STIR                                                            R. Singh
Internet-Draft                                              Vencore Labs
Intended status: Standards Track                                M. Dolly
Expires: January 1, March 18, 2018                                             AT&T
                                                                  S. Das
                                                            Vencore Labs
                                                               A. Nguyen
                                   Office of Emergency Communication/DHS
                                                           June 30,
                                                      September 14, 2017

         PASSporT Extension for Resource-Priority Authorization


   This document extends the PASSporT object to convey
   cryptographically-signed assertions of authorization for
   communications 'Resource-Priority'.  It extends PASSporT to allow
   cryptographic-signing of the SIP 'Resource-Priority" header field
   which is used for communications resource prioritization.  It also
   describes how the PASSPorT extension is used in SIP signaling to
   convey assertions of authorization of the information in the SIP
   'Resource-Priority' header field.

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Table of Contents

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

1.  Introduction

   PASSporT [I-D.ietf-stir-passport] is a token format based on JWT
   [RFC7519] for conveying 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.  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,
   including, Public Switched Telephone Network (PSTN) gateways and
   terminals, and SIP proxy servers to influence prioritization afforded
   to communication sessions,including PSTN calls.  However, the SIP
   'Resource-Priority' header field could be spoofed and abused by
   unauthorized entities.

   The STIR architecture 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 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 can use a PASSPorT claim to
   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 authorizating Resource-Priority.  Cryptographically-signed
   SIP 'Resource-Priority' headers will allow a receiving entity to
   verify and act on the information with confidence that the
   information have 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].

3.  PASSporT 'rph' Claim

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

   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:

   {  "typ":"passport",

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

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

    { "orig":{"tn":"12155551212"}

   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 authorizating Resource-
   Priority) used to create the signature must have authority over 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.

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:

info= "";alg=ES256;ppt="rph"

   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
   based on [RFC4412].  The authentication service derives the value of
   the PASSPorT claim by verifying the authorization for 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 "." r-priority" pairs, either in
   a single SIP Resource-Priority header or across multiple SIP
   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 the content of a SIP Resource-Priority header
   for which it has authority (e.g., a specific "namespace "."

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 would in turn be used for
   priority treatment in accordance with local policy for the associated
   communication service.

   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 would in turn be used for
   priority treatment in accordance with local policy for the associated
   communication service.

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

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 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 8.3.  Details 6.2.  The definition of extensions to 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 Registration

   o  Claim Name: "rph"

   o  Claim Description: Resource Priority Header

   o  Change Controller: IESG

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

6.2.  PASSporT RPH '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 a new registry
   for PASSporT RPH "rph" types.  Registration of new PASSporT RPH "rph" types
   shall be under the specification required policy.  This registry is
   to be initially populated with a single value for
   "namespace" "auth" which is
   specified in [RFCThis].

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 past attacks

   The PASSporT extension with a "ppt" value of "rph" MUST only be sent
   with SIP INVITE when 'Resource-Priority' header 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 "ppt" value rph "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 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.

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 for his valuable inputs.

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,

   [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,

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,

   [RFC6919]  Barnes, R., Kent, S., and E. Rescorla, "Further Key Words
              for Use in RFCs to Indicate Requirement Levels", RFC 6919,
              DOI 10.17487/RFC6919, April 2013,

   [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