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rfc:rfc4210

Network Working Group C. Adams Request for Comments: 4210 University of Ottawa Obsoletes: 2510 S. Farrell Category: Standards Track Trinity College Dublin

                                                              T. Kause
                                                                   SSH
                                                            T. Mononen
                                                               SafeNet
                                                        September 2005
             Internet X.509 Public Key Infrastructure
               Certificate Management Protocol (CMP)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 This document describes the Internet X.509 Public Key Infrastructure
 (PKI) Certificate Management Protocol (CMP).  Protocol messages are
 defined for X.509v3 certificate creation and management.  CMP
 provides on-line interactions between PKI components, including an
 exchange between a Certification Authority (CA) and a client system.

Table of Contents

 1. Introduction ....................................................5
 2. Requirements ....................................................5
 3. PKI Management Overview .........................................5
    3.1. PKI Management Model .......................................6
         3.1.1. Definitions of PKI Entities .........................6
                3.1.1.1. Subjects and End Entities ..................6
                3.1.1.2. Certification Authority ....................7
                3.1.1.3. Registration Authority .....................7
         3.1.2. PKI Management Requirements .........................8
         3.1.3. PKI Management Operations ..........................10
 4. Assumptions and Restrictions ...................................14
    4.1. End Entity Initialization .................................14

Adams, et al. Standards Track [Page 1] RFC 4210 CMP September 2005

    4.2. Initial Registration/Certification ........................14
         4.2.1. Criteria Used ......................................15
                4.2.1.1. Initiation of Registration/Certification ..15
                4.2.1.2. End Entity Message Origin Authentication ..15
                4.2.1.3. Location of Key Generation ................15
                4.2.1.4. Confirmation of Successful Certification ..16
         4.2.2. Mandatory Schemes ..................................16
                4.2.2.1. Centralized Scheme ........................16
                4.2.2.2. Basic Authenticated Scheme ................17
    4.3. Proof-of-Possession (POP) of Private Key ..................17
         4.3.1. Signature Keys .....................................18
         4.3.2. Encryption Keys ....................................18
         4.3.3. Key Agreement Keys .................................19
    4.4. Root CA Key Update ........................................19
         4.4.1. CA Operator Actions ................................20
         4.4.2. Verifying Certificates .............................21
                4.4.2.1. Verification in Cases 1, 4, 5, and 8 ......22
                4.4.2.2. Verification in Case 2 ....................22
                4.4.2.3. Verification in Case 3 ....................23
                4.4.2.4. Failure of Verification in Case 6 .........23
                4.4.2.5. Failure of Verification in Case 7 .........23
         4.4.3. Revocation - Change of CA Key ......................23
 5. Data Structures ................................................24
    5.1. Overall PKI Message .......................................24
         5.1.1. PKI Message Header .................................24
                5.1.1.1. ImplicitConfirm ...........................27
                5.1.1.2. ConfirmWaitTime ...........................27
         5.1.2. PKI Message Body ...................................27
         5.1.3. PKI Message Protection .............................28
                5.1.3.1. Shared Secret Information .................29
                5.1.3.2. DH Key Pairs ..............................30
                5.1.3.3. Signature .................................30
                5.1.3.4. Multiple Protection .......................30
    5.2. Common Data Structures ....................................31
         5.2.1. Requested Certificate Contents .....................31
         5.2.2. Encrypted Values ...................................31
         5.2.3. Status codes and Failure Information for
                PKI Messages .......................................32
         5.2.4. Certificate Identification .........................33
         5.2.5. Out-of-band root CA Public Key .....................33
         5.2.6. Archive Options ....................................34
         5.2.7. Publication Information ............................34
         5.2.8. Proof-of-Possession Structures .....................34
                5.2.8.1. Inclusion of the Private Key ..............35
                5.2.8.2. Indirect Method ...........................35
                5.2.8.3. Challenge-Response Protocol ...............35
                5.2.8.4. Summary of PoP Options ....................37

Adams, et al. Standards Track [Page 2] RFC 4210 CMP September 2005

    5.3. Operation-Specific Data Structures ........................38
         5.3.1. Initialization Request .............................38
         5.3.2. Initialization Response ............................39
         5.3.3. Certification Request ..............................39
         5.3.4. Certification Response .............................39
         5.3.5. Key Update Request Content .........................40
         5.3.6. Key Update Response Content ........................41
         5.3.7. Key Recovery Request Content .......................41
         5.3.8. Key Recovery Response Content ......................41
         5.3.9. Revocation Request Content .........................41
         5.3.10. Revocation Response Content .......................42
         5.3.11. Cross Certification Request Content ...............42
         5.3.12. Cross Certification Response Content ..............42
         5.3.13. CA Key Update Announcement Content ................42
         5.3.14. Certificate Announcement ..........................43
         5.3.15. Revocation Announcement ...........................43
         5.3.16. CRL Announcement ..................................43
         5.3.17. PKI Confirmation Content ..........................43
         5.3.18. Certificate Confirmation Content ..................44
         5.3.19. PKI General Message Content .......................44
                5.3.19.1. CA Protocol Encryption Certificate .......44
                5.3.19.2. Signing Key Pair Types ...................45
                5.3.19.3. Encryption/Key Agreement Key Pair Types ..45
                5.3.19.4. Preferred Symmetric Algorithm ............45
                5.3.19.5. Updated CA Key Pair ......................45
                5.3.19.6. CRL ......................................46
                5.3.19.7. Unsupported Object Identifiers ...........46
                5.3.19.8. Key Pair Parameters ......................46
                5.3.19.9. Revocation Passphrase ....................46
                5.3.19.10. ImplicitConfirm .........................46
                5.3.19.11. ConfirmWaitTime .........................47
                5.3.19.12. Original PKIMessage .....................47
                5.3.19.13. Supported Language Tags .................47
         5.3.20. PKI General Response Content ......................47
         5.3.21. Error Message Content .............................47
         5.3.22. Polling Request and Response ......................48
 6. Mandatory PKI Management Functions .............................51
    6.1. Root CA Initialization ....................................51
    6.2. Root CA Key Update ........................................51
    6.3. Subordinate CA Initialization .............................51
    6.4. CRL production ............................................52
    6.5. PKI Information Request ...................................52
    6.6. Cross Certification .......................................52
         6.6.1. One-Way Request-Response Scheme: ...................52
    6.7. End Entity Initialization .................................54
         6.7.1. Acquisition of PKI Information .....................54
         6.7.2. Out-of-Band Verification of Root-CA Key ............55
    6.8. Certificate Request .......................................55

Adams, et al. Standards Track [Page 3] RFC 4210 CMP September 2005

    6.9. Key Update ................................................55
 7. Version Negotiation ............................................56
    7.1. Supporting RFC 2510 Implementations .......................56
         7.1.1. Clients Talking to RFC 2510 Servers ................56
         7.1.2. Servers Receiving Version cmp1999 PKIMessages ......57
 8. Security Considerations ........................................57
    8.1. Proof-Of-Possession with a Decryption Key .................57
    8.2. Proof-Of-Possession by Exposing the Private Key ...........57
    8.3. Attack Against Diffie-Hellman Key Exchange ................57
 9. IANA Considerations ............................................58
 Normative References ..............................................58
 Informative References ............................................59
 A. Reasons for the Presence of RAs ................................61
 B. The Use of Revocation Passphrase ...............................61
 C. Request Message Behavioral Clarifications ......................63
 D. PKI Management Message Profiles (REQUIRED) .....................65
    D.1. General Rules for Interpretation of These Profiles ........65
    D.2. Algorithm Use Profile .....................................66
    D.3. Proof-of-Possession Profile ...............................68
    D.4. Initial Registration/Certification (Basic
         Authenticated Scheme) .....................................68
    D.5. Certificate Request .......................................74
    D.6. Key Update Request ........................................75
 E. PKI Management Message Profiles (OPTIONAL) .....................75
    E.1. General Rules for Interpretation of These Profiles ........76
    E.2. Algorithm Use Profile .....................................76
    E.3. Self-Signed Certificates ..................................76
    E.4. Root CA Key Update ........................................77
    E.5. PKI Information Request/Response ..........................77
    E.6. Cross Certification Request/Response (1-way) ..............79
    E.7. In-Band Initialization Using External Identity
         Certificate  ..............................................82
 F. Compilable ASN.1 Definitions ...................................83
 G. Acknowledgements ...............................................93

Adams, et al. Standards Track [Page 4] RFC 4210 CMP September 2005

1. Introduction

 This document describes the Internet X.509 Public Key Infrastructure
 (PKI) Certificate Management Protocol (CMP).  Protocol messages are
 defined for certificate creation and management.  The term
 "certificate" in this document refers to an X.509v3 Certificate as
 defined in [X509].
 This specification obsoletes RFC 2510.  This specification differs
 from RFC 2510 in the following areas:
    The PKI management message profile section is split to two
    appendices: the required profile and the optional profile.  Some
    of the formerly mandatory functionality is moved to the optional
    profile.
    The message confirmation mechanism has changed substantially.
    A new polling mechanism is introduced, deprecating the old polling
    method at the CMP transport level.
    The CMP transport protocol issues are handled in a separate
    document [CMPtrans], thus the Transports section is removed.
    A new implicit confirmation method is introduced to reduce the
    number of protocol messages exchanged in a transaction.
    The new specification contains some less prominent protocol
    enhancements and improved explanatory text on several issues.

2. Requirements

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

3. PKI Management Overview

 The PKI must be structured to be consistent with the types of
 individuals who must administer it.  Providing such administrators
 with unbounded choices not only complicates the software required,
 but also increases the chances that a subtle mistake by an
 administrator or software developer will result in broader
 compromise.  Similarly, restricting administrators with cumbersome
 mechanisms will cause them not to use the PKI.

Adams, et al. Standards Track [Page 5] RFC 4210 CMP September 2005

 Management protocols are REQUIRED to support on-line interactions
 between Public Key Infrastructure (PKI) components.  For example, a
 management protocol might be used between a Certification Authority
 (CA) and a client system with which a key pair is associated, or
 between two CAs that issue cross-certificates for each other.

3.1. PKI Management Model

 Before specifying particular message formats and procedures, we first
 define the entities involved in PKI management and their interactions
 (in terms of the PKI management functions required).  We then group
 these functions in order to accommodate different identifiable types
 of end entities.

3.1.1. Definitions of PKI Entities

 The entities involved in PKI management include the end entity (i.e.,
 the entity to whom the certificate is issued) and the certification
 authority (i.e., the entity that issues the certificate).  A
 registration authority MAY also be involved in PKI management.

3.1.1.1. Subjects and End Entities

 The term "subject" is used here to refer to the entity to whom the
 certificate is issued, typically named in the subject or
 subjectAltName field of a certificate.  When we wish to distinguish
 the tools and/or software used by the subject (e.g., a local
 certificate management module), we will use the term "subject
 equipment".  In general, the term "end entity" (EE), rather than
 "subject", is preferred in order to avoid confusion with the field
 name.  It is important to note that the end entities here will
 include not only human users of applications, but also applications
 themselves (e.g., for IP security).  This factor influences the
 protocols that the PKI management operations use; for example,
 application software is far more likely to know exactly which
 certificate extensions are required than are human users.  PKI
 management entities are also end entities in the sense that they are
 sometimes named in the subject or subjectAltName field of a
 certificate or cross-certificate.  Where appropriate, the term "end-
 entity" will be used to refer to end entities who are not PKI
 management entities.
 All end entities require secure local access to some information --
 at a minimum, their own name and private key, the name of a CA that
 is directly trusted by this entity, and that CA's public key (or a
 fingerprint of the public key where a self-certified version is
 available elsewhere).  Implementations MAY use secure local storage
 for more than this minimum (e.g., the end entity's own certificate or

Adams, et al. Standards Track [Page 6] RFC 4210 CMP September 2005

 application-specific information).  The form of storage will also
 vary -- from files to tamper-resistant cryptographic tokens.  The
 information stored in such local, trusted storage is referred to here
 as the end entity's Personal Security Environment (PSE).
 Though PSE formats are beyond the scope of this document (they are
 very dependent on equipment, et cetera), a generic interchange format
 for PSEs is defined here: a certification response message MAY be
 used.

3.1.1.2. Certification Authority

 The certification authority (CA) may or may not actually be a real
 "third party" from the end entity's point of view.  Quite often, the
 CA will actually belong to the same organization as the end entities
 it supports.
 Again, we use the term "CA" to refer to the entity named in the
 issuer field of a certificate.  When it is necessary to distinguish
 the software or hardware tools used by the CA, we use the term "CA
 equipment".
 The CA equipment will often include both an "off-line" component and
 an "on-line" component, with the CA private key only available to the
 "off-line" component.  This is, however, a matter for implementers
 (though it is also relevant as a policy issue).
 We use the term "root CA" to indicate a CA that is directly trusted
 by an end entity; that is, securely acquiring the value of a root CA
 public key requires some out-of-band step(s).  This term is not meant
 to imply that a root CA is necessarily at the top of any hierarchy,
 simply that the CA in question is trusted directly.
 A "subordinate CA" is one that is not a root CA for the end entity in
 question.  Often, a subordinate CA will not be a root CA for any
 entity, but this is not mandatory.

3.1.1.3. Registration Authority

 In addition to end-entities and CAs, many environments call for the
 existence of a Registration Authority (RA) separate from the
 Certification Authority.  The functions that the registration
 authority may carry out will vary from case to case but MAY include
 personal authentication, token distribution, revocation reporting,
 name assignment, key generation, archival of key pairs, et cetera.

Adams, et al. Standards Track [Page 7] RFC 4210 CMP September 2005

 This document views the RA as an OPTIONAL component: when it is not
 present, the CA is assumed to be able to carry out the RA's functions
 so that the PKI management protocols are the same from the end-
 entity's point of view.
 Again, we distinguish, where necessary, between the RA and the tools
 used (the "RA equipment").
 Note that an RA is itself an end entity.  We further assume that all
 RAs are in fact certified end entities and that RAs have private keys
 that are usable for signing.  How a particular CA equipment
 identifies some end entities as RAs is an implementation issue (i.e.,
 this document specifies no special RA certification operation).  We
 do not mandate that the RA is certified by the CA with which it is
 interacting at the moment (so one RA may work with more than one CA
 whilst only being certified once).
 In some circumstances, end entities will communicate directly with a
 CA even where an RA is present.  For example, for initial
 registration and/or certification, the subject may use its RA, but
 communicate directly with the CA in order to refresh its certificate.

3.1.2. PKI Management Requirements

 The protocols given here meet the following requirements on PKI
 management
 1.   PKI management must conform to the ISO/IEC 9594-8/ITU-T X.509
      standards.
 2.   It must be possible to regularly update any key pair without
      affecting any other key pair.
 3.   The use of confidentiality in PKI management protocols must be
      kept to a minimum in order to ease acceptance in environments
      where strong confidentiality might cause regulatory problems.
 4.   PKI management protocols must allow the use of different
      industry-standard cryptographic algorithms (specifically
      including RSA, DSA, MD5, and SHA-1).  This means that any given
      CA, RA, or end entity may, in principle, use whichever
      algorithms suit it for its own key pair(s).
 5.   PKI management protocols must not preclude the generation of key
      pairs by the end-entity concerned, by an RA, or by a CA.  Key
      generation may also occur elsewhere, but for the purposes of PKI
      management we can regard key generation as occurring wherever
      the key is first present at an end entity, RA, or CA.

Adams, et al. Standards Track [Page 8] RFC 4210 CMP September 2005

 6.   PKI management protocols must support the publication of
      certificates by the end-entity concerned, by an RA, or by a CA.
      Different implementations and different environments may choose
      any of the above approaches.
 7.   PKI management protocols must support the production of
      Certificate Revocation Lists (CRLs) by allowing certified end
      entities to make requests for the revocation of certificates.
      This must be done in such a way that the denial-of-service
      attacks, which are possible, are not made simpler.
 8.   PKI management protocols must be usable over a variety of
      "transport" mechanisms, specifically including mail, http,
      TCP/IP and ftp.
 9.   Final authority for certification creation rests with the CA.
      No RA or end-entity equipment can assume that any certificate
      issued by a CA will contain what was requested; a CA may alter
      certificate field values or may add, delete, or alter extensions
      according to its operating policy.  In other words, all PKI
      entities (end-entities, RAs, and CAs) must be capable of
      handling responses to requests for certificates in which the
      actual certificate issued is different from that requested (for
      example, a CA may shorten the validity period requested).  Note
      that policy may dictate that the CA must not publish or
      otherwise distribute the certificate until the requesting entity
      has reviewed and accepted the newly-created certificate
      (typically through use of the certConf message).
 10.  A graceful, scheduled change-over from one non-compromised CA
      key pair to the next (CA key update) must be supported (note
      that if the CA key is compromised, re-initialization must be
      performed for all entities in the domain of that CA).  An end
      entity whose PSE contains the new CA public key (following a CA
      key update) must also be able to verify certificates verifiable
      using the old public key.  End entities who directly trust the
      old CA key pair must also be able to verify certificates signed
      using the new CA private key (required for situations where the
      old CA public key is "hardwired" into the end entity's
      cryptographic equipment).
 11.  The functions of an RA may, in some implementations or
      environments, be carried out by the CA itself.  The protocols
      must be designed so that end entities will use the same protocol
      regardless of whether the communication is with an RA or CA.
      Naturally, the end entity must use the correct RA of CA public
      key to protect the communication.

Adams, et al. Standards Track [Page 9] RFC 4210 CMP September 2005

 12.  Where an end entity requests a certificate containing a given
      public key value, the end entity must be ready to demonstrate
      possession of the corresponding private key value.  This may be
      accomplished in various ways, depending on the type of
      certification request.  See Section 4.3 for details of the in-
      band methods defined for the PKIX-CMP (i.e., Certificate
      Management Protocol) messages.

3.1.3. PKI Management Operations

 The following diagram shows the relationship between the entities
 defined above in terms of the PKI management operations.  The letters
 in the diagram indicate "protocols" in the sense that a defined set
 of PKI management messages can be sent along each of the lettered
 lines.

Adams, et al. Standards Track [Page 10] RFC 4210 CMP September 2005

   +---+     cert. publish        +------------+      j
   |   |  <---------------------  | End Entity | <-------
   | C |             g            +------------+      "out-of-band"
   | e |                            | ^                loading
   | r |                            | |      initial
   | t |                          a | | b     registration/
   |   |                            | |       certification
   | / |                            | |      key pair recovery
   |   |                            | |      key pair update
   | C |                            | |      certificate update
   | R |  PKI "USERS"               V |      revocation request
   | L | -------------------+-+-----+-+------+-+-------------------
   |   |  PKI MANAGEMENT    | ^              | ^
   |   |    ENTITIES      a | | b          a | | b
   | R |                    V |              | |
   | e |             g   +------+    d       | |
   | p |   <------------ | RA   | <-----+    | |
   | o |      cert.      |      | ----+ |    | |
   | s |       publish   +------+   c | |    | |
   | i |                              | |    | |
   | t |                              V |    V |
   | o |          g                 +------------+   i
   | r |   <------------------------|     CA     |------->
   | y |          h                 +------------+  "out-of-band"
   |   |      cert. publish              | ^         publication
   |   |      CRL publish                | |
   +---+                                 | |    cross-certification
                                       e | | f  cross-certificate
                                         | |       update
                                         | |
                                         V |
                                       +------+
                                       | CA-2 |
                                       +------+
 Figure 1 - PKI Entities
   At a high level, the set of operations for which management
   messages are defined can be grouped as follows.
 1.  CA establishment: When establishing a new CA, certain steps are
     required (e.g., production of initial CRLs, export of CA public
     key).
 2.  End entity initialization: this includes importing a root CA
     public key and requesting information about the options supported
     by a PKI management entity.

Adams, et al. Standards Track [Page 11] RFC 4210 CMP September 2005

 3.  Certification: various operations result in the creation of new
     certificates:
     1.  initial registration/certification: This is the process
         whereby an end entity first makes itself known to a CA or RA,
         prior to the CA issuing a certificate or certificates for
         that end entity.  The end result of this process (when it is
         successful) is that a CA issues a certificate for an end
         entity's public key, and returns that certificate to the end
         entity and/or posts that certificate in a public repository.
         This process may, and typically will, involve multiple
         "steps", possibly including an initialization of the end
         entity's equipment.  For example, the end entity's equipment
         must be securely initialized with the public key of a CA, to
         be used in validating certificate paths.  Furthermore, an end
         entity typically needs to be initialized with its own key
         pair(s).
     2.  key pair update: Every key pair needs to be updated regularly
         (i.e., replaced with a new key pair), and a new certificate
         needs to be issued.
     3.  certificate update: As certificates expire, they may be
         "refreshed" if nothing relevant in the environment has
         changed.
     4.  CA key pair update: As with end entities, CA key pairs need
         to be updated regularly; however, different mechanisms are
         required.
     5.  cross-certification request: One CA requests issuance of a
         cross-certificate from another CA.  For the purposes of this
         standard, the following terms are defined.  A "cross-
         certificate" is a certificate in which the subject CA and the
         issuer CA are distinct and SubjectPublicKeyInfo contains a
         verification key (i.e., the certificate has been issued for
         the subject CA's signing key pair).  When it is necessary to
         distinguish more finely, the following terms may be used: a
         cross-certificate is called an "inter-domain cross-
         certificate" if the subject and issuer CAs belong to
         different administrative domains; it is called an "intra-
         domain cross-certificate" otherwise.
         1.  Note 1.  The above definition of "cross-certificate"
             aligns with the defined term "CA-certificate" in X.509.
             Note that this term is not to be confused with the X.500
             "cACertificate" attribute type, which is unrelated.

Adams, et al. Standards Track [Page 12] RFC 4210 CMP September 2005

         2.  Note 2.  In many environments, the term "cross-
             certificate", unless further qualified, will be
             understood to be synonymous with "inter-domain cross-
             certificate" as defined above.
         3.  Note 3.  Issuance of cross-certificates may be, but is
             not necessarily, mutual; that is, two CAs may issue
             cross-certificates for each other.
     6.  cross-certificate update: Similar to a normal certificate
         update, but involving a cross-certificate.
 4.  Certificate/CRL discovery operations: some PKI management
     operations result in the publication of certificates or CRLs:
     1.  certificate publication: Having gone to the trouble of
         producing a certificate, some means for publishing it is
         needed.  The "means" defined in PKIX MAY involve the messages
         specified in Sections 5.3.13 to 5.3.16, or MAY involve other
         methods (LDAP, for example) as described in [RFC2559],
         [RFC2585] (the "Operational Protocols" documents of the PKIX
         series of specifications).
     2.  CRL publication: As for certificate publication.
 5.  Recovery operations: some PKI management operations are used when
     an end entity has "lost" its PSE:
     1.  key pair recovery: As an option, user client key materials
         (e.g., a user's private key used for decryption purposes) MAY
         be backed up by a CA, an RA, or a key backup system
         associated with a CA or RA.  If an entity needs to recover
         these backed up key materials (e.g., as a result of a
         forgotten password or a lost key chain file), a protocol
         exchange may be needed to support such recovery.
 6.  Revocation operations: some PKI operations result in the creation
     of new CRL entries and/or new CRLs:
     1.  revocation request: An authorized person advises a CA of an
         abnormal situation requiring certificate revocation.
 7.  PSE operations: whilst the definition of PSE operations (e.g.,
     moving a PSE, changing a PIN, etc.) are beyond the scope of this
     specification, we do define a PKIMessage (CertRepMessage) that
     can form the basis of such operations.

Adams, et al. Standards Track [Page 13] RFC 4210 CMP September 2005

 Note that on-line protocols are not the only way of implementing the
 above operations.  For all operations, there are off-line methods of
 achieving the same result, and this specification does not mandate
 use of on-line protocols.  For example, when hardware tokens are
 used, many of the operations MAY be achieved as part of the physical
 token delivery.
 Later sections define a set of standard messages supporting the above
 operations.  Transport protocols for conveying these exchanges in
 different environments (file-based, on-line, E-mail, and WWW) are
 beyond the scope of this document and are specified separately.

4. Assumptions and Restrictions

4.1. End Entity Initialization

 The first step for an end entity in dealing with PKI management
 entities is to request information about the PKI functions supported
 and to securely acquire a copy of the relevant root CA public key(s).

4.2. Initial Registration/Certification

 There are many schemes that can be used to achieve initial
 registration and certification of end entities.  No one method is
 suitable for all situations due to the range of policies that a CA
 may implement and the variation in the types of end entity which can
 occur.
 However, we can classify the initial registration/certification
 schemes that are supported by this specification.  Note that the word
 "initial", above, is crucial: we are dealing with the situation where
 the end entity in question has had no previous contact with the PKI.
 Where the end entity already possesses certified keys, then some
 simplifications/alternatives are possible.
 Having classified the schemes that are supported by this
 specification we can then specify some as mandatory and some as
 optional.  The goal is that the mandatory schemes cover a sufficient
 number of the cases that will arise in real use, whilst the optional
 schemes are available for special cases that arise less frequently.
 In this way, we achieve a balance between flexibility and ease of
 implementation.
 We will now describe the classification of initial
 registration/certification schemes.

Adams, et al. Standards Track [Page 14] RFC 4210 CMP September 2005

4.2.1. Criteria Used

4.2.1.1. Initiation of Registration/Certification

 In terms of the PKI messages that are produced, we can regard the
 initiation of the initial registration/certification exchanges as
 occurring wherever the first PKI message relating to the end entity
 is produced.  Note that the real-world initiation of the
 registration/certification procedure may occur elsewhere (e.g., a
 personnel department may telephone an RA operator).
 The possible locations are at the end entity, an RA, or a CA.

4.2.1.2. End Entity Message Origin Authentication

 The on-line messages produced by the end entity that requires a
 certificate may be authenticated or not.  The requirement here is to
 authenticate the origin of any messages from the end entity to the
 PKI (CA/RA).
 In this specification, such authentication is achieved by the PKI
 (CA/RA) issuing the end entity with a secret value (initial
 authentication key) and reference value (used to identify the secret
 value) via some out-of-band means.  The initial authentication key
 can then be used to protect relevant PKI messages.
 Thus, we can classify the initial registration/certification scheme
 according to whether or not the on-line end entity -> PKI messages
 are authenticated or not.
 Note 1: We do not discuss the authentication of the PKI -> end entity
 messages here, as this is always REQUIRED.  In any case, it can be
 achieved simply once the root-CA public key has been installed at the
 end entity's equipment or it can be based on the initial
 authentication key.
 Note 2: An initial registration/certification procedure can be secure
 where the messages from the end entity are authenticated via some
 out-of-band means (e.g., a subsequent visit).

4.2.1.3. Location of Key Generation

 In this specification, "key generation" is regarded as occurring
 wherever either the public or private component of a key pair first
 occurs in a PKIMessage.  Note that this does not preclude a
 centralized key generation service; the actual key pair MAY have been

Adams, et al. Standards Track [Page 15] RFC 4210 CMP September 2005

 generated elsewhere and transported to the end entity, RA, or CA
 using a (proprietary or standardized) key generation request/response
 protocol (outside the scope of this specification).
 Thus, there are three possibilities for the location of "key
 generation":  the end entity, an RA, or a CA.

4.2.1.4. Confirmation of Successful Certification

 Following the creation of an initial certificate for an end entity,
 additional assurance can be gained by having the end entity
 explicitly confirm successful receipt of the message containing (or
 indicating the creation of) the certificate.  Naturally, this
 confirmation message must be protected (based on the initial
 authentication key or other means).
 This gives two further possibilities: confirmed or not.

4.2.2. Mandatory Schemes

 The criteria above allow for a large number of initial
 registration/certification schemes.  This specification mandates that
 conforming CA equipment, RA equipment, and EE equipment MUST support
 the second scheme listed below (Section 4.2.2.2).  Any entity MAY
 additionally support other schemes, if desired.

4.2.2.1. Centralized Scheme

 In terms of the classification above, this scheme is, in some ways,
 the simplest possible, where:
 o  initiation occurs at the certifying CA;
 o  no on-line message authentication is required;
 o  "key generation" occurs at the certifying CA (see Section
    4.2.1.3);
 o  no confirmation message is required.
 In terms of message flow, this scheme means that the only message
 required is sent from the CA to the end entity.  The message must
 contain the entire PSE for the end entity.  Some out-of-band means
 must be provided to allow the end entity to authenticate the message
 received and to decrypt any encrypted values.

Adams, et al. Standards Track [Page 16] RFC 4210 CMP September 2005

4.2.2.2. Basic Authenticated Scheme

 In terms of the classification above, this scheme is where:
 o  initiation occurs at the end entity;
 o  message authentication is REQUIRED;
 o  "key generation" occurs at the end entity (see Section 4.2.1.3);
 o  a confirmation message is REQUIRED.
 In terms of message flow, the basic authenticated scheme is as
 follows:
   End entity                                          RA/CA
   ==========                                      =============
        out-of-band distribution of Initial Authentication
        Key (IAK) and reference value (RA/CA -> EE)
   Key generation
   Creation of certification request
   Protect request with IAK
                 -->>-- certification request -->>--
                                                  verify request
                                                  process request
                                                  create response
                 --<<-- certification response --<<--
   handle response
   create confirmation
                 -->>-- cert conf message      -->>--
                                                  verify confirmation
                                                  create response
                 --<<-- conf ack (optional)    --<<--
   handle response
 (Where verification of the cert confirmation message fails, the RA/CA
 MUST revoke the newly issued certificate if it has been published or
 otherwise made available.)

4.3. Proof-of-Possession (POP) of Private Key

 In order to prevent certain attacks and to allow a CA/RA to properly
 check the validity of the binding between an end entity and a key
 pair, the PKI management operations specified here make it possible
 for an end entity to prove that it has possession of (i.e., is able
 to use) the private key corresponding to the public key for which a
 certificate is requested.  A given CA/RA is free to choose how to
 enforce POP (e.g., out-of-band procedural means versus PKIX-CMP

Adams, et al. Standards Track [Page 17] RFC 4210 CMP September 2005

 in-band messages) in its certification exchanges (i.e., this may be a
 policy issue).  However, it is REQUIRED that CAs/RAs MUST enforce POP
 by some means because there are currently many non-PKIX operational
 protocols in use (various electronic mail protocols are one example)
 that do not explicitly check the binding between the end entity and
 the private key.  Until operational protocols that do verify the
 binding (for signature, encryption, and key agreement key pairs)
 exist, and are ubiquitous, this binding can only be assumed to have
 been verified by the CA/RA.  Therefore, if the binding is not
 verified by the CA/RA, certificates in the Internet Public-Key
 Infrastructure end up being somewhat less meaningful.
 POP is accomplished in different ways depending upon the type of key
 for which a certificate is requested.  If a key can be used for
 multiple purposes (e.g., an RSA key) then any appropriate method MAY
 be used (e.g., a key that may be used for signing, as well as other
 purposes, SHOULD NOT be sent to the CA/RA in order to prove
 possession).
 This specification explicitly allows for cases where an end entity
 supplies the relevant proof to an RA and the RA subsequently attests
 to the CA that the required proof has been received (and validated!).
 For example, an end entity wishing to have a signing key certified
 could send the appropriate signature to the RA, which then simply
 notifies the relevant CA that the end entity has supplied the
 required proof.  Of course, such a situation may be disallowed by
 some policies (e.g., CAs may be the only entities permitted to verify
 POP during certification).

4.3.1. Signature Keys

 For signature keys, the end entity can sign a value to prove
 possession of the private key.

4.3.2. Encryption Keys

 For encryption keys, the end entity can provide the private key to
 the CA/RA, or can be required to decrypt a value in order to prove
 possession of the private key (see Section 5.2.8).  Decrypting a
 value can be achieved either directly or indirectly.
 The direct method is for the RA/CA to issue a random challenge to
 which an immediate response by the EE is required.

Adams, et al. Standards Track [Page 18] RFC 4210 CMP September 2005

 The indirect method is to issue a certificate that is encrypted for
 the end entity (and have the end entity demonstrate its ability to
 decrypt this certificate in the confirmation message).  This allows a
 CA to issue a certificate in a form that can only be used by the
 intended end entity.
 This specification encourages use of the indirect method because it
 requires no extra messages to be sent (i.e., the proof can be
 demonstrated using the {request, response, confirmation} triple of
 messages).

4.3.3. Key Agreement Keys

 For key agreement keys, the end entity and the PKI management entity
 (i.e., CA or RA) must establish a shared secret key in order to prove
 that the end entity has possession of the private key.
 Note that this need not impose any restrictions on the keys that can
 be certified by a given CA.  In particular, for Diffie-Hellman keys
 the end entity may freely choose its algorithm parameters provided
 that the CA can generate a short-term (or one-time) key pair with the
 appropriate parameters when necessary.

4.4. Root CA Key Update

 This discussion only applies to CAs that are directly trusted by some
 end entities.  Self-signed CAs SHALL be considered as directly
 trusted CAs.  Recognizing whether a non-self-signed CA is supposed to
 be directly trusted for some end entities is a matter of CA policy
 and is thus beyond the scope of this document.
 The basis of the procedure described here is that the CA protects its
 new public key using its previous private key and vice versa.  Thus,
 when a CA updates its key pair it must generate two extra
 cACertificate attribute values if certificates are made available
 using an X.500 directory (for a total of four: OldWithOld,
 OldWithNew, NewWithOld, and NewWithNew).
 When a CA changes its key pair, those entities who have acquired the
 old CA public key via "out-of-band" means are most affected.  It is
 these end entities who will need access to the new CA public key
 protected with the old CA private key.  However, they will only
 require this for a limited period (until they have acquired the new
 CA public key via the "out-of-band" mechanism).  This will typically
 be easily achieved when these end entities' certificates expire.

Adams, et al. Standards Track [Page 19] RFC 4210 CMP September 2005

 The data structure used to protect the new and old CA public keys is
 a standard certificate (which may also contain extensions).  There
 are no new data structures required.
 Note 1.  This scheme does not make use of any of the X.509 v3
 extensions as it must be able to work even for version 1
 certificates.  The presence of the KeyIdentifier extension would make
 for efficiency improvements.
 Note 2.  While the scheme could be generalized to cover cases where
 the CA updates its key pair more than once during the validity period
 of one of its end entities' certificates, this generalization seems
 of dubious value.  Not having this generalization simply means that
 the validity periods of certificates issued with the old CA key pair
 cannot exceed the end of the OldWithNew validity period.
 Note 3.  This scheme ensures that end entities will acquire the new
 CA public key, at the latest by the expiry of the last certificate
 they owned that was signed with the old CA private key (via the
 "out-of-band" means).  Certificate and/or key update operations
 occurring at other times do not necessarily require this (depending
 on the end entity's equipment).

4.4.1. CA Operator Actions

 To change the key of the CA, the CA operator does the following:
 1.  Generate a new key pair;
 2.  Create a certificate containing the old CA public key signed with
     the new private key (the "old with new" certificate);
 3.  Create a certificate containing the new CA public key signed with
     the old private key (the "new with old" certificate);
 4.  Create a certificate containing the new CA public key signed with
     the new private key (the "new with new" certificate);
 5.  Publish these new certificates via the repository and/or other
     means (perhaps using a CAKeyUpdAnn message);
 6.  Export the new CA public key so that end entities may acquire it
     using the "out-of-band" mechanism (if required).
 The old CA private key is then no longer required.  However, the old
 CA public key will remain in use for some time.  The old CA public
 key is no longer required (other than for non-repudiation) when all
 end entities of this CA have securely acquired the new CA public key.

Adams, et al. Standards Track [Page 20] RFC 4210 CMP September 2005

 The "old with new" certificate must have a validity period starting
 at the generation time of the old key pair and ending at the expiry
 date of the old public key.
 The "new with old" certificate must have a validity period starting
 at the generation time of the new key pair and ending at the time by
 which all end entities of this CA will securely possess the new CA
 public key (at the latest, the expiry date of the old public key).
 The "new with new" certificate must have a validity period starting
 at the generation time of the new key pair and ending at or before
 the time by which the CA will next update its key pair.

4.4.2. Verifying Certificates

 Normally when verifying a signature, the verifier verifies (among
 other things) the certificate containing the public key of the
 signer.  However, once a CA is allowed to update its key there are a
 range of new possibilities.  These are shown in the table below.
              Repository contains NEW     Repository contains only OLD
                and OLD public keys        public key (due to, e.g.,
                                            delay in publication)
                 PSE      PSE Contains  PSE Contains    PSE Contains
              Contains     OLD public    NEW public      OLD public
             NEW public       key            key            key
                 key
  Signer's   Case 1:      Case 3:       Case 5:        Case 7:
  certifi-   This is      In this case  Although the   In this case
  cate is    the          the verifier  CA operator    the CA
  protected  standard     must access   has not        operator  has
  using NEW  case where   the           updated the    not updated
  public     the          repository in repository the the repository
  key        verifier     order to get  verifier can   and so the
             can          the value of  verify the     verification
             directly     the NEW       certificate    will FAIL
             verify the   public key    directly -
             certificate                this is thus
             without                    the same as
             using the                  case 1.
             repository

Adams, et al. Standards Track [Page 21] RFC 4210 CMP September 2005

  Signer's   Case 2:      Case 4:       Case 6:        Case 8:
  certifi-   In this      In this case  The verifier   Although the
  cate is    case the     the verifier  thinks this    CA operator
  protected  verifier     can directly  is the         has not
  using OLD  must         verify the    situation of   updated the
  public     access the   certificate   case 2 and     repository the
  key        repository   without       will access    verifier can
             in order     using the     the            verify the
             to get the   repository    repository;    certificate
             value of                   however, the   directly -
             the OLD                    verification   this is thus
             public key                 will FAIL      the same as
                                                       case 4.

4.4.2.1. Verification in Cases 1, 4, 5, and 8

 In these cases, the verifier has a local copy of the CA public key
 that can be used to verify the certificate directly.  This is the
 same as the situation where no key change has occurred.
 Note that case 8 may arise between the time when the CA operator has
 generated the new key pair and the time when the CA operator stores
 the updated attributes in the repository.  Case 5 can only arise if
 the CA operator has issued both the signer's and verifier's
 certificates during this "gap" (the CA operator SHOULD avoid this as
 it leads to the failure cases described below)

4.4.2.2. Verification in Case 2

 In case 2, the verifier must get access to the old public key of the
 CA.  The verifier does the following:
 1.  Look up the caCertificate attribute in the repository and pick
     the OldWithNew certificate (determined based on validity periods;
     note that the subject and issuer fields must match);
 2.  Verify that this is correct using the new CA key (which the
     verifier has locally);
 3.  If correct, check the signer's certificate using the old CA key.
 Case 2 will arise when the CA operator has issued the signer's
 certificate, then changed the key, and then issued the verifier's
 certificate; so it is quite a typical case.

Adams, et al. Standards Track [Page 22] RFC 4210 CMP September 2005

4.4.2.3. Verification in Case 3

 In case 3, the verifier must get access to the new public key of the
 CA.  The verifier does the following:
 1.  Look up the CACertificate attribute in the repository and pick
     the NewWithOld certificate (determined based on validity periods;
     note that the subject and issuer fields must match);
 2.  Verify that this is correct using the old CA key (which the
     verifier has stored locally);
 3.  If correct, check the signer's certificate using the new CA key.
 Case 3 will arise when the CA operator has issued the verifier's
 certificate, then changed the key, and then issued the signer's
 certificate; so it is also quite a typical case.

4.4.2.4. Failure of Verification in Case 6

 In this case, the CA has issued the verifier's PSE, which contains
 the new key, without updating the repository attributes.  This means
 that the verifier has no means to get a trustworthy version of the
 CA's old key and so verification fails.
 Note that the failure is the CA operator's fault.

4.4.2.5. Failure of Verification in Case 7

 In this case, the CA has issued the signer's certificate protected
 with the new key without updating the repository attributes.  This
 means that the verifier has no means to get a trustworthy version of
 the CA's new key and so verification fails.
 Note that the failure is again the CA operator's fault.

4.4.3. Revocation - Change of CA Key

 As we saw above, the verification of a certificate becomes more
 complex once the CA is allowed to change its key.  This is also true
 for revocation checks as the CA may have signed the CRL using a newer
 private key than the one within the user's PSE.
 The analysis of the alternatives is the same as for certificate
 verification.

Adams, et al. Standards Track [Page 23] RFC 4210 CMP September 2005

5. Data Structures

 This section contains descriptions of the data structures required
 for PKI management messages.  Section 6 describes constraints on
 their values and the sequence of events for each of the various PKI
 management operations.

5.1. Overall PKI Message

 All of the messages used in this specification for the purposes of
 PKI management use the following structure:
    PKIMessage ::= SEQUENCE {
       header           PKIHeader,
       body             PKIBody,
       protection   [0] PKIProtection OPTIONAL,
       extraCerts   [1] SEQUENCE SIZE (1..MAX) OF CMPCertificate
                        OPTIONAL
   }
   PKIMessages ::= SEQUENCE SIZE (1..MAX) OF PKIMessage
 The PKIHeader contains information that is common to many PKI
 messages.
 The PKIBody contains message-specific information.
 The PKIProtection, when used, contains bits that protect the PKI
 message.
 The extraCerts field can contain certificates that may be useful to
 the recipient.  For example, this can be used by a CA or RA to
 present an end entity with certificates that it needs to verify its
 own new certificate (if, for example, the CA that issued the end
 entity's certificate is not a root CA for the end entity).  Note that
 this field does not necessarily contain a certification path; the
 recipient may have to sort, select from, or otherwise process the
 extra certificates in order to use them.

5.1.1. PKI Message Header

 All PKI messages require some header information for addressing and
 transaction identification.  Some of this information will also be
 present in a transport-specific envelope.  However, if the PKI
 message is protected, then this information is also protected (i.e.,
 we make no assumption about secure transport).

Adams, et al. Standards Track [Page 24] RFC 4210 CMP September 2005

 The following data structure is used to contain this information:
   PKIHeader ::= SEQUENCE {
       pvno                INTEGER     { cmp1999(1), cmp2000(2) },
       sender              GeneralName,
       recipient           GeneralName,
       messageTime     [0] GeneralizedTime         OPTIONAL,
       protectionAlg   [1] AlgorithmIdentifier     OPTIONAL,
       senderKID       [2] KeyIdentifier           OPTIONAL,
       recipKID        [3] KeyIdentifier           OPTIONAL,
       transactionID   [4] OCTET STRING            OPTIONAL,
       senderNonce     [5] OCTET STRING            OPTIONAL,
       recipNonce      [6] OCTET STRING            OPTIONAL,
       freeText        [7] PKIFreeText             OPTIONAL,
       generalInfo     [8] SEQUENCE SIZE (1..MAX) OF
                           InfoTypeAndValue     OPTIONAL
   }
   PKIFreeText ::= SEQUENCE SIZE (1..MAX) OF UTF8String
 The pvno field is fixed (at 2) for this version of this
 specification.
 The sender field contains the name of the sender of the PKIMessage.
 This name (in conjunction with senderKID, if supplied) should be
 sufficient to indicate the key to use to verify the protection on the
 message.  If nothing about the sender is known to the sending entity
 (e.g., in the init. req. message, where the end entity may not know
 its own Distinguished Name (DN), e-mail name, IP address, etc.), then
 the "sender" field MUST contain a "NULL" value; that is, the SEQUENCE
 OF relative distinguished names is of zero length.  In such a case,
 the senderKID field MUST hold an identifier (i.e., a reference
 number) that indicates to the receiver the appropriate shared secret
 information to use to verify the message.
 The recipient field contains the name of the recipient of the
 PKIMessage.  This name (in conjunction with recipKID, if supplied)
 should be usable to verify the protection on the message.
 The protectionAlg field specifies the algorithm used to protect the
 message.  If no protection bits are supplied (note that PKIProtection
 is OPTIONAL) then this field MUST be omitted; if protection bits are
 supplied, then this field MUST be supplied.
 senderKID and recipKID are usable to indicate which keys have been
 used to protect the message (recipKID will normally only be required
 where protection of the message uses Diffie-Hellman (DH) keys).

Adams, et al. Standards Track [Page 25] RFC 4210 CMP September 2005

 These fields MUST be used if required to uniquely identify a key
 (e.g., if more than one key is associated with a given sender name)
 and SHOULD be omitted otherwise.
 The transactionID field within the message header is to be used to
 allow the recipient of a message to correlate this with an ongoing
 transaction.  This is needed for all transactions that consist of
 more than just a single request/response pair.  For transactions that
 consist of a single request/response pair, the rules are as follows.
 A client MAY populate the transactionID field of the request.  If a
 server receives such a request that has the transactionID field set,
 then it MUST set the transactionID field of the response to the same
 value.  If a server receives such request with a missing
 transactionID field, then it MAY set transactionID field of the
 response.
 For transactions that consist of more than just a single
 request/response pair, the rules are as follows.  Clients SHOULD
 generate a transactionID for the first request.  If a server receives
 such a request that has the transactionID field set, then it MUST set
 the transactionID field of the response to the same value.  If a
 server receives such request with a missing transactionID field, then
 it MUST populate the transactionID field of the response with a
 server-generated ID.  Subsequent requests and responses MUST all set
 the transactionID field to the thus established value.  In all cases
 where a transactionID is being used, a given client MUST NOT have
 more than one transaction with the same transactionID in progress at
 any time (to a given server).  Servers are free to require uniqueness
 of the transactionID or not, as long as they are able to correctly
 associate messages with the corresponding transaction.  Typically,
 this means that a server will require the {client, transactionID}
 tuple to be unique, or even the transactionID alone to be unique, if
 it cannot distinguish clients based on transport-level information.
 A server receiving the first message of a transaction (which requires
 more than a single request/response pair) that contains a
 transactionID that does not allow it to meet the above constraints
 (typically because the transactionID is already in use) MUST send
 back an ErrorMsgContent with a PKIFailureInfo of transactionIdInUse.
 It is RECOMMENDED that the clients fill the transactionID field with
 128 bits of (pseudo-) random data for the start of a transaction to
 reduce the probability of having the transactionID in use at the
 server.
 The senderNonce and recipNonce fields protect the PKIMessage against
 replay attacks.  The senderNonce will typically be 128 bits of
 (pseudo-) random data generated by the sender, whereas the recipNonce
 is copied from the senderNonce of the previous message in the
 transaction.

Adams, et al. Standards Track [Page 26] RFC 4210 CMP September 2005

 The messageTime field contains the time at which the sender created
 the message.  This may be useful to allow end entities to
 correct/check their local time for consistency with the time on a
 central system.
 The freeText field may be used to send a human-readable message to
 the recipient (in any number of languages).  The first language used
 in this sequence indicates the desired language for replies.
 The generalInfo field may be used to send machine-processable
 additional data to the recipient.  The following generalInfo
 extensions are defined and MAY be supported.

5.1.1.1. ImplicitConfirm

 This is used by the EE to inform the CA that it does not wish to send
 a certificate confirmation for issued certificates.
       implicitConfirm OBJECT IDENTIFIER ::= {id-it 13}
       ImplicitConfirmValue ::= NULL
 If the CA grants the request to the EE, it MUST put the same
 extension in the PKIHeader of the response.  If the EE does not find
 the extension in the response, it MUST send the certificate
 confirmation.

5.1.1.2. ConfirmWaitTime

 This is used by the CA to inform the EE how long it intends to wait
 for the certificate confirmation before revoking the certificate and
 deleting the transaction.
       confirmWaitTime OBJECT IDENTIFIER ::= {id-it 14}
       ConfirmWaitTimeValue ::= GeneralizedTime

5.1.2. PKI Message Body

      PKIBody ::= CHOICE {
        ir       [0]  CertReqMessages,       --Initialization Req
        ip       [1]  CertRepMessage,        --Initialization Resp
        cr       [2]  CertReqMessages,       --Certification Req
        cp       [3]  CertRepMessage,        --Certification Resp
        p10cr    [4]  CertificationRequest,  --PKCS #10 Cert.  Req.
        popdecc  [5]  POPODecKeyChallContent --pop Challenge
        popdecr  [6]  POPODecKeyRespContent, --pop Response
        kur      [7]  CertReqMessages,       --Key Update Request
        kup      [8]  CertRepMessage,        --Key Update Response
        krr      [9]  CertReqMessages,       --Key Recovery Req

Adams, et al. Standards Track [Page 27] RFC 4210 CMP September 2005

        krp      [10] KeyRecRepContent,      --Key Recovery Resp
        rr       [11] RevReqContent,         --Revocation Request
        rp       [12] RevRepContent,         --Revocation Response
        ccr      [13] CertReqMessages,       --Cross-Cert.  Request
        ccp      [14] CertRepMessage,        --Cross-Cert.  Resp
        ckuann   [15] CAKeyUpdAnnContent,    --CA Key Update Ann.
        cann     [16] CertAnnContent,        --Certificate Ann.
        rann     [17] RevAnnContent,         --Revocation Ann.
        crlann   [18] CRLAnnContent,         --CRL Announcement
        pkiconf  [19] PKIConfirmContent,     --Confirmation
        nested   [20] NestedMessageContent,  --Nested Message
        genm     [21] GenMsgContent,         --General Message
        genp     [22] GenRepContent,         --General Response
        error    [23] ErrorMsgContent,       --Error Message
        certConf [24] CertConfirmContent,    --Certificate confirm
        pollReq  [25] PollReqContent,        --Polling request
        pollRep  [26] PollRepContent         --Polling response
        }
 The specific types are described in Section 5.3 below.

5.1.3. PKI Message Protection

 Some PKI messages will be protected for integrity.  (Note that if an
 asymmetric algorithm is used to protect a message and the relevant
 public component has been certified already, then the origin of the
 message can also be authenticated.  On the other hand, if the public
 component is uncertified, then the message origin cannot be
 automatically authenticated, but may be authenticated via out-of-band
 means.)
 When protection is applied, the following structure is used:
      PKIProtection ::= BIT STRING
 The input to the calculation of PKIProtection is the DER encoding of
 the following data structure:
      ProtectedPart ::= SEQUENCE {
          header    PKIHeader,
          body      PKIBody
      }
 There MAY be cases in which the PKIProtection BIT STRING is
 deliberately not used to protect a message (i.e., this OPTIONAL field
 is omitted) because other protection, external to PKIX, will be
 applied instead.  Such a choice is explicitly allowed in this
 specification.  Examples of such external protection include PKCS #7

Adams, et al. Standards Track [Page 28] RFC 4210 CMP September 2005

 [PKCS7] and Security Multiparts [RFC1847] encapsulation of the
 PKIMessage (or simply the PKIBody (omitting the CHOICE tag), if the
 relevant PKIHeader information is securely carried in the external
 mechanism).  It is noted, however, that many such external mechanisms
 require that the end entity already possesses a public-key
 certificate, and/or a unique Distinguished Name, and/or other such
 infrastructure-related information.  Thus, they may not be
 appropriate for initial registration, key-recovery, or any other
 process with "boot-strapping" characteristics.  For those cases it
 may be necessary that the PKIProtection parameter be used.  In the
 future, if/when external mechanisms are modified to accommodate
 boot-strapping scenarios, the use of PKIProtection may become rare or
 non-existent.
 Depending on the circumstances, the PKIProtection bits may contain a
 Message Authentication Code (MAC) or signature.  Only the following
 cases can occur:

5.1.3.1. Shared Secret Information

 In this case, the sender and recipient share secret information
 (established via out-of-band means or from a previous PKI management
 operation).  PKIProtection will contain a MAC value and the
 protectionAlg will be the following (see also Appendix D.2):
   id-PasswordBasedMac OBJECT IDENTIFIER ::= {1 2 840 113533 7 66 13}
   PBMParameter ::= SEQUENCE {
     salt                OCTET STRING,
     owf                 AlgorithmIdentifier,
     iterationCount      INTEGER,
     mac                 AlgorithmIdentifier
   }
 In the above protectionAlg, the salt value is appended to the shared
 secret input.  The OWF is then applied iterationCount times, where
 the salted secret is the input to the first iteration and, for each
 successive iteration, the input is set to be the output of the
 previous iteration.  The output of the final iteration (called
 "BASEKEY" for ease of reference, with a size of "H") is what is used
 to form the symmetric key.  If the MAC algorithm requires a K-bit key
 and K <= H, then the most significant K bits of BASEKEY are used.  If
 K > H, then all of BASEKEY is used for the most significant H bits of
 the key, OWF("1" || BASEKEY) is used for the next most significant H
 bits of the key, OWF("2" || BASEKEY) is used for the next most
 significant H bits of the key, and so on, until all K bits have been
 derived.  [Here "N" is the ASCII byte encoding the number N and "||"
 represents concatenation.]

Adams, et al. Standards Track [Page 29] RFC 4210 CMP September 2005

 Note: it is RECOMMENDED that the fields of PBMParameter remain
 constant throughout the messages of a single transaction (e.g.,
 ir/ip/certConf/pkiConf) in order to reduce the overhead associated
 with PasswordBasedMac computation).

5.1.3.2. DH Key Pairs

 Where the sender and receiver possess Diffie-Hellman certificates
 with compatible DH parameters, in order to protect the message the
 end entity must generate a symmetric key based on its private DH key
 value and the DH public key of the recipient of the PKI message.
 PKIProtection will contain a MAC value keyed with this derived
 symmetric key and the protectionAlg will be the following:
      id-DHBasedMac OBJECT IDENTIFIER ::= {1 2 840 113533 7 66 30}
      DHBMParameter ::= SEQUENCE {
          owf                 AlgorithmIdentifier,
          -- AlgId for a One-Way Function (SHA-1 recommended)
          mac                 AlgorithmIdentifier
          -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
      }   -- or HMAC [RFC2104, RFC2202])
 In the above protectionAlg, OWF is applied to the result of the
 Diffie-Hellman computation.  The OWF output (called "BASEKEY" for
 ease of reference, with a size of "H") is what is used to form the
 symmetric key.  If the MAC algorithm requires a K-bit key and K <= H,
 then the most significant K bits of BASEKEY are used.  If K > H, then
 all of BASEKEY is used for the most significant H bits of the key,
 OWF("1" || BASEKEY) is used for the next most significant H bits of
 the key, OWF("2" || BASEKEY) is used for the next most significant H
 bits of the key, and so on, until all K bits have been derived.
 [Here "N" is the ASCII byte encoding the number N and "||" represents
 concatenation.]

5.1.3.3. Signature

 In this case, the sender possesses a signature key pair and simply
 signs the PKI message.  PKIProtection will contain the signature
 value and the protectionAlg will be an AlgorithmIdentifier for a
 digital signature (e.g., md5WithRSAEncryption or dsaWithSha-1).

5.1.3.4. Multiple Protection

 In cases where an end entity sends a protected PKI message to an RA,
 the RA MAY forward that message to a CA, attaching its own protection
 (which MAY be a MAC or a signature, depending on the information and
 certificates shared between the RA and the CA).  This is accomplished

Adams, et al. Standards Track [Page 30] RFC 4210 CMP September 2005

 by nesting the entire message sent by the end entity within a new PKI
 message.  The structure used is as follows.
        NestedMessageContent ::= PKIMessages
 (The use of PKIMessages, a SEQUENCE OF PKIMessage, lets the RA batch
 the requests of several EEs in a single new message.  For simplicity,
 all messages in the batch MUST be of the same type (e.g., ir).)  If
 the RA wishes to modify the message(s) in some way (e.g., add
 particular field values or new extensions), then it MAY create its
 own desired PKIBody.  The original PKIMessage from the EE MAY be
 included in the generalInfo field of PKIHeader (to accommodate, for
 example, cases in which the CA wishes to check POP or other
 information on the original EE message).  The infoType to be used in
 this situation is {id-it 15} (see Section 5.3.19 for the value of
 id-it) and the infoValue is PKIMessages (contents MUST be in the same
 order as the requests in PKIBody).

5.2. Common Data Structures

 Before specifying the specific types that may be placed in a PKIBody,
 we define some data structures that are used in more than one case.

5.2.1. Requested Certificate Contents

 Various PKI management messages require that the originator of the
 message indicate some of the fields that are required to be present
 in a certificate.  The CertTemplate structure allows an end entity or
 RA to specify as much as it wishes about the certificate it requires.
 CertTemplate is identical to a Certificate, but with all fields
 optional.
 Note that even if the originator completely specifies the contents of
 a certificate it requires, a CA is free to modify fields within the
 certificate actually issued.  If the modified certificate is
 unacceptable to the requester, the requester MUST send back a
 certConf message that either does not include this certificate (via a
 CertHash), or does include this certificate (via a CertHash) along
 with a status of "rejected".  See Section 5.3.18 for the definition
 and use of CertHash and the certConf message.
 See Appendix C and [CRMF] for CertTemplate syntax.

5.2.2. Encrypted Values

 Where encrypted values (restricted, in this specification, to be
 either private keys or certificates) are sent in PKI messages, the
 EncryptedValue data structure is used.

Adams, et al. Standards Track [Page 31] RFC 4210 CMP September 2005

 See [CRMF] for EncryptedValue syntax.
 Use of this data structure requires that the creator and intended
 recipient be able to encrypt and decrypt, respectively.  Typically,
 this will mean that the sender and recipient have, or are able to
 generate, a shared secret key.
 If the recipient of the PKIMessage already possesses a private key
 usable for decryption, then the encSymmKey field MAY contain a
 session key encrypted using the recipient's public key.

5.2.3. Status codes and Failure Information for PKI Messages

 All response messages will include some status information.  The
 following values are defined.
      PKIStatus ::= INTEGER {
          accepted               (0),
          grantedWithMods        (1),
          rejection              (2),
          waiting                (3),
          revocationWarning      (4),
          revocationNotification (5),
          keyUpdateWarning       (6)
      }
 Responders may use the following syntax to provide more information
 about failure cases.
      PKIFailureInfo ::= BIT STRING {
          badAlg              (0),
          badMessageCheck     (1),
          badRequest          (2),
          badTime             (3),
          badCertId           (4),
          badDataFormat       (5),
          wrongAuthority      (6),
          incorrectData       (7),
          missingTimeStamp    (8),
          badPOP              (9),
          certRevoked         (10),
          certConfirmed       (11),
          wrongIntegrity      (12),
          badRecipientNonce   (13),
          timeNotAvailable    (14),
          unacceptedPolicy    (15),
          unacceptedExtension (16),
          addInfoNotAvailable (17),

Adams, et al. Standards Track [Page 32] RFC 4210 CMP September 2005

          badSenderNonce      (18),
          badCertTemplate     (19),
          signerNotTrusted    (20),
          transactionIdInUse  (21),
          unsupportedVersion  (22),
          notAuthorized       (23),
          systemUnavail       (24),
          systemFailure       (25),
          duplicateCertReq    (26)
      }
      PKIStatusInfo ::= SEQUENCE {
          status        PKIStatus,
          statusString  PKIFreeText     OPTIONAL,
          failInfo      PKIFailureInfo  OPTIONAL
      }

5.2.4. Certificate Identification

 In order to identify particular certificates, the CertId data
 structure is used.
 See [CRMF] for CertId syntax.

5.2.5. Out-of-band root CA Public Key

 Each root CA must be able to publish its current public key via some
 "out-of-band" means.  While such mechanisms are beyond the scope of
 this document, we define data structures that can support such
 mechanisms.
 There are generally two methods available: either the CA directly
 publishes its self-signed certificate, or this information is
 available via the Directory (or equivalent) and the CA publishes a
 hash of this value to allow verification of its integrity before use.
      OOBCert ::= Certificate
 The fields within this certificate are restricted as follows:
 o  The certificate MUST be self-signed (i.e., the signature must be
    verifiable using the SubjectPublicKeyInfo field);
 o  The subject and issuer fields MUST be identical;
 o  If the subject field is NULL, then both subjectAltNames and
    issuerAltNames extensions MUST be present and have exactly the
    same value;

Adams, et al. Standards Track [Page 33] RFC 4210 CMP September 2005

 o  The values of all other extensions must be suitable for a self-
    signed certificate (e.g., key identifiers for subject and issuer
    must be the same).
      OOBCertHash ::= SEQUENCE {
          hashAlg     [0] AlgorithmIdentifier     OPTIONAL,
          certId      [1] CertId                  OPTIONAL,
          hashVal         BIT STRING
      }
 The intention of the hash value is that anyone who has securely
 received the hash value (via the out-of-band means) can verify a
 self-signed certificate for that CA.

5.2.6. Archive Options

 Requesters may indicate that they wish the PKI to archive a private
 key value using the PKIArchiveOptions structure.
 See [CRMF] for PKIArchiveOptions syntax.

5.2.7. Publication Information

 Requesters may indicate that they wish the PKI to publish a
 certificate using the PKIPublicationInfo structure.
 See [CRMF] for PKIPublicationInfo syntax.

5.2.8. Proof-of-Possession Structures

 If the certification request is for a signing key pair (i.e., a
 request for a verification certificate), then the proof-of-possession
 of the private signing key is demonstrated through use of the
 POPOSigningKey structure.
 See Appendix C and [CRMF] for POPOSigningKey syntax, but note that
 POPOSigningKeyInput has the following semantic stipulations in this
 specification.
      POPOSigningKeyInput ::= SEQUENCE {
          authInfo            CHOICE {
              sender              [0] GeneralName,
              publicKeyMAC            PKMACValue
          },
          publicKey           SubjectPublicKeyInfo
      }

Adams, et al. Standards Track [Page 34] RFC 4210 CMP September 2005

 On the other hand, if the certification request is for an encryption
 key pair (i.e., a request for an encryption certificate), then the
 proof-of-possession of the private decryption key may be demonstrated
 in one of three ways.

5.2.8.1. Inclusion of the Private Key

 By the inclusion of the private key (encrypted) in the CertRequest
 (in the thisMessage field of POPOPrivKey (see Appendix C) or in the
 PKIArchiveOptions control structure, depending upon whether or not
 archival of the private key is also desired).

5.2.8.2. Indirect Method

 By having the CA return not the certificate, but an encrypted
 certificate (i.e., the certificate encrypted under a randomly-
 generated symmetric key, and the symmetric key encrypted under the
 public key for which the certification request is being made) -- this
 is the "indirect" method mentioned previously in Section 4.3.2. The
 end entity proves knowledge of the private decryption key to the CA
 by providing the correct CertHash for this certificate in the
 certConf message.  This demonstrates POP because the EE can only
 compute the correct CertHash if it is able to recover the
 certificate, and it can only recover the certificate if it is able to
 decrypt the symmetric key using the required private key.  Clearly,
 for this to work, the CA MUST NOT publish the certificate until the
 certConf message arrives (when certHash is to be used to demonstrate
 POP).  See Section 5.3.18 for further details.

5.2.8.3. Challenge-Response Protocol

 By having the end entity engage in a challenge-response protocol
 (using the messages POPODecKeyChall and POPODecKeyResp; see below)
 between CertReqMessages and CertRepMessage -- this is the "direct"
 method mentioned previously in Section 4.3.2.  (This method would
 typically be used in an environment in which an RA verifies POP and
 then makes a certification request to the CA on behalf of the end
 entity.  In such a scenario, the CA trusts the RA to have done POP
 correctly before the RA requests a certificate for the end entity.)
 The complete protocol then looks as follows (note that req' does not
 necessarily encapsulate req as a nested message):

Adams, et al. Standards Track [Page 35] RFC 4210 CMP September 2005

                 EE            RA            CA
                  ---- req ---->
                  <--- chall ---
                  ---- resp --->
                                ---- req' --->
                                <--- rep -----
                                ---- conf --->
                                <--- ack -----
                  <--- rep -----
                  ---- conf --->
                  <--- ack -----
 This protocol is obviously much longer than the 3-way exchange given
 in choice (2) above, but allows a local Registration Authority to be
 involved and has the property that the certificate itself is not
 actually created until the proof-of-possession is complete.  In some
 environments, a different order of the above messages may be
 required, such as the following (this may be determined by policy):
                 EE            RA            CA
                  ---- req ---->
                  <--- chall ---
                  ---- resp --->
                                ---- req' --->
                                <--- rep -----
                  <--- rep -----
                  ---- conf --->
                                ---- conf --->
                                <--- ack -----
                  <--- ack -----
 If the cert. request is for a key agreement key (KAK) pair, then the
 POP can use any of the 3 ways described above for enc. key pairs,
 with the following changes: (1) the parenthetical text of bullet 2)
 is replaced with "(i.e., the certificate encrypted under the
 symmetric key derived from the CA's private KAK and the public key
 for which the certification request is being made)"; (2) the first
 parenthetical text of the challenge field of "Challenge" below is
 replaced with "(using PreferredSymmAlg (see Section 5.3.19.4 and
 Appendix E.5) and a symmetric key derived from the CA's private KAK
 and the public key for which the certification request is being
 made)".  Alternatively, the POP can use the POPOSigningKey structure
 given in [CRMF] (where the alg field is DHBasedMAC and the signature
 field is the MAC) as a fourth alternative for demonstrating POP if
 the CA already has a D-H certificate that is known to the EE.

Adams, et al. Standards Track [Page 36] RFC 4210 CMP September 2005

 The challenge-response messages for proof-of-possession of a private
 decryption key are specified as follows (see [MvOV97], p.404 for
 details).  Note that this challenge-response exchange is associated
 with the preceding cert. request message (and subsequent cert.
 response and confirmation messages) by the transactionID used in the
 PKIHeader and by the protection (MACing or signing) applied to the
 PKIMessage.
      POPODecKeyChallContent ::= SEQUENCE OF Challenge
      Challenge ::= SEQUENCE {
          owf                 AlgorithmIdentifier  OPTIONAL,
          witness             OCTET STRING,
          challenge           OCTET STRING
      }
 Note that the size of Rand needs to be appropriate for encryption
 under the public key of the requester.  Given that "int" will
 typically not be longer than 64 bits, this leaves well over 100 bytes
 of room for the "sender" field when the modulus is 1024 bits.  If, in
 some environment, names are so long that they cannot fit (e.g., very
 long DNs), then whatever portion will fit should be used (as long as
 it includes at least the common name, and as long as the receiver is
 able to deal meaningfully with the abbreviation).
      POPODecKeyRespContent ::= SEQUENCE OF INTEGER

5.2.8.4. Summary of PoP Options

 The text in this section provides several options with respect to POP
 techniques.  Using "SK" for "signing key", "EK" for "encryption key",
 and "KAK" for "key agreement key", the techniques may be summarized
 as follows:
       RAVerified;
       SKPOP;
       EKPOPThisMessage;
       KAKPOPThisMessage;
       KAKPOPThisMessageDHMAC;
       EKPOPEncryptedCert;
       KAKPOPEncryptedCert;
       EKPOPChallengeResp; and
       KAKPOPChallengeResp.
 Given this array of options, it is natural to ask how an end entity
 can know what is supported by the CA/RA (i.e., which options it may
 use when requesting certificates).  The following guidelines should
 clarify this situation for EE implementers.

Adams, et al. Standards Track [Page 37] RFC 4210 CMP September 2005

 RAVerified.  This is not an EE decision; the RA uses this if and only
 if it has verified POP before forwarding the request on to the CA, so
 it is not possible for the EE to choose this technique.
 SKPOP.  If the EE has a signing key pair, this is the only POP method
 specified for use in the request for a corresponding certificate.
 EKPOPThisMessage and KAKPOPThisMessage.  Whether or not to give up
 its private key to the CA/RA is an EE decision.  If the EE decides to
 reveal its key, then these are the only POP methods available in this
 specification to achieve this (and the key pair type will determine
 which of these two methods to use).
 KAKPOPThisMessageDHMAC.  The EE can only use this method if (1) the
 CA has a DH certificate available for this purpose, and (2) the EE
 already has a copy of this certificate.  If both these conditions
 hold, then this technique is clearly supported and may be used by the
 EE, if desired.
 EKPOPEncryptedCert, KAKPOPEncryptedCert, EKPOPChallengeResp,
 KAKPOPChallengeResp.  The EE picks one of these (in the
 subsequentMessage field) in the request message, depending upon
 preference and key pair type.  The EE is not doing POP at this point;
 it is simply indicating which method it wants to use.  Therefore, if
 the CA/RA replies with a "badPOP" error, the EE can re-request using
 the other POP method chosen in subsequentMessage.  Note, however,
 that this specification encourages the use of the EncryptedCert
 choice and, furthermore, says that the challenge-response would
 typically be used when an RA is involved and doing POP verification.
 Thus, the EE should be able to make an intelligent decision regarding
 which of these POP methods to choose in the request message.

5.3. Operation-Specific Data Structures

5.3.1. Initialization Request

 An Initialization request message contains as the PKIBody a
 CertReqMessages data structure, which specifies the requested
 certificate(s).  Typically, SubjectPublicKeyInfo, KeyId, and Validity
 are the template fields which may be supplied for each certificate
 requested (see Appendix D profiles for further information).  This
 message is intended to be used for entities when first initializing
 into the PKI.
 See Appendix C and [CRMF] for CertReqMessages syntax.

Adams, et al. Standards Track [Page 38] RFC 4210 CMP September 2005

5.3.2. Initialization Response

 An Initialization response message contains as the PKIBody an
 CertRepMessage data structure, which has for each certificate
 requested a PKIStatusInfo field, a subject certificate, and possibly
 a private key (normally encrypted with a session key, which is itself
 encrypted with the protocolEncrKey).
 See Section 5.3.4 for CertRepMessage syntax.  Note that if the PKI
 Message Protection is "shared secret information" (see Section
 5.1.3), then any certificate transported in the caPubs field may be
 directly trusted as a root CA certificate by the initiator.

5.3.3. Certification Request

 A Certification request message contains as the PKIBody a
 CertReqMessages data structure, which specifies the requested
 certificates.  This message is intended to be used for existing PKI
 entities who wish to obtain additional certificates.
 See Appendix C and [CRMF] for CertReqMessages syntax.
 Alternatively, the PKIBody MAY be a CertificationRequest (this
 structure is fully specified by the ASN.1 structure
 CertificationRequest given in [PKCS10]).  This structure may be
 required for certificate requests for signing key pairs when
 interoperation with legacy systems is desired, but its use is
 strongly discouraged whenever not absolutely necessary.

5.3.4. Certification Response

 A Certification response message contains as the PKIBody a
 CertRepMessage data structure, which has a status value for each
 certificate requested, and optionally has a CA public key, failure
 information, a subject certificate, and an encrypted private key.
   CertRepMessage ::= SEQUENCE {
       caPubs          [1] SEQUENCE SIZE (1..MAX) OF Certificate
                           OPTIONAL,
       response            SEQUENCE OF CertResponse
   }
   CertResponse ::= SEQUENCE {
       certReqId           INTEGER,
       status              PKIStatusInfo,
       certifiedKeyPair    CertifiedKeyPair    OPTIONAL,
       rspInfo             OCTET STRING        OPTIONAL
       -- analogous to the id-regInfo-utf8Pairs string defined

Adams, et al. Standards Track [Page 39] RFC 4210 CMP September 2005

  1. - for regInfo in CertReqMsg [CRMF]

}

   CertifiedKeyPair ::= SEQUENCE {
       certOrEncCert       CertOrEncCert,
       privateKey      [0] EncryptedValue      OPTIONAL,
       -- see [CRMF] for comment on encoding
       publicationInfo [1] PKIPublicationInfo  OPTIONAL
   }
   CertOrEncCert ::= CHOICE {
       certificate     [0] Certificate,
       encryptedCert   [1] EncryptedValue
   }
 Only one of the failInfo (in PKIStatusInfo) and certificate (in
 CertifiedKeyPair) fields can be present in each CertResponse
 (depending on the status).  For some status values (e.g., waiting),
 neither of the optional fields will be present.
 Given an EncryptedCert and the relevant decryption key, the
 certificate may be obtained.  The purpose of this is to allow a CA to
 return the value of a certificate, but with the constraint that only
 the intended recipient can obtain the actual certificate.  The
 benefit of this approach is that a CA may reply with a certificate
 even in the absence of a proof that the requester is the end entity
 that can use the relevant private key (note that the proof is not
 obtained until the certConf message is received by the CA).  Thus,
 the CA will not have to revoke that certificate in the event that
 something goes wrong with the proof-of-possession (but MAY do so
 anyway, depending upon policy).

5.3.5. Key Update Request Content

 For key update requests the CertReqMessages syntax is used.
 Typically, SubjectPublicKeyInfo, KeyId, and Validity are the template
 fields that may be supplied for each key to be updated.  This message
 is intended to be used to request updates to existing (non-revoked
 and non-expired) certificates (therefore, it is sometimes referred to
 as a "Certificate Update" operation).  An update is a replacement
 certificate containing either a new subject public key or the current
 subject public key (although the latter practice may not be
 appropriate for some environments).
 See Appendix C and [CRMF] for CertReqMessages syntax.

Adams, et al. Standards Track [Page 40] RFC 4210 CMP September 2005

5.3.6. Key Update Response Content

 For key update responses, the CertRepMessage syntax is used.  The
 response is identical to the initialization response.
 See Section 5.3.4 for CertRepMessage syntax.

5.3.7. Key Recovery Request Content

 For key recovery requests the syntax used is identical to the
 initialization request CertReqMessages.  Typically,
 SubjectPublicKeyInfo and KeyId are the template fields that may be
 used to supply a signature public key for which a certificate is
 required (see Appendix D profiles for further information).
 See Appendix C and [CRMF] for CertReqMessages syntax.  Note that if a
 key history is required, the requester must supply a Protocol
 Encryption Key control in the request message.

5.3.8. Key Recovery Response Content

 For key recovery responses, the following syntax is used.  For some
 status values (e.g., waiting) none of the optional fields will be
 present.
  KeyRecRepContent ::= SEQUENCE {
      status          PKIStatusInfo,
      newSigCert  [0] Certificate                   OPTIONAL,
      caCerts     [1] SEQUENCE SIZE (1..MAX) OF
                                   Certificate      OPTIONAL,
      keyPairHist [2] SEQUENCE SIZE (1..MAX) OF
                                   CertifiedKeyPair OPTIONAL
  }

5.3.9. Revocation Request Content

 When requesting revocation of a certificate (or several
 certificates), the following data structure is used.  The name of the
 requester is present in the PKIHeader structure.
  RevReqContent ::= SEQUENCE OF RevDetails
  RevDetails ::= SEQUENCE {
      certDetails         CertTemplate,
      crlEntryDetails     Extensions       OPTIONAL
  }

Adams, et al. Standards Track [Page 41] RFC 4210 CMP September 2005

5.3.10. Revocation Response Content

 The revocation response is the response to the above message.  If
 produced, this is sent to the requester of the revocation.  (A
 separate revocation announcement message MAY be sent to the subject
 of the certificate for which revocation was requested.)
   RevRepContent ::= SEQUENCE {
       status        SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
       revCerts  [0] SEQUENCE SIZE (1..MAX) OF CertId OPTIONAL,
       crls      [1] SEQUENCE SIZE (1..MAX) OF CertificateList
                     OPTIONAL
   }

5.3.11. Cross Certification Request Content

 Cross certification requests use the same syntax (CertReqMessages) as
 normal certification requests, with the restriction that the key pair
 MUST have been generated by the requesting CA and the private key
 MUST NOT be sent to the responding CA.  This request MAY also be used
 by subordinate CAs to get their certificates signed by the parent CA.
 See Appendix C and [CRMF] for CertReqMessages syntax.

5.3.12. Cross Certification Response Content

 Cross certification responses use the same syntax (CertRepMessage) as
 normal certification responses, with the restriction that no
 encrypted private key can be sent.
 See Section 5.3.4 for CertRepMessage syntax.

5.3.13. CA Key Update Announcement Content

 When a CA updates its own key pair, the following data structure MAY
 be used to announce this event.
  CAKeyUpdAnnContent ::= SEQUENCE {
     oldWithNew         Certificate,
     newWithOld         Certificate,
     newWithNew         Certificate
  }

Adams, et al. Standards Track [Page 42] RFC 4210 CMP September 2005

5.3.14. Certificate Announcement

 This structure MAY be used to announce the existence of certificates.
 Note that this message is intended to be used for those cases (if
 any) where there is no pre-existing method for publication of
 certificates; it is not intended to be used where, for example, X.500
 is the method for publication of certificates.
      CertAnnContent ::= Certificate

5.3.15. Revocation Announcement

 When a CA has revoked, or is about to revoke, a particular
 certificate, it MAY issue an announcement of this (possibly upcoming)
 event.
      RevAnnContent ::= SEQUENCE {
          status              PKIStatus,
          certId              CertId,
          willBeRevokedAt     GeneralizedTime,
          badSinceDate        GeneralizedTime,
          crlDetails          Extensions  OPTIONAL
      }
 A CA MAY use such an announcement to warn (or notify) a subject that
 its certificate is about to be (or has been) revoked.  This would
 typically be used where the request for revocation did not come from
 the subject concerned.
 The willBeRevokedAt field contains the time at which a new entry will
 be added to the relevant CRLs.

5.3.16. CRL Announcement

 When a CA issues a new CRL (or set of CRLs) the following data
 structure MAY be used to announce this event.
      CRLAnnContent ::= SEQUENCE OF CertificateList

5.3.17. PKI Confirmation Content

 This data structure is used in the protocol exchange as the final
 PKIMessage.  Its content is the same in all cases -- actually there
 is no content since the PKIHeader carries all the required
 information.
      PKIConfirmContent ::= NULL

Adams, et al. Standards Track [Page 43] RFC 4210 CMP September 2005

 Use of this message for certificate confirmation is NOT RECOMMENDED;
 certConf SHOULD be used instead.  Upon receiving a PKIConfirm for a
 certificate response, the recipient MAY treat it as a certConf with
 all certificates being accepted.

5.3.18. Certificate Confirmation Content

 This data structure is used by the client to send a confirmation to
 the CA/RA to accept or reject certificates.
       CertConfirmContent ::= SEQUENCE OF CertStatus
       CertStatus ::= SEQUENCE {
          certHash    OCTET STRING,
          certReqId   INTEGER,
          statusInfo  PKIStatusInfo OPTIONAL
       }
 For any particular CertStatus, omission of the statusInfo field
 indicates ACCEPTANCE of the specified certificate.  Alternatively,
 explicit status details (with respect to acceptance or rejection) MAY
 be provided in the statusInfo field, perhaps for auditing purposes at
 the CA/RA.
 Within CertConfirmContent, omission of a CertStatus structure
 corresponding to a certificate supplied in the previous response
 message indicates REJECTION of the certificate.  Thus, an empty
 CertConfirmContent (a zero-length SEQUENCE) MAY be used to indicate
 rejection of all supplied certificates.  See Section 5.2.8, item (2),
 for a discussion of the certHash field with respect to proof-of-
 possession.

5.3.19. PKI General Message Content

   InfoTypeAndValue ::= SEQUENCE {
       infoType               OBJECT IDENTIFIER,
       infoValue              ANY DEFINED BY infoType  OPTIONAL
   }
   -- where {id-it} = {id-pkix 4} = {1 3 6 1 5 5 7 4}
   GenMsgContent ::= SEQUENCE OF InfoTypeAndValue

5.3.19.1. CA Protocol Encryption Certificate

 This MAY be used by the EE to get a certificate from the CA to use to
 protect sensitive information during the protocol.

Adams, et al. Standards Track [Page 44] RFC 4210 CMP September 2005

    GenMsg:    {id-it 1}, < absent >
    GenRep:    {id-it 1}, Certificate | < absent >
 EEs MUST ensure that the correct certificate is used for this
 purpose.

5.3.19.2. Signing Key Pair Types

 This MAY be used by the EE to get the list of signature algorithms
 (e.g., RSA, DSA) whose subject public key values the CA is willing to
 certify.  Note that for the purposes of this exchange, rsaEncryption
 and rsaWithSHA1, for example, are considered to be equivalent; the
 question being asked is, "Is the CA willing to certify an RSA public
 key?"
    GenMsg:    {id-it 2}, < absent >
    GenRep:    {id-it 2}, SEQUENCE SIZE (1..MAX) OF
                          AlgorithmIdentifier

5.3.19.3. Encryption/Key Agreement Key Pair Types

 This MAY be used by the client to get the list of encryption/key
 agreement algorithms whose subject public key values the CA is
 willing to certify.
    GenMsg:    {id-it 3}, < absent >
    GenRep:    {id-it 3}, SEQUENCE SIZE (1..MAX) OF
                          AlgorithmIdentifier

5.3.19.4. Preferred Symmetric Algorithm

 This MAY be used by the client to get the CA-preferred symmetric
 encryption algorithm for any confidential information that needs to
 be exchanged between the EE and the CA (for example, if the EE wants
 to send its private decryption key to the CA for archival purposes).
    GenMsg:    {id-it 4}, < absent >
    GenRep:    {id-it 4}, AlgorithmIdentifier

5.3.19.5. Updated CA Key Pair

 This MAY be used by the CA to announce a CA key update event.
    GenMsg:    {id-it 5}, CAKeyUpdAnnContent

Adams, et al. Standards Track [Page 45] RFC 4210 CMP September 2005

5.3.19.6. CRL

 This MAY be used by the client to get a copy of the latest CRL.
    GenMsg:    {id-it 6}, < absent >
    GenRep:    {id-it 6}, CertificateList

5.3.19.7. Unsupported Object Identifiers

 This is used by the server to return a list of object identifiers
 that it does not recognize or support from the list submitted by the
 client.
    GenRep:    {id-it 7}, SEQUENCE SIZE (1..MAX) OF OBJECT IDENTIFIER

5.3.19.8. Key Pair Parameters

 This MAY be used by the EE to request the domain parameters to use
 for generating the key pair for certain public-key algorithms.  It
 can be used, for example, to request the appropriate P, Q, and G to
 generate the DH/DSA key, or to request a set of well-known elliptic
 curves.
    GenMsg:    {id-it 10}, OBJECT IDENTIFIER -- (Algorithm object-id)
    GenRep:    {id-it 11}, AlgorithmIdentifier | < absent >
 An absent infoValue in the GenRep indicates that the algorithm
 specified in GenMsg is not supported.
 EEs MUST ensure that the parameters are acceptable to it and that the
 GenRep message is authenticated (to avoid substitution attacks).

5.3.19.9. Revocation Passphrase

 This MAY be used by the EE to send a passphrase to a CA/RA for the
 purpose of authenticating a later revocation request (in the case
 that the appropriate signing private key is no longer available to
 authenticate the request).  See Appendix B for further details on the
 use of this mechanism.
    GenMsg:    {id-it 12}, EncryptedValue
    GenRep:    {id-it 12}, < absent >

5.3.19.10. ImplicitConfirm

 See Section 5.1.1.1 for the definition and use of {id-it 13}.

Adams, et al. Standards Track [Page 46] RFC 4210 CMP September 2005

5.3.19.11. ConfirmWaitTime

 See Section 5.1.1.2 for the definition and use of {id-it 14}.

5.3.19.12 Original PKIMessage

 See Section 5.1.3 for the definition and use of {id-it 15}.

5.3.19.13. Supported Language Tags

 This MAY be used to determine the appropriate language tag to use in
 subsequent messages.  The sender sends its list of supported
 languages (in order, most preferred to least); the receiver returns
 the one it wishes to use.  (Note: each UTF8String MUST include a
 language tag.)  If none of the offered tags are supported, an error
 MUST be returned.
    GenMsg:    {id-it 16}, SEQUENCE SIZE (1..MAX) OF UTF8String
    GenRep:    {id-it 16}, SEQUENCE SIZE (1) OF UTF8String

5.3.20. PKI General Response Content

    GenRepContent ::= SEQUENCE OF InfoTypeAndValue
 Examples of GenReps that MAY be supported include those listed in the
 subsections of Section 5.3.19.

5.3.21. Error Message Content

 This data structure MAY be used by EE, CA, or RA to convey error
 info.
  ErrorMsgContent ::= SEQUENCE {
      pKIStatusInfo          PKIStatusInfo,
      errorCode              INTEGER           OPTIONAL,
      errorDetails           PKIFreeText       OPTIONAL
  }
 This message MAY be generated at any time during a PKI transaction.
 If the client sends this request, the server MUST respond with a
 PKIConfirm response, or another ErrorMsg if any part of the header is
 not valid.  Both sides MUST treat this message as the end of the
 transaction (if a transaction is in progress).
 If protection is desired on the message, the client MUST protect it
 using the same technique (i.e., signature or MAC) as the starting
 message of the transaction.  The CA MUST always sign it with a
 signature key.

Adams, et al. Standards Track [Page 47] RFC 4210 CMP September 2005

5.3.22. Polling Request and Response

 This pair of messages is intended to handle scenarios in which the
 client needs to poll the server in order to determine the status of
 an outstanding ir, cr, or kur transaction (i.e., when the "waiting"
 PKIStatus has been received).
  PollReqContent ::= SEQUENCE OF SEQUENCE {
      certReqId    INTEGER }
  PollRepContent ::= SEQUENCE OF SEQUENCE {
      certReqId    INTEGER,
      checkAfter   INTEGER,  -- time in seconds
      reason       PKIFreeText OPTIONAL }
 The following clauses describe when polling messages are used, and
 how they are used.  It is assumed that multiple certConf messages can
 be sent during transactions.  There will be one sent in response to
 each ip, cp, or kup that contains a CertStatus for an issued
 certificate.
 1.  In response to an ip, cp, or kup message, an EE will send a
     certConf for all issued certificates and, following the ack, a
     pollReq for all pending certificates.
 2.  In response to a pollReq, a CA/RA will return an ip, cp, or kup
     if one or more of the pending certificates is ready; otherwise,
     it will return a pollRep.
 3.  If the EE receives a pollRep, it will wait for at least as long
     as the checkAfter value before sending another pollReq.
 4.  If an ip, cp, or kup is received in response to a pollReq, then
     it will be treated in the same way as the initial response.

Adams, et al. Standards Track [Page 48] RFC 4210 CMP September 2005

                             START
                               |
                               v
                            Send ir
                               | ip
                               v
                          Check status
                          of returned <------------------------+
                             certs                             |
                               |                               |
     +------------------------>|<------------------+           |
     |                         |                   |           |
     |        (issued)         v       (waiting)   |           |
   Add to <----------- Check CertResponse ------> Add to       |
  conf list           for each certificate      pending list   |
                               /                               |
                              /                                |
                 (conf list) /     (empty conf list)           |
                            /                     ip           |
                           /                 +----------------+
    (empty pending list)  /                  |    pRep
      END <---- Send certConf         Send pReq------------>Wait
                       |                 ^   ^               |
                       |                 |   |               |
                       +-----------------+   +---------------+
                          (pending list)

Adams, et al. Standards Track [Page 49] RFC 4210 CMP September 2005

 In the following exchange, the end entity is enrolling for two
 certificates in one request.
  Step  End Entity                       PKI
  --------------------------------------------------------------------
  1   Format ir
  2                    -> ir      ->
  3                                    Handle ir
  4                                    Manual intervention is
                                       required for both certs.
  5                    <- ip      <-
  6   Process ip
  7   Format pReq
  8                    -> pReq     ->
  9                                    Check status of cert requests
  10                                   Certificates not ready
  11                                   Format pRep
  12                   <- pRep     <-
  13  Wait
  14  Format pReq
  15                   -> pReq     ->
  16                                   Check status of cert requests
  17                                   One certificate is ready
  18                                   Format ip
  19                   <- ip       <-
  20  Handle ip
  21  Format certConf
  22                   -> certConf ->
  23                                   Handle certConf
  24                                   Format ack
  25                   <- pkiConf   <-
  26  Format pReq
  27                   -> pReq     ->
  28                                   Check status of certificate
  29                                   Certificate is ready
  30                                   Format ip
  31                   <- ip       <-
  31  Handle ip
  32  Format certConf
  33                   -> certConf ->
  34                                   Handle certConf
  35                                   Format ack
  36                   <- pkiConf  <-

Adams, et al. Standards Track [Page 50] RFC 4210 CMP September 2005

6. Mandatory PKI Management Functions

 Some of the PKI management functions outlined in Section 3.1 above
 are described in this section.
 This section deals with functions that are "mandatory" in the sense
 that all end entity and CA/RA implementations MUST be able to provide
 the functionality described.  This part is effectively the profile of
 the PKI management functionality that MUST be supported.  Note,
 however, that the management functions described in this section do
 not need to be accomplished using the PKI messages defined in Section
 5 if alternate means are suitable for a given environment (see
 Appendix D for profiles of the PKIMessages that MUST be supported).

6.1. Root CA Initialization

 [See Section 3.1.1.2 for this document's definition of "root CA".]
 A newly created root CA must produce a "self-certificate", which is a
 Certificate structure with the profile defined for the "newWithNew"
 certificate issued following a root CA key update.
 In order to make the CA's self certificate useful to end entities
 that do not acquire the self certificate via "out-of-band" means, the
 CA must also produce a fingerprint for its certificate.  End entities
 that acquire this fingerprint securely via some "out-of-band" means
 can then verify the CA's self-certificate and, hence, the other
 attributes contained therein.
 The data structure used to carry the fingerprint is the OOBCertHash.

6.2. Root CA Key Update

 CA keys (as all other keys) have a finite lifetime and will have to
 be updated on a periodic basis.  The certificates NewWithNew,
 NewWithOld, and OldWithNew (see Section 4.4.1) MAY be issued by the
 CA to aid existing end entities who hold the current self-signed CA
 certificate (OldWithOld) to transition securely to the new self-
 signed CA certificate (NewWithNew), and to aid new end entities who
 will hold NewWithNew to acquire OldWithOld securely for verification
 of existing data.

6.3. Subordinate CA Initialization

 [See Section 3.1.1.2 for this document's definition of "subordinate
 CA".]

Adams, et al. Standards Track [Page 51] RFC 4210 CMP September 2005

 From the perspective of PKI management protocols, the initialization
 of a subordinate CA is the same as the initialization of an end
 entity.  The only difference is that the subordinate CA must also
 produce an initial revocation list.

6.4. CRL production

 Before issuing any certificates, a newly established CA (which issues
 CRLs) must produce "empty" versions of each CRL which are to be
 periodically produced.

6.5. PKI Information Request

 When a PKI entity (CA, RA, or EE) wishes to acquire information about
 the current status of a CA, it MAY send that CA a request for such
 information.
 The CA MUST respond to the request by providing (at least) all of the
 information requested by the requester.  If some of the information
 cannot be provided, then an error must be conveyed to the requester.
 If PKIMessages are used to request and supply this PKI information,
 then the request MUST be the GenMsg message, the response MUST be the
 GenRep message, and the error MUST be the Error message.  These
 messages are protected using a MAC based on shared secret information
 (i.e., PasswordBasedMAC) or using any other authenticated means (if
 the end entity has an existing certificate).

6.6. Cross Certification

 The requester CA is the CA that will become the subject of the
 cross-certificate; the responder CA will become the issuer of the
 cross-certificate.
 The requester CA must be "up and running" before initiating the
 cross-certification operation.

6.6.1. One-Way Request-Response Scheme:

 The cross-certification scheme is essentially a one way operation;
 that is, when successful, this operation results in the creation of
 one new cross-certificate.  If the requirement is that cross-
 certificates be created in "both directions", then each CA, in turn,
 must initiate a cross-certification operation (or use another
 scheme).

Adams, et al. Standards Track [Page 52] RFC 4210 CMP September 2005

 This scheme is suitable where the two CAs in question can already
 verify each other's signatures (they have some common points of
 trust) or where there is an out-of-band verification of the origin of
 the certification request.
 Detailed Description:
 Cross certification is initiated at one CA known as the responder.
 The CA administrator for the responder identifies the CA it wants to
 cross certify and the responder CA equipment generates an
 authorization code.  The responder CA administrator passes this
 authorization code by out-of-band means to the requester CA
 administrator.  The requester CA administrator enters the
 authorization code at the requester CA in order to initiate the on-
 line exchange.
 The authorization code is used for authentication and integrity
 purposes.  This is done by generating a symmetric key based on the
 authorization code and using the symmetric key for generating Message
 Authentication Codes (MACs) on all messages exchanged.
 (Authentication may alternatively be done using signatures instead of
 MACs, if the CAs are able to retrieve and validate the required
 public keys by some means, such as an out-of-band hash comparison.)
 The requester CA initiates the exchange by generating a cross-
 certification request (ccr) with a fresh random number (requester
 random number).  The requester CA then sends the ccr message to the
 responder CA.  The fields in this message are protected from
 modification with a MAC based on the authorization code.
 Upon receipt of the ccr message, the responder CA validates the
 message and the MAC, saves the requester random number, and generates
 its own random number (responder random number).  It then generates
 (and archives, if desired) a new requester certificate that contains
 the requester CA public key and is signed with the responder CA
 signature private key.  The responder CA responds with the cross
 certification response (ccp) message.  The fields in this message are
 protected from modification with a MAC based on the authorization
 code.
 Upon receipt of the ccp message, the requester CA validates the
 message (including the received random numbers) and the MAC.  The
 requester CA responds with the certConf message.  The fields in this
 message are protected from modification with a MAC based on the
 authorization code.  The requester CA MAY write the requester
 certificate to the Repository as an aid to later certificate path
 construction.

Adams, et al. Standards Track [Page 53] RFC 4210 CMP September 2005

 Upon receipt of the certConf message, the responder CA validates the
 message and the MAC, and sends back an acknowledgement using the
 PKIConfirm message.  It MAY also publish the requester certificate as
 an aid to later path construction.
 Notes:
 1.  The ccr message must contain a "complete" certification request;
     that is, all fields except the serial number (including, e.g., a
     BasicConstraints extension) must be specified by the requester
     CA.
 2.  The ccp message SHOULD contain the verification certificate of
     the responder CA; if present, the requester CA must then verify
     this certificate (for example, via the "out-of-band" mechanism).
 (A simpler, non-interactive model of cross-certification may also be
 envisioned, in which the issuing CA acquires the subject CA's public
 key from some repository, verifies it via some out-of-band mechanism,
 and creates and publishes the cross-certificate without the subject
 CA's explicit involvement.  This model may be perfectly legitimate
 for many environments, but since it does not require any protocol
 message exchanges, its detailed description is outside the scope of
 this specification.)

6.7. End Entity Initialization

 As with CAs, end entities must be initialized.  Initialization of end
 entities requires at least two steps:
 o  acquisition of PKI information
 o  out-of-band verification of one root-CA public key
 (other possible steps include the retrieval of trust condition
 information and/or out-of-band verification of other CA public keys).

6.7.1. Acquisition of PKI Information

 The information REQUIRED is:
 o  the current root-CA public key
 o  (if the certifying CA is not a root-CA) the certification path
    from the root CA to the certifying CA together with appropriate
    revocation lists

Adams, et al. Standards Track [Page 54] RFC 4210 CMP September 2005

 o  the algorithms and algorithm parameters that the certifying CA
    supports for each relevant usage
 Additional information could be required (e.g., supported extensions
 or CA policy information) in order to produce a certification request
 that will be successful.  However, for simplicity we do not mandate
 that the end entity acquires this information via the PKI messages.
 The end result is simply that some certification requests may fail
 (e.g., if the end entity wants to generate its own encryption key,
 but the CA doesn't allow that).
 The required information MAY be acquired as described in Section 6.5.

6.7.2. Out-of-Band Verification of Root-CA Key

 An end entity must securely possess the public key of its root CA.
 One method to achieve this is to provide the end entity with the CA's
 self-certificate fingerprint via some secure "out-of-band" means.
 The end entity can then securely use the CA's self-certificate.
 See Section 6.1 for further details.

6.8. Certificate Request

 An initialized end entity MAY request an additional certificate at
 any time (for any purpose).  This request will be made using the
 certification request (cr) message.  If the end entity already
 possesses a signing key pair (with a corresponding verification
 certificate), then this cr message will typically be protected by the
 entity's digital signature.  The CA returns the new certificate (if
 the request is successful) in a CertRepMessage.

6.9. Key Update

 When a key pair is due to expire, the relevant end entity MAY request
 a key update; that is, it MAY request that the CA issue a new
 certificate for a new key pair (or, in certain circumstances, a new
 certificate for the same key pair).  The request is made using a key
 update request (kur) message (referred to, in some environments, as a
 "Certificate Update" operation).  If the end entity already possesses
 a signing key pair (with a corresponding verification certificate),
 then this message will typically be protected by the entity's digital
 signature.  The CA returns the new certificate (if the request is
 successful) in a key update response (kup) message, which is
 syntactically identical to a CertRepMessage.

Adams, et al. Standards Track [Page 55] RFC 4210 CMP September 2005

7. Version Negotiation

 This section defines the version negotiation used to support older
 protocols between client and servers.
 If a client knows the protocol version(s) supported by the server
 (e.g., from a previous PKIMessage exchange or via some out-of-band
 means), then it MUST send a PKIMessage with the highest version
 supported by both it and the server.  If a client does not know what
 version(s) the server supports, then it MUST send a PKIMessage using
 the highest version it supports.
 If a server receives a message with a version that it supports, then
 the version of the response message MUST be the same as the received
 version.  If a server receives a message with a version higher or
 lower than it supports, then it MUST send back an ErrorMsg with the
 unsupportedVersion bit set (in the failureInfo field of the
 pKIStatusInfo).  If the received version is higher than the highest
 supported version, then the version in the error message MUST be the
 highest version the server supports; if the received version is lower
 than the lowest supported version then the version in the error
 message MUST be the lowest version the server supports.
 If a client gets back an ErrorMsgContent with the unsupportedVersion
 bit set and a version it supports, then it MAY retry the request with
 that version.

7.1. Supporting RFC 2510 Implementations

 RFC 2510 did not specify the behaviour of implementations receiving
 versions they did not understand since there was only one version in
 existence.  With the introduction of the present revision of the
 specification, the following versioning behaviour is recommended.

7.1.1. Clients Talking to RFC 2510 Servers

 If, after sending a cmp2000 message, a client receives an
 ErrorMsgContent with a version of cmp1999, then it MUST abort the
 current transaction.  It MAY subsequently retry the transaction using
 version cmp1999 messages.
 If a client receives a non-error PKIMessage with a version of
 cmp1999, then it MAY decide to continue the transaction (if the
 transaction hasn't finished) using RFC 2510 semantics.  If it does
 not choose to do so and the transaction is not finished, then it MUST
 abort the transaction and send an ErrorMsgContent with a version of
 cmp1999.

Adams, et al. Standards Track [Page 56] RFC 4210 CMP September 2005

7.1.2. Servers Receiving Version cmp1999 PKIMessages

 If a server receives a version cmp1999 message it MAY revert to RFC
 2510 behaviour and respond with version cmp1999 messages.  If it does
 not choose to do so, then it MUST send back an ErrorMsgContent as
 described above in Section 7.

8. Security Considerations

8.1. Proof-Of-Possession with a Decryption Key

 Some cryptographic considerations are worth explicitly spelling out.
 In the protocols specified above, when an end entity is required to
 prove possession of a decryption key, it is effectively challenged to
 decrypt something (its own certificate).  This scheme (and many
 others!) could be vulnerable to an attack if the possessor of the
 decryption key in question could be fooled into decrypting an
 arbitrary challenge and returning the cleartext to an attacker.
 Although in this specification a number of other failures in security
 are required in order for this attack to succeed, it is conceivable
 that some future services (e.g., notary, trusted time) could
 potentially be vulnerable to such attacks.  For this reason, we re-
 iterate the general rule that implementations should be very careful
 about decrypting arbitrary "ciphertext" and revealing recovered
 "plaintext" since such a practice can lead to serious security
 vulnerabilities.

8.2. Proof-Of-Possession by Exposing the Private Key

 Note also that exposing a private key to the CA/RA as a proof-of-
 possession technique can carry some security risks (depending upon
 whether or not the CA/RA can be trusted to handle such material
 appropriately).  Implementers are advised to:
    Exercise caution in selecting and using this particular POP
    mechanism
    When appropriate, have the user of the application explicitly
    state that they are willing to trust the CA/RA to have a copy of
    their private key before proceeding to reveal the private key.

8.3. Attack Against Diffie-Hellman Key Exchange

 A small subgroup attack during a Diffie-Hellman key exchange may be
 carried out as follows.  A malicious end entity may deliberately
 choose D-H parameters that enable him/her to derive (a significant
 number of bits of) the D-H private key of the CA during a key
 archival or key recovery operation.  Armed with this knowledge, the

Adams, et al. Standards Track [Page 57] RFC 4210 CMP September 2005

 EE would then be able to retrieve the decryption private key of
 another unsuspecting end entity, EE2, during EE2's legitimate key
 archival or key recovery operation with that CA.  In order to avoid
 the possibility of such an attack, two courses of action are
 available.  (1) The CA may generate a fresh D-H key pair to be used
 as a protocol encryption key pair for each EE with which it
 interacts.  (2) The CA may enter into a key validation protocol (not
 specified in this document) with each requesting end entity to ensure
 that the EE's protocol encryption key pair will not facilitate this
 attack.  Option (1) is clearly simpler (requiring no extra protocol
 exchanges from either party) and is therefore RECOMMENDED.

9. IANA Considerations

 The PKI General Message types are identified by object identifiers
 (OIDs).  The OIDs for the PKI General Message types defined in this
 document were assigned from an arc delegated by the IANA to the PKIX
 Working Group.
 The cryptographic algorithms referred to in this document are
 identified by object identifiers (OIDs).  The OIDs for cryptographic
 algorithms were assigned from several arcs owned by various
 organizations, including RSA Security, Entrust Technologies, IANA and
 IETF.
 Should additional encryption algorithms be introduced, the advocates
 for such algorithms are expected to assign the necessary OIDs from
 their own arcs.
 No further action by the IANA is necessary for this document or any
 anticipated updates.

Normative References

 [X509]       International Organization for Standardization and
              International Telecommunications Union, "Information
              technology - Open Systems Interconnection - The
              Directory:  Public-key and attribute certificate
              frameworks", ISO Standard 9594-8:2001, ITU-T
              Recommendation X.509, March 2000.
 [MvOV97]     Menezes, A., van Oorschot, P. and S. Vanstone, "Handbook
              of Applied Cryptography", CRC Press ISBN 0-8493-8523-7,
              1996.

Adams, et al. Standards Track [Page 58] RFC 4210 CMP September 2005

 [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.
 [RFC2202]    Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and
              HMAC-SHA-1", RFC 2202, September 1997.
 [RFC3629]    Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.
 [RFC2482]    Whistler, K. and G. Adams, "Language Tagging in Unicode
              Plain Text", RFC 2482, January 1999.
 [CRMF]       Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              September 2005.
 [RFC3066]    Alvestrand, H., "Tags for the Identification of
              Languages", BCP 47, RFC 3066, January 2001.

Informative References

 [CMPtrans]   Kapoor, A., Tschalar, R. and T. Kause, "Internet X.509
              Public Key Infrastructure -- Transport Protocols for
              CMP", Work in Progress.  2004.
 [PKCS7]      RSA Laboratories, "The Public-Key Cryptography Standards
              - Cryptographic Message Syntax Standard.  Version 1.5",
              PKCS 7, November 1993.
 [PKCS10]     Nystrom, M., and B. Kaliski, "The Public-Key
              Cryptography Standards - Certification Request Syntax
              Standard, Version 1.7", RFC 2986, May 2000.
 [PKCS11]     RSA Laboratories, "The Public-Key Cryptography Standards
              - Cryptographic Token Interface Standard.  Version
              2.10", PKCS 11, December 1999.
 [RFC1847]    Galvin, J., Murphy, S., Crocker, S., and N. Freed,
              "Security Multiparts for MIME: Multipart/Signed and
              Multipart/Encrypted", RFC 1847, October 1995.

Adams, et al. Standards Track [Page 59] RFC 4210 CMP September 2005

 [RFC2559]    Boeyen, S., Howes, T. and P. Richard, "Internet X.509
              Public Key Infrastructure Operational Protocols -
              LDAPv2", RFC 2559, April 1999.
 [RFC2585]    Housley, R. and P. Hoffman, "Internet X.509 Public Key
              Infrastructure Operational Protocols: FTP and HTTP", RFC
              2585, May 1999.
 [FIPS-180]   National Institute of Standards and Technology, "Secure
              Hash Standard", FIPS PUB 180-1, May 1994.
 [FIPS-186]   National Institute of Standards and Technology, "Digital
              Signature Standard", FIPS PUB 186, May 1994.
 [ANSI-X9.42] American National Standards Institute, "Public Key
              Cryptography for The Financial Services Industry:
              Agreement of Symmetric Keys Using Discrete Logarithm
              Cryptography", ANSI X9.42, February 2000.

Adams, et al. Standards Track [Page 60] RFC 4210 CMP September 2005

Appendix A. Reasons for the Presence of RAs

 The reasons that justify the presence of an RA can be split into
 those that are due to technical factors and those which are
 organizational in nature.  Technical reasons include the following.
 o  If hardware tokens are in use, then not all end entities will have
    the equipment needed to initialize these; the RA equipment can
    include the necessary functionality (this may also be a matter of
    policy).
 o  Some end entities may not have the capability to publish
    certificates; again, the RA may be suitably placed for this.
 o  The RA will be able to issue signed revocation requests on behalf
    of end entities associated with it, whereas the end entity may not
    be able to do this (if the key pair is completely lost).
 Some of the organizational reasons that argue for the presence of an
 RA are the following.
 o  It may be more cost effective to concentrate functionality in the
    RA equipment than to supply functionality to all end entities
    (especially if special token initialization equipment is to be
    used).
 o  Establishing RAs within an organization can reduce the number of
    CAs required, which is sometimes desirable.
 o  RAs may be better placed to identify people with their
    "electronic" names, especially if the CA is physically remote from
    the end entity.
 o  For many applications, there will already be in place some
    administrative structure so that candidates for the role of RA are
    easy to find (which may not be true of the CA).

Appendix B. The Use of Revocation Passphrase

 A revocation request must incorporate suitable security mechanisms,
 including proper authentication, in order to reduce the probability
 of successful denial-of-service attacks.  A digital signature on the
 request -- MANDATORY to support within this specification if
 revocation requests are supported -- can provide the authentication
 required, but there are circumstances under which an alternative
 mechanism may be desirable (e.g., when the private key is no longer
 accessible and the entity wishes to request a revocation prior to
 re-certification of another key pair).  In order to accommodate such

Adams, et al. Standards Track [Page 61] RFC 4210 CMP September 2005

 circumstances, a PasswordBasedMAC on the request is also MANDATORY to
 support within this specification (subject to local security policy
 for a given environment) if revocation requests are supported and if
 shared secret information can be established between the requester
 and the responder prior to the need for revocation.
 A mechanism that has seen use in some environments is "revocation
 passphrase", in which a value of sufficient entropy (i.e., a
 relatively long passphrase rather than a short password) is shared
 between (only) the entity and the CA/RA at some point prior to
 revocation; this value is later used to authenticate the revocation
 request.
 In this specification, the following technique to establish shared
 secret information (i.e., a revocation passphrase) is OPTIONAL to
 support.  Its precise use in CMP messages is as follows.
 o  The OID and value specified in Section 5.3.19.9 MAY be sent in a
    GenMsg message at any time, or MAY be sent in the generalInfo
    field of the PKIHeader of any PKIMessage at any time.  (In
    particular, the EncryptedValue may be sent in the header of the
    certConf message that confirms acceptance of certificates
    requested in an initialization request or certificate request
    message.)  This conveys a revocation passphrase chosen by the
    entity (i.e., the decrypted bytes of the encValue field) to the
    relevant CA/RA; furthermore, the transfer is accomplished with
    appropriate confidentiality characteristics (because the
    passphrase is encrypted under the CA/RA's protocolEncryptionKey).
 o  If a CA/RA receives the revocation passphrase (OID and value
    specified in Section 5.3.19.9) in a GenMsg, it MUST construct and
    send a GenRep message that includes the OID (with absent value)
    specified in Section 5.3.19.9. If the CA/RA receives the
    revocation passphrase in the generalInfo field of a PKIHeader of
    any PKIMessage, it MUST include the OID (with absent value) in the
    generalInfo field of the PKIHeader of the corresponding response
    PKIMessage.  If the CA/RA is unable to return the appropriate
    response message for any reason, it MUST send an error message
    with a status of "rejection" and, optionally, a failInfo reason
    set.
 o  The valueHint field of EncryptedValue MAY contain a key identifier
    (chosen by the entity, along with the passphrase itself) to assist
    in later retrieval of the correct passphrase (e.g., when the
    revocation request is constructed by the entity and received by
    the CA/RA).

Adams, et al. Standards Track [Page 62] RFC 4210 CMP September 2005

 o  The revocation request message is protected by a PasswordBasedMAC,
    with the revocation passphrase as the key.  If appropriate, the
    senderKID field in the PKIHeader MAY contain the value previously
    transmitted in valueHint.
 Using the technique specified above, the revocation passphrase may be
 initially established and updated at any time without requiring extra
 messages or out-of-band exchanges.  For example, the revocation
 request message itself (protected and authenticated through a MAC
 that uses the revocation passphrase as a key) may contain, in the
 PKIHeader, a new revocation passphrase to be used for authenticating
 future revocation requests for any of the entity's other
 certificates.  In some environments this may be preferable to
 mechanisms that reveal the passphrase in the revocation request
 message, since this can allow a denial-of-service attack in which the
 revealed passphrase is used by an unauthorized third party to
 authenticate revocation requests on the entity's other certificates.
 However, because the passphrase is not revealed in the request
 message, there is no requirement that the passphrase must always be
 updated when a revocation request is made (that is, the same
 passphrase MAY be used by an entity to authenticate revocation
 requests for different certificates at different times).
 Furthermore, the above technique can provide strong cryptographic
 protection over the entire revocation request message even when a
 digital signature is not used.  Techniques that do authentication of
 the revocation request by simply revealing the revocation passphrase
 typically do not provide cryptographic protection over the fields of
 the request message (so that a request for revocation of one
 certificate may be modified by an unauthorized third party to a
 request for revocation of another certificate for that entity).

Appendix C. Request Message Behavioral Clarifications

 In the case of updates to [CRMF], which cause interpretation or
 interoperability issues, [CRMF] SHALL be the normative document.
 The following definitions are from [CRMF].  They are included here in
 order to codify behavioral clarifications to that request message;
 otherwise, all syntax and semantics are identical to [CRMF].
 CertRequest ::= SEQUENCE {
     certReqId     INTEGER,
     certTemplate  CertTemplate,
     controls      Controls OPTIONAL }
  1. - If certTemplate is an empty SEQUENCE (i.e., all fields
  2. - omitted), then controls MAY contain the

Adams, et al. Standards Track [Page 63] RFC 4210 CMP September 2005

  1. - id-regCtrl-altCertTemplate control, specifying a template
  2. - for a certificate other than an X.509v3 public-key
  3. - certificate. Conversely, if certTemplate is not empty
  4. - (i.e., at least one field is present), then controls MUST
  5. - NOT contain id-regCtrl- altCertTemplate. The new control is
  6. - defined as follows:
 id-regCtrl-altCertTemplate OBJECT IDENTIFIER ::= {id-regCtrl 7}
 AltCertTemplate ::= AttributeTypeAndValue
 POPOSigningKey ::= SEQUENCE {
     poposkInput           [0] POPOSigningKeyInput OPTIONAL,
     algorithmIdentifier   AlgorithmIdentifier,
     signature             BIT STRING }
  1. - – * For the purposes of this specification, the ASN.1 comment – * given in [CRMF] pertains not only to certTemplate, but – * also to the altCertTemplate control. That is, –
  2. - * The signature (using "algorithmIdentifier") is on the
  3. - * DER-encoded value of poposkInput (i.e., the "value" OCTETs
  4. - * of the POPOSigningKeyInput DER). NOTE: If CertReqMsg
  5. - * certReq certTemplate (or the altCertTemplate control)
  6. - * contains the subject and publicKey values, then poposkInput
  7. - * MUST be omitted and the signature MUST be computed on the
  8. - * DER-encoded value of CertReqMsg certReq (or the DER-
  9. - * encoded value of AltCertTemplate). If
  10. - * certTemplate/altCertTemplate does not contain both the
  11. - * subject and public key values (i.e., if it contains only
  12. - * one of these, or neither), then poposkInput MUST be present
  13. - * and MUST be signed.
  14. - POPOPrivKey ::= CHOICE { thisMessage [0] BIT STRING, –
  15. - * the type of "thisMessage" is given as BIT STRING in
  16. - * [CRMF]; it should be "EncryptedValue" (in accordance
  17. - * with Section 5.2.2, "Encrypted Values", of this specification).
  18. - * Therefore, this document makes the behavioral clarification
  19. - * of specifying that the contents of "thisMessage" MUST be encoded
  20. - * as an EncryptedValue and then wrapped in a BIT STRING. This
  21. - * allows the necessary conveyance and protection of the
  22. - * private key while maintaining bits-on-the-wire compatibility
  23. - * with [CRMF].
  24. - **

Adams, et al. Standards Track [Page 64] RFC 4210 CMP September 2005

     subsequentMessage [1] SubsequentMessage,
     dhMAC             [2] BIT STRING }

Appendix D. PKI Management Message Profiles (REQUIRED).

 This appendix contains detailed profiles for those PKIMessages that
 MUST be supported by conforming implementations (see Section 6).
 Profiles for the PKIMessages used in the following PKI management
 operations are provided:
 o  initial registration/certification
 o  basic authenticated scheme
 o  certificate request
 o  key update

D.1. General Rules for Interpretation of These Profiles.

 1.  Where OPTIONAL or DEFAULT fields are not mentioned in individual
     profiles, they SHOULD be absent from the relevant message (i.e.,
     a receiver can validly reject a message containing such fields as
     being syntactically incorrect).  Mandatory fields are not
     mentioned if they have an obvious value (e.g., in this version of
     the specification, pvno is always 2).
 2.  Where structures occur in more than one message, they are
     separately profiled as appropriate.
 3.  The algorithmIdentifiers from PKIMessage structures are profiled
     separately.
 4.  A "special" X.500 DN is called the "NULL-DN"; this means a DN
     containing a zero-length SEQUENCE OF RelativeDistinguishedNames
     (its DER encoding is then '3000'H).
 5.  Where a GeneralName is required for a field, but no suitable
     value is available (e.g., an end entity produces a request before
     knowing its name), then the GeneralName is to be an X.500 NULL-DN
     (i.e., the Name field of the CHOICE is to contain a NULL-DN).
     This special value can be called a "NULL-GeneralName".
 6.  Where a profile omits to specify the value for a GeneralName,
     then the NULL-GeneralName value is to be present in the relevant
     PKIMessage field.  This occurs with the sender field of the
     PKIHeader for some messages.

Adams, et al. Standards Track [Page 65] RFC 4210 CMP September 2005

 7.  Where any ambiguity arises due to naming of fields, the profile
     names these using a "dot" notation (e.g., "certTemplate.subject"
     means the subject field within a field called certTemplate).
 8.  Where a "SEQUENCE OF types" is part of a message, a zero-based
     array notation is used to describe fields within the SEQUENCE OF
     (e.g., crm[0].certReq.certTemplate.subject refers to a subfield
     of the first CertReqMsg contained in a request message).
 9.  All PKI message exchanges in Appendix D.4 to D.6 require a
     certConf message to be sent by the initiating entity and a
     PKIConfirm to be sent by the responding entity.  The PKIConfirm
     is not included in some of the profiles given since its body is
     NULL and its header contents are clear from the context.  Any
     authenticated means can be used for the protectionAlg (e.g.,
     password-based MAC, if shared secret information is known, or
     signature).

D.2. Algorithm Use Profile

 The following table contains definitions of algorithm uses within PKI
 management protocols.  The columns in the table are:
 Name: an identifier used for message profiles
 Use: description of where and for what the algorithm is used
 Mandatory: an AlgorithmIdentifier which MUST be supported by
    conforming implementations
 Others: alternatives to the mandatory AlgorithmIdentifier
  Name         Use                      Mandatory        Others
  MSG_SIG_ALG  Protection of PKI        DSA/SHA-1        RSA/MD5,
               messages using signature                  ECDSA, ...
  MSG_MAC_ALG  protection of PKI        PasswordBasedMac HMAC,
               messages using MACing                     X9.9...
  SYM_PENC_ALG symmetric encryption of  3-DES (3-key-    AES,RC5,
               an end entity's private  EDE, CBC mode)   CAST-128...
               key where symmetric
               key is distributed
               out-of-band
  PROT_ENC_ALG asymmetric algorithm     D-H              RSA,
               used for encryption of                    ECDH, ...
               (symmetric keys for
               encryption of) private
               keys transported in

Adams, et al. Standards Track [Page 66] RFC 4210 CMP September 2005

               PKIMessages
  PROT_SYM_ALG symmetric encryption     3-DES (3-key-    AES,RC5,
               algorithm used for       EDE, CBC mode)   CAST-128...
               encryption of private
               key bits (a key of this
               type is encrypted using
               PROT_ENC_ALG)
 Mandatory AlgorithmIdentifiers and Specifications:
 DSA/SHA-1:
   AlgId: {1 2 840 10040 4 3};
 Digital Signature Standard [FIPS-186]
   Public Modulus size: 1024 bits.
 PasswordBasedMac:
   AlgId: {1 2 840 113533 7 66 13}, with SHA-1 {1 3 14 3 2 26} as the
          owf parameter and HMAC-SHA1 {1 3 6 1 5 5 8 1 2} as the mac
          parameter;
   (this specification), along with
 Secure Hash Standard [FIPS-180] and [RFC2104]
   HMAC key size:  160 bits (i.e., "K" = "H" in Section 5.1.3.1,
                             "Shared secret information")
 3-DES:
   AlgId: {1 2 840 113549 3 7};
   (used in RSA's BSAFE and in S/MIME).
 D-H:
   AlgId:  {1 2 840 10046 2 1};
 [ANSI-X9.42]
   Public Modulus Size:  1024 bits.
   DomainParameters ::= SEQUENCE {
      p       INTEGER, -- odd prime, p=jq +1
      g       INTEGER, -- generator, g^q = 1 mod p
      q       INTEGER, -- prime factor of p-1
      j       INTEGER OPTIONAL, -- cofactor, j>=2
      validationParms  ValidationParms OPTIONAL

Adams, et al. Standards Track [Page 67] RFC 4210 CMP September 2005

   }
   ValidationParms ::= SEQUENCE {
      seed          BIT STRING, -- seed for prime generation
      pGenCounter   INTEGER     -- parameter verification
   }

D.3. Proof-of-Possession Profile

 POP fields for use (in signature field of pop field of
 ProofOfPossession structure) when proving possession of a private
 signing key that corresponds to a public verification key for which a
 certificate has been requested.
  Field               Value         Comment
  algorithmIdentifier MSG_SIG_ALG   only signature protection is
                                    allowed for this proof
  signature           present       bits calculated using MSG_SIG_ALG
 Proof-of-possession of a private decryption key that corresponds to a
 public encryption key for which a certificate has been requested does
 not use this profile; the CertHash field of the certConf message is
 used instead.
 Not every CA/RA will do Proof-of-Possession (of signing key,
 decryption key, or key agreement key) in the PKIX-CMP in-band
 certification request protocol (how POP is done MAY ultimately be a
 policy issue that is made explicit for any given CA in its publicized
 Policy OID and Certification Practice Statement).  However, this
 specification MANDATES that CA/RA entities MUST do POP (by some
 means) as part of the certification process.  All end entities MUST
 be prepared to provide POP (i.e., these components of the PKIX-CMP
 protocol MUST be supported).

D.4. Initial Registration/Certification (Basic Authenticated Scheme)

 An (uninitialized) end entity requests a (first) certificate from a
 CA.  When the CA responds with a message containing a certificate,
 the end entity replies with a certificate confirmation.  The CA sends
 a PKIConfirm back, closing the transaction.  All messages are
 authenticated.
 This scheme allows the end entity to request certification of a
 locally-generated public key (typically a signature key).  The end
 entity MAY also choose to request the centralized generation and
 certification of another key pair (typically an encryption key pair).

Adams, et al. Standards Track [Page 68] RFC 4210 CMP September 2005

 Certification may only be requested for one locally generated public
 key (for more, use separate PKIMessages).
 The end entity MUST support proof-of-possession of the private key
 associated with the locally-generated public key.
 Preconditions:
 1.  The end entity can authenticate the CA's signature based on out-
     of-band means
 2.  The end entity and the CA share a symmetric MACing key
 Message flow:
  Step# End entity                           PKI
    1   format ir
    2                      ->   ir      ->
    3                                        handle ir
    4                                        format ip
    5                      <-   ip      <-
    6   handle ip
    7   format certConf
    8                      ->   certConf ->
    9                                        handle certConf
   10                                        format PKIConf
   11                      <-   PKIConf  <-
   12   handle PKIConf
 For this profile, we mandate that the end entity MUST include all
 (i.e., one or two) CertReqMsg in a single PKIMessage, and that the
 PKI (CA) MUST produce a single response PKIMessage that contains the
 complete response (i.e., including the OPTIONAL second key pair, if
 it was requested and if centralized key generation is supported).
 For simplicity, we also mandate that this message MUST be the final
 one (i.e., no use of "waiting" status value).
 The end entity has an out-of-band interaction with the CA/RA.  This
 transaction established the shared secret, the referenceNumber and
 OPTIONALLY the distinguished name used for both sender and subject
 name in the certificate template.  It is RECOMMENDED that the shared
 secret be at least 12 characters long.
 Initialization Request -- ir
 Field                Value
 recipient            CA name

Adams, et al. Standards Track [Page 69] RFC 4210 CMP September 2005

  1. - the name of the CA who is being asked to produce a certificate

protectionAlg MSG_MAC_ALG

  1. - only MAC protection is allowed for this request, based
  2. - on initial authentication key

senderKID referenceNum

  1. - the reference number which the CA has previously issued
  2. - to the end entity (together with the MACing key)

transactionID present

  1. - implementation-specific value, meaningful to end
  2. - entity.
  3. - [If already in use at the CA, then a rejection message MUST
  4. - be produced by the CA]
 senderNonce          present
   -- 128 (pseudo-)random bits
 freeText             any valid value
 body                 ir (CertReqMessages)
                      only one or two CertReqMsg
                      are allowed
   -- if more certificates are required, requests MUST be
   -- packaged in separate PKIMessages
 CertReqMsg           one or two present
   -- see below for details, note: crm[0] means the first
   -- (which MUST be present), crm[1] means the second (which
   -- is OPTIONAL, and used to ask for a centrally-generated key)
 crm[0].certReq.      fixed value of zero
    certReqId
   -- this is the index of the template within the message
 crm[0].certReq       present
    certTemplate
   -- MUST include subject public key value, otherwise unconstrained
 crm[0].pop...        optionally present if public key
    POPOSigningKey    from crm[0].certReq.certTemplate is
                      a signing key
   -- proof-of-possession MAY be required in this exchange
   -- (see Appendix D.3 for details)
 crm[0].certReq.      optionally present
    controls.archiveOptions
   -- the end entity MAY request that the locally-generated
   -- private key be archived
 crm[0].certReq.      optionally present
    controls.publicationInfo
   -- the end entity MAY ask for publication of resulting cert.
 crm[1].certReq       fixed value of one

Adams, et al. Standards Track [Page 70] RFC 4210 CMP September 2005

    certReqId
   -- the index of the template within the message
 crm[1].certReq       present
    certTemplate
    -- MUST NOT include actual public key bits, otherwise
    -- unconstrained (e.g., the names need not be the same as in
    -- crm[0]).  Note that subjectPublicKeyInfo MAY be present
    -- and contain an AlgorithmIdentifier followed by a
    -- zero-length BIT STRING for the subjectPublicKey if it is
    -- desired to inform the CA/RA of algorithm and parameter
    -- preferences regarding the to-be-generated key pair.
 crm[1].certReq.      present [object identifier MUST be PROT_ENC_ALG]
    controls.protocolEncrKey
   -- if centralized key generation is supported by this CA,
   -- this short-term asymmetric encryption key (generated by
   -- the end entity) will be used by the CA to encrypt (a
   -- symmetric key used to encrypt) a private key generated by
   -- the CA on behalf of the end entity
 crm[1].certReq.      optionally present
    controls.archiveOptions
 crm[1].certReq.      optionally present
    controls.publicationInfo
 protection           present
   -- bits calculated using MSG_MAC_ALG
 Initialization Response -- ip
 Field                Value
 sender               CA name
   -- the name of the CA who produced the message
 messageTime          present
   -- time at which CA produced message
 protectionAlg        MS_MAC_ALG
   -- only MAC protection is allowed for this response
 senderKID             referenceNum
   -- the reference number that the CA has previously issued to the
   -- end entity (together with the MACing key)
 transactionID        present
   -- value from corresponding ir message
 senderNonce          present
   -- 128 (pseudo-)random bits
 recipNonce           present
   -- value from senderNonce in corresponding ir message
 freeText             any valid value

Adams, et al. Standards Track [Page 71] RFC 4210 CMP September 2005

 body                 ip (CertRepMessage)
                      contains exactly one response
                      for each request
  1. - The PKI (CA) responds to either one or two requests as
  2. - appropriate. crc[0] denotes the first (always present);
  3. - crc[1] denotes the second (only present if the ir message
  4. - contained two requests and if the CA supports centralized
  5. - key generation).

crc[0]. fixed value of zero

    certReqId
   -- MUST contain the response to the first request in the
   -- corresponding ir message
 crc[0].status.       present, positive values allowed:
    status               "accepted", "grantedWithMods"
                      negative values allowed:
                         "rejection"
 crc[0].status.       present if and only if
    failInfo          crc[0].status.status is "rejection"
 crc[0].              present if and only if
    certifiedKeyPair  crc[0].status.status is
                         "accepted" or "grantedWithMods"
 certificate          present unless end entity's public
                      key is an encryption key and POP
                      is done in this in-band exchange
 encryptedCert        present if and only if end entity's
                      public key is an encryption key and
                      POP done in this in-band exchange
 publicationInfo      optionally present
  1. - indicates where certificate has been published (present
  2. - at discretion of CA)
 crc[1].              fixed value of one
    certReqId
   -- MUST contain the response to the second request in the
   -- corresponding ir message
 crc[1].status.       present, positive values allowed:
    status               "accepted", "grantedWithMods"
                      negative values allowed:
                         "rejection"
 crc[1].status.       present if and only if
    failInfo          crc[0].status.status is "rejection"
 crc[1].              present if and only if
    certifiedKeyPair  crc[0].status.status is "accepted"
                      or "grantedWithMods"
 certificate          present

Adams, et al. Standards Track [Page 72] RFC 4210 CMP September 2005

 privateKey           present
   -- see Appendix C, Request Message Behavioral Clarifications
 publicationInfo      optionally present
   -- indicates where certificate has been published (present
   -- at discretion of CA)
 protection           present
   -- bits calculated using MSG_MAC_ALG
 extraCerts           optionally present
   -- the CA MAY provide additional certificates to the end
   -- entity
 Certificate confirm; certConf
 Field                Value
 sender               present
   -- same as in ir
 recipient            CA name
   -- the name of the CA who was asked to produce a certificate
 transactionID        present
   -- value from corresponding ir and ip messages
 senderNonce          present
   -- 128 (pseudo-) random bits
 recipNonce           present
   -- value from senderNonce in corresponding ip message
 protectionAlg        MSG_MAC_ALG
   -- only MAC protection is allowed for this message.  The
   -- MAC is based on the initial authentication key shared
   -- between the EE and the CA.
 senderKID            referenceNum
   -- the reference number which the CA has previously issued
   -- to the end entity (together with the MACing key)
 body                 certConf
   -- see Section 5.3.18, "PKI Confirmation Content", for the
   -- contents of the certConf fields.
   -- Note: two CertStatus structures are required if both an
   -- encryption and a signing certificate were sent.
 protection           present
   -- bits calculated using MSG_MAC_ALG
 Confirmation; PKIConf
 Field                Value

Adams, et al. Standards Track [Page 73] RFC 4210 CMP September 2005

 sender               present
   -- same as in ip
 recipient            present
   -- sender name from certConf
 transactionID        present
   -- value from certConf message
 senderNonce          present
   -- 128 (pseudo-) random bits
 recipNonce           present
   -- value from senderNonce from certConf message
 protectionAlg        MSG_MAC_ALG
   -- only MAC protection is allowed for this message.
 senderKID            referenceNum
 body                 PKIConf
 protection           present
   -- bits calculated using MSG_MAC_ALG

D.5. Certificate Request

 An (initialized) end entity requests a certificate from a CA (for any
 reason).  When the CA responds with a message containing a
 certificate, the end entity replies with a certificate confirmation.
 The CA replies with a PKIConfirm, to close the transaction.  All
 messages are authenticated.
 The profile for this exchange is identical to that given in Appendix
 D.4, with the following exceptions:
 o  sender name SHOULD be present
 o  protectionAlg of MSG_SIG_ALG MUST be supported (MSG_MAC_ALG MAY
    also be supported) in request, response, certConfirm, and
    PKIConfirm messages;
 o  senderKID and recipKID are only present if required for message
    verification;
 o  body is cr or cp;
 o  body may contain one or two CertReqMsg structures, but either
    CertReqMsg may be used to request certification of a locally-
    generated public key or a centrally-generated public key (i.e.,
    the position-dependence requirement of Appendix D.4 is removed);
 o  protection bits are calculated according to the protectionAlg
    field.

Adams, et al. Standards Track [Page 74] RFC 4210 CMP September 2005

D.6. Key Update Request

 An (initialized) end entity requests a certificate from a CA (to
 update the key pair and/or corresponding certificate that it already
 possesses).  When the CA responds with a message containing a
 certificate, the end entity replies with a certificate confirmation.
 The CA replies with a PKIConfirm, to close the transaction.  All
 messages are authenticated.
 The profile for this exchange is identical to that given in Appendix
 D.4, with the following exceptions:
 1.  sender name SHOULD be present
 2.  protectionAlg of MSG_SIG_ALG MUST be supported (MSG_MAC_ALG MAY
     also be supported) in request, response, certConfirm, and
     PKIConfirm messages;
 3.  senderKID and recipKID are only present if required for message
     verification;
 4.  body is kur or kup;
 5.  body may contain one or two CertReqMsg structures, but either
     CertReqMsg may be used to request certification of a locally-
     generated public key or a centrally-generated public key (i.e.,
     the position-dependence requirement of Appendix D.4 is removed);
 6.  protection bits are calculated according to the protectionAlg
     field;
 7.  regCtrl OldCertId SHOULD be used (unless it is clear to both
     sender and receiver -- by means not specified in this document --
     that it is not needed).

Appendix E. PKI Management Message Profiles (OPTIONAL).

 This appendix contains detailed profiles for those PKIMessages that
 MAY be supported by implementations (in addition to the messages
 which MUST be supported; see Section 6 and Appendix D).
 Profiles for the PKIMessages used in the following PKI management
 operations are provided:
 o  root CA key update
 o  information request/response

Adams, et al. Standards Track [Page 75] RFC 4210 CMP September 2005

 o  cross-certification request/response (1-way)
 o  in-band initialization using external identity certificate
 Later versions of this document may extend the above to include
 profiles for the operations listed below (along with other
 operations, if desired).
 o  revocation request
 o  certificate publication
 o  CRL publication

E.1. General Rules for Interpretation of These Profiles.

 Identical to Appendix D.1.

E.2. Algorithm Use Profile

 Identical to Appendix D.2.

E.3. Self-Signed Certificates

 Profile of how a Certificate structure may be "self-signed".  These
 structures are used for distribution of CA public keys.  This can
 occur in one of three ways (see Section 4.4 above for a description
 of the use of these structures):
 Type          Function
 -----------------------------------------------------------------
 newWithNew a true "self-signed" certificate; the contained
            public key MUST be usable to verify the signature
            (though this provides only integrity and no
            authentication whatsoever)
 oldWithNew previous root CA public key signed with new private key
 newWithOld new root CA public key signed with previous private key
 Such certificates (including relevant extensions) must contain
 "sensible" values for all fields.  For example, when present,
 subjectAltName MUST be identical to issuerAltName, and, when present,
 keyIdentifiers must contain appropriate values, et cetera.

Adams, et al. Standards Track [Page 76] RFC 4210 CMP September 2005

E.4. Root CA Key Update

 A root CA updates its key pair.  It then produces a CA key update
 announcement message that can be made available (via some transport
 mechanism) to the relevant end entities.  A confirmation message is
 NOT REQUIRED from the end entities.
 ckuann message:
  Field        Value                        Comment
 --------------------------------------------------------------
  sender       CA name CA name
  body         ckuann(CAKeyUpdAnnContent)
  oldWithNew   present                  see Appendix E.3 above
  newWithOld   present                  see Appendix E.3 above
  newWithNew   present                  see Appendix E.3 above
  extraCerts   optionally present       can be used to "publish"
                                        certificates (e.g.,
                                        certificates signed using
                                        the new private key)

E.5. PKI Information Request/Response

 The end entity sends a general message to the PKI requesting details
 that will be required for later PKI management operations.  RA/CA
 responds with a general response.  If an RA generates the response,
 then it will simply forward the equivalent message that it previously
 received from the CA, with the possible addition of certificates to
 the extraCerts fields of the PKIMessage.  A confirmation message is
 NOT REQUIRED from the end entity.
 Message Flows:
 Step# End entity                        PKI
    1  format genm
    2                ->   genm   ->
    3                                    handle genm
    4                                    produce genp
    5                <-   genp   <-
    6  handle genp
 genM:
 Field               Value
 recipient           CA name
   -- the name of the CA as contained in issuerAltName

Adams, et al. Standards Track [Page 77] RFC 4210 CMP September 2005

  1. - extensions or issuer fields within certificates

protectionAlg MSG_MAC_ALG or MSG_SIG_ALG

  1. - any authenticated protection alg.

SenderKID present if required

  1. - must be present if required for verification of message
  2. - protection

freeText any valid value

 body                genr (GenReqContent)
 GenMsgContent       empty SEQUENCE
   -- all relevant information requested
 protection          present
   -- bits calculated using MSG_MAC_ALG or MSG_SIG_ALG
 genP:
 Field                Value
 sender               CA name
   -- name of the CA which produced the message
 protectionAlg        MSG_MAC_ALG or MSG_SIG_ALG
   -- any authenticated protection alg.
 senderKID            present if required
   -- must be present if required for verification of message
   -- protection
 body                 genp (GenRepContent)
 CAProtEncCert        present (object identifier one
                      of PROT_ENC_ALG), with relevant
                      value
   -- to be used if end entity needs to encrypt information for
   -- the CA (e.g., private key for recovery purposes)
 SignKeyPairTypes     present, with relevant value
   -- the set of signature algorithm identifiers that this CA will
   -- certify for subject public keys
 EncKeyPairTypes      present, with relevant value
   -- the set of encryption/key agreement algorithm identifiers that
   -- this CA will certify for subject public keys
 PreferredSymmAlg     present (object identifier one
                      of PROT_SYM_ALG) , with relevant
                      value
   -- the symmetric algorithm that this CA expects to be used
   -- in later PKI messages (for encryption)
 CAKeyUpdateInfo      optionally present, with
                      relevant value
   -- the CA MAY provide information about a relevant root CA
   -- key pair using this field (note that this does not imply
   -- that the responding CA is the root CA in question)
 CurrentCRL           optionally present, with relevant value

Adams, et al. Standards Track [Page 78] RFC 4210 CMP September 2005

  1. - the CA MAY provide a copy of a complete CRL (i.e.,
  2. - fullest possible one)

protection present

  1. - bits calculated using MSG_MAC_ALG or MSG_SIG_ALG

extraCerts optionally present

  1. - can be used to send some certificates to the end
  2. - entity. An RA MAY add its certificate here.

E.6. Cross Certification Request/Response (1-way)

 Creation of a single cross-certificate (i.e., not two at once).  The
 requesting CA MAY choose who is responsible for publication of the
 cross-certificate created by the responding CA through use of the
 PKIPublicationInfo control.
 Preconditions:
 1.  Responding CA can verify the origin of the request (possibly
     requiring out-of-band means) before processing the request.
 2.  Requesting CA can authenticate the authenticity of the origin of
     the response (possibly requiring out-of-band means) before
     processing the response
 The use of certificate confirmation and the corresponding server
 confirmation is determined by the generalInfo field in the PKIHeader
 (see Section 5.1.1).  The following profile does not mandate support
 for either confirmation.
 Message Flows:
 Step# Requesting CA                       Responding CA
   1   format ccr
   2                   ->    ccr    ->
   3                                       handle ccr
   4                                       produce ccp
   5                   <-    ccp    <-
   6   handle ccp
 ccr:
 Field                 Value
 sender                Requesting CA name
   -- the name of the CA who produced the message
 recipient             Responding CA name
   -- the name of the CA who is being asked to produce a certificate
 messageTime           time of production of message

Adams, et al. Standards Track [Page 79] RFC 4210 CMP September 2005

  1. - current time at requesting CA

protectionAlg MSG_SIG_ALG

  1. - only signature protection is allowed for this request

senderKID present if required

  1. - must be present if required for verification of message
  2. - protection

recipKID present if required

  1. - must be present if required for verification of message
  2. - protection

transactionID present

  1. - implementation-specific value, meaningful to requesting CA.
  2. - [If already in use at responding CA then a rejection message
  3. - MUST be produced by responding CA]

senderNonce present

  1. - 128 (pseudo-)random bits

freeText any valid value

 body                  ccr (CertReqMessages)
                       only one CertReqMsg
                       allowed
   -- if multiple cross certificates are required, they MUST be
   -- packaged in separate PKIMessages
 certTemplate          present
   -- details follow
 version               v1 or v3
   -- v3 STRONGLY RECOMMENDED
 signingAlg            present
   -- the requesting CA must know in advance with which algorithm it
   -- wishes the certificate to be signed
 subject               present
   -- may be NULL-DN only if subjectAltNames extension value proposed
 validity              present
   -- MUST be completely specified (i.e., both fields present)
 issuer                present
   -- may be NULL-DN only if issuerAltNames extension value proposed
 publicKey             present
   -- the key to be certified (which must be for a signing algorithm)
 extensions            optionally present
   -- a requesting CA must propose values for all extensions
   -- that it requires to be in the cross-certificate
 POPOSigningKey        present
   -- see Section D3: Proof-of-possession profile
 protection            present
   -- bits calculated using MSG_SIG_ALG
 extraCerts            optionally present
   -- MAY contain any additional certificates that requester wishes
   -- to include

Adams, et al. Standards Track [Page 80] RFC 4210 CMP September 2005

 ccp:
 Field                 Value
 sender                Responding CA name
   -- the name of the CA who produced the message
 recipient             Requesting CA name
   -- the name of the CA who asked for production of a certificate
 messageTime           time of production of message
   -- current time at responding CA
 protectionAlg         MSG_SIG_ALG
   -- only signature protection is allowed for this message
 senderKID             present if required
   -- must be present if required for verification of message
   -- protection
 recipKID              present if required
 transactionID         present
   -- value from corresponding ccr message
 senderNonce           present
   -- 128 (pseudo-)random bits
 recipNonce            present
 -- senderNonce from corresponding ccr message
 freeText              any valid value
 body                  ccp (CertRepMessage)
                       only one CertResponse allowed
   -- if multiple cross certificates are required they MUST be
   -- packaged in separate PKIMessages
 response              present
 status                present
 PKIStatusInfo.status  present
   -- if PKIStatusInfo.status is one of:
   --   accepted, or
   --   grantedWithMods,
   -- then certifiedKeyPair MUST be present and failInfo MUST
   -- be absent
 failInfo              present depending on
                       PKIStatusInfo.status
   -- if PKIStatusInfo.status is:
   --   rejection
   -- then certifiedKeyPair MUST be absent and failInfo MUST be
   -- present and contain appropriate bit settings
 certifiedKeyPair      present depending on
                       PKIStatusInfo.status
 certificate           present depending on
                       certifiedKeyPair

Adams, et al. Standards Track [Page 81] RFC 4210 CMP September 2005

  1. - content of actual certificate must be examined by requesting CA
  2. - before publication

protection present

  1. - bits calculated using MSG_SIG_ALG

extraCerts optionally present

  1. - MAY contain any additional certificates that responder wishes
  2. - to include

E.7. In-Band Initialization Using External Identity Certificate

 An (uninitialized) end entity wishes to initialize into the PKI with
 a CA, CA-1.  It uses, for authentication purposes, a pre-existing
 identity certificate issued by another (external) CA, CA-X.  A trust
 relationship must already have been established between CA-1 and CA-X
 so that CA-1 can validate the EE identity certificate signed by CA-X.
 Furthermore, some mechanism must already have been established within
 the Personal Security Environment (PSE) of the EE that would allow it
 to authenticate and verify PKIMessages signed by CA-1 (as one
 example, the PSE may contain a certificate issued for the public key
 of CA-1, signed by another CA that the EE trusts on the basis of
 out-of-band authentication techniques).
 The EE sends an initialization request to start the transaction.
 When CA-1 responds with a message containing the new certificate, the
 end entity replies with a certificate confirmation.  CA-1 replies
 with a PKIConfirm to close the transaction.  All messages are signed
 (the EE messages are signed using the private key that corresponds to
 the public key in its external identity certificate; the CA-1
 messages are signed using the private key that corresponds to the
 public key in a
 certificate that can be chained to a trust anchor in the EE's PSE).
 The profile for this exchange is identical to that given in Appendix
 D.4, with the following exceptions:
 o  the EE and CA-1 do not share a symmetric MACing key (i.e., there
    is no out-of-band shared secret information between these
    entities);
 o  sender name in ir MUST be present (and identical to the subject
    name present in the external identity certificate);
 o  protectionAlg of MSG_SIG_ALG MUST be used in all messages;
 o  external identity cert.  MUST be carried in ir extraCerts field
 o  senderKID and recipKID are not used;

Adams, et al. Standards Track [Page 82] RFC 4210 CMP September 2005

 o  body is ir or ip;
 o  protection bits are calculated according to the protectionAlg
    field.

Appendix F. Compilable ASN.1 Definitions

   PKIXCMP {iso(1) identified-organization(3)
         dod(6) internet(1) security(5) mechanisms(5) pkix(7)
         id-mod(0) id-mod-cmp2000(16)}
   DEFINITIONS EXPLICIT TAGS ::=
   BEGIN
  1. - EXPORTS ALL –
   IMPORTS
       Certificate, CertificateList, Extensions, AlgorithmIdentifier,
       UTF8String -- if required; otherwise, comment out
              FROM PKIX1Explicit88 {iso(1) identified-organization(3)
              dod(6) internet(1) security(5) mechanisms(5) pkix(7)
              id-mod(0) id-pkix1-explicit-88(1)}
       GeneralName, KeyIdentifier
              FROM PKIX1Implicit88 {iso(1) identified-organization(3)
              dod(6) internet(1) security(5) mechanisms(5) pkix(7)
              id-mod(0) id-pkix1-implicit-88(2)}
       CertTemplate, PKIPublicationInfo, EncryptedValue, CertId,
       CertReqMessages
              FROM PKIXCRMF-2005 {iso(1) identified-organization(3)
              dod(6) internet(1) security(5) mechanisms(5) pkix(7)
              id-mod(0) id-mod-crmf2005(36)}
  1. - see also the behavioral clarifications to CRMF codified in
  2. - Appendix C of this specification
       CertificationRequest
              FROM PKCS-10 {iso(1) member-body(2)
                            us(840) rsadsi(113549)
                            pkcs(1) pkcs-10(10) modules(1) pkcs-10(1)}
  1. - (specified in RFC 2986 with 1993 ASN.1 syntax and IMPLICIT
  2. - tags). Alternatively, implementers may directly include
  3. - the [PKCS10] syntax in this module

Adams, et al. Standards Track [Page 83] RFC 4210 CMP September 2005

       ;
  1. - the rest of the module contains locally-defined OIDs and
  2. - constructs
    CMPCertificate ::= CHOICE {
       x509v3PKCert        Certificate
    }
 -- This syntax, while bits-on-the-wire compatible with the
 -- standard X.509 definition of "Certificate", allows the
 -- possibility of future certificate types (such as X.509
 -- attribute certificates, WAP WTLS certificates, or other kinds
 -- of certificates) within this certificate management protocol,
 -- should a need ever arise to support such generality.  Those
 -- implementations that do not foresee a need to ever support
 -- other certificate types MAY, if they wish, comment out the
 -- above structure and "un-comment" the following one prior to
 -- compiling this ASN.1 module.  (Note that interoperability
 -- with implementations that don't do this will be unaffected by
 -- this change.)
  1. - CMPCertificate ::= Certificate
    PKIMessage ::= SEQUENCE {
       header           PKIHeader,
       body             PKIBody,
       protection   [0] PKIProtection OPTIONAL,
       extraCerts   [1] SEQUENCE SIZE (1..MAX) OF CMPCertificate
                        OPTIONAL
   }
   PKIMessages ::= SEQUENCE SIZE (1..MAX) OF PKIMessage
   PKIHeader ::= SEQUENCE {
       pvno                INTEGER     { cmp1999(1), cmp2000(2) },
       sender              GeneralName,
       -- identifies the sender
       recipient           GeneralName,
       -- identifies the intended recipient
       messageTime     [0] GeneralizedTime         OPTIONAL,
       -- time of production of this message (used when sender
       -- believes that the transport will be "suitable"; i.e.,
       -- that the time will still be meaningful upon receipt)
       protectionAlg   [1] AlgorithmIdentifier     OPTIONAL,
       -- algorithm used for calculation of protection bits
       senderKID       [2] KeyIdentifier           OPTIONAL,
       recipKID        [3] KeyIdentifier           OPTIONAL,
       -- to identify specific keys used for protection

Adams, et al. Standards Track [Page 84] RFC 4210 CMP September 2005

       transactionID   [4] OCTET STRING            OPTIONAL,
       -- identifies the transaction; i.e., this will be the same in
       -- corresponding request, response, certConf, and PKIConf
       -- messages
       senderNonce     [5] OCTET STRING            OPTIONAL,
       recipNonce      [6] OCTET STRING            OPTIONAL,
       -- nonces used to provide replay protection, senderNonce
       -- is inserted by the creator of this message; recipNonce
       -- is a nonce previously inserted in a related message by
       -- the intended recipient of this message
       freeText        [7] PKIFreeText             OPTIONAL,
       -- this may be used to indicate context-specific instructions
       -- (this field is intended for human consumption)
       generalInfo     [8] SEQUENCE SIZE (1..MAX) OF
                              InfoTypeAndValue     OPTIONAL
       -- this may be used to convey context-specific information
       -- (this field not primarily intended for human consumption)
   }
   PKIFreeText ::= SEQUENCE SIZE (1..MAX) OF UTF8String
       -- text encoded as UTF-8 String [RFC3629] (note: each
       -- UTF8String MAY include an [RFC3066] language tag
       -- to indicate the language of the contained text
       -- see [RFC2482] for details)
   PKIBody ::= CHOICE {       -- message-specific body elements
       ir       [0]  CertReqMessages,        --Initialization Request
       ip       [1]  CertRepMessage,         --Initialization Response
       cr       [2]  CertReqMessages,        --Certification Request
       cp       [3]  CertRepMessage,         --Certification Response
       p10cr    [4]  CertificationRequest,   --imported from [PKCS10]
       popdecc  [5]  POPODecKeyChallContent, --pop Challenge
       popdecr  [6]  POPODecKeyRespContent,  --pop Response
       kur      [7]  CertReqMessages,        --Key Update Request
       kup      [8]  CertRepMessage,         --Key Update Response
       krr      [9]  CertReqMessages,        --Key Recovery Request
       krp      [10] KeyRecRepContent,       --Key Recovery Response
       rr       [11] RevReqContent,          --Revocation Request
       rp       [12] RevRepContent,          --Revocation Response
       ccr      [13] CertReqMessages,        --Cross-Cert. Request
       ccp      [14] CertRepMessage,         --Cross-Cert. Response
       ckuann   [15] CAKeyUpdAnnContent,     --CA Key Update Ann.
       cann     [16] CertAnnContent,         --Certificate Ann.
       rann     [17] RevAnnContent,          --Revocation Ann.
       crlann   [18] CRLAnnContent,          --CRL Announcement
       pkiconf  [19] PKIConfirmContent,      --Confirmation
       nested   [20] NestedMessageContent,   --Nested Message
       genm     [21] GenMsgContent,          --General Message

Adams, et al. Standards Track [Page 85] RFC 4210 CMP September 2005

       genp     [22] GenRepContent,          --General Response
       error    [23] ErrorMsgContent,        --Error Message
       certConf [24] CertConfirmContent,     --Certificate confirm
       pollReq  [25] PollReqContent,         --Polling request
       pollRep  [26] PollRepContent          --Polling response
   }
   PKIProtection ::= BIT STRING
   ProtectedPart ::= SEQUENCE {
       header    PKIHeader,
       body      PKIBody
   }
   id-PasswordBasedMac OBJECT IDENTIFIER ::= {1 2 840 113533 7 66 13}
   PBMParameter ::= SEQUENCE {
       salt                OCTET STRING,
       -- note:  implementations MAY wish to limit acceptable sizes
       -- of this string to values appropriate for their environment
       -- in order to reduce the risk of denial-of-service attacks
       owf                 AlgorithmIdentifier,
       -- AlgId for a One-Way Function (SHA-1 recommended)
       iterationCount      INTEGER,
       -- number of times the OWF is applied
       -- note:  implementations MAY wish to limit acceptable sizes
       -- of this integer to values appropriate for their environment
       -- in order to reduce the risk of denial-of-service attacks
       mac                 AlgorithmIdentifier
       -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
   }   -- or HMAC [RFC2104, RFC2202])
   id-DHBasedMac OBJECT IDENTIFIER ::= {1 2 840 113533 7 66 30}
   DHBMParameter ::= SEQUENCE {
       owf                 AlgorithmIdentifier,
       -- AlgId for a One-Way Function (SHA-1 recommended)
       mac                 AlgorithmIdentifier
       -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
   }   -- or HMAC [RFC2104, RFC2202])
   NestedMessageContent ::= PKIMessages
   PKIStatus ::= INTEGER {
       accepted                (0),
       -- you got exactly what you asked for
       grantedWithMods        (1),
       -- you got something like what you asked for; the
       -- requester is responsible for ascertaining the differences

Adams, et al. Standards Track [Page 86] RFC 4210 CMP September 2005

       rejection              (2),
       -- you don't get it, more information elsewhere in the message
       waiting                (3),
       -- the request body part has not yet been processed; expect to
       -- hear more later (note: proper handling of this status
       -- response MAY use the polling req/rep PKIMessages specified
       -- in Section 5.3.22; alternatively, polling in the underlying
       -- transport layer MAY have some utility in this regard)
       revocationWarning      (4),
       -- this message contains a warning that a revocation is
       -- imminent
       revocationNotification (5),
       -- notification that a revocation has occurred
       keyUpdateWarning       (6)
       -- update already done for the oldCertId specified in
       -- CertReqMsg
   }
   PKIFailureInfo ::= BIT STRING {
   -- since we can fail in more than one way!
   -- More codes may be added in the future if/when required.
       badAlg              (0),
       -- unrecognized or unsupported Algorithm Identifier
       badMessageCheck     (1),
       -- integrity check failed (e.g., signature did not verify)
       badRequest          (2),
       -- transaction not permitted or supported
       badTime             (3),
       -- messageTime was not sufficiently close to the system time,
       -- as defined by local policy
       badCertId           (4),
       -- no certificate could be found matching the provided criteria
       badDataFormat       (5),
       -- the data submitted has the wrong format
       wrongAuthority      (6),
       -- the authority indicated in the request is different from the
       -- one creating the response token
       incorrectData       (7),
       -- the requester's data is incorrect (for notary services)
       missingTimeStamp    (8),
       -- when the timestamp is missing but should be there
       -- (by policy)
       badPOP              (9),
       -- the proof-of-possession failed
       certRevoked         (10),
          -- the certificate has already been revoked
       certConfirmed       (11),
          -- the certificate has already been confirmed

Adams, et al. Standards Track [Page 87] RFC 4210 CMP September 2005

       wrongIntegrity      (12),
          -- invalid integrity, password based instead of signature or
          -- vice versa
       badRecipientNonce   (13),
          -- invalid recipient nonce, either missing or wrong value
       timeNotAvailable    (14),
          -- the TSA's time source is not available
       unacceptedPolicy    (15),
          -- the requested TSA policy is not supported by the TSA.
       unacceptedExtension (16),
          -- the requested extension is not supported by the TSA.
       addInfoNotAvailable (17),
          -- the additional information requested could not be
          -- understood or is not available
       badSenderNonce      (18),
          -- invalid sender nonce, either missing or wrong size
       badCertTemplate     (19),
          -- invalid cert. template or missing mandatory information
       signerNotTrusted    (20),
          -- signer of the message unknown or not trusted
       transactionIdInUse  (21),
          -- the transaction identifier is already in use
       unsupportedVersion  (22),
          -- the version of the message is not supported
       notAuthorized       (23),
          -- the sender was not authorized to make the preceding
          -- request or perform the preceding action
       systemUnavail       (24),
       -- the request cannot be handled due to system unavailability
       systemFailure       (25),
       -- the request cannot be handled due to system failure
       duplicateCertReq    (26)
       -- certificate cannot be issued because a duplicate
       -- certificate already exists
   }
   PKIStatusInfo ::= SEQUENCE {
       status        PKIStatus,
       statusString  PKIFreeText     OPTIONAL,
       failInfo      PKIFailureInfo  OPTIONAL
   }
   OOBCert ::= CMPCertificate
   OOBCertHash ::= SEQUENCE {
       hashAlg     [0] AlgorithmIdentifier     OPTIONAL,
       certId      [1] CertId                  OPTIONAL,
       hashVal         BIT STRING

Adams, et al. Standards Track [Page 88] RFC 4210 CMP September 2005

  1. - hashVal is calculated over the DER encoding of the
  2. - self-signed certificate with the identifier certID.

}

   POPODecKeyChallContent ::= SEQUENCE OF Challenge
   -- One Challenge per encryption key certification request (in the
   -- same order as these requests appear in CertReqMessages).
   Challenge ::= SEQUENCE {
       owf                 AlgorithmIdentifier  OPTIONAL,
  1. - MUST be present in the first Challenge; MAY be omitted in
  2. - any subsequent Challenge in POPODecKeyChallContent (if
  3. - omitted, then the owf used in the immediately preceding
  4. - Challenge is to be used).
       witness             OCTET STRING,
       -- the result of applying the one-way function (owf) to a
       -- randomly-generated INTEGER, A.  [Note that a different
       -- INTEGER MUST be used for each Challenge.]
       challenge           OCTET STRING
       -- the encryption (under the public key for which the cert.
       -- request is being made) of Rand, where Rand is specified as
       --   Rand ::= SEQUENCE {
       --      int      INTEGER,
       --       - the randomly-generated INTEGER A (above)
       --      sender   GeneralName
       --       - the sender's name (as included in PKIHeader)
       --   }
   }
   POPODecKeyRespContent ::= SEQUENCE OF INTEGER
   -- One INTEGER per encryption key certification request (in the
   -- same order as these requests appear in CertReqMessages).  The
   -- retrieved INTEGER A (above) is returned to the sender of the
   -- corresponding Challenge.
   CertRepMessage ::= SEQUENCE {
       caPubs       [1] SEQUENCE SIZE (1..MAX) OF CMPCertificate
                        OPTIONAL,
       response         SEQUENCE OF CertResponse
   }
   CertResponse ::= SEQUENCE {
       certReqId           INTEGER,
       -- to match this response with corresponding request (a value
       -- of -1 is to be used if certReqId is not specified in the
       -- corresponding request)

Adams, et al. Standards Track [Page 89] RFC 4210 CMP September 2005

       status              PKIStatusInfo,
       certifiedKeyPair    CertifiedKeyPair    OPTIONAL,
       rspInfo             OCTET STRING        OPTIONAL
       -- analogous to the id-regInfo-utf8Pairs string defined
       -- for regInfo in CertReqMsg [CRMF]
   }
   CertifiedKeyPair ::= SEQUENCE {
       certOrEncCert       CertOrEncCert,
       privateKey      [0] EncryptedValue      OPTIONAL,
       -- see [CRMF] for comment on encoding
       publicationInfo [1] PKIPublicationInfo  OPTIONAL
   }
   CertOrEncCert ::= CHOICE {
       certificate     [0] CMPCertificate,
       encryptedCert   [1] EncryptedValue
   }
   KeyRecRepContent ::= SEQUENCE {
       status                  PKIStatusInfo,
       newSigCert          [0] CMPCertificate OPTIONAL,
       caCerts             [1] SEQUENCE SIZE (1..MAX) OF
                                           CMPCertificate OPTIONAL,
       keyPairHist         [2] SEQUENCE SIZE (1..MAX) OF
                                           CertifiedKeyPair OPTIONAL
   }
   RevReqContent ::= SEQUENCE OF RevDetails
   RevDetails ::= SEQUENCE {
       certDetails         CertTemplate,
       -- allows requester to specify as much as they can about
       -- the cert. for which revocation is requested
       -- (e.g., for cases in which serialNumber is not available)
       crlEntryDetails     Extensions       OPTIONAL
       -- requested crlEntryExtensions
   }
   RevRepContent ::= SEQUENCE {
       status       SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
       -- in same order as was sent in RevReqContent
       revCerts [0] SEQUENCE SIZE (1..MAX) OF CertId
                                           OPTIONAL,
       -- IDs for which revocation was requested
       -- (same order as status)
       crls     [1] SEQUENCE SIZE (1..MAX) OF CertificateList
                                           OPTIONAL

Adams, et al. Standards Track [Page 90] RFC 4210 CMP September 2005

  1. - the resulting CRLs (there may be more than one)

}

   CAKeyUpdAnnContent ::= SEQUENCE {
       oldWithNew   CMPCertificate, -- old pub signed with new priv
       newWithOld   CMPCertificate, -- new pub signed with old priv
       newWithNew   CMPCertificate  -- new pub signed with new priv
   }
   CertAnnContent ::= CMPCertificate
   RevAnnContent ::= SEQUENCE {
       status              PKIStatus,
       certId              CertId,
       willBeRevokedAt     GeneralizedTime,
       badSinceDate        GeneralizedTime,
       crlDetails          Extensions  OPTIONAL
       -- extra CRL details (e.g., crl number, reason, location, etc.)
   }
   CRLAnnContent ::= SEQUENCE OF CertificateList
   CertConfirmContent ::= SEQUENCE OF CertStatus
   CertStatus ::= SEQUENCE {
      certHash    OCTET STRING,
      -- the hash of the certificate, using the same hash algorithm
      -- as is used to create and verify the certificate signature
      certReqId   INTEGER,
      -- to match this confirmation with the corresponding req/rep
      statusInfo  PKIStatusInfo OPTIONAL
   }
   PKIConfirmContent ::= NULL
   InfoTypeAndValue ::= SEQUENCE {
       infoType               OBJECT IDENTIFIER,
       infoValue              ANY DEFINED BY infoType  OPTIONAL
   }
   -- Example InfoTypeAndValue contents include, but are not limited
   -- to, the following (un-comment in this ASN.1 module and use as
   -- appropriate for a given environment):
   --
   --   id-it-caProtEncCert    OBJECT IDENTIFIER ::= {id-it 1}
   --      CAProtEncCertValue      ::= CMPCertificate
   --   id-it-signKeyPairTypes OBJECT IDENTIFIER ::= {id-it 2}
   --      SignKeyPairTypesValue   ::= SEQUENCE OF AlgorithmIdentifier
   --   id-it-encKeyPairTypes  OBJECT IDENTIFIER ::= {id-it 3}

Adams, et al. Standards Track [Page 91] RFC 4210 CMP September 2005

  1. - EncKeyPairTypesValue ::= SEQUENCE OF AlgorithmIdentifier
  2. - id-it-preferredSymmAlg OBJECT IDENTIFIER ::= {id-it 4}
  3. - PreferredSymmAlgValue ::= AlgorithmIdentifier
  4. - id-it-caKeyUpdateInfo OBJECT IDENTIFIER ::= {id-it 5}
  5. - CAKeyUpdateInfoValue ::= CAKeyUpdAnnContent
  6. - id-it-currentCRL OBJECT IDENTIFIER ::= {id-it 6}
  7. - CurrentCRLValue ::= CertificateList
  8. - id-it-unsupportedOIDs OBJECT IDENTIFIER ::= {id-it 7}
  9. - UnsupportedOIDsValue ::= SEQUENCE OF OBJECT IDENTIFIER
  10. - id-it-keyPairParamReq OBJECT IDENTIFIER ::= {id-it 10}
  11. - KeyPairParamReqValue ::= OBJECT IDENTIFIER
  12. - id-it-keyPairParamRep OBJECT IDENTIFIER ::= {id-it 11}
  13. - KeyPairParamRepValue ::= AlgorithmIdentifer
  14. - id-it-revPassphrase OBJECT IDENTIFIER ::= {id-it 12}
  15. - RevPassphraseValue ::= EncryptedValue
  16. - id-it-implicitConfirm OBJECT IDENTIFIER ::= {id-it 13}
  17. - ImplicitConfirmValue ::= NULL
  18. - id-it-confirmWaitTime OBJECT IDENTIFIER ::= {id-it 14}
  19. - ConfirmWaitTimeValue ::= GeneralizedTime
  20. - id-it-origPKIMessage OBJECT IDENTIFIER ::= {id-it 15}
  21. - OrigPKIMessageValue ::= PKIMessages
  22. - id-it-suppLangTags OBJECT IDENTIFIER ::= {id-it 16}
  23. - SuppLangTagsValue ::= SEQUENCE OF UTF8String
  24. -
  25. - where
  26. -
  27. - id-pkix OBJECT IDENTIFIER ::= {
  28. - iso(1) identified-organization(3)
  29. - dod(6) internet(1) security(5) mechanisms(5) pkix(7)}
  30. - and
  31. - id-it OBJECT IDENTIFIER ::= {id-pkix 4}
  32. -
  33. -
  34. - This construct MAY also be used to define new PKIX Certificate
  35. - Management Protocol request and response messages, or general-
  36. - purpose (e.g., announcement) messages for future needs or for
  37. - specific environments.
   GenMsgContent ::= SEQUENCE OF InfoTypeAndValue
  1. - May be sent by EE, RA, or CA (depending on message content).
  2. - The OPTIONAL infoValue parameter of InfoTypeAndValue will
  3. - typically be omitted for some of the examples given above.
  4. - The receiver is free to ignore any contained OBJ. IDs that it
  5. - does not recognize. If sent from EE to CA, the empty set
  6. - indicates that the CA may send
  7. - any/all information that it wishes.

Adams, et al. Standards Track [Page 92] RFC 4210 CMP September 2005

   GenRepContent ::= SEQUENCE OF InfoTypeAndValue
   -- Receiver MAY ignore any contained OIDs that it does not
   -- recognize.
   ErrorMsgContent ::= SEQUENCE {
       pKIStatusInfo          PKIStatusInfo,
       errorCode              INTEGER           OPTIONAL,
       -- implementation-specific error codes
       errorDetails           PKIFreeText       OPTIONAL
       -- implementation-specific error details
   }
   PollReqContent ::= SEQUENCE OF SEQUENCE {
       certReqId              INTEGER
   }
   PollRepContent ::= SEQUENCE OF SEQUENCE {
       certReqId              INTEGER,
       checkAfter             INTEGER,  -- time in seconds
       reason                 PKIFreeText OPTIONAL
   }
   END -- of CMP module

Appendix G. Acknowledgements

 The authors gratefully acknowledge the contributions of various
 members of the IETF PKIX Working Group and the ICSA CA-talk mailing
 list (a list solely devoted to discussing CMP interoperability
 efforts).  Many of these contributions significantly clarified and
 improved the utility of this specification.  Tomi Kause thanks Vesa
 Suontama and Toni Tammisalo for review and comments.

Adams, et al. Standards Track [Page 93] RFC 4210 CMP September 2005

Authors' Addresses

 Carlisle Adams
 University of Ottawa
 800 King Edward Avenue
 P.O.Box 450, Station A
 Ottawa, Ontario  K1N 6N5
 CA
 Phone: (613) 562-5800 ext. 2345
 Fax:   (613) 562-5664
 EMail: cadams@site.uottawa.ca
 Stephen Farrell
 Trinity College Dublin
 Distributed Systems Group
 Computer Science Department
 Dublin
 IE
 Phone: +353-1-608-2945
 EMail: stephen.farrell@cs.tcd.ie
 Tomi Kause
 SSH Communications Security Corp
 Valimotie 17
 Helsinki  00380
 FI
 Phone: +358 20 500 7415
 EMail: toka@ssh.com
 Tero Mononen
 SafeNet, Inc.
 Fredrikinkatu 47
 Helsinki  00100
 FI
 Phone: +358 20 500 7814
 EMail: tmononen@safenet-inc.com

Adams, et al. Standards Track [Page 94] RFC 4210 CMP September 2005

Full Copyright Statement

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 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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Adams, et al. Standards Track [Page 95]

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