSKPP response
 message.  The status codes are defined in the schema in the
 <StatusCode> type definition contained in the XML schema in
 Section 8.  The following summarizes the registry:
 Related Registry:
    KEYPROV DSKPP Registries, Status codes for DSKPP
 Defining RFC:
    RFC 6063.
 Registration/Assignment Procedures:
    Following the policies outlined in [RFC3575], the IANA policy for
    assigning new values for the status codes for DSKPP MUST be
    "Specification Required" and their meanings MUST be documented in
    an RFC or in some other permanent and readily available reference,
    in sufficient detail that interoperability between independent
    implementations is possible.  No mechanism to mark entries as
    "deprecated" is envisioned.  It is possible to update entries from
    the registry.
 Registrant Contact:
    IETF, KEYPROV working group (keyprov@ietf.org),
    Andrea Doherty (andrea.doherty@rsa.com)

12.5. DSKPP Version Registration

 This section registers DSKPP version numbers.  The registry has the
 following structure:
 +-------------------------------------------+
 |  DSKPP Version    | Specification         |
 +-------------------------------------------+
 |  1.0              | This document         |
 +-------------------------------------------+
 Standards action is required to define new versions of DSKPP.  It is
 not envisioned to deprecate, delete, or modify existing DSKPP
 versions.

12.6. PRF Algorithm ID Sub-Registry

 This specification relies on a cryptographic primitive, called
 "DSKPP-PRF" that provides a deterministic transformation of a secret
 key k and a varying length octet string s to a bit string of
 specified length dsLen.  From the point of view of this
 specification, DSKPP-PRF is a "black-box" function that, given the
 inputs, generates a pseudorandom value that can be realized by any

Doherty, et al. Standards Track [Page 70] RFC 6063 DSKPP December 2010

 appropriate and competent cryptographic technique.  Section 3.4.2
 provides two realizations of DSKPP-PRF, DSKPP-PRF-AES, and DSKPP-PRF-
 SHA256.
 This section registers the identifiers associated with these
 realizations.  PRF Algorithm ID Sub-registries are to be subject to
 "Specification Required" as per RFC 5226 [RFC5226].  Updates MUST be
 documented in an RFC or in some other permanent and readily available
 reference, in sufficient detail that interoperability between
 independent implementations is possible.
 Expert approval is required to deprecate a sub-registry.  Once
 deprecated, the PRF Algorithm ID SHOULD NOT be used in any new
 implementations.

12.6.1. DSKPP-PRF-AES

 This section registers the following in the IETF XML namespace
 registry.
 Common Name:
    DSKPP-PRF-AES
 URI:
    urn:ietf:params:xml:ns:keyprov:dskpp:prf-aes-128
 Identifier Definition:
    The DSKPP-PRF-AES algorithm realization is defined in
    Appendix D.2.2 of this document.
 Registrant Contact:
    IETF, KEYPROV working group (keyprov@ietf.org),
    Andrea Doherty (andrea.doherty@rsa.com)

12.6.2. DSKPP-PRF-SHA256

 This section registers the following in the IETF XML namespace
 registry.
 Common Name:
    DSKPP-PRF-SHA256
 URI:
    urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
 Identifier Definition:
    The DSKPP-PRF-SHA256 algorithm realization is defined in
    Appendix D.3.2 of this document.

Doherty, et al. Standards Track [Page 71] RFC 6063 DSKPP December 2010

 Registrant Contact:
    IETF, KEYPROV working group (keyprov@ietf.org),
    Andrea Doherty (andrea.doherty@rsa.com)

12.7. Key Container Registration

 This section registers the Key Container type.
 Key Container:
    The registration name for the Key Container.
 Specification:
    Key Container defines a key package format that specifies how a
    key should be protected using the three key protection methods
    provided in Section 5.1.
 Registration Procedure:
    Following the policies outlined in [RFC3575], the IANA policy for
    assigning new values for the status codes for DSKPP MUST be
    "Specification Required" and their meanings MUST be documented in
    an RFC or in some other permanent and readily available reference,
    in sufficient detail that interoperability between independent
    implementations is possible.
 Deprecated:
    TRUE if based on expert approval this entry has been deprecated
    and SHOULD NOT be used in any new implementations.  Otherwise,
    FALSE.
 Identifiers:
    The initial URIs for the Key Container defined for this version of
    the document are listed here:
    Name:  PSKC Key Container
    URI:  urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
    Specification:  [RFC6030]
    Deprecated:  FALSE
    Name:  SKPC Key Container
    URI:  urn:ietf:params:xml:ns:keyprov:dskpp:skpc-key-container
    Specification:  [RFC6031]
    Deprecated:  FALSE
    Name:  PKCS12 Key Container
    URI:  urn:ietf:params:xml:ns:keyprov:dskpp:pkcs12-key-container
    Specification:  [PKCS-12]
    Deprecated:  FALSE

Doherty, et al. Standards Track [Page 72] RFC 6063 DSKPP December 2010

    Name:  PKCS5-XML Key Container
    URI:  urn:ietf:params:xml:ns:keyprov:dskpp:pkcs5-xml-key-container
    Specification:  [PKCS-5-XML]
    Deprecated:  FALSE
 Registrant Contact:
    IETF, KEYPROV working group (keyprov@ietf.org),
    Andrea Doherty (andrea.doherty@rsa.com)

13. Intellectual Property Considerations

 RSA and RSA Security are registered trademarks or trademarks of RSA
 Security, Inc. in the United States and/or other countries.  The
 names of other products and services mentioned may be the trademarks
 of their respective owners.

14. Contributors

 This work is based on information contained in [RFC4758], authored by
 Magnus Nystrom, with enhancements borrowed from an individual
 document coauthored by Mingliang Pei and Salah Machani (e.g., user
 authentication, and support for multiple key package formats).
 We would like to thank Philip Hoyer for his work in aligning DSKPP
 and PSKC schemas.
 We would also like to thank Hannes Tschofenig and Phillip Hallam-
 Baker for their reviews, feedback, and text contributions.

15. Acknowledgements

 We would like to thank the following for review of previous DSKPP
 document versions:
 o  Dr. Ulrike Meyer (Review June 2007)
 o  Niklas Neumann (Review June 2007)
 o  Shuh Chang (Review June 2007)
 o  Hannes Tschofenig (Review June 2007 and again in August 2007)
 o  Sean Turner (Reviews August 2007 and again in July 2008)
 o  John Linn (Review August 2007)
 o  Philip Hoyer (Review September 2007)
 o  Thomas Roessler (Review November 2007)
 o  Lakshminath Dondeti (Comments December 2007)
 o  Pasi Eronen (Comments December 2007)
 o  Phillip Hallam-Baker (Review and Edits November 2008 and again in
    January 2009)
 o  Alexey Melnikov (Review May 2010)
 o  Peter Saint-Andre (Review May 2010)

Doherty, et al. Standards Track [Page 73] RFC 6063 DSKPP December 2010

 We would also like to thank the following for their input to selected
 design aspects of DSKPP:
 o  Anders Rundgren (Key Package Format and Client Authentication
    Data)
 o  Thomas Roessler (HTTP Binding)
 o  Hannes Tschofenig (HTTP Binding)
 o  Phillip Hallam-Baker (Registry for Algorithms)
 o  N. Asokan (original observation of weakness in Authentication
    Data)
 Finally, we would like to thank Robert Griffin for opening
 communication channels for us with the IEEE P1619.3 Key Management
 Group, and facilitating our groups in staying informed of potential
 areas (especially key provisioning and global key identifiers of
 collaboration) of collaboration.

16. References

16.1. Normative References

 [FIPS180-SHA]     National Institute of Standards and Technology,
                   "Secure Hash Standard", FIPS 180-2, February 2004,
                   <http://csrc.nist.gov/publications/fips/fips180-2/
                   fips180-2withchangenotice.pdf>.
 [FIPS197-AES]     National Institute of Standards and Technology,
                   "Specification for the Advanced Encryption Standard
                   (AES)", FIPS 197, November 2001, <http://
                   csrc.nist.gov/publications/fips/fips197/
                   fips-197.pdf>.
 [ISO3309]         International Organization for Standardization,
                   "ISO Information Processing Systems - Data
                   Communication - High-Level Data Link Control
                   Procedure - Frame Structure", ISO 3309,
                   3rd Edition, October 1984.
 [PKCS-1]          RSA Laboratories, "RSA Cryptography Standard",
                   PKCS #1 Version 2.1, June 2002,
                   <http://www.rsasecurity.com/rsalabs/pkcs/>.
 [PKCS-5]          RSA Laboratories, "Password-Based Cryptography
                   Standard", PKCS #5 Version 2.0, March 1999,
                   <http://www.rsasecurity.com/rsalabs/pkcs/>.

Doherty, et al. Standards Track [Page 74] RFC 6063 DSKPP December 2010

 [PKCS-5-XML]      RSA Laboratories, "XML Schema for PKCS #5 Version
                   2.0", PKCS #5 Version 2.0 Amd.1 (FINAL DRAFT),
                   October 2006,
                   <http://www.rsasecurity.com/rsalabs/pkcs/>.
 [RFC2104]         Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
                   Keyed-Hashing for Message Authentication",
                   RFC 2104, February 1997.
 [RFC2119]         Bradner, S., "Key words for use in RFCs to Indicate
                   Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2616]         Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                   Masinter, L., Leach, P., and T. Berners-Lee,
                   "Hypertext Transfer Protocol -- HTTP/1.1",
                   RFC 2616, June 1999.
 [RFC3394]         Schaad, J. and R. Housley, "Advanced Encryption
                   Standard (AES) Key Wrap Algorithm", RFC 3394,
                   September 2002.
 [RFC3629]         Yergeau, F., "UTF-8, a transformation format of ISO
                   10646", STD 63, RFC 3629, November 2003.
 [RFC4013]         Zeilenga, K., "SASLprep: Stringprep Profile for
                   User Names and Passwords", RFC 4013, February 2005.
 [RFC4210]         Adams, C., Farrell, S., Kause, T., and T. Mononen,
                   "Internet X.509 Public Key Infrastructure
                   Certificate Management Protocol (CMP)", RFC 4210,
                   September 2005.
 [RFC5272]         Schaad, J. and M. Myers, "Certificate Management
                   over CMS (CMC)", RFC 5272, June 2008.
 [RFC5280]         Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
                   Housley, R., and W. Polk, "Internet X.509 Public
                   Key Infrastructure Certificate and Certificate
                   Revocation List (CRL) Profile", RFC 5280, May 2008.
 [RFC5649]         Housley, R. and M. Dworkin, "Advanced Encryption
                   Standard (AES) Key Wrap with Padding Algorithm",
                   RFC 5649, September 2009.
 [RFC6030]         Hoyer, P., Pei, M., and S. Machani, "Portable
                   Symmetric Key Container (PSKC)", RFC 6030,
                   October 2010.

Doherty, et al. Standards Track [Page 75] RFC 6063 DSKPP December 2010

 [UNICODE]         Davis, M. and M. Duerst, "Unicode Normalization
                   Forms", March 2001, <http://www.unicode.org/
                   unicode/reports/tr15/tr15-21.html>.
 [XML]             W3C, "Extensible Markup Language (XML) 1.0 (Fifth
                   Edition)", W3C Recommendation, November 2008,
                   <http://www.w3.org/TR/2006/REC-xml-20060816/>.
 [XMLDSIG]         W3C, "XML Signature Syntax and Processing",
                   W3C Recommendation, February 2002, <http://
                   www.w3.org/TR/2002/REC-xmldsig-core-20020212/>.
 [XMLENC]          W3C, "XML Encryption Syntax and Processing",
                   W3C Recommendation, December 2002, <http://
                   www.w3.org/TR/2002/REC-xmldsig-core-20020212/>.

16.2. Informative References

 [CT-KIP-P11]      RSA Laboratories, "PKCS #11 Mechanisms for the
                   Cryptographic Token Key Initialization Protocol",
                   PKCS #11 Version 2.20 Amd.2, December 2005,
                   <http://www.rsasecurity.com/rsalabs/pkcs/>.
 [FAQ]             RSA Laboratories, "Frequently Asked Questions About
                   Today's Cryptography",  Version 4.1, 2000.
 [NIST-PWD]        National Institute of Standards and Technology,
                   "Password Usage", FIPS 112, May 1985,
                   <http://www.itl.nist.gov/fipspubs/fip112.htm>.
 [NIST-SP800-38B]  International Organization for Standardization,
                   "Recommendations for Block Cipher Modes of
                   Operation: The CMAC Mode for Authentication",
                   NIST SP800-38B, May 2005, <http://csrc.nist.gov/
                   publications/nistpubs/800-38B/SP_800-38B.pdf>.
 [NIST-SP800-57]   National Institute of Standards and Technology,
                   "Recommendation for Key Management - Part I:
                   General (Revised)", NIST 800-57, March 2007, <http:
                   //csrc.nist.gov/publications/nistpubs/800-57/
                   sp800-57-Part1-revised2_Mar08-2007.pdf>.
 [PKCS-11]         RSA Laboratories, "Cryptographic Token Interface
                   Standard", PKCS #11 Version 2.20, June 2004,
                   <http://www.rsasecurity.com/rsalabs/pkcs/>.

Doherty, et al. Standards Track [Page 76] RFC 6063 DSKPP December 2010

 [PKCS-12]         "Personal Information Exchange Syntax Standard",
                   PKCS #12 Version 1.0, 2005, <ftp://
                   ftp.rsasecurity.com/pub/pkcs/pkcs-12/
                   pkcs-12v1.pdf>.
 [RFC2818]         Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
 [RFC3023]         Murata, M., St. Laurent, S., and D. Kohn, "XML
                   Media Types", RFC 3023, January 2001.
 [RFC3575]         Aboba, B., "IANA Considerations for RADIUS (Remote
                   Authentication Dial In User Service)", RFC 3575,
                   July 2003.
 [RFC3688]         Mealling, M., "The IETF XML Registry", BCP 81,
                   RFC 3688, January 2004.
 [RFC3986]         Berners-Lee, T., Fielding, R., and L. Masinter,
                   "Uniform Resource Identifier (URI): Generic
                   Syntax", STD 66, RFC 3986, January 2005.
 [RFC4758]         Nystroem, M., "Cryptographic Token Key
                   Initialization Protocol (CT-KIP) Version 1.0
                   Revision 1", RFC 4758, November 2006.
 [RFC5226]         Narten, T. and H. Alvestrand, "Guidelines for
                   Writing an IANA Considerations Section in RFCs",
                   BCP 26, RFC 5226, May 2008.
 [RFC5246]         Dierks, T. and E. Rescorla, "The Transport Layer
                   Security (TLS) Protocol Version 1.2", RFC 5246,
                   August 2008.
 [RFC6031]         Turner, S. and R. , "Cryptographic Message Syntax
                   (CMS) Symmetric Key Package Content Type",
                   RFC 6031, December 2010.
 [XMLNS]           W3C, "Namespaces in XML", W3C Recommendation,
                   January 1999,
                   <http://www.w3.org/TR/2009/REC-xml-names-20091208>.

Doherty, et al. Standards Track [Page 77] RFC 6063 DSKPP December 2010

Appendix A. Usage Scenarios

 DSKPP is expected to be used to provision symmetric keys to
 cryptographic modules in a number of different scenarios, each with
 its own special requirements, as described below.  This appendix
 forms an informative part of the document.

A.1. Single Key Request

 The usual scenario is that a cryptographic module makes a request for
 a symmetric key from a provisioning server that is located on the
 local network or somewhere on the Internet.  Depending upon the
 deployment scenario, the provisioning server may generate a new key
 on-the-fly or use a pre-generated key, e.g., one provided by a legacy
 back-end issuance server.  The provisioning server assigns a unique
 key ID to the symmetric key and provisions it to the cryptographic
 module.

A.2. Multiple Key Requests

 A cryptographic module makes multiple requests for symmetric keys
 from the same provisioning server.  The symmetric keys need not be of
 the same type, i.e., the keys may be used with different symmetric
 key cryptographic algorithms, including one-time password
 authentication algorithms, and the AES encryption algorithm.

A.3. User Authentication

 In some deployment scenarios, a key issuer may rely on a third-party
 provisioning service.  In this case, the issuer directs provisioning
 requests from the cryptographic module to the provisioning service.
 As such, it is the responsibility of the issuer to authenticate the
 user through some out-of-band means before granting him rights to
 acquire keys.  Once the issuer has granted those rights, the issuer
 provides an Authentication Code to the user and makes it available to
 the provisioning service, so that the user can prove that he is
 authorized to acquire keys.

A.4. Provisioning Time-Out Policy

 An issuer may provide a time-limited Authentication Code to a user
 during registration, which the user will input into the cryptographic
 module to authenticate themselves with the provisioning server.  The
 server will allow a key to be provisioned to the cryptographic module
 hosted by the user's device when user authentication is required only
 if the user inputs a valid Authentication Code within the fixed time
 period established by the issuer.

Doherty, et al. Standards Track [Page 78] RFC 6063 DSKPP December 2010

A.5. Key Renewal

 A cryptographic module requests renewal of the symmetric key material
 attached to a key ID, as opposed to keeping the key value constant
 and refreshing the metadata.  Such a need may occur in the case when
 a user wants to upgrade her device that houses the cryptographic
 module or when a key has expired.  When a user uses the same
 cryptographic module for example, to perform strong authentication at
 multiple Web login sites, keeping the same key ID removes the need
 for the user to register a new key ID at each site.

A.6. Pre-Loaded Key Replacement

 This scenario represents a special case of symmetric key renewal in
 which a local administrator can authenticate the user procedurally
 before initiating the provisioning process.  It also allows for a
 device issuer to pre-load a key onto a cryptographic module with a
 restriction that the key is replaced with a new key prior to use of
 the cryptographic module.  Another variation of this scenario is the
 organization who recycles devices.  In this case, a key issuer would
 provision a new symmetric key to a cryptographic module hosted on a
 device that was previously owned by another user.
 Note that this usage scenario is essentially the same as the previous
 scenario wherein the same key ID is used for renewal.

A.7. Pre-Shared Manufacturing Key

 A cryptographic module is loaded onto a smart card after the card is
 issued to a user.  The symmetric key for the cryptographic module
 will then be provisioned using a secure channel mechanism present in
 many smart card platforms.  This allows a direct secure channel to be
 established between the smart card chip and the provisioning server.
 For example, the card commands (i.e., Application Protocol Data
 Units, or APDUs) are encrypted with a pre-issued card manufacturer's
 key and sent directly to the smart card chip, allowing secure post-
 issuance in-the-field provisioning.  This secure flow can pass
 Transport Layer Security (TLS) [RFC5246] and other transport security
 boundaries.
 Note that two pre-conditions for this usage scenario are for the
 protocol to be tunneled and the provisioning server to know the
 correct pre-established manufacturer's key.

Doherty, et al. Standards Track [Page 79] RFC 6063 DSKPP December 2010

A.8. End-to-End Protection of Key Material

 In this scenario, Transport Layer Security does not provide end-to-
 end protection of keying material transported from the provisioning
 server to the cryptographic module.  For example, TLS may terminate
 at an application hosted on a PC rather than at the cryptographic
 module (i.e., the endpoint) located on a data storage device
 [RFC5246].  Mutually authenticated key agreement provides end-to-end
 protection, which TLS cannot provide.

Appendix B. Examples

 This appendix contains example messages that illustrate parameters,
 encoding, and semantics in four- and two-pass DSKPP exchanges.  The
 examples are written using XML, and are syntactically correct.  MAC
 and cipher values are fictitious, however.  This appendix forms an
 informative part of the document.

B.1. Trigger Message

 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvTrigger Version="1.0"
   xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
   xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc">
   <dskpp:InitializationTrigger>
     <dskpp:DeviceIdentifierData>
         <dskpp:DeviceId>
             <pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>
             <pskc:SerialNo>987654321</pskc:SerialNo>
             <pskc:StartDate>2009-09-01T00:00:00Z</pskc:StartDate>
             <pskc:ExpiryDate>2014-09-01T00:00:00Z</pskc:ExpiryDate>
         </dskpp:DeviceId>
     </dskpp:DeviceIdentifierData>
     <dskpp:KeyID>SE9UUDAwMDAwMDAx</dskpp:KeyID>
     <dskpp:TokenPlatformInfo KeyLocation="Hardware"
       AlgorithmLocation="Software"/>
     <dskpp:AuthenticationData>
       <dskpp:ClientID>31300257</dskpp:ClientID>
       <dskpp:AuthenticationCodeMac>
         <dskpp:IterationCount>512</dskpp:IterationCount>
         <dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
       </dskpp:AuthenticationCodeMac>
     </dskpp:AuthenticationData>
     <dskpp:ServerUrl>keyprovservice.example.com
       </dskpp:ServerUrl>
   </dskpp:InitializationTrigger>
 </dskpp:KeyProvTrigger>

Doherty, et al. Standards Track [Page 80] RFC 6063 DSKPP December 2010

B.2. Four-Pass Protocol

B.2.1. <KeyProvClientHello> without a Preceding Trigger

  <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <dskpp:KeyProvClientHello
      xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
      xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
      xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
      xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
      Version="1.0">
      <dskpp:DeviceIdentifierData>
          <dskpp:DeviceId>
              <pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>
              <pskc:SerialNo>987654321</pskc:SerialNo>
              <pskc:StartDate>2009-09-01T00:00:00Z</pskc:StartDate>
              <pskc:ExpiryDate>2014-09-01T00:00:00Z</pskc:ExpiryDate>
          </dskpp:DeviceId>
      </dskpp:DeviceIdentifierData>
      <dskpp:SupportedKeyTypes>
          <dskpp:Algorithm>
              urn:ietf:params:xml:ns:keyprov:pskc:hotp
          </dskpp:Algorithm>
          <dskpp:Algorithm>
  http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
          </dskpp:Algorithm>
      </dskpp:SupportedKeyTypes>
      <dskpp:SupportedEncryptionAlgorithms>
          <dskpp:Algorithm>
              http://www.w3.org/2001/04/xmlenc#aes128-cbc
          </dskpp:Algorithm>
      </dskpp:SupportedEncryptionAlgorithms>
      <dskpp:SupportedMacAlgorithms>
          <dskpp:Algorithm>
              urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
          </dskpp:Algorithm>
      </dskpp:SupportedMacAlgorithms>
      <dskpp:SupportedProtocolVariants>
          <dskpp:FourPass/>
      </dskpp:SupportedProtocolVariants>
      <dskpp:SupportedKeyPackages>
          <dskpp:KeyPackageFormat>
              urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
          </dskpp:KeyPackageFormat>
      </dskpp:SupportedKeyPackages>
  </dskpp:KeyProvClientHello>

Doherty, et al. Standards Track [Page 81] RFC 6063 DSKPP December 2010

B.2.2. <KeyProvClientHello> Assuming a Preceding Trigger

  <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <dskpp:KeyProvClientHello
      xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
      xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
      xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
      xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
      Version="1.0">
      <dskpp:DeviceIdentifierData>
          <dskpp:DeviceId>
              <pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>
              <pskc:SerialNo>987654321</pskc:SerialNo>
              <pskc:StartDate>2009-09-01T00:00:00Z</pskc:StartDate>
              <pskc:ExpiryDate>2014-09-01T00:00:00Z</pskc:ExpiryDate>
          </dskpp:DeviceId>
      </dskpp:DeviceIdentifierData>
      <dskpp:KeyID>SE9UUDAwMDAwMDAx</dskpp:KeyID>
      <dskpp:SupportedKeyTypes>
          <dskpp:Algorithm>
              urn:ietf:params:xml:ns:keyprov:pskc:hotp
          </dskpp:Algorithm>
          <dskpp:Algorithm>
  http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
          </dskpp:Algorithm>
      </dskpp:SupportedKeyTypes>
      <dskpp:SupportedEncryptionAlgorithms>
          <dskpp:Algorithm>
              http://www.w3.org/2001/04/xmlenc#aes128-cbc
          </dskpp:Algorithm>
      </dskpp:SupportedEncryptionAlgorithms>
      <dskpp:SupportedMacAlgorithms>
          <dskpp:Algorithm>
              urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
          </dskpp:Algorithm>
      </dskpp:SupportedMacAlgorithms>
      <dskpp:SupportedProtocolVariants>
        <dskpp:FourPass/>
      </dskpp:SupportedProtocolVariants>
      <dskpp:SupportedKeyPackages>
          <dskpp:KeyPackageFormat>
              urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
          </dskpp:KeyPackageFormat>
      </dskpp:SupportedKeyPackages>
  </dskpp:KeyProvClientHello>

Doherty, et al. Standards Track [Page 82] RFC 6063 DSKPP December 2010

B.2.3. <KeyProvServerHello> Without a Preceding Trigger

 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvServerHello
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     Version="1.0"
     Status="Continue"
     SessionID="4114">
     <dskpp:KeyType>
         urn:ietf:params:xml:ns:keyprov:pskc:hotp
     </dskpp:KeyType>
     <dskpp:EncryptionAlgorithm>
         http://www.w3.org/2001/04/xmlenc#aes128-cbc
     </dskpp:EncryptionAlgorithm>
     <dskpp:MacAlgorithm>
         urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
     </dskpp:MacAlgorithm>
     <dskpp:EncryptionKey>
       <ds:KeyName>Example-Key1</ds:KeyName>
     </dskpp:EncryptionKey>
     <dskpp:KeyPackageFormat>
         urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
     </dskpp:KeyPackageFormat>
     <dskpp:Payload>
         <dskpp:Nonce>EjRWeJASNFZ4kBI0VniQEg==</dskpp:Nonce>
     </dskpp:Payload>
 </dskpp:KeyProvServerHello>

Doherty, et al. Standards Track [Page 83] RFC 6063 DSKPP December 2010

B.2.4. <KeyProvServerHello> Assuming Key Renewal

  <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <dskpp:KeyProvServerHello
    xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
    xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
    xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
    xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
    Version="1.0"
    SessionID="4114"
    Status="Continue">
    <dskpp:KeyType>
      urn:ietf:params:xml:schema:keyprov:otpalg#SecurID-AES
    </dskpp:KeyType>
    <dskpp:EncryptionAlgorithm>
       http://www.w3.org/2001/04/xmlenc#aes128-cbc
    </dskpp:EncryptionAlgorithm>
    <dskpp:MacAlgorithm>
       urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
    </dskpp:MacAlgorithm>
    <dskpp:EncryptionKey>
      <ds:KeyName>Example-Key1</ds:KeyName>
    </dskpp:EncryptionKey>
    <dskpp:KeyPackageFormat>
      urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
    </dskpp:KeyPackageFormat>
    <dskpp:Payload>
      <dskpp:Nonce>qw2ewasde312asder394jw==</dskpp:Nonce>
    </dskpp:Payload>
    <dskpp:Mac
      MacAlgorithm="urn:ietf:params:xml:ns:keyprov:dskpp:prf-aes-128">
      cXcycmFuZG9tMzEyYXNkZXIzOTRqdw==
    </dskpp:Mac>
  </dskpp:KeyProvServerHello>

Doherty, et al. Standards Track [Page 84] RFC 6063 DSKPP December 2010

B.2.5. <KeyProvClientNonce> Using Default Encryption

 This message contains the nonce chosen by the cryptographic module,
 R_C, encrypted by the specified encryption key and encryption
 algorithm.
  <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <dskpp:KeyProvClientNonce
      xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
      xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
      xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
      xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
      SessionID="4114"
      Version="1.0">
      <dskpp:EncryptedNonce>
          oTvo+S22nsmS2Z/RtcoF8CTwadRa1PVsRXkZnCihHkU1rPueggrd0NpEWVZR
          16Rg16+FHuTg33GK1wH3wffDZQ==
      </dskpp:EncryptedNonce>
  </dskpp:KeyProvClientNonce>

B.2.6. <KeyProvServerFinished> Using Default Encryption

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <dskpp:KeyProvServerFinished
        xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
        xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
        xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
        xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
        Version="1.0"
        Status="Success"
        SessionID="4114">
        <dskpp:KeyPackage>
            <dskpp:KeyContainer Version="1.0" Id="KC0001">
                <pskc:KeyPackage>
                    <pskc:DeviceInfo>
                        <pskc:Manufacturer>
                           TokenVendorAcme
                        </pskc:Manufacturer>
                        <pskc:SerialNo>
                           987654321
                        </pskc:SerialNo>
                        <pskc:StartDate>
                           2009-09-01T00:00:00Z
                        </pskc:StartDate>
                        <pskc:ExpiryDate>
                           2014-09-01T00:00:00Z
                        </pskc:ExpiryDate>
                    </pskc:DeviceInfo>

Doherty, et al. Standards Track [Page 85] RFC 6063 DSKPP December 2010

                    <pskc:CryptoModuleInfo>
                        <pskc:Id>CM_ID_001</pskc:Id>
                    </pskc:CryptoModuleInfo>
                    <pskc:Key
                       Id="MBK000000001"
                       Algorithm=
                          "urn:ietf:params:xml:ns:keyprov:pskc:hotp">
                       <pskc:Issuer>Example-Issuer</pskc:Issuer>
                       <pskc:AlgorithmParameters>
                           <pskc:ResponseFormat Length="6"
                              Encoding="DECIMAL"/>
                        </pskc:AlgorithmParameters>
                        <pskc:Data>
                            <pskc:Counter>
                                <pskc:PlainValue>0</pskc:PlainValue>
                            </pskc:Counter>
                        </pskc:Data>
                        <pskc:Policy>
                            <pskc:KeyUsage>OTP</pskc:KeyUsage>
                        </pskc:Policy>
                    </pskc:Key>
                </pskc:KeyPackage>
            </dskpp:KeyContainer>
        </dskpp:KeyPackage>
        <dskpp:Mac
            MacAlgorithm=
               "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
            151yAR2NqU5dJzETK+SGYqN6sq6DEH5AgHohra3Jpp4=
        </dskpp:Mac>
    </dskpp:KeyProvServerFinished>

B.3. Two-Pass Protocol

B.3.1. Example Using the Key Transport Method

 The client indicates support for all the Key Transport, Key Wrap, and
 Passphrase-Based Key Wrap key protection methods:
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvClientHello
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     Version="1.0">
     <dskpp:DeviceIdentifierData>
         <dskpp:DeviceId>
             <pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>

Doherty, et al. Standards Track [Page 86] RFC 6063 DSKPP December 2010

             <pskc:SerialNo>987654321</pskc:SerialNo>
             <pskc:StartDate>2009-09-01T00:00:00Z</pskc:StartDate>
             <pskc:ExpiryDate>2014-09-01T00:00:00Z</pskc:ExpiryDate>
         </dskpp:DeviceId>
     </dskpp:DeviceIdentifierData>
     <dskpp:SupportedKeyTypes>
         <dskpp:Algorithm>
             urn:ietf:params:xml:ns:keyprov:pskc:hotp
         </dskpp:Algorithm>
         <dskpp:Algorithm>
 http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
         </dskpp:Algorithm>
     </dskpp:SupportedKeyTypes>
     <dskpp:SupportedEncryptionAlgorithms>
         <dskpp:Algorithm>
             http://www.w3.org/2001/04/xmlenc#rsa_1_5
         </dskpp:Algorithm>
     </dskpp:SupportedEncryptionAlgorithms>
     <dskpp:SupportedMacAlgorithms>
         <dskpp:Algorithm>
             urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
         </dskpp:Algorithm>
     </dskpp:SupportedMacAlgorithms>
     <dskpp:SupportedProtocolVariants>
         <dskpp:TwoPass>
             <dskpp:SupportedKeyProtectionMethod>
                 urn:ietf:params:xml:schema:keyprov:dskpp:transport
             </dskpp:SupportedKeyProtectionMethod>
             <dskpp:Payload>
                 <ds:KeyInfo>
                     <ds:X509Data>
                         <ds:X509Certificate>
 MIIB5zCCAVCgAwIBAgIESZp/vDANBgkqhkiG9w0BAQUFADA4MQ0wCwYDVQQKEwRJRVRGM
 RMwEQYDVQQLEwpLZXlQcm92IFdHMRIwEAYDVQQDEwlQU0tDIFRlc3QwHhcNMDkwMjE3MD
 kxMzMyWhcNMTEwMjE3MDkxMzMyWjA4MQ0wCwYDVQQKEwRJRVRGMRMwEQYDVQQLEwpLZXl
 Qcm92IFdHMRIwEAYDVQQDEwlQU0tDIFRlc3QwgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJ
 AoGBALCWLDa2ItYJ6su80hd1gL4cggQYdyyKK17btt/aS6Q/eDsKjsPyFIODsxeKVV/uA
 3wLT4jQJM5euKJXkDajzGGOy92+ypfzTX4zDJMkh61SZwlHNJxBKilAM5aW7C+BQ0RvCx
 vdYtzx2LTdB+X/KMEBA7uIYxLfXH2Mnub3WIh1AgMBAAEwDQYJKoZIhvcNAQEFBQADgYE
 Ae875m84sYUJ8qPeZ+NG7REgTvlHTmoCdoByU0LBBLotUKuqfrnRuXJRMeZXaaEGmzY1k
 LonVjQGzjAkU4dJ+RPmiDlYuHLZS41Pg6VMwY+03lhk6I5A/w4rnqdkmwZX/NgXg06aln
 c2pBsXWhL4O7nk0S2ZrLMsQZ6HcsXgdmHo=
                         </ds:X509Certificate>
                     </ds:X509Data>
                 </ds:KeyInfo>
             </dskpp:Payload>
         </dskpp:TwoPass>
     </dskpp:SupportedProtocolVariants>

Doherty, et al. Standards Track [Page 87] RFC 6063 DSKPP December 2010

     <dskpp:SupportedKeyPackages>
         <dskpp:KeyPackageFormat>
             urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
         </dskpp:KeyPackageFormat>
     </dskpp:SupportedKeyPackages>
     <dskpp:AuthenticationData>
         <dskpp:ClientID>AC00000A</dskpp:ClientID>
         <dskpp:AuthenticationCodeMac>
             <dskpp:Nonce>
                 ESIzRFVmd4iZqrvM3e7/ESIzRFVmd4iZqrvM3e7/ESI=
             </dskpp:Nonce>
             <dskpp:IterationCount>100000</dskpp:IterationCount>
             <dskpp:Mac
                 MacAlgorithm=
                 "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
                 3eRz51ILqiG+dJW2iLcjuA==
             </dskpp:Mac>
         </dskpp:AuthenticationCodeMac>
     </dskpp:AuthenticationData>
 </dskpp:KeyProvClientHello>
 In this example, the server responds to the previous request by
 returning a key package in which the provisioning key was encrypted
 using the Key Transport key protection method.
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvServerFinished
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:dkey="http://www.w3.org/2009/xmlsec-derivedkey#"
     xmlns:pkcs5=
        "http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
     Version="1.0"
     Status="Success"
     SessionID="4114">
     <dskpp:KeyPackage>
         <dskpp:KeyContainer Version="1.0" Id="KC0001">
             <pskc:EncryptionKey>
                 <ds:X509Data>
                     <ds:X509Certificate>
 MIIB5zCCAVCgAwIBAgIESZp/vDANBgkqhkiG9w0BAQUFADA4MQ0wCwYDVQQKEwRJRVRGM
 RMwEQYDVQQLEwpLZXlQcm92IFdHMRIwEAYDVQQDEwlQU0tDIFRlc3QwHhcNMDkwMjE3MD
 kxMzMyWhcNMTEwMjE3MDkxMzMyWjA4MQ0wCwYDVQQKEwRJRVRGMRMwEQYDVQQLEwpLZXl
 Qcm92IFdHMRIwEAYDVQQDEwlQU0tDIFRlc3QwgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJ
 AoGBALCWLDa2ItYJ6su80hd1gL4cggQYdyyKK17btt/aS6Q/eDsKjsPyFIODsxeKVV/uA
 3wLT4jQJM5euKJXkDajzGGOy92+ypfzTX4zDJMkh61SZwlHNJxBKilAM5aW7C+BQ0RvCx

Doherty, et al. Standards Track [Page 88] RFC 6063 DSKPP December 2010

 vdYtzx2LTdB+X/KMEBA7uIYxLfXH2Mnub3WIh1AgMBAAEwDQYJKoZIhvcNAQEFBQADgYE
 Ae875m84sYUJ8qPeZ+NG7REgTvlHTmoCdoByU0LBBLotUKuqfrnRuXJRMeZXaaEGmzY1k
 LonVjQGzjAkU4dJ+RPmiDlYuHLZS41Pg6VMwY+03lhk6I5A/w4rnqdkmwZX/NgXg06aln
 c2pBsXWhL4O7nk0S2ZrLMsQZ6HcsXgdmHo=
                     </ds:X509Certificate>
                 </ds:X509Data>
             </pskc:EncryptionKey>
             <pskc:KeyPackage>
                 <pskc:DeviceInfo>
                     <pskc:Manufacturer>
                        TokenVendorAcme
                     </pskc:Manufacturer>
                     <pskc:SerialNo>
                        987654321
                     </pskc:SerialNo>
                     <pskc:StartDate>
                        2009-09-01T00:00:00Z
                     </pskc:StartDate>
                     <pskc:ExpiryDate>
                        2014-09-01T00:00:00Z
                     </pskc:ExpiryDate>
                 </pskc:DeviceInfo>
                 <pskc:Key
                     Id="MBK000000001"
                     Algorithm=
                        "urn:ietf:params:xml:ns:keyprov:pskc:hotp">
                     <pskc:Issuer>Example-Issuer</pskc:Issuer>
                     <pskc:AlgorithmParameters>
                         <pskc:ResponseFormat Length="6"
                            Encoding="DECIMAL"/>
                     </pskc:AlgorithmParameters>
                     <pskc:Data>
                         <pskc:Secret>
                             <pskc:EncryptedValue>
                                 <xenc:EncryptionMethod
                                  Algorithm=
                          "http://www.w3.org/2001/04/xmlenc#rsa_1_5"/>
                                 <xenc:CipherData>
                                     <xenc:CipherValue>
 eyjr23WMy9S2UdKgGnQEbs44T1jmX1TNWEBq48xfS20PK2VWF4ZK1iSctHj/u3uk+7+y8
 uKrAzHEm5mujKPAU4DCbb5mSibXMnAbbIoAi2cJW60/l8FlzwaU4EZsZ1LyQ1GcBQKACE
 eylG5vK8NTo47vZTatL5UxmbmOX2HvaVQ=
                                     </xenc:CipherValue>
                                 </xenc:CipherData>
                             </pskc:EncryptedValue>
                         </pskc:Secret>
                         <pskc:Counter>
                             <pskc:PlainValue>0</pskc:PlainValue>

Doherty, et al. Standards Track [Page 89] RFC 6063 DSKPP December 2010

                         </pskc:Counter>
                     </pskc:Data>
                     <pskc:Policy>
                         <pskc:KeyUsage>OTP</pskc:KeyUsage>
                     </pskc:Policy>
                 </pskc:Key>
             </pskc:KeyPackage>
         </dskpp:KeyContainer>
     </dskpp:KeyPackage>
     <dskpp:Mac
         MacAlgorithm=
            "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
         GHZ0H6Y+KpxdlVZ7zgcJDiDdqc8Gcmlcf+HQi4EUxYU=
     </dskpp:Mac>
 </dskpp:KeyProvServerFinished>

B.3.2. Example Using the Key Wrap Method

 The client sends a request that specifies a shared key to protect the
 K_TOKEN, and the server responds using the Key Wrap key protection
 method.  Authentication Data in this example is based on an
 Authentication Code rather than a device certificate.
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvClientHello
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     Version="1.0">
     <dskpp:DeviceIdentifierData>
         <dskpp:DeviceId>
             <pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>
             <pskc:SerialNo>987654321</pskc:SerialNo>
             <pskc:StartDate>2009-09-01T00:00:00Z</pskc:StartDate>
             <pskc:ExpiryDate>2014-09-01T00:00:00Z</pskc:ExpiryDate>
         </dskpp:DeviceId>
     </dskpp:DeviceIdentifierData>
     <dskpp:SupportedKeyTypes>
         <dskpp:Algorithm>
             urn:ietf:params:xml:ns:keyprov:pskc:hotp
         </dskpp:Algorithm>
         <dskpp:Algorithm>
  http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
         </dskpp:Algorithm>
     </dskpp:SupportedKeyTypes>
     <dskpp:SupportedEncryptionAlgorithms>
         <dskpp:Algorithm>

Doherty, et al. Standards Track [Page 90] RFC 6063 DSKPP December 2010

             http://www.w3.org/2001/04/xmlenc#aes128-cbc
         </dskpp:Algorithm>
     </dskpp:SupportedEncryptionAlgorithms>
     <dskpp:SupportedMacAlgorithms>
         <dskpp:Algorithm>
             urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
         </dskpp:Algorithm>
     </dskpp:SupportedMacAlgorithms>
     <dskpp:SupportedProtocolVariants>
         <dskpp:TwoPass>
             <dskpp:SupportedKeyProtectionMethod>
                 urn:ietf:params:xml:schema:keyprov:dskpp:wrap
             </dskpp:SupportedKeyProtectionMethod>
             <dskpp:Payload>
                 <ds:KeyInfo>
                     <ds:KeyName>Pre-shared-key-1</ds:KeyName>
                 </ds:KeyInfo>
             </dskpp:Payload>
         </dskpp:TwoPass>
     </dskpp:SupportedProtocolVariants>
     <dskpp:SupportedKeyPackages>
         <dskpp:KeyPackageFormat>
             urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
         </dskpp:KeyPackageFormat>
     </dskpp:SupportedKeyPackages>
     <dskpp:AuthenticationData>
         <dskpp:ClientID>AC00000A</dskpp:ClientID>
         <dskpp:AuthenticationCodeMac>
             <dskpp:Nonce>
                 ESIzRFVmd4iZqrvM3e7/ESIzRFVmd4iZqrvM3e7/ESI=
             </dskpp:Nonce>
             <dskpp:IterationCount>1</dskpp:IterationCount>
             <dskpp:Mac
                 MacAlgorithm=
                 "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
                 3eRz51ILqiG+dJW2iLcjuA==
             </dskpp:Mac>
         </dskpp:AuthenticationCodeMac>
     </dskpp:AuthenticationData>
 </dskpp:KeyProvClientHello>
 In this example, the server responds to the previous request by
 returning a key package in which the provisioning key was encrypted
 using the Key Wrap key protection method.
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvServerFinished
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"

Doherty, et al. Standards Track [Page 91] RFC 6063 DSKPP December 2010

     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:dkey="http://www.w3.org/2009/xmlsec-derivedkey#"
     xmlns:pkcs5=
         "http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
     Version="1.0"
     Status="Success"
     SessionID="4114">
     <dskpp:KeyPackage>
          <dskpp:KeyContainer Version="1.0" Id="KC0001">
              <pskc:EncryptionKey>
                 <ds:KeyName>Pre-shared-key-1</ds:KeyName>
              </pskc:EncryptionKey>
              <pskc:MACMethod
                  Algorithm=
                     "http://www.w3.org/2000/09/xmldsig#hmac-sha1">
                  <pskc:MACKey>
                      <xenc:EncryptionMethod
                          Algorithm=
                       "http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
                      <xenc:CipherData>
                          <xenc:CipherValue>
      2GTTnLwM3I4e5IO5FkufoMUBJBuAf25hARFv0Z7MFk9Ecdb04PWY/qaeCbrgz7Es
                           </xenc:CipherValue>
                      </xenc:CipherData>
                  </pskc:MACKey>
              </pskc:MACMethod>
              <pskc:KeyPackage>
                  <pskc:DeviceInfo>
                      <pskc:Manufacturer>
                         TokenVendorAcme
                      </pskc:Manufacturer>
                      <pskc:SerialNo>
                         987654321
                      </pskc:SerialNo>
                      <pskc:StartDate>
                         2009-09-01T00:00:00Z
                      </pskc:StartDate>
                      <pskc:ExpiryDate>
                         2014-09-01T00:00:00Z
                      </pskc:ExpiryDate>
                  </pskc:DeviceInfo>
                  <pskc:CryptoModuleInfo>
                      <pskc:Id>CM_ID_001</pskc:Id>
                  </pskc:CryptoModuleInfo>
                  <pskc:Key
                      Id="MBK000000001"

Doherty, et al. Standards Track [Page 92] RFC 6063 DSKPP December 2010

                      Algorithm=
                         "urn:ietf:params:xml:ns:keyprov:pskc:hotp">
                      <pskc:Issuer>Example-Issuer</pskc:Issuer>
                      <pskc:AlgorithmParameters>
                        <pskc:ResponseFormat Length="6"
                           Encoding="DECIMAL"/>
                      </pskc:AlgorithmParameters>
                      <pskc:Data>
                          <pskc:Secret>
                              <pskc:EncryptedValue>
                                <xenc:EncryptionMethod
                                Algorithm=
                       "http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
                                  <xenc:CipherData>
                                      <xenc:CipherValue>
                                          oTvo+S22nsmS2Z/RtcoF8AabC6vr
                                          09sh0QIU+E224S96sZjpV+6nFYgn
                                          6525OoepbPnL/fGuuey64WCYXoqh
                                          Tg==
                                      </xenc:CipherValue>
                                  </xenc:CipherData>
                             </pskc:EncryptedValue>
                             <pskc:ValueMAC>
                                 o+e9xgMVUbYuZH9UHe0W9dIo88A=
                             </pskc:ValueMAC>
                         </pskc:Secret>
                         <pskc:Counter>
                             <pskc:PlainValue>0</pskc:PlainValue>
                         </pskc:Counter>
                     </pskc:Data>
                     <pskc:Policy>
                         <pskc:KeyUsage>OTP</pskc:KeyUsage>
                     </pskc:Policy>
                 </pskc:Key>
             </pskc:KeyPackage>
         </dskpp:KeyContainer>
     </dskpp:KeyPackage>
     <dskpp:Mac
         MacAlgorithm=
            "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
         l53BmSO6qUzoIgbQegimsKk2es+WRpEl0YFqaOp5PGE=
     </dskpp:Mac>
 </dskpp:KeyProvServerFinished>

Doherty, et al. Standards Track [Page 93] RFC 6063 DSKPP December 2010

B.3.3. Example Using the Passphrase-Based Key Wrap Method

 The client sends a request similar to that in Appendix B.3.1 with
 Authentication Data based on an Authentication Code, and the server
 responds using the Passphrase-Based Key Wrap method to encrypt the
 provisioning key (note that the encryption is derived from the
 password component of the Authentication Code).  The Authentication
 Data is set in clear text when it is sent over a secure transport
 channel such as TLS [RFC5246].
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvClientHello
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     Version="1.0">
     <dskpp:DeviceIdentifierData>
         <dskpp:DeviceId>
             <pskc:Manufacturer>TokenVendorAcme</pskc:Manufacturer>
             <pskc:SerialNo>987654321</pskc:SerialNo>
             <pskc:StartDate>2009-09-01T00:00:00Z</pskc:StartDate>
             <pskc:ExpiryDate>2014-09-01T00:00:00Z</pskc:ExpiryDate>
         </dskpp:DeviceId>
     </dskpp:DeviceIdentifierData>
     <dskpp:SupportedKeyTypes>
         <dskpp:Algorithm>
             urn:ietf:params:xml:ns:keyprov:pskc:hotp
         </dskpp:Algorithm>
         <dskpp:Algorithm>
  http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
         </dskpp:Algorithm>
     </dskpp:SupportedKeyTypes>
     <dskpp:SupportedEncryptionAlgorithms>
         <dskpp:Algorithm>
             http://www.w3.org/2001/04/xmlenc#rsa_1_5
         </dskpp:Algorithm>
     </dskpp:SupportedEncryptionAlgorithms>
     <dskpp:SupportedMacAlgorithms>
         <dskpp:Algorithm>
             urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
         </dskpp:Algorithm>
     </dskpp:SupportedMacAlgorithms>
     <dskpp:SupportedProtocolVariants>
         <dskpp:TwoPass>
             <dskpp:SupportedKeyProtectionMethod>
              urn:ietf:params:xml:schema:keyprov:dskpp:passphrase-wrap
             </dskpp:SupportedKeyProtectionMethod>

Doherty, et al. Standards Track [Page 94] RFC 6063 DSKPP December 2010

             <dskpp:Payload>
                 <ds:KeyInfo>
                     <ds:KeyName>Passphrase-1</ds:KeyName>
                 </ds:KeyInfo>
             </dskpp:Payload>
         </dskpp:TwoPass>
     </dskpp:SupportedProtocolVariants>
     <dskpp:SupportedKeyPackages>
         <dskpp:KeyPackageFormat>
             urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
         </dskpp:KeyPackageFormat>
     </dskpp:SupportedKeyPackages>
     <dskpp:AuthenticationData>
         <dskpp:ClientID>AC00000A</dskpp:ClientID>
         <dskpp:AuthenticationCodeMac>
             <dskpp:Nonce>
                 ESIzRFVmd4iZqrvM3e7/ESIzRFVmd4iZqrvM3e7/ESI=
             </dskpp:Nonce>
             <dskpp:IterationCount>1</dskpp:IterationCount>
             <dskpp:Mac
                 MacAlgorithm=
                "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
                K4YvLMN6Q1DZvtShoCxQag==
             </dskpp:Mac>
         </dskpp:AuthenticationCodeMac>
     </dskpp:AuthenticationData>
 </dskpp:KeyProvClientHello>
 In this example, the server responds to the previous request by
 returning a key package in which the provisioning key was encrypted
 using the Passphrase-Based Key Wrap key protection method.
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <dskpp:KeyProvServerFinished
     xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
     xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:dskpp"
     xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:dkey="http://www.w3.org/2009/xmlsec-derivedkey#"
     xmlns:pkcs5=
        "http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
     Version="1.0"
     Status="Success"
     SessionID="4114">
     <dskpp:KeyPackage>
         <dskpp:KeyContainer Version="1.0" Id="KC0002">
             <pskc:EncryptionKey>
                 <dkey:DerivedKey>

Doherty, et al. Standards Track [Page 95] RFC 6063 DSKPP December 2010

                     <dkey:KeyDerivationMethod
                     Algorithm=
                     "http://www.rsasecurity.com/rsalabs/pkcs/schemas/
                     pkcs-5v2-0#pbkdf2">
                         <pkcs5:PBKDF2-params>
                             <Salt>
                                 <Specified>Ej7/PEpyEpw=</Specified>
                             </Salt>
                             <IterationCount>1000</IterationCount>
                             <KeyLength>16</KeyLength>
                         </pkcs5:PBKDF2-params>
                     </dkey:KeyDerivationMethod>
                     <xenc:ReferenceList>
                         <xenc:DataReference URI="#ED"/>
                     </xenc:ReferenceList>
                     <dkey:MasterKeyName>
                        Passphrase1
                     </dkey:MasterKeyName>
                 </dkey:DerivedKey>
             </pskc:EncryptionKey>
             <pskc:MACMethod
                 Algorithm=
                    "http://www.w3.org/2000/09/xmldsig#hmac-sha1">
                 <pskc:MACKey>
                     <xenc:EncryptionMethod
                         Algorithm=
                       "http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
                     <xenc:CipherData>
                         <xenc:CipherValue>
      2GTTnLwM3I4e5IO5FkufoOEiOhNj91fhKRQBtBJYluUDsPOLTfUvoU2dStyOwYZx
                         </xenc:CipherValue>
                     </xenc:CipherData>
                 </pskc:MACKey>
             </pskc:MACMethod>
             <pskc:KeyPackage>
                 <pskc:DeviceInfo>
                     <pskc:Manufacturer>
                        TokenVendorAcme
                     </pskc:Manufacturer>
                     <pskc:SerialNo>
                        987654321
                     </pskc:SerialNo>
                     <pskc:StartDate>
                        2009-09-01T00:00:00Z
                     </pskc:StartDate>
                     <pskc:ExpiryDate>
                        2014-09-01T00:00:00Z
                     </pskc:ExpiryDate>

Doherty, et al. Standards Track [Page 96] RFC 6063 DSKPP December 2010

                 </pskc:DeviceInfo>
                 <pskc:CryptoModuleInfo>
                     <pskc:Id>CM_ID_001</pskc:Id>
                 </pskc:CryptoModuleInfo>
                 <pskc:Key
                     Id="MBK000000001"
                     Algorithm=
                        "urn:ietf:params:xml:ns:keyprov:pskc:hotp">
                     <pskc:Issuer>Example-Issuer</pskc:Issuer>
                     <pskc:AlgorithmParameters>
                        <pskc:ResponseFormat Length="6"
                           Encoding="DECIMAL"/>
                     </pskc:AlgorithmParameters>
                     <pskc:Data>
                         <pskc:Secret>
                             <pskc:EncryptedValue>
                                 <xenc:EncryptionMethod
                                     Algorithm=
                                     "http://www.w3.org/2001/04/
                                     xmlenc#aes128-cbc"/>
                                 <xenc:CipherData>
                                     <xenc:CipherValue>
                                       oTvo+S22nsmS2Z/RtcoF8HX385uMWgJ
                                       myIFMESBmcvtHQXp/6T1TgCS9CsgKtm
                                       cOrF8VoK254tZKnrAjiD5cdw==
                                     </xenc:CipherValue>
                                 </xenc:CipherData>
                             </pskc:EncryptedValue>
                             <pskc:ValueMAC>
                                 pbgEbVYxoYs0x41wdeC7eDRbUEk=
                             </pskc:ValueMAC>
                         </pskc:Secret>
                         <pskc:Counter>
                             <pskc:PlainValue>0</pskc:PlainValue>
                         </pskc:Counter>
                     </pskc:Data>
                     <pskc:Policy>
                         <pskc:KeyUsage>OTP</pskc:KeyUsage>
                     </pskc:Policy>
                 </pskc:Key>
             </pskc:KeyPackage>
         </dskpp:KeyContainer>
     </dskpp:KeyPackage>
     <dskpp:Mac MacAlgorithm=
         "urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256">
         Jc4VsNODYXgfbDmTn9qQZgcL3cKoa//j/NRT7sTpKOM=
     </dskpp:Mac>
 </dskpp:KeyProvServerFinished>

Doherty, et al. Standards Track [Page 97] RFC 6063 DSKPP December 2010

Appendix C. Integration with PKCS #11

 A DSKPP Client that needs to communicate with a connected
 cryptographic module to perform a DSKPP exchange MAY use PKCS #11
 [PKCS-11] as a programming interface as described herein.  This
 appendix forms an informative part of the document.

C.1. The Four-Pass Variant

 When performing four-pass DSKPP with a cryptographic module using the
 PKCS #11 programming interface, the procedure described in
 [CT-KIP-P11], Appendix B, is RECOMMENDED.

C.2. The Two-Pass Variant

 A suggested procedure to perform two-pass DSKPP with a cryptographic
 module through the PKCS #11 interface using the mechanisms defined in
 [CT-KIP-P11] is as follows:
 a.  On the client side,
     1.  The client selects a suitable slot and token (e.g., through
         use of the <DeviceIdentifier> or the <PlatformInfo> element
         of the DSKPP trigger message).
     2.  A nonce R is generated, e.g., by calling C_SeedRandom and
         C_GenerateRandom.
     3.  The client sends its first message to the server, including
         the nonce R.
 b.  On the server side,
     1.  A generic key K_PROV = K_TOKEN | K_MAC (where '|' denotes
         concatenation) is generated, e.g., by calling C_GenerateKey
         (using key type CKK_GENERIC_SECRET).  The template for K_PROV
         MUST allow it to be exported (but only in wrapped form, i.e.,
         CKA_SENSITIVE MUST be set to CK_TRUE and CKA_EXTRACTABLE MUST
         also be set to CK_TRUE), and also to be used for further key
         derivation.  From K, a token key K_TOKEN of suitable type is
         derived by calling C_DeriveKey using the PKCS #11 mechanism
         CKM_EXTRACT_KEY_FROM_KEY and setting the CK_EXTRACT_PARAMS to
         the first bit of the generic secret key (i.e., set to 0).
         Likewise, a MAC key K_MAC is derived from K_PROV by calling
         C_DeriveKey using the CKM_EXTRACT_KEY_FROM_KEY mechanism,
         this time setting CK_EXTRACT_PARAMS to the length of K_PROV
         (in bits) divided by two.

Doherty, et al. Standards Track [Page 98] RFC 6063 DSKPP December 2010

     2.  The server wraps K_PROV with either the public key of the
         DSKPP Client or device, the pre-shared secret key, or the
         derived shared secret key by using C_WrapKey.  If use of the
         DSKPP key wrap algorithm has been negotiated, then the
         CKM_KIP_WRAP mechanism MUST be used to wrap K.  When calling
         C_WrapKey, the hKey handle in the CK_KIP_PARAMS structure
         MUST be set to NULL_PTR.  The pSeed parameter in the
         CK_KIP_PARAMS structure MUST point to the nonce R provided by
         the DSKPP Client, and the ulSeedLen parameter MUST indicate
         the length of R.  The hWrappingKey parameter in the call to
         C_WrapKey MUST be set to refer to the key wrapping key.
     3.  Next, the server needs to calculate a MAC using K_MAC.  If
         use of the DSKPP MAC algorithm has been negotiated, then the
         MAC is calculated by calling C_SignInit with the CKM_KIP_MAC
         mechanism followed by a call to C_Sign.  In the call to
         C_SignInit, K_MAC MUST be the signature key, the hKey
         parameter in the CK_KIP_PARAMS structure MUST be set to
         NULL_PTR, the pSeed parameter of the CT_KIP_PARAMS structure
         MUST be set to NULL_PTR, and the ulSeedLen parameter MUST be
         set to zero.  In the call to C_Sign, the pData parameter MUST
         be set to the concatenation of the string ServerID and the
         nonce R, and the ulDataLen parameter MUST be set to the
         length of the concatenated string.  The desired length of the
         MAC MUST be specified through the pulSignatureLen parameter
         and MUST be set to the length of R.
     4.  If the server also needs to authenticate its message (due to
         an existing K_TOKEN being replaced), the server MUST
         calculate a second MAC.  Again, if use of the DSKPP MAC
         algorithm has been negotiated, then the MAC is calculated by
         calling C_SignInit with the CKM_KIP_MAC mechanism followed by
         a call to C_Sign.  In this call to C_SignInit, the K_MAC'
         existing before this DSKPP run MUST be the signature key (the
         implementation may specify K_MAC' to be the value of the
         K_TOKEN that is being replaced, or a version of K_MAC from
         the previous protocol run), the hKey parameter in the
         CK_KIP_PARAMS structure MUST be set to NULL, the pSeed
         parameter of the CT_KIP_PARAMS structure MUST be set to
         NULL_PTR, and the ulSeedLen parameter MUST be set to zero.
         In the call to C_Sign, the pData parameter MUST be set to the
         concatenation of the string ServerID and the nonce R, and the
         ulDataLen parameter MUST be set to the length of concatenated
         string.  The desired length of the MAC MUST be specified
         through the pulSignatureLen parameter and MUST be set to the
         length of R.

Doherty, et al. Standards Track [Page 99] RFC 6063 DSKPP December 2010

     5.  The server sends its message to the client, including the
         wrapped key K_TOKEN, the MAC and possibly also the
         authenticating MAC.
 c.  On the client side,
     1.  The client calls C_UnwrapKey to receive a handle to K.  After
         this, the client calls C_DeriveKey twice: once to derive
         K_TOKEN and once to derive K_MAC.  The client MUST use the
         same mechanism (CKM_EXTRACT_KEY_FROM_KEY) and the same
         mechanism parameters as used by the server above.  When
         calling C_UnwrapKey and C_DeriveKey, the pTemplate parameter
         MUST be used to set additional key attributes in accordance
         with local policy and as negotiated and expressed in the
         protocol.  In particular, the value of the <KeyID> element in
         the server's response message MAY be used as CKA_ID for
         K_TOKEN.  The key K_PROV MUST be destroyed after deriving
         K_TOKEN and K_MAC.
     2.  The MAC is verified in a reciprocal fashion as it was
         generated by the server.  If use of the CKM_KIP_MAC mechanism
         has been negotiated, then in the call to C_VerifyInit, the
         hKey parameter in the CK_KIP_PARAMS structure MUST be set to
         NULL_PTR, the pSeed parameter MUST be set to NULL_PTR, and
         ulSeedLen MUST be set to 0.  The hKey parameter of
         C_VerifyInit MUST refer to K_MAC.  In the call to C_Verify,
         pData MUST be set to the concatenation of the string ServerID
         and the nonce R, and the ulDataLen parameter MUST be set to
         the length of the concatenated string, pSignature to the MAC
         value received from the server, and ulSignatureLen to the
         length of the MAC.  If the MAC does not verify the protocol
         session ends with a failure.  The token MUST be constructed
         to not "commit" to the new K_TOKEN or the new K_MAC unless
         the MAC verifies.
     3.  If an authenticating MAC was received (REQUIRED if the new
         K_TOKEN will replace an existing key on the token), then it
         is verified in a similar vein but using the K_MAC' associated
         with this server and existing before the protocol run (the
         implementation may specify K_MAC' to be the value of the
         K_TOKEN that is being replaced, or a version of K_MAC from
         the previous protocol run).  Again, if the MAC does not
         verify the protocol session ends with a failure, and the
         token MUST be constructed not to "commit" to the new K_TOKEN
         or the new K_MAC unless the MAC verifies.

Doherty, et al. Standards Track [Page 100] RFC 6063 DSKPP December 2010

Appendix D. Example of DSKPP-PRF Realizations

D.1. Introduction

 This example appendix defines DSKPP-PRF in terms of AES [FIPS197-AES]
 and HMAC [RFC2104].  This appendix forms a normative part of the
 document.

D.2. DSKPP-PRF-AES

D.2.1. Identification

 For cryptographic modules supporting this realization of DSKPP-PRF,
 the following URN MUST be used to identify this algorithm in DSKPP:
 urn:ietf:params:xml:ns:keyprov:dskpp:prf-aes-128
 When this URN is used to identify the encryption algorithm, the
 method for encryption of R_C values described in Section 4.2.4 MUST
 be used.

D.2.2. Definition

 DSKPP-PRF-AES (k, s, dsLen)
 Input:
 k         Encryption key to use
 s         Octet string consisting of randomizing material.  The
           length of the string s is sLen.
 dsLen     Desired length of the output
 Output:
 DS        A pseudorandom string, dsLen-octets long
 Steps:
 1.  Let bLen be the output block size of AES in octets:
     bLen = (AES output block length in octets)
     (normally, bLen = 16)
 2.  If dsLen > (2**32 - 1) * bLen, output "derived data too long" and
     stop

Doherty, et al. Standards Track [Page 101] RFC 6063 DSKPP December 2010

 3.  Let n be the number of bLen-octet blocks in the output data,
     rounding up, and let j be the number of octets in the last block:
     n = CEILING( dsLen / bLen)
     j = dsLen - (n - 1) * bLen
 4.  For each block of the pseudorandom string DS, apply the function
     F defined below to the key k, the string s and the block index to
     compute the block:
     B1 = F (k, s, 1) ,
     B2 = F (k, s, 2) ,
     ...
     Bn = F (k, s, n)
 The function F is defined in terms of the CMAC construction from
 [NIST-SP800-38B], using AES as the block cipher:
 F (k, s, i) = CMAC-AES (k, INT (i) || s)
 where INT (i) is a four-octet encoding of the integer i, most
 significant octet first, and the output length of CMAC is set to
 bLen.
 Concatenate the blocks and extract the first dsLen octets to produce
 the desired data string DS:
 DS = B1 || B2 || ... || Bn<0..j-1>
 Output the derived data DS.

D.2.3. Example

 If we assume that dsLen = 16, then:
 n = 16 / 16 = 1
 j = 16 - (1 - 1) * 16 = 16
 DS = B1 = F (k, s, 1) = CMAC-AES (k, INT (1) || s)

Doherty, et al. Standards Track [Page 102] RFC 6063 DSKPP December 2010

D.3. DSKPP-PRF-SHA256

D.3.1. Identification

 For cryptographic modules supporting this realization of DSKPP-PRF,
 the following URN MUST be used to identify this algorithm in DSKPP:
 urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
 When this URN is used to identify the encryption algorithm to use,
 the method for encryption of R_C values described in Section 4.2.4
 MUST be used.

D.3.2. Definition

 DSKPP-PRF-SHA256 (k, s, dsLen)
 Input:
 k         Encryption key to use
 s         Octet string consisting of randomizing material.  The
           length of the string s is sLen.
 dsLen     Desired length of the output
 Output:
 DS        A pseudorandom string, dsLen-octets long
 Steps:
 1.  Let bLen be the output size of SHA-256 in octets of [FIPS180-SHA]
     (no truncation is done on the HMAC output):
     bLen = 32
     (normally, bLen = 16)
 2.  If dsLen > (2**32 - 1) * bLen, output "derived data too long" and
     stop
 3.  Let n be the number of bLen-octet blocks in the output data,
     rounding up, and let j be the number of octets in the last block:
     n = CEILING( dsLen / bLen)
     j = dsLen - (n - 1) * bLen
 4.  For each block of the pseudorandom string DS, apply the function
     F defined below to the key k, the string s and the block index to
     compute the block:

Doherty, et al. Standards Track [Page 103] RFC 6063 DSKPP December 2010

     B1 = F (k, s, 1),
     B2 = F (k, s, 2),
     ...
     Bn = F (k, s, n)
 The function F is defined in terms of the HMAC construction from
 [RFC2104], using SHA-256 as the digest algorithm:
 F (k, s, i) = HMAC-SHA256 (k, INT (i) || s)
 where INT (i) is a four-octet encoding of the integer i, most
 significant octet first, and the output length of HMAC is set to
 bLen.
 Concatenate the blocks and extract the first dsLen octets to produce
 the desired data string DS:
 DS = B1 || B2 || ... || Bn<0..j-1>
 Output the derived data DS.

D.3.3. Example

 If we assume that sLen = 256 (two 128-octet long values) and dsLen =
 16, then:
 n = CEILING( 16 / 32 ) = 1
 j = 16 - (1 - 1) * 32 = 16
 B1 = F (k, s, 1) = HMAC-SHA256 (k, INT (1) || s)
 DS = B1<0 ... 15>
 That is, the result will be the first 16 octets of the HMAC output.

Doherty, et al. Standards Track [Page 104] RFC 6063 DSKPP December 2010

Authors' Addresses

 Andrea Doherty
 RSA, The Security Division of EMC
 174 Middlesex Turnpike
 Bedford, MA  01730
 USA
 EMail: andrea.doherty@rsa.com
 Mingliang Pei
 VeriSign, Inc.
 487 E. Middlefield Road
 Mountain View, CA  94043
 USA
 EMail: mpei@verisign.com
 Salah Machani
 Diversinet Corp.
 2225 Sheppard Avenue East, Suite 1801
 Toronto, Ontario  M2J 5C2
 Canada
 EMail: smachani@diversinet.com
 Magnus Nystrom
 Microsoft Corp.
 One Microsoft Way
 Redmond, WA  98052
 USA
 EMail: mnystrom@microsoft.com

Doherty, et al. Standards Track [Page 105]

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