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rfc:rfc8588

Internet Engineering Task Force (IETF) C. Wendt Request for Comments: 8588 Comcast Category: Standards Track M. Barnes ISSN: 2070-1721 iconectiv

                                                              May 2019
 Personal Assertion Token (PaSSporT) Extension for Signature-based
       Handling of Asserted information using toKENs (SHAKEN)

Abstract

 This document extends the Personal Assertion Token (PASSporT), which
 is a token object that conveys cryptographically signed information
 about the participants involved in communications.  The extension is
 defined based on the "Signature-based Handling of Asserted
 information using toKENs (SHAKEN)" specification by the ATIS/SIP
 Forum IP-NNI Task Group.  It provides both (1) a specific set of
 levels of confidence in the correctness of the originating identity
 of a call originated in a SIP-based telephone network as well as (2)
 an identifier that allows the Service Provider (SP) to uniquely
 identify the origin of the call within its network.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8588.

Wendt & Barnes Standards Track [Page 1] RFC 8588 SHAKEN May 2019

Copyright Notice

 Copyright (c) 2019 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
 3.  Overview of   "shaken" PASSporT Extension . . . . . . . . . .   4
 4.  PASSporT "attest" Claim . . . . . . . . . . . . . . . . . . .   4
 5.  PASSporT "origid" Claim . . . . . . . . . . . . . . . . . . .   4
 6.  Example "shaken" PASSporT . . . . . . . . . . . . . . . . . .   5
 7.  Using "shaken" in SIP . . . . . . . . . . . . . . . . . . . .   5
 8.  Order of Claim Keys . . . . . . . . . . . . . . . . . . . . .   5
 9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
 10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .   6
 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   11.1.  JSON Web Token claims  . . . . . . . . . . . . . . . . .   7
   11.2.  PASSporT Types . . . . . . . . . . . . . . . . . . . . .   7
 12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   12.1.  Normative References . . . . . . . . . . . . . . . . . .   7
   12.2.  Informative References . . . . . . . . . . . . . . . . .   8
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   9
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

Wendt & Barnes Standards Track [Page 2] RFC 8588 SHAKEN May 2019

1. Introduction

 The Signature-based Handling of Asserted information using toKENs
 (SHAKEN) [ATIS-1000074] specification defines a framework for using
 Secure Telephone Identity Revisited (STIR) protocols including the
 Personal Assertion Token (PASSporT) [RFC8225], SIP Authenticated
 Identity Management [RFC8224], and the STIR certificate framework
 [RFC8226] for implementing the cryptographic validation of an
 authorized originator of telephone calls using SIP.  Because the
 current telephone network contains traffic originated from both VoIP
 and TDM/SS7 (Time Division Multiplexing / Signaling System 7), there
 are many scenarios that need to be accounted for where PASSporT
 signatures may represent either direct or indirect call origination
 scenarios.  The SHAKEN [ATIS-1000074] specification defines levels of
 attestation of the origination of the call as well as an origination
 identifier that can help create a unique association between the
 origin of a particular call to the point in the VoIP or TDM telephone
 network the call came from to identify, for example, either a
 customer or class of service that call represents.  This document
 specifies these values as claims to extend the base set of PASSporT
 claims.

2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.
 In addition, the following terms are used in this document:
 o  Verified association: Typically defined as an authenticated
    relationship between a customer and a device that initiated a call
    on behalf of that customer, for example, a subscriber account with
    a specific SIM card or set of SIP credentials.
 o  PASSporT: Defined in [RFC8225] is a JSON Web Token [RFC7519]
    defined specifically for securing the identity of an initiator of
    personal communication.  This document defines a specific
    extension to PASSporT.

Wendt & Barnes Standards Track [Page 3] RFC 8588 SHAKEN May 2019

3. Overview of "shaken" PASSporT Extension

 The SHAKEN framework is designed to use PASSporT [RFC8225] as a
 method of asserting the caller's telephone identity.  In addition to
 the PASSporT base claims, there are two additional claims that have
 been defined for the needs of a service provider to signal
 information beyond just the telephone identity.  First, in order to
 help bridge the transition of the state of the current telephone
 network (which has calls with no authentication and non-SIP [RFC3261]
 signaling not compatible with the use of PASSporT and Secure
 Telephone Identity (STI) in general), there is an attestation claim.
 This provides three levels of attestation: a full attestation when
 the service provider can fully attest to the calling identity, a
 partial attestation when the service provider originated a telephone
 call but cannot fully attest to the calling identity, and a gateway
 attestation, which is the lowest level of attestation and represents
 the service provider receiving a call from a telephone gateway that
 does not support PASSporT or STI.
 The second claim is a unique origination identifier that should be
 used by the service provider to identify different sources of
 telephone calls to support a traceback mechanism that can be used for
 enforcement and identification of a source of illegitimate calls.
 The use of the compact form of PASSporT is not specified in this
 document and is not specified for use in SHAKEN [ATIS-1000074].
 The next two sections define these new claims.

4. PASSporT "attest" Claim

 This indicator allows for both identifying the service provider that
 is vouching for the call as well as clearly indicating what
 information the service provider is attesting to.  The "attest" claim
 can be one of the following three values: 'A', 'B', or 'C'.  These
 values correspond to 'Full Attestation', 'Partial Attestation', and
 'Gateway Attestation', respectively.  See [ATIS-1000074] for the
 definitions of these three levels of attestation.

5. PASSporT "origid" Claim

 The purpose of the "origid" claim is described in [ATIS-1000074].
 The value of "origid" claim is a Universally Unique Identifier (UUID)
 as defined in [RFC4122].  Please refer to Section 10 for a discussion
 of the privacy considerations around the use of this value.

Wendt & Barnes Standards Track [Page 4] RFC 8588 SHAKEN May 2019

6. Example "shaken" PASSporT

 Protected Header
 {
    "alg":"ES256",
    "typ":"passport",
    "ppt":"shaken",
    "x5u":"https://cert.example.org/passport.cer"
 }
 Payload
 {
    "attest":"A"
    "dest":{"tn":["12155550131"]}
    "iat":"1443208345",
    "orig":{"tn":"12155550121"},
    "origid":"123e4567-e89b-12d3-a456-426655440000"
 }

7. Using "shaken" in SIP

 The use of the "shaken" PASSporT type and the "attest" and "origid"
 claims for SIP is formally defined in [ATIS-1000074] using the SIP
 [RFC3261] Identity header field defined in [RFC8224].

8. Order of Claim Keys

 The order of the claim keys MUST follow the rules of Section 9 of
 [RFC8225]; the claim keys MUST appear in lexicographic order.
 Therefore, the claim keys discussed in this document appear in the
 PASSporT Payload in the following order:
 o  attest
 o  dest
 o  iat
 o  orig
 o  origid

Wendt & Barnes Standards Track [Page 5] RFC 8588 SHAKEN May 2019

9. Security Considerations

 This document defines a new PASSporT [RFC8225] extension.  The
 considerations related to the security of the PASSporT object itself
 are the same as those described in [RFC8225].
 [RFC8224] defines how to compare the values of the "dest", "orig",
 and "iat" claims against fields in a SIP message containing a
 PASSporT as part of validating that request.  The values of the new
 "attest" and "origid" claims added by this extension are not used in
 such a validation step.  They are not compared to fields in the SIP
 message.  Instead, they simply carry additional information from the
 signer to the consumer of the PASSporT.  This new information shares
 the same integrity protection and non-repudiation properties as the
 base claims in the PASSporT.

10. Privacy Considerations

 As detailed in Section 26 of [RFC3261], SIP messages inherently carry
 identifying information of the caller and callee.  The addition of
 STIR cryptographically attests that the signing party vouches for the
 information given about the callee, as is discussed in the Privacy
 Considerations of [RFC8224].
 SHAKEN [ATIS-1000074] furthermore adds an "origid" value to the STIR
 PASSporT, which is an opaque unique identifier representing an
 element on the path of a given SIP request.  This identifier is
 generated by an originating telephone service provider to identify
 where within their network (e.g. a gateway or particular service
 element) a call was initiated; "origid" can facilitate forensic
 analysis of call origins when identifying and stopping bad actors
 trying to spoof identities or make fraudulent calls.
 The opacity of the "origid" claim value is intended to minimize
 exposure of information about the origination of calls labeled with
 an "origid" value.  It is therefore RECOMMENDED that implementations
 generate a unique "origid" value per call in such a way that only the
 generator of the "origid" can determine when two "origid" values
 represent the same or different elements.  If deployed systems
 instead use a common or related "origid" for service elements in
 their network, the potential for discovering patterns through
 correlation of those calls exists.  This could allow a recipient of
 calls to, for instance, learn that a set of callers are using a
 particular service or coming through a common gateway.  It is
 expected that SHAKEN PASSporTs are shared only within an [RFC3324]
 trust domain and will be stripped before calls exit that trust
 domain, but this information still could be used by analytics on

Wendt & Barnes Standards Track [Page 6] RFC 8588 SHAKEN May 2019

 intermediary and terminating systems to reveal information that could
 include geographic location and even device-level information,
 depending on how the "origid" is generated.

11. IANA Considerations

11.1. JSON Web Token claims

 IANA has added two new claims to the "JSON Web Token Claims" registry
 as defined in [RFC7519].
 Claim Name: attest
 Claim Description: Attestation level as defined in SHAKEN framework
 Change Controller: IESG
 Specification Document(s): RFC 8588
 Claim Name: origid
 Claim Description: Originating Identifier as defined in SHAKEN
    framework
 Change Controller: IESG
 Specification Document(s): RFC 8588

11.2. PASSporT Types

 IANA has added a new entry in the "Personal Assertion Token
 (PASSporT) Extensions" registry for the type "shaken", which is
 specified in this document.

12. References

12.1. Normative References

 [ATIS-1000074]
            ATIS/SIP Forum IP-NNI Task Group, "Signature-based
            Handling of Asserted information using toKENs (SHAKEN)",
            January 2017, <https://access.atis.org/apps/group_public/
            download.php/32237/ATIS-1000074.pdf>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
            Unique IDentifier (UUID) URN Namespace", RFC 4122,
            DOI 10.17487/RFC4122, July 2005,
            <https://www.rfc-editor.org/info/rfc4122>.

Wendt & Barnes Standards Track [Page 7] RFC 8588 SHAKEN May 2019

 [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
            (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
            <https://www.rfc-editor.org/info/rfc7519>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8224]  Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
            "Authenticated Identity Management in the Session
            Initiation Protocol (SIP)", RFC 8224,
            DOI 10.17487/RFC8224, February 2018,
            <https://www.rfc-editor.org/info/rfc8224>.
 [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
            Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
            <https://www.rfc-editor.org/info/rfc8225>.
 [RFC8226]  Peterson, J. and S. Turner, "Secure Telephone Identity
            Credentials: Certificates", RFC 8226,
            DOI 10.17487/RFC8226, February 2018,
            <https://www.rfc-editor.org/info/rfc8226>.

12.2. Informative References

 [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
            A., Peterson, J., Sparks, R., Handley, M., and E.
            Schooler, "SIP: Session Initiation Protocol", RFC 3261,
            DOI 10.17487/RFC3261, June 2002,
            <https://www.rfc-editor.org/info/rfc3261>.
 [RFC3324]  Watson, M., "Short Term Requirements for Network Asserted
            Identity", RFC 3324, DOI 10.17487/RFC3324, November 2002,
            <https://www.rfc-editor.org/info/rfc3324>.

Wendt & Barnes Standards Track [Page 8] RFC 8588 SHAKEN May 2019

Acknowledgements

 The authors would like to thank those that helped review and
 contribute to this document including specific contributions from Jon
 Peterson, Russ Housley, Robert Sparks, and Andrew Jurczak.  The
 authors would like to acknowledge the work of the ATIS/SIP Forum
 IP-NNI Task Force to develop the concepts behind this document.

Authors' Addresses

 Chris Wendt
 Comcast
 One Comcast Center
 Philadelphia, PA  19103
 United States of America
 Email: chris-ietf@chriswendt.net
 Mary Barnes
 iconectiv
 Email: mary.ietf.barnes@gmail.com

Wendt & Barnes Standards Track [Page 9]

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