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Personal Assertion Token (PASSporT) Extension for Resource Priority Authorization

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 8443.
Authors Ray P. Singh , Martin Dolly , Subir Das , An Nguyen
Last updated 2018-08-31 (Latest revision 2018-05-24)
Replaces draft-singh-stir-rph
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 Russ Housley
Shepherd write-up Show Last changed 2018-01-04
IESG IESG state Became RFC 8443 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Adam Roach
Send notices to Russ Housley <>
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
STIR                                                            R. Singh
Internet-Draft                                              Vencore Labs
Intended status: Standards Track                                M. Dolly
Expires: November 25, 2018                                          AT&T
                                                                  S. Das
                                                            Vencore Labs
                                                               A. Nguyen
                                   Office of Emergency Communication/DHS
                                                            May 24, 2018

         PASSporT Extension for Resource Priority Authorization


   This document extends the PASSporT (Personal Assertion Token)
   specification defined in [RFC8225] to allow the inclusion of
   cryptographically signed assertions of authorization for the values
   populated in the 'Session Initiation Protocol (SIP) Resource-
   Priority' header field, which is used for communications resource

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 November 25, 2018.

Copyright Notice

   Copyright (c) 2018 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

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  PASSporT 'rph' Claim  . . . . . . . . . . . . . . . . . . . .   3
   4.  'rph' in SIP  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Authentication Service Behavior . . . . . . . . . . . . .   5
     4.2.  Verification Service Behavior . . . . . . . . . . . . . .   5
   5.  Further Information Associated with 'Resource-Priority' . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  JSON Web Token Claims . . . . . . . . . . . . . . . . . .   6
     6.2.  PASSporT Types  . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     7.1.  Avoidance of replay and cut and paste attacks . . . . . .   7
     7.2.  Solution Considerations . . . . . . . . . . . . . . . . .   7
     7.3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   PASSporT [RFC8225] is a token format based on JSON Web Token (JWT)
   [RFC7519] for conveying cryptographically signed information about
   the identities involved in personal communications.  PASSporT with
   STIR [RFC8224] provides a mechanism by which an authority on the
   originating side of a call via a protocol like SIP [RFC3261] can
   provide a cryptographic assurance of the validity of the calling
   party telephone number in order to prevent impersonation attacks.

   [RFC4412] defines the 'SIP Resource-Priority' header field for
   communications 'Resource-Priority'.  As specified in [RFC4412], the
   'SIP Resource-Priority' header field may be used by SIP user agents
   [RFC3261] (including Public Switched Telephone Network (PSTN)
   gateways and SIP proxy servers) to influence prioritization afforded
   to communication sessions including PSTN calls (e.g., to manage
   scarce network resources during network congestion scenarios).
   However, the 'SIP Resource-Priority' header field could be spoofed
   and abused by unauthorized entities, the threat models and use cases
   of which are described in [RFC7375] and [RFC7340], respectively.

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   Compromise of the 'SIP Resource-Priority' header field [RFC4412]
   could lead to misuse of network resource (i.e., during congestion
   scenarios) resulting in impacts to the application services supported
   using the 'SIP Resource-Priority' header field.

   [RFC8225]  allows extensions by which an authority on the originating
   side verifying the authorization of a particular communication for
   'SIP Resource-Priority' can use a PASSPorT claim to cryptographically
   sign the 'SIP Resource-Priority' header field and convey assertion of
   the authorization for 'Resource-Priority'.  Signed 'SIP Resource-
   Priority' header field will allow a receiving entity (including
   entities located in different network domains/boundaries) to verify
   the validity of assertions authorizing 'Resource-Priority' and to act
   on the information with confidence that the information has not been
   spoofed or compromised.

   This specification documents an extension to PASSporT and the
   associated STIR mechanisms to provide a function to cryptographically
   sign the 'SIP Resource-Priority' header field.  This PASSporT object
   is used to provide attestation of a calling user authorization for
   priority communications.  This is necessary in addition to the
   PASSporT object that is used for calling user telephone number
   attestation.  How this extension to PASSporT is used for real-time
   communications supported using 'SIP Resource-Priority' header field
   is outside the scope of this document.  In addition, the PASSPorT
   extension defined in this document is intended for use in
   environments where there are means to verify that the signer of the
   'SIP Resource-Priority' header field is authoritative.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119] and
   in RFC 8174 [RFC8174].

3.  PASSporT 'rph' Claim

   This specification defines a new JSON Web Token claim for "rph",
   which provides an assertion for information in 'SIP Resource-
   Priority' header field.

   The creator of a PASSporT object adds a "ppt" value of "rph" to the
   header of a PASSporT object, in which case the PASSporT claims MUST
   contain a "rph" claim, and any entities verifying the PASSporT object
   will be required to understand the "ppt" extension in order to
   process the PASSporT in question.  A PASSPorT header with the "ppt"
   included will look as follows:

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   The "rph" claim will provide an assertion of authorization, "auth",
   for information in the 'SIP Resource-Priority' header field based on
   [RFC4412] and the syntax is:

   Resource-Priority = "Resource-Priority" : r-value,
   r-value= namespace  "."  r-priority

   Specifically, the "rph" claim includes an assertion of the priority-
   level of the user to be used for a given communication session.  The
   value of the "rph" claim is an Object with one or more keys.  Each
   key is associated with a JSON Array.  These arrays contain Strings
   that correspond to the r-values indicated in the 'SIP Resource-
   Priority' header field.

   The following is an example "rph" claim for a 'SIP Resource-Priority'
   header field with one r-value of "ets.0" and with another r-value of

     "rph":{"auth":["ets.0", "wps.0"]}

   After the header and claims PASSporT objects have been constructed,
   their signature is generated normally per the guidance in [RFC8225]
   using the full form of PASSPorT.  The credentials (i.e., Certificate)
   used to create the signature must have authority over the namespace
   of the "rph" claim and there is only one authority per claim.  The
   authority MUST use its credentials associated with the specific
   service supported by the resource priority namespace in the claim.
   If r-values are added or dropped by the intermediaries along the
   path, intermediaries must generate a new "rph" header and sign the
   claim with its own authority.

   The use of the compact form of PASSporT is not specified in this

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4.  'rph' in SIP

   This section specifies SIP-specific usage for the "rph" claim in

4.1.  Authentication Service Behavior

   The Authentication Service will create the "rph" claim using the
   values discussed in section 3 of this document that are based on
   [RFC4412].  The construction of "rph" claim follows the steps
   described in Section 4.1 of [RFC8224].

   The resulting Identity header for "rph" might look as
   follows(backslashes shown for line folding only):


   A SIP authentication service will derive the value of "rph" from the
   'SIP Resource-Priority' header field based on policy associated with
   service specific use of the "namespace "." r-priority" for r-values
   based on [RFC4412].  The authentication service derives the value of
   the PASSPorT claim by verifying the authorization for 'SIP Resource-
   Priority' (i.e., verifying a calling user privilege for 'Resource-
   Priority' based on its identity) which might be derived from customer
   profile data or from access to external services.

   [RFC4412] allows multiple "namespace "." priority value" pairs,
   either in a single 'SIP Resource-Priority' header field or across
   multiple 'SIP Resource-Priority' headers.  An authority is
   responsible for signing all the content of a 'SIP Resource-Priority'
   header field for which it has the authority.

4.2.  Verification Service Behavior

   [RFC8224] Section 6.2 Step 5 requires that specifications defining
   "ppt" values describe any additional verifier behavior.  The behavior
   specified for the "ppt" values of "rph" is as follows:

   The verification service MUST extract the value associated with the
   "auth" key in a full form PASSPorT with a "ppt" value of "rph".  If
   the signature validates, then the verification service can use the
   value of the "rph" claim as validation that the calling party is

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   authorized for 'SIP Resource-Priority' as indicated in the claim.
   This value would in turn be used for priority treatment in accordance
   with local policy for the associated communication service.  If the
   signature validation fails, the verification service should infer
   that the calling party is not authorized for 'SIP Resource-Priority'
   as indicated in the claim.  In such cases, the priority treatment for
   the associated communication service is handled as per the local
   policy of the verifier.  In such scenarios, 'SIP Resource-Priority'
   header field SHOULD be stripped from SIP request and the network
   entities should treat the call as an ordinary call.

   In addition, [RFC8224] Section 6.2 Step 4 requires the "iat" value in
   "rph" claim to be verified.

   The behavior of a SIP UA upon receiving an INVITE containing a
   PASSporT object with a "rph" claim will largely remain a matter of
   implementation policy for the specific communication service.  In
   most cases, implementations would act based on confidence in the
   veracity of this information.

5.  Further Information Associated with 'Resource-Priority'

   There may be additional information about the calling party or the
   call that could be relevant to authorization for 'SIP Resource-
   Priority'.  This may include information related to the device
   subscription of the caller, or to any institutions that the caller or
   device is associated with, or even categories of institutions.  All
   of these data elements would benefit from the secure attestations
   provided by the STIR and PASSporT frameworks.  The specification of
   the "rph" claim could entail the optional presence of one or more
   such additional information fields applicable to 'SIP Resource-

   A new IANA registry has been defined to hold potential values of the
   "rph" array; see Section 6.2.  The definition of the "rph" claim may
   have one or more such additional information field(s).  Details of
   such "rph" claim to encompass other data elements are left for future
   version of this specification.

6.  IANA Considerations

6.1.  JSON Web Token Claims

   This specification requests that the IANA add a new claim to the JSON
   Web Token Claims registry as defined in [RFC7519].

   o  Claim Name: "rph"

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   o  Claim Description: Resource Priority Header Authorization

   o  Change Controller: IESG

   o  Specification Document(s): Section 3 of [RFCThis]

6.2.  PASSporT Types

   This specification also requests that the IANA creates a new entry to
   the PASSporT Types registry for the type "rph" which is specified in
   [RFCThis].  In addition, another registry needs to be created in
   which each entry must contain two fields: the name of the "rph" type
   and the specification in which the type is described.  This registry
   is to be initially populated with a single value for "auth" which is
   specified in [RFCThis].  Registration of new "rph" types shall be
   under the specification required policy.

7.  Security Considerations

   The security considerations discussed in [RFC8224] in Section 12 are
   applicable here.

7.1.  Avoidance of replay and cut and paste attacks

   The PASSporT extension with a "ppt" value of "rph" MUST only be sent
   with SIP INVITE when 'Resource-Priority' header field is used to
   convey the priority of the communication as defined in [RFC4412].  To
   avoid replay, and cut and paste attacks, the recommendations provided
   in Section 12.1 of [RFC8224] MUST be followed.

7.2.  Solution Considerations

   Using extensions to PASSporT tokens with a "ppt" value of "rph"
   requires knowledge of the authentication, authorization, and
   reputation of the signer to attest to the identity being asserted,
   including validating the digital signature and the associated
   certificate chain to a trust anchor.  The following considerations
   should be recognized when using PASSporT extensions with a "ppt"
   value of "rph":

   o  A signer is only allowed to sign the content of a 'SIP Resource-
      Priority' header field for which it has the proper authorization.
      Before signing tokens, the signer MUST have a secure method for
      authentication of the end user or the device being granted a

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   o  The verification of the signature MUST include means of verifying
      that the signer is authoritative for the signed content of the
      resource priority namespace in the PASSporT.

7.3.  Acknowledgements

   We would like to thank STIR WG members, ATIS/SIP Forum Task Force on
   IPNNI members, and the NS/EP Priority Services community for
   contributions to this problem statement and specification.  We would
   also like to thank David Hancock and Ning Zhang for their valuable

8.  References

8.1.  Normative References

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

   [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,

   [RFC4412]  Schulzrinne, H. and J. Polk, "Communications Resource
              Priority for the Session Initiation Protocol (SIP)",
              RFC 4412, DOI 10.17487/RFC4412, February 2006,

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

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

   [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,

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

8.2.  Informative References

   [RFC7340]  Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
              Telephone Identity Problem Statement and Requirements",
              RFC 7340, DOI 10.17487/RFC7340, September 2014,

   [RFC7375]  Peterson, J., "Secure Telephone Identity Threat Model",
              RFC 7375, DOI 10.17487/RFC7375, October 2014,

Authors' Addresses

   Ray P. Singh
   Vencore Labs
   150 Mount Airy Road
   New Jersey, NJ  07920


   Martin Dolly
   200 Laurel Avenue
   Middletown, NJ 07748


   Subir Das
   Vencore Labs
   150 Mount Airy Road
   New Jersey, NJ  07920


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   An Nguyen
   Office of Emergency Communication/DHS
   245 Murray Lane, Building 410
   Washington, DC 20528

   Email: an.p.nguyen@HQ.DHS.GOV

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