STIR                                                            M. Dolly
Internet-Draft                                                      AT&T
Intended status: Standards Track                                C. Wendt
Expires: April 9, May 6, 2021                                             Comcast
                                                        October 06,
                                                       November 02, 2020

Assertion Values for a Resource Priority Header Claim and a SIP Priority
         Header Claim in Support of Emergency Services Networks


   This document adds new assertion values for a Resource Priority
   Header ("rph") claim and a new SIP Priority Header claim ("sph") for
   protection of the "psap-callback" value as part of the "rph" PASSporT
   extension, in support of the security of Emergency Services Networks
   for emergency call origination and callback.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  New Assertion Values for "rph" claim  . . . . . . . . . . . .   3
   4.  The SIP Priority header "sph" claim . . . . . . . . . . . . .   4
   5.  Order of Claim Keys . . . . . . . . . . . . . . . . . . . . .   5
   6.  Compact Form of PASSporT  . . . . . . . . . . . . . . . . . .   5   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  JSON Web Token claims . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Personal Assertion Token (PASSporT) Extension for Resource Priority
   Authorization [RFC8443] extended the Personal Assertion Token
   (PASSporT) 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 [RFC4412].  [I-D.rosen-stir-emergency-calls]
   introduces the need and justification for the protection of both the
   SIP "Resource-Priority" and "Priority" header fields, used for
   categorizing the priority use of the call in the telephone network,
   specifically for emergency calls.

   Compromise of the SIP "Resource-Priority" or "Priority" header fields
   could lead to misuse of network resources (i.e., during congestion
   scenarios), impacting the application services supported using the
   SIP "Resource-Priority" header field and the handling of Public
   Saftey Answering Point (PSAP) callbacks.

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

   This document adds new "auth" array key values for a Resource
   Priority Header ("rph") claim defined in [RFC8443], in support of
   Emergency Services Networks for emergency call origination and
   callback.  This document additionally defines a new PASSporT claim,
   "sph", including protection of the SIP Priority header for the
   indication of an emergency service call-back assigned the value
   "psap-callback" as defined in [RFC7090].  The use of the newly
   defined claim and key values corresponding to the SIP 'Resource-
   Priority' and 'Priority' header fields for emergency services is
   introduced in [I-D.rosen-stir-emergency-calls] but otherwise out-of-
   scope of this document.  In addition, the PASSPorT claims and values
   defined in this document are intended for use in environments where
   there are means to verify that the signer of the SIP 'Resource-
   Priority' and 'Priority' header fields is authoritative.

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.

3.  New Assertion Values for "rph" claim

   This specification defines the ability to sign the SIP Resource-
   Priority Header field namespace for local emergency communications
   defined in [RFC7135] and represented by the string "esnet.x" where x
   is the priority-level allowed in the esnet namespace.  As of the
   writing of this specification the priority-level is between 0 and 4,
   but may be extended by future specifications.

   Similar to the values allowed by [RFC8443] for the "auth" JSON object
   key inside the "rph" claim, the string "esnet.x" with the appropriate
   value should be used when resource priority is required for local
   emergency communications corresponding and exactly matching the SIP
   Resource-Priority header string representing the namespace invoked in
   the call.

   When using "esnet.x" as the "auth" assertion value in emergency
   service destined calls, the "orig" claim of the PASSporT MUST
   represent the calling party number that initiates the call to
   emergency services.  The "dest" claim MUST either be a country or
   region specific dial string (e.g., "911" for North America or "112"
   GSM defined string used in Europe and other countries) or
   "urn:service:sos" as defined in [RFC5031], representing the emergency
   services destination of the call.

   The following is an example of an "rph" claim for SIP 'Resource-
   Priority' header field with an "esnet.1" assertion:


   For emergency services callbacks, the "orig" claim of the "rph"
   PASSporT MUST represent the Public Saftey Answering Point (PSAP)
   telephone number.  The "dest" claim MUST be the telephone number
   representing the original calling party of the emergency service call
   that is being called back.

   The following is an example of an "rph" claim for SIP 'Resource-
   Priority' header field with a "esnet.0" assertion:


   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, the intermediaries must generate a new "rph" header and sign
   the claim with their own authority.

4.  The SIP Priority header "sph" claim

   As defined in [RFC7090] the SIP Priority header may be set to the
   value "psap-callback" for emergency services callback calls.  Because
   some SIP networks may act on this value and provide priority or other
   special routing based on this value, it is important to protect and
   validate the authoritative use associated with it.

   Therefore, we define a new claim key as part of the "rph" PASSporT,
   "sph", which
   "sph".  This is an optional claim that MUST only be used only for with an
   "auth" claim with an "esnet.x" value indicating an authorized
   emergency callbacks callback call and
   correspond corresponding to a SIP Priority header
   with the value "psap-callback".

   The value of the "sph" claim key should only be "psap-callback" to which
   MUST match the SIP Priority header field value for authorized
   emergency services callbacks.  If the value is anything other than
   "psap-callback", the PASSporT validation MUST be considered a failure

   Note: Because the intended use of this specification is only for
   emergency services, there is also an explicit assumption that the
   signer of the "rph" PASSporT can authoritatively represent both the
   content of the Resource Priority Header and Priority Header
   information associated specifically with a emergency services
   callback case where both could exist.  This document is not intended
   to be a general mechanism for protecting SIP Priority Header fields,
   this could be accomplished as part of future work with a new PASSporT
   extension or new claim added to either an existing PASSporT or
   PASSporT extension usage.

   The following is an example of an "sph" claim for SIP 'Priority'
   header field with the value "psap-callback":


5.  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,

   o  dest

   o  iat

   o  orig

   o  rph
   o  sph

6.  Compact Form of PASSporT

   The use of the compact form of PASSporT is not specified in this
   document or recommended for 'rph' PASSporTs.

7.  Acknowledgements

   The authors would like to thank Brian Rosen, Terry Reese, and Jon
   Peterson for helpful suggestions, comments, and corrections.

8.  IANA Considerations

8.1.  JSON Web Token claims

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

   Claim Name: "sph"

   Claim Description: SIP Priority header field

   Change Controller: IESG

   Specification Document(s): [RFCThis]

9.  Security Considerations

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

10.  References

10.1.  Normative References

              Rosen, B., "Non-Interactive Emergency Calls", draft-rosen-
              stir-emergency-calls-00 (work in progress), March 2020.

   [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,

   [RFC5031]  Schulzrinne, H., "A Uniform Resource Name (URN) for
              Emergency and Other Well-Known Services", RFC 5031,
              DOI 10.17487/RFC5031, January 2008,

   [RFC7090]  Schulzrinne, H., Tschofenig, H., Holmberg, C., and M.
              Patel, "Public Safety Answering Point (PSAP) Callback",
              RFC 7090, DOI 10.17487/RFC7090, April 2014,

   [RFC7135]  Polk, J., "Registering a SIP Resource Priority Header
              Field Namespace for Local Emergency Communications",
              RFC 7135, DOI 10.17487/RFC7135, May 2014,

   [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,

   [RFC8443]  Singh, R., Dolly, M., Das, S., and A. Nguyen, "Personal
              Assertion Token (PASSporT) Extension for Resource Priority
              Authorization", RFC 8443, DOI 10.17487/RFC8443, August
              2018, <>.

10.2.  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,

   [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,

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,

   [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

   Martin Dolly


   Chris Wendt
   Comcast Technology Center
   Philadelphia, PA  19103