STIR M. Dolly Internet-Draft AT&T Intended status: Standards Track C. Wendt Expires: September 12, 2021 Comcast March 11, 2021 Assertion Values for a Resource Priority Header Claim and a SIP Priority Header Claim in Support of Emergency Services Networks draft-ietf-stir-rph-emergency-services-07 Abstract 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. 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 https://datatracker.ietf.org/drafts/current/. 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 12, 2021. Copyright Notice Copyright (c) 2021 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 (https://trustee.ietf.org/license-info) in effect on the date of 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 Dolly & Wendt Expires September 12, 2021 [Page 1] Internet-Draft RPH Values for Emergency Services March 2021 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. 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 . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 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 Dolly & Wendt Expires September 12, 2021 [Page 2] Internet-Draft RPH Values for Emergency Services March 2021 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 field 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", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "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, inclusive, but may be extended by future specifications. Similar to the values defined 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 field 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 Dolly & Wendt Expires September 12, 2021 [Page 3] Internet-Draft RPH Values for Emergency Services March 2021 "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: { "dest":{"uri":["urn:service:sos"]}, "iat":1615471428, "orig":{"tn":"12155551212"}, "rph":{"auth":["esnet.1"]} } 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: { "dest":{"tn":["12155551212"]}, "iat":1615471428, "orig":{"tn":"12155551213"}, "rph":{"auth":["esnet.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, the intermediaries must generate a new "rph" identity header and sign the claim with their own authority. 4. The SIP Priority header "sph" claim As defined in [RFC7090] the SIP Priority header field 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. Dolly & Wendt Expires September 12, 2021 [Page 4] Internet-Draft RPH Values for Emergency Services March 2021 Therefore, we define a new claim key as part of the "rph" PASSporT, "sph". This is an optional claim that MUST only be used only with an "auth" claim with an "esnet.x" value indicating an authorized emergency callback call and corresponding to a SIP Priority header field with the value "psap-callback". The value of the "sph" claim key should only be "psap-callback" 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 case. 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 field and Priority Header field 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": { "dest":{"tn":["12155551212"]}, "iat":1615471428, "orig":{"tn":"12155551213"}, "rph":{"auth":["esnet.0"]}, "sph":"psap-callback" } 5. Order of Claim Keys The order of the claim keys MUST follow the rules of [RFC8225] Section 9 which defines the deterministic JSON serialization used for signature generation (and validation); 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 Dolly & Wendt Expires September 12, 2021 [Page 5] Internet-Draft RPH Values for Emergency Services March 2021 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], [RFC8225], and [RFC8443] are applicable here. 10. References 10.1. Normative References [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, . Dolly & Wendt Expires September 12, 2021 [Page 6] Internet-Draft RPH Values for Emergency Services March 2021 [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, . [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 [I-D.rosen-stir-emergency-calls] Rosen, B., "Non-Interactive Emergency Calls", draft-rosen- stir-emergency-calls-00 (work in progress), March 2020. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Dolly & Wendt Expires September 12, 2021 [Page 7] Internet-Draft RPH Values for Emergency Services March 2021 Authors' Addresses Martin Dolly AT&T Email: md3135@att.com Chris Wendt Comcast Comcast Technology Center Philadelphia, PA 19103 USA Email: chris-ietf@chriswendt.net Dolly & Wendt Expires September 12, 2021 [Page 8]