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

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8588.
Authors Chris Wendt , Mary Barnes
Last updated 2021-08-12 (Latest revision 2019-03-10)
Replaces draft-wendt-stir-passport-shaken
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Robert Sparks
Shepherd write-up Show Last changed 2018-10-18
IESG IESG state Became RFC 8588 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Adam Roach
Send notices to Robert Sparks <>
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
STIR                                                            C. Wendt
Internet-Draft                                                   Comcast
Intended status: Standards Track                               M. Barnes
Expires: September 11, 2019                                    iconectiv
                                                          March 10, 2019

                   PASSporT SHAKEN Extension (SHAKEN)


   This document extends PASSporT, which is a token object that conveys
   cryptographically-signed information about the participants involved
   in communications.  The extension is defined, corresponding to the
   SHAKEN specification, to provide both a specific set of levels-of-
   confidence in the correctness of the originating identity for a SIP
   based Communication Service Provider (CSP) telephone network
   originated call as well as an identifier that allows the CSP to
   uniquely identify the origin of the call within its network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 11, 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

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

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
   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 both
   VoIP and TDM/SS7 originated traffic, 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.

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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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: is 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.

3.  Overview of 'shaken' PASSporT extension

   The SHAKEN framework is designed to use PASSporT [RFC8225] as a
   method of asserting the telephone number calling 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, including 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 can not 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 non-
   PASSporT and non-STI supporting telephone gateway.

   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.

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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 UUID as defined in [RFC4122].
   Please refer to Section 10 for a discussion of the privacy
   considerations around the use of this value.

6.  Example "shaken" PASSporT

   Protected Header

7.  Using 'shaken' in SIP

   The use of the 'shaken' PASSporT type and the claims 'attest' and
   'origid' are formally defined in [ATIS-1000074] for usage in SIP
   [RFC3261] aligned with the use of the identity header field defined
   in [RFC8224].

8.  Order of Claim Keys

   The order of the claim keys MUST follow the rules of [RFC8225]
   Section 9; 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,

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   o  attest

   o  dest

   o  iat

   o  orig

   o  origid

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 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 [RFC3261] Section 26, 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 labelled 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

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   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
   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

   This specification requests that the IANA add 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): [RFCThis]

   Claim Name: "origid"

   Claim Description: Originating Identifier as defined in SHAKEN

   Change Controller: IESG

   Specification Document(s): [RFCThis]

11.2.  PASSporT Types

   This specification requests that the IANA add a new entry to the
   Personal Assertion Token (PASSporT) Extensions registry for the type
   "shaken" which is specified in [RFCThis].

12.  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

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   authors would like to acknowledge the work of the ATIS/SIP Forum IP-
   NNI Task Force to develop the concepts behind this document.

13.  References

13.1.  Normative References

              ATIS/SIP Forum IP-NNI Task Group, "Signature-based
              Handling of Asserted information using toKENs (SHAKEN)",
              January 2017, <

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,

   [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,

   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,

   [RFC8226]  Peterson, J. and S. Turner, "Secure Telephone Identity
              Credentials: Certificates", RFC 8226,
              DOI 10.17487/RFC8226, February 2018,

13.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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   [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,

   [RFC3323]  Peterson, J., "A Privacy Mechanism for the Session
              Initiation Protocol (SIP)", RFC 3323,
              DOI 10.17487/RFC3323, November 2002,

   [RFC3324]  Watson, M., "Short Term Requirements for Network Asserted
              Identity", RFC 3324, DOI 10.17487/RFC3324, November 2002,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

Authors' Addresses

   Chris Wendt
   One Comcast Center
   Philadelphia, PA  19103


   Mary Barnes


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