STIR                                                            R. Singh
Internet-Draft                                              Vencore Labs
Intended status: Standards Track                                M. Dolly
Expires: July 8, August 5, 2018                                             AT&T
                                                                  S. Das
                                                            Vencore Labs
                                                               A. Nguyen
                                   Office of Emergency Communication/DHS
                                                        January 04,
                                                       February 01, 2018

         PASSporT Extension for Resource-Priority Authorization


   This document extends the STIR PASSporT Secure Telephone Identity Revisited (STIR)
   Personal Assertion Token (PASSporT) specification defined in
   [I-D.ietf-stir-passport] to allow the inclusion of cryptographically-signed cryptographically
   signed assertions of authorization for the values populated in the SIP
   Session Initiation Protocol (SIP) 'Resource-Priority' header field,
   which is used for communications resource prioritization.

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Table of Contents

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

1.  Introduction

   PASSporT [I-D.ietf-stir-passport] is a token format based on JWT JSON Web
   Token (JWT) [RFC7519] for conveying cryptographically-signed cryptographically signed
   information about the identities involved in personal communications;
   it is used with STIR [I-D.ietf-stir-rfc4474bis] to convey a signed
   assertion of the identity of the participants in real-time
   communications established via a protocol like SIP. SIP [RFC3261].  This
   specification extends PASSporT to allow cryptographic-signing of the
   SIP 'Resource-Priority' header field defined in [RFC4412].

   [RFC4412] defines the SIP 'Resource-Priority' header field for
   communications Resource Priority.  As specified in [RFC4412], the
   'Resource-Priority' header field may be used by SIP user agents
   [RFC3261], including, including Public Switched Telephone Network (PSTN)
   gateways and terminals, and by SIP proxy servers servers, to influence
   prioritization afforded to communication sessions,including sessions, including PSTN
   calls.  However, the SIP 'Resource-Priority' header field could be
   spoofed and abused by unauthorized entities.

   The STIR architecture [RFC7340]assumes [RFC7340] assumes that an authority on the
   originating side of a call provides a cryptographic assurance of the
   validity of the calling party number in order to prevent
   impersonation attacks.  The STIR architecture allows extension extensions that
   can be utilized by authorities supporting real-time communication
   services using the 'Resource-Priority' header field to
   cryptographically sign the SIP 'Resource-Priority' header field and
   convey assertion of the authorization for 'Resource-Priority'.  For
   example, the authority on the originating side verifying the
   authorization of a particular communication for Resource-Priority 'Resource-Priority'
   can use a PASSPorT claim to cryptographically-sign cryptographically sign the SIP 'Resource-
   Priority' header field and convey an assertion of the authorization
   for 'Resource-Priority'.  This will allow a receiving entity
   (including entities located in different network domains/boundaries)
   to verify the validity of assertions authorizing Resource-Priority.
   Cryptographically-signed 'Resource-Priority'.
   Cryptographically signed SIP 'Resource-Priority' headers header fields will
   allow a receiving entity to verify and act on the information with
   confidence that the information have has not been spoofed or compromised.

   This specification documents an optional extension to PASSporT and
   the associated STIR mechanisms to provide a function to 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 the
   optional extension to PASSporT is used for real-time communications
   supported using SIP 'Resource-Priority' header field is defined in
   other documents and is outside the
   scope of this document.

2.  Terminology

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


   The "rph" claim will provide an assertion of authorization,"auth", authorization, "auth",
   for information in the SIP "Resource-Priority" 'Resource-Priority' header field (i.e.,
   Resource-Priority: namespace
   Resource-Priority = "Resource-Priority": r-value, where r-value=
   "namespace "." r-priority) priority value") based on [RFC4412].  Specifically,
   the "rph" claim includes assertion of the priority-
   level priority-level of the user
   to be used for a given communication session.  The value of the "rph"
   claim is an array containing Object with one or more of keys.  Each key is associated
   with a JSON
   objects for Array.  These arrays contain Strings that correspond to
   the content of r-values indicated in the SIP 'Resource-Priority' header that is
   being asserted of which one of the "rph" object, is mandatory. field.

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

    { "orig":{"tn":"12155551212"}
     "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
   [I-D.ietf-stir-passport] using the full form of PASSPorT.  The
   credentials (e.g., authority responsible for authorizing Resource-
   Priority) 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 (i.e., CERT)
   associated with the specific service supported by the SIP 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

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 based on [RFC4412].  The construction
   of "rph" claim follows the steps described in Section 4 of

   The resulting Identity header for "rph" might look as follows:

   oos2P2Dyw"; info= "";alg=ES256;
   follows(backslashes shown for line folding only):


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

   [RFC4412] allows multiple "namespace "." r-priority" priority value" pairs,
   either in a single SIP Resource-Priority 'Resource-Priority' header field or across
   multiple SIP
   Resource-Priority 'Resource-Priority' headers.  However, it is not necessary to sign all
   content of a SIP Resource-Priority header or all SIP Resource-
   Priority headers in a given SIP message.  An authority is only
   responsible for signing all the content of a SIP Resource-Priority 'Resource-Priority'
   header field for which it has authority (e.g., a specific "namespace "."
   r-priority"). the authority.

4.2.  Verification Service Behavior

   [I-D.ietf-stir-rfc4474bis] 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

   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
   authorized for Resource-Priority, which '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 'Resource-Priority' as
   indicated in the claim.  In such cases, the priority treatment for
   the associated communication service is handled as per the local

   In addition, [I-D.ietf-stir-rfc4474bis] Section 6.2 Step 4 requires
   "iat" value in "rph" claim to be verified.

   The behavior of a SIP UAs 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 cases, implementations would act based on confidence in the
   veracity of this information.  The use of the compact form of
   PASSporT is not specified in this document.

5.  Further Information Associated with Resource-Priority 'Resource-Priority'

   There may be additional information about the calling party or the
   call that could be relevant to authorization for Resource-Priority. '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.

   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  PASSporT Extension Claims Registration

   This document registers a new "ppt" value for the "Personal Assertion
   Token (PASSporT) Extensions" table.

   o  Claim Name: "rph"

   o  Claim Description: Resource Priority Header Authorization
   o  Change Controller: IESG

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

6.2.  PASSporT  'rph' Types

   This document requests that the IANA add a new entry to the PASSporT
   Types registry for the type "rph" which is specified in [RFCThis].
   This specification also requests that the IANA create creates a new registry
   for PASSporT "rph" types.  Registration  Each registry entry must contain two fields: the
   name of new PASSporT the "rph" types
   shall be under type and the specification required policy. 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 [I-D.ietf-stir-rfc4474bis]
   in Section 10 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 the replay, and cut and paste attacks, the procedures described
   in Section 10.1 of [I-D.ietf-stir-rfc4474bis] MUST be followed.

7.2.  Solution Considerations

   The use of extension to PASSporT tokens with "ppt" value "rph" based
   on the validation of the digital signature and the associated
   certificate requires consideration of the authentication and
   authority or reputation of the signer to attest to the identity being
   asserted.  The following considerations should be recognized when
   using PASSporT extension with "ppt" value of "rph":

   o  An authority (signer) is only allowed to sign the content of a SIP
      'Resource-Priority' header field for which it has the right
      authority.  The authority that signs the token MUST have a secure
      method for authentication of the end user or the device.

   o  The verification of the signature MUST include means of verifying
      that the signer is authoritative for the signed content of the SIP
      'Resource-Priority' header.
      resource priority namespace in the PASSporT.

7.3.  Acknowledgements

   We would like to thank STIR 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 his their valuable

8.  References

8.1.  Normative References

              Wendt, C. and J. Peterson, "Personal Assertion Token
              (PASSporT)", February 2017.

              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", February 2017.

   [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, <>.

8.2.  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,

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


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

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