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Wendt 5 Expires: May 6, 2021 Comcast 6 November 02, 2020 8 Assertion Values for a Resource Priority Header Claim and a SIP Priority 9 Header Claim in Support of Emergency Services Networks 10 draft-ietf-stir-rph-emergency-services-04 12 Abstract 14 This document adds new assertion values for a Resource Priority 15 Header ("rph") claim and a new SIP Priority Header claim ("sph") for 16 protection of the "psap-callback" value as part of the "rph" PASSporT 17 extension, in support of the security of Emergency Services Networks 18 for emergency call origination and callback. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on May 6, 2021. 37 Copyright Notice 39 Copyright (c) 2020 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3. New Assertion Values for "rph" claim . . . . . . . . . . . . 3 57 4. The SIP Priority header "sph" claim . . . . . . . . . . . . . 4 58 5. Order of Claim Keys . . . . . . . . . . . . . . . . . . . . . 5 59 6. Compact Form of PASSporT . . . . . . . . . . . . . . . . . . 6 60 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 61 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 62 8.1. JSON Web Token claims . . . . . . . . . . . . . . . . . . 6 63 9. Security Considerations . . . . . . . . . . . . . . . . . . . 6 64 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 65 10.1. Normative References . . . . . . . . . . . . . . . . . . 6 66 10.2. Informative References . . . . . . . . . . . . . . . . . 7 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 69 1. Introduction 71 Personal Assertion Token (PASSporT) Extension for Resource Priority 72 Authorization [RFC8443] extended the Personal Assertion Token 73 (PASSporT) specification defined in [RFC8225] to allow the inclusion 74 of cryptographically signed assertions of authorization for the 75 values populated in the Session Initiation Protocol (SIP) "Resource- 76 Priority" header field [RFC4412]. [I-D.rosen-stir-emergency-calls] 77 introduces the need and justification for the protection of both the 78 SIP "Resource-Priority" and "Priority" header fields, used for 79 categorizing the priority use of the call in the telephone network, 80 specifically for emergency calls. 82 Compromise of the SIP "Resource-Priority" or "Priority" header fields 83 could lead to misuse of network resources (i.e., during congestion 84 scenarios), impacting the application services supported using the 85 SIP "Resource-Priority" header field and the handling of Public 86 Saftey Answering Point (PSAP) callbacks. 88 [RFC8225] allows extensions by which an authority on the originating 89 side verifying the authorization of a particular communication for 90 the SIP "Resource-Priority" header field or the SIP "Priority" header 91 field can use PASSPorT claims to cryptographically sign the 92 information associated with either the SIP "Resource-Priority" or 93 "Priority" header field and convey assertion of those values by the 94 signing party authorization. A signed SIP "Resource-Priority" or 95 "Priority" header field will allow a receiving entity (including 96 entities located in different network domains/boundaries) to verify 97 the validity of assertions to act on the information with confidence 98 that the information has not been spoofed or compromised. 100 This document adds new "auth" array key values for a Resource 101 Priority Header ("rph") claim defined in [RFC8443], in support of 102 Emergency Services Networks for emergency call origination and 103 callback. This document additionally defines a new PASSporT claim, 104 "sph", including protection of the SIP Priority header for the 105 indication of an emergency service call-back assigned the value 106 "psap-callback" as defined in [RFC7090]. The use of the newly 107 defined claim and key values corresponding to the SIP 'Resource- 108 Priority' and 'Priority' header fields for emergency services is 109 introduced in [I-D.rosen-stir-emergency-calls] but otherwise out-of- 110 scope of this document. In addition, the PASSPorT claims and values 111 defined in this document are intended for use in environments where 112 there are means to verify that the signer of the SIP 'Resource- 113 Priority' and 'Priority' header fields is authoritative. 115 2. Terminology 117 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 118 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 119 "OPTIONAL" in this document are to be interpreted as described in BCP 120 14 [RFC2119] [RFC8174] when, and only when, they appear in all 121 capitals, as shown here. 123 3. New Assertion Values for "rph" claim 125 This specification defines the ability to sign the SIP Resource- 126 Priority Header field namespace for local emergency communications 127 defined in [RFC7135] and represented by the string "esnet.x" where x 128 is the priority-level allowed in the esnet namespace. As of the 129 writing of this specification the priority-level is between 0 and 4, 130 but may be extended by future specifications. 132 Similar to the values allowed by [RFC8443] for the "auth" JSON object 133 key inside the "rph" claim, the string "esnet.x" with the appropriate 134 value should be used when resource priority is required for local 135 emergency communications corresponding and exactly matching the SIP 136 Resource-Priority header string representing the namespace invoked in 137 the call. 139 When using "esnet.x" as the "auth" assertion value in emergency 140 service destined calls, the "orig" claim of the PASSporT MUST 141 represent the calling party number that initiates the call to 142 emergency services. The "dest" claim MUST either be a country or 143 region specific dial string (e.g., "911" for North America or "112" 144 GSM defined string used in Europe and other countries) or 145 "urn:service:sos" as defined in [RFC5031], representing the emergency 146 services destination of the call. 148 The following is an example of an "rph" claim for SIP 'Resource- 149 Priority' header field with an "esnet.1" assertion: 151 { 152 "orig":{"tn":"12155551212"}, 153 "dest":{"uri":["urn:service:sos"]}, 154 "iat":1443208345, 155 "rph":{"auth":["esnet.1"]} 156 } 158 For emergency services callbacks, the "orig" claim of the "rph" 159 PASSporT MUST represent the Public Saftey Answering Point (PSAP) 160 telephone number. The "dest" claim MUST be the telephone number 161 representing the original calling party of the emergency service call 162 that is being called back. 164 The following is an example of an "rph" claim for SIP 'Resource- 165 Priority' header field with a "esnet.0" assertion: 167 { 168 "orig":{"tn":"12155551213"}, 169 "dest":{"tn":["12155551212"]}, 170 "iat":1443208345, 171 "rph":{"auth":["esnet.0"]} 172 } 174 After the header and claims PASSporT objects have been constructed, 175 their signature is generated normally per the guidance in [RFC8225] 176 using the full form of PASSPorT. The credentials (i.e., Certificate) 177 used to create the signature must have authority over the namespace 178 of the "rph" claim, and there is only one authority per claim. The 179 authority MUST use its credentials associated with the specific 180 service supported by the resource priority namespace in the claim. 181 If r-values are added or dropped by the intermediaries along the 182 path, the intermediaries must generate a new "rph" header and sign 183 the claim with their own authority. 185 4. The SIP Priority header "sph" claim 187 As defined in [RFC7090] the SIP Priority header may be set to the 188 value "psap-callback" for emergency services callback calls. Because 189 some SIP networks may act on this value and provide priority or other 190 special routing based on this value, it is important to protect and 191 validate the authoritative use associated with it. 193 Therefore, we define a new claim key as part of the "rph" PASSporT, 194 "sph". This is an optional claim that MUST only be used only with an 195 "auth" claim with an "esnet.x" value indicating an authorized 196 emergency callback call and corresponding to a SIP Priority header 197 with the value "psap-callback". 199 The value of the "sph" claim key should only be "psap-callback" which 200 MUST match the SIP Priority header field value for authorized 201 emergency services callbacks. If the value is anything other than 202 "psap-callback", the PASSporT validation MUST be considered a failure 203 case. 205 Note: Because the intended use of this specification is only for 206 emergency services, there is also an explicit assumption that the 207 signer of the "rph" PASSporT can authoritatively represent both the 208 content of the Resource Priority Header and Priority Header 209 information associated specifically with a emergency services 210 callback case where both could exist. This document is not intended 211 to be a general mechanism for protecting SIP Priority Header fields, 212 this could be accomplished as part of future work with a new PASSporT 213 extension or new claim added to either an existing PASSporT or 214 PASSporT extension usage. 216 The following is an example of an "sph" claim for SIP 'Priority' 217 header field with the value "psap-callback": 219 { 220 "orig":{"tn":"12155551213"}, 221 "dest":{"tn":["12155551212"]}, 222 "iat":1443208345, 223 "rph":{"auth":["esnet.0"]}, 224 "sph":"psap-callback" 225 } 227 5. Order of Claim Keys 229 The order of the claim keys MUST follow the rules of [RFC8225] 230 Section 9; the claim keys MUST appear in lexicographic order. 231 Therefore, the claim keys discussed in this document appear in the 232 PASSporT Payload in the following order, 234 o dest 236 o iat 238 o orig 240 o rph 241 o sph 243 6. Compact Form of PASSporT 245 The use of the compact form of PASSporT is not specified in this 246 document or recommended for 'rph' PASSporTs. 248 7. Acknowledgements 250 The authors would like to thank Brian Rosen, Terry Reese, and Jon 251 Peterson for helpful suggestions, comments, and corrections. 253 8. IANA Considerations 255 8.1. JSON Web Token claims 257 This specification requests that the IANA add one new claim to the 258 JSON Web Token Claims registry as defined in [RFC7519]. 260 Claim Name: "sph" 262 Claim Description: SIP Priority header field 264 Change Controller: IESG 266 Specification Document(s): [RFCThis] 268 9. Security Considerations 270 The security considerations discussed in [RFC8224], Section 12, are 271 applicable here. 273 10. References 275 10.1. Normative References 277 [I-D.rosen-stir-emergency-calls] 278 Rosen, B., "Non-Interactive Emergency Calls", draft-rosen- 279 stir-emergency-calls-00 (work in progress), March 2020. 281 [RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource 282 Priority for the Session Initiation Protocol (SIP)", 283 RFC 4412, DOI 10.17487/RFC4412, February 2006, 284 . 286 [RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for 287 Emergency and Other Well-Known Services", RFC 5031, 288 DOI 10.17487/RFC5031, January 2008, 289 . 291 [RFC7090] Schulzrinne, H., Tschofenig, H., Holmberg, C., and M. 292 Patel, "Public Safety Answering Point (PSAP) Callback", 293 RFC 7090, DOI 10.17487/RFC7090, April 2014, 294 . 296 [RFC7135] Polk, J., "Registering a SIP Resource Priority Header 297 Field Namespace for Local Emergency Communications", 298 RFC 7135, DOI 10.17487/RFC7135, May 2014, 299 . 301 [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 302 (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, 303 . 305 [RFC8224] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt, 306 "Authenticated Identity Management in the Session 307 Initiation Protocol (SIP)", RFC 8224, 308 DOI 10.17487/RFC8224, February 2018, 309 . 311 [RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion 312 Token", RFC 8225, DOI 10.17487/RFC8225, February 2018, 313 . 315 [RFC8443] Singh, R., Dolly, M., Das, S., and A. Nguyen, "Personal 316 Assertion Token (PASSporT) Extension for Resource Priority 317 Authorization", RFC 8443, DOI 10.17487/RFC8443, August 318 2018, . 320 10.2. Informative References 322 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 323 Requirement Levels", BCP 14, RFC 2119, 324 DOI 10.17487/RFC2119, March 1997, 325 . 327 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 328 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 329 May 2017, . 331 Authors' Addresses 333 Martin Dolly 334 AT&T 336 Email: md3135@att.com 338 Chris Wendt 339 Comcast 340 Comcast Technology Center 341 Philadelphia, PA 19103 342 USA 344 Email: chris-ietf@chriswendt.net