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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Peterson 3 Internet-Draft Neustar 4 Intended status: Standards Track S. Turner 5 Expires: January 6, 2016 IECA 6 July 5, 2015 8 Secure Telephone Identity Credentials: Certificates 9 draft-ietf-stir-certificates-02.txt 11 Abstract 13 In order to prove ownership of telephone numbers on the Internet, 14 some kind of public infrastructure needs to exist that binds 15 cryptographic keys to authority over telephone numbers. This 16 document describes a certificate-based credential system for 17 telephone numbers, which could be used as a part of a broader 18 architecture for managing telephone numbers as identities in 19 protocols like SIP. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on January 6, 2016. 38 Copyright Notice 40 Copyright (c) 2015 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Enrollment and Authorization . . . . . . . . . . . . . . . . 3 58 3.1. Certificate Scope and Structure . . . . . . . . . . . . . 4 59 3.2. Provisioning Private Keying Material . . . . . . . . . . 5 60 4. Acquiring Credentials to Verify Signatures . . . . . . . . . 5 61 4.1. Verifying Certificate Scope . . . . . . . . . . . . . . . 6 62 4.2. Certificate Freshness and Revocation . . . . . . . . . . 8 63 4.2.1. Choosing a Verification Method . . . . . . . . . . . 8 64 4.2.2. Using OCSP with STIR Certificates . . . . . . . . . . 9 65 4.2.2.1. OCSP Extension Specification . . . . . . . . . . 10 66 4.2.3. Acquiring TN Lists By Reference . . . . . . . . . . . 11 67 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 69 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 70 8. Informative References . . . . . . . . . . . . . . . . . . . 12 71 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 14 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 74 1. Introduction 76 As is discussed in the STIR problem statement 77 [I-D.ietf-stir-problem-statement], the primary enabler of 78 robocalling, vishing, swatting and related attacks is the capability 79 to impersonate a calling party number. The starkest examples of 80 these attacks are cases where automated callees on the PSTN rely on 81 the calling number as a security measure, for example to access a 82 voicemail system. Robocallers use impersonation as a means of 83 obscuring identity; while robocallers can, in the ordinary PSTN, 84 block (that is, withhold) their caller identity, callees are less 85 likely to pick up calls from blocked identities, and therefore 86 appearing to calling from some number, any number, is preferable. 87 Robocallers however prefer not to call from a number that can trace 88 back to the robocaller, and therefore they impersonate numbers that 89 are not assigned to them. 91 One of the most important components of a system to prevent 92 impersonation is an authority responsible for issuing credentials to 93 parties who control telephone numbers. With these credentials, 94 parties can prove that they are in fact authorized to use telephony 95 numbers, and thus distinguish themselves from impersonators unable to 96 present credentials. This document describes a credential system for 97 telephone numbers based on X.509 version 3 certificates in accordance 98 with [RFC5280]. While telephone numbers have long been a part of the 99 X.509 standard, the certificates described in this document may 100 contain telephone number blocks or ranges, and accordingly it uses an 101 alternate syntax. 103 In the STIR in-band architecture, two basic types of entities need 104 access to these credentials: authentication services, and 105 verification services (or verifiers); see [I-D.ietf-stir-rfc4474bis]. 106 An authentication service must be operated by an entity enrolled with 107 the certification authority (see Section 3), whereas a verifier need 108 only trust the root certificate of the authority, and have a means to 109 acquire and validate certificates. 111 This document attempts to specify only the basic elements necessary 112 for this architecture. Only through deployment experience will it be 113 possible to decide directions for future work. 115 2. Terminology 117 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 118 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 119 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 120 described in RFC 2119 [RFC2119] and RFC 6919 [RFC6919]. 122 3. Enrollment and Authorization 124 This document assumes a threefold model for certificate enrollment. 126 The first enrollment model is one where the certification authority 127 acts in concert with national numbering authorities to issue 128 credentials to those parties to whom numbers are assigned. In the 129 United States, for example, telephone number blocks are assigned to 130 Local Exchange Carriers (LECs) by the North American Numbering Plan 131 Administrator (NANPA), who is in turn directed by the national 132 regulator. LECs may also receive numbers in smaller allocations, 133 through number pooling, or via an individual assignment through 134 number portability. LECs assign numbers to customers, who may be 135 private individuals or organizations - and organizations take 136 responsibility for assigning numbers within their own enterprise. 138 The second enrollment model is one where a certification authority 139 requires that an entity prove control by means of some sort of test. 140 For example, an authority might send a text message to a telephone 141 number containing a URL (which might be dereferenced by the 142 recipient) as a means of verifying that a user has control of 143 terminal corresponding to that number. Checks of this form are 144 frequently used in commercial systems today to validate telephone 145 numbers provided by users. This is comparable to existing enrollment 146 systems used by some certificate authorities for issuing S/MIME 147 credentials for email by verifying that the party applying for a 148 credential receives mail at the email address in question. 150 The third enrollment model is delegation: that is, the holder of a 151 certificate (assigned by either of the two methods above) may 152 delegate some or all of their authority to another party. In some 153 cases, multiple levels of delegation could occur: a LEC, for example, 154 might delegate authority to customer organization for a block of 100 155 numbers, and the organization might in turn delegate authority for a 156 particular number to an individual employee. This is analogous to 157 delegation of organizational identities in traditional hierarchical 158 Public Key Infrastructures (PKIs) who use the name constraints 159 extension [RFC5280]; the root CA delegates names in sales to the 160 sales department CA, names in development to the development CA, etc. 161 As lengthy certificate delegation chains are brittle, however, and 162 can cause delays in the verification process, this document considers 163 optimizations to reduce the complexity of verification. 165 [TBD] Future versions of this specification may address adding a 166 level of assurance indication to certificates to differentiate those 167 enrolled from proof-of-possession versus delegation. 169 [TBD] Future versions of this specification may also discuss methods 170 of partial delegation, where certificate holders delegate only part 171 of their authority. For example, individual assignees may want to 172 delegate to a service authority for text messages associated with 173 their telephone number, but not for other functions. 175 3.1. Certificate Scope and Structure 177 The subjects of telephone number certificates are the administrative 178 entities to whom numbers are assigned or delegated. For example, a 179 LEC might hold a certificate for a range of telephone numbers. 181 [TBD - what if the subject is considered a privacy leak?] 183 This specification places no limits on the number of telephone 184 numbers that can be associated with any given certificate. Some 185 service providers may be assigned millions of numbers, and may wish 186 to have a single certificate that is capable of signing for any one 187 of those numbers. Others may wish to compartmentalize authority over 188 subsets of the numbers they control. 190 Moreover, service providers may wish to have multiple certificates 191 with the same scope of authority. For example, a service provider 192 with several regional gateway systems may want each system to be 193 capable of signing for each of their numbers, but not want to have 194 each system share the same private key. 196 The set of telephone numbers for which a particular certificate is 197 valid is expressed in the certificate through a certificate 198 extension; the certificate's extensibility mechanism is defined in 199 [RFC5280] but the telephone number authorization extension is defined 200 in this document. 202 3.2. Provisioning Private Keying Material 204 In order for authentication services to sign calls via the procedures 205 described in [I-D.ietf-stir-rfc4474bis], they must possess a private 206 key corresponding to a certificate with authority over the calling 207 number. This specification does not require that any particular 208 entity sign requests, only that it be an entity with an appropriate 209 private key; the authentication service role may be instantiated by 210 any entity in a SIP network. For a certificate granting authority 211 only over a particular number which has been issued to an end user, 212 for example, an end user device might hold the private key and 213 generate the signature. In the case of a service provider with 214 authority over large blocks of numbers, an intermediary might hold 215 the private key and sign calls. 217 The specification recommends distribution of private keys through 218 PKCS#8 objects signed by a trusted entity, for example through the 219 CMS package specified in [RFC5958]. 221 4. Acquiring Credentials to Verify Signatures 223 This specification documents multiple ways that a verifier can gain 224 access to the credentials needed to verify a request. As the 225 validity of certificates does not depend on the circumstances of 226 their acquisition, there is no need to standardize any single 227 mechanism for this purpose. All entities that comply with 228 [I-D.ietf-stir-rfc4474bis] necessarily support SIP, and consequently 229 SIP itself can serve as a way to acquire certificates. This specific 230 does allow delivery through alternate means as well. 232 The simplest way for a verifier to acquire the certificate needed to 233 verify a signature is for the certificate be conveyed along with the 234 signature itself. In SIP, for example, a certificate could be 235 carried in a multipart MIME body [RFC2046], and the URI in the 236 Identity-Info header could specify that body with a CID URI 237 [RFC2392]. However, in many environments this is not feasible due to 238 message size restrictions or lack of necessary support for multipart 239 MIME. 241 Alternatively, the Identity-Info header of a SIP request may contain 242 a URI that the verifier dereferences with a network call. 243 Implementations of this specification are required to support the use 244 of SIP for this function (via the SUBSCRIBE/NOTIFY mechanism), as 245 well as HTTP, via the Enrollment over Secure Transport mechanisms 246 described in RFC 7030 [RFC7030]. 248 A verifier can however have access to a service that grants access to 249 certificates for a particular telephone number. Note however that 250 there may be multiple valid certificates that can sign a call setup 251 request for a telephone number, and that as a consequence, there 252 needs to be some discriminator that the signer uses to identify their 253 credentials. The Identity-Info header itself can serve as such a 254 discriminator. 256 4.1. Verifying Certificate Scope 258 The subjects of these certificates are the administrative entities to 259 whom numbers are assigned or delegated. When a verifier is 260 validating a caller's identity, local policy always determines the 261 circumstances under which any particular subject may be trusted, but 262 for the purpose of validating a caller's identity, this certificate 263 extension establishes whether or not a signer is authorized to sign 264 for a particular number. 266 The Telephony Number (TN) Authorization List certificate extension is 267 identified by the following object identifier: 269 id-ce-TNAuthList OBJECT IDENTIFIER ::= { TBD } 271 The TN Authorization List certificate extension has the following 272 syntax: 274 TNAuthorizationList ::= SEQUENCE SIZE (1..MAX) OF TNAuthorization 276 TNAuthorization ::= SEQUENCE SIZE (1..MAX) OF TNEntry 278 TNEntry ::= CHOICE { 280 spid ServiceProviderIdentifierList, 282 range TelephoneNumberRange, 284 one E164Number } 286 ServiceProviderIdentifierList ::= SEQUENCE SIZE (1..3) OF 288 OCTET STRING 290 -- When all three are present: SPID, Alt SPID, and Last Alt SPID 292 TelephoneNumberRange ::= SEQUENCE { 294 start E164Number, 296 count INTEGER } 298 E164Number ::= IA5String (SIZE (1..15)) (FROM ("0123456789")) 300 [TBD- do we really need to do IA5String? The alternative would be 301 UTF8String, e.g.: UTF8String (SIZE (1..15)) (FROM ("0123456789")) ] 303 The TN Authorization List certificate extension indicates the 304 authorized phone numbers for the call setup signer. It indicates one 305 or more blocks of telephone number entries that have been authorized 306 for use by the call setup signer. There are three ways to identify 307 the block: 1) a Service Provider Identifier (SPID) can be used to 308 indirectly name all of the telephone numbers associated with that 309 service provider, 2) telephone numbers can be listed in a range, and 310 3) a single telephone number can be listed. 312 Note that because large-scale service providers may want to associate 313 many numbers, possibly millions of numbers, with a particular 314 certificate, optimizations are required for those cases to prevent 315 certificate size from becoming unmanageable. In these cases, the TN 316 Authorization List may be given by reference rather than by value, 317 through the presence of a separate certificate extension that permits 318 verifiers to either securely download the list of numbers associated 319 with a certificate, or to verify that a single number is under the 320 authority of this certificate. This optimization will be detailed in 321 future version of this specification. 323 4.2. Certificate Freshness and Revocation 325 The problem of certificate freshness gains a new wrinkle in the 326 telephone number context, because verifiers must establish not only 327 that a certificate remains valid, but also that the certificate's 328 scope contains the telephone number that the verifier is validating. 329 Dynamic changes to number assignments can occur due to number 330 portability, for example. So even if a verifier has a valid cached 331 certificate for a telephone number (or a range containing the 332 number), the verifier must determine that the entity that signed is 333 still a proper authority for that number. 335 To verify the status of the certificate, the verifier needs the 336 certificate, which is included with the call, and then would need to 337 either: 339 Rely on short-lived certificates and not check the certificate's 340 status, or 342 Rely on status information from the authority 344 The tradeoff between short lived certificates and using status 345 information is the former's burden is on the front end (i.e., 346 enrollment) and the latter's burden is on the back end (i.e., 347 verification). Both impact call setup time, but it is assumed that 348 performing enrollment for each call is more of an impact that using 349 status information. This document therefore recommends relying on 350 status information. 352 4.2.1. Choosing a Verification Method 354 There are three common certificate verification mechanisms employed 355 by CAs: 357 Certificate Revocation Lists (CRLs) [RFC5280] 359 Online Certificate Status Protocol (OCSP) [RFC6960], and 361 Server-based Certificate Validation Protocol (SCVP) [RFC5055]. 363 When relying on status information, the verifier needs to obtain the 364 status information - but before that can happen, the verifier needs 365 to know where to locate it. Placing the location of the status 366 information in the certificate makes the certificate larger, but it 367 eases the client workload. The CRL Distribution Point certificate 368 extension includes the location of the CRL and the Authority 369 Information Access certificate extension includes the location of 370 OCSP and/or SCVP servers; both of these extensions are defined in 371 [RFC5280]. In all cases, the status information location is provided 372 in the form of an URI. 374 CRLs are an obviously attractive solution because they are supported 375 by every CA. CRLs have a reputation of being quite large (10s of 376 MBytes), because CAs maintain and issue one monolithic CRL with all 377 of their revoked certificates, but CRLs do support a variety of 378 mechanisms to scope the size of the CRLs based on revocation reasons 379 (e.g., key compromise vs CA compromise), user certificates only, and 380 CA certificates only as well as just operationally deciding to keep 381 the CRLs small. However, scoping the CRL introduces other issues 382 (i.e., does the RP have all of the CRL partitions). 384 CAs in the STIR architecture will likely all create CRLs for audit 385 purposes, but it NOT RECOMMENDED that they be relying upon for status 386 information. Instead, one of the two "online" options is preferred. 387 Between the two, OCSP is much more widely deployed and this document 388 therefore recommends the use of OCSP in high-volume environments for 389 validating the freshness of certificates, based on [RFC6960], 390 incorporating some (but not all) of the optimizations of [RFC5019]. 392 4.2.2. Using OCSP with STIR Certificates 394 Certificates compliant with this specification therefore SHOULD 395 include a URL pointing to an OCSP service in the Authority 396 Information Access (AIA) certificate extension, via the "id-ad-ocsp" 397 accessMethod specified in [RFC5280]. Baseline OCSP however supports 398 only three possible response values: good, revoked, or unknown. With 399 some extension, OCSP would not indicate whether the certificate is 400 authorized for a particular telephone number that the verifier is 401 validating. 403 [TBD] What would happen in the unknown case? Can we profile OCSP 404 usage so that unknown is never returned for our extension? 406 At a high level, there are two ways that a client might pose this 407 authorization question: 409 For this certificate, is the following number currently in its 410 scope of validity? 411 What are all the telephone numbers associated with this 412 certificate, or this certificate subject? 414 Only the former lends itself to piggybacking on the OCSP status 415 mechanism; since the verifier is already asking an authority about 416 the certificate's status, why not reuse that mechanism, instead of 417 creating a new service that requires additional round trips? Like 418 most PKIX-developed protocols, OCSP is extensible; OCSP supports 419 request extensions (including sending multiple requests at once) and 420 per-request extensions. It seems unlikely that the verifier will be 421 requesting authorization checks on multiple telephone numbers in one 422 request, so a per-request extension is what is needed. 424 [TBD] HVE OCSP requires SHA-1 be used as the hash algorithm, 425 we're6960 obviously going to change this to be SHA-256. 427 The requirement to consult OCSP in real time results in a network 428 round-trip time of day, which is something to consider because it 429 will add to the call setup time. OCSP server implementations 430 commonly pre-generate responses, and to speed up HTTPS connections, 431 servers often provide OCSP responses for each certificate in their 432 hierarchy. If possible, both of these OCSP concepts should be 433 adopted for use with STIR. 435 4.2.2.1. OCSP Extension Specification 437 The extension mechanism for OCSP follows X.509 v3 certificate 438 extensions, and thus requires an OID, a criticality flag, and ASN.1 439 syntax as defined by the OID. The criticality specified here is 440 optional: per [RFC6960] Section 4.4, support for all OCSP extensions 441 is optional. If the OCSP server does not understand the requested 442 extension, it will still provide the baseline validation of the 443 certificate itself. Moreover, in practical STIR deployments, the 444 issuer of the certificate will set the accessLocation for the OCSP 445 AIA extension to point to an OCSP service that supports this 446 extension, so the risk of interoperability failure due to lack of 447 support for this extension is minimal. 449 The OCSP TNQuery extension is included as one of the 450 requestExtensions in requests. It may also appear in the 451 responseExtensions. When an OCSP server includes a number in the 452 responseExtensions, this informs the client that the certificate is 453 still valid for the number that appears in the TNQuery extension 454 field. If the TNQuery is absent from a response to a query 455 containing a TNQuery in its requestExtensions, then the server is not 456 able to validate that the number is still in the scope of authority 457 of the certificate. 459 id-pkix-ocsp-stir-tn OBJECT IDENTIFIER ::= { id-pkix-ocsp TBD } 461 TNQuery ::= E164Number 463 Note that HVE OCSP profile [RFC5019] prohibits the use of per-request 464 extensions. As it is anticipated that STIR will use OCSP in a high- 465 volume environment, many of the optimizations recommended by HVE are 466 desirable for the STIR environment. This document therefore uses 467 these extensions in a baseline OCSP environment with some HVE 468 optimizations. [More TBD] 470 Ideally, once a certificate has been acquired by a verifier, some 471 sort of asynchronous mechanism could notify and update the verifier 472 if the scope of the certificate changes so that verifiers could 473 implement a cache. While not all possible categories of verifiers 474 could implement such behavior, some sort of event-driven notification 475 of certificate status is another potential subject of future work. 476 One potential direction is that a future SIP SUBSCRIBE/NOTIFY-based 477 accessMethod for AIA might be defined (which would also be applicable 478 to the method described in the following section) by some future 479 specification. 481 4.2.3. Acquiring TN Lists By Reference 483 Acquiring a list of the telephone numbers associated with a 484 certificate or its subject lends itself to an application-layer 485 query/response interaction outside of OCSP, one which could be 486 initiated through a separate URI included in the certificate. The 487 AIA extension (see [RFC5280]) supports such a mechanism: it 488 designates an OID to identify the accessMethod and an accessLocation, 489 which would most likely be a URI. A verifier would then follow the 490 URI to ascertain whether the list of TNs authorized for use by the 491 caller. 493 HTTPS is the most obvious candidate for a protocol to be used for 494 fetching the list of telephone number associated with a particular 495 certificate. This document defines a new AIA accessMethod, called 496 "id-ad-stir-tn", which uses the following AIA OID: 498 id-ad-stir-tn OBJECT IDENTIFIER ::= { id-ad TBD } 500 When the "id-ad-stir-tn" accessMethod is used, the accessLocation 501 MUST be an HTTPS URI. The document returned by dereferencing that 502 URI will contain the complete TN Authorization List (see Section 4.1) 503 for the certificate. 505 Delivering the entire list of telephone numbers associated with a 506 particular certificate will divulge to STIR verifiers information 507 about telephone numbers other than the one associated with the 508 particular call that the verifier is checking. In some environments, 509 where STIR verifiers handle a high volume of calls, maintaining an 510 up-to-date and complete cache for the numbers associated with crucial 511 certificate holders could give an important boost to performance. 513 5. Acknowledgments 515 Russ Housley, Brian Rosen, Cullen Jennings and Eric Rescorla provided 516 key input to the discussions leading to this document. 518 6. IANA Considerations 520 This document makes use of object identifiers for the TN Certificate 521 Extension defined in Section 4.1, TN-HVE OCSP extension in 522 Section 4.2.2.1, and the TN by reference AIA access descriptor 523 defined in Section 4.2.3. It therefore requests that the IANA make 524 the following assignments: 526 - TN Certificate Extension in the SMI Security for PKIX 527 Certificate Extension registry: http://www.iana.org/assignments/ 528 smi-numbers/smi-numbers.xhtml#smi-numbers-1.3.6.1.5.5.7.1 530 - TN-HVE OCSP extension in the SMI Security for PKIX Online 531 Certificate Status Protocol (OCSP) registry: 532 http://www.iana.org/assignments/smi-numbers/smi-numbers.xhtml#smi- 533 numbers-1.3.6.1.5.5.7.48.1 535 - TNS by reference access descriptor in the SMI Security for PKIX 536 Access Descriptor registry: http://www.iana.org/assignments/smi- 537 numbers/smi-numbers.xhtml#smi-numbers-1.3.6.1.5.5.7.48 539 7. Security Considerations 541 This document is entirely about security. For further information on 542 certificate security and practices, see RFC 3280 [RFC3280], in 543 particular its Security Considerations. 545 8. Informative References 547 [I-D.ietf-stir-problem-statement] 548 Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure 549 Telephone Identity Problem Statement and Requirements", 550 draft-ietf-stir-problem-statement-05 (work in progress), 551 May 2014. 553 [I-D.ietf-stir-rfc4474bis] 554 Peterson, J., Jennings, C., and E. Rescorla, 555 "Authenticated Identity Management in the Session 556 Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-03 557 (work in progress), March 2015. 559 [I-D.peterson-sipping-retarget] 560 Peterson, J., "Retargeting and Security in SIP: A 561 Framework and Requirements", draft-peterson-sipping- 562 retarget-00 (work in progress), February 2005. 564 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 565 Extensions (MIME) Part Two: Media Types", RFC 2046, 566 November 1996. 568 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 569 Requirement Levels", BCP 14, RFC 2119, March 1997. 571 [RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource 572 Locators", RFC 2392, August 1998. 574 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 576 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 577 A., Peterson, J., Sparks, R., Handley, M., and E. 578 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 579 June 2002. 581 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 582 Protocol (SIP): Locating SIP Servers", RFC 3263, June 583 2002. 585 [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet 586 X.509 Public Key Infrastructure Certificate and 587 Certificate Revocation List (CRL) Profile", RFC 3280, 588 April 2002. 590 [RFC5019] Deacon, A. and R. Hurst, "The Lightweight Online 591 Certificate Status Protocol (OCSP) Profile for High-Volume 592 Environments", RFC 5019, September 2007. 594 [RFC5055] Freeman, T., Housley, R., Malpani, A., Cooper, D., and W. 595 Polk, "Server-Based Certificate Validation Protocol 596 (SCVP)", RFC 5055, December 2007. 598 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 599 Housley, R., and W. Polk, "Internet X.509 Public Key 600 Infrastructure Certificate and Certificate Revocation List 601 (CRL) Profile", RFC 5280, May 2008. 603 [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, August 604 2010. 606 [RFC6919] Barnes, R., Kent, S., and E. Rescorla, "Further Key Words 607 for Use in RFCs to Indicate Requirement Levels", RFC 6919, 608 April 2013. 610 [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., 611 Galperin, S., and C. Adams, "X.509 Internet Public Key 612 Infrastructure Online Certificate Status Protocol - OCSP", 613 RFC 6960, June 2013. 615 [RFC7030] Pritikin, M., Yee, P., and D. Harkins, "Enrollment over 616 Secure Transport", RFC 7030, October 2013. 618 [RFC7299] Housley, R., "Object Identifier Registry for the PKIX 619 Working Group", RFC 7299, July 2014. 621 [X.680] USC/Information Sciences Institute, "Information 622 Technology - Abstract Syntax Notation One.", ITU-T X.680, 623 ISO/IEC 8824-1:2002, 2002. 625 [X.681] USC/Information Sciences Institute, "Information 626 Technology - Abstract Syntax Notation One: Information 627 Object Specification", ITU-T X.681, ISO/IEC 8824-2:2002, 628 2002. 630 [X.682] USC/Information Sciences Institute, "Information 631 Technology - Abstract Syntax Notation One: Constraint 632 Specification", ITU-T X.682, ISO/IEC 8824-3:2002, 2002. 634 [X.683] USC/Information Sciences Institute, "Information 635 Technology - Abstract Syntax Notation One: 636 Parameterization of ASN.1 Specifications", ITU-T X.683, 637 ISO/IEC 8824-4:2002, 2002. 639 Appendix A. ASN.1 Module 641 This appendix provides the normative ASN.1 [X.680] definitions for 642 the structures described in this specification using ASN.1, as 643 defined in [X.680] through [X.683]. 645 TBD 647 Authors' Addresses 649 Jon Peterson 650 Neustar, Inc. 651 1800 Sutter St Suite 570 652 Concord, CA 94520 653 US 655 Email: jon.peterson@neustar.biz 657 Sean Turner 658 IECA, Inc. 659 3057 Nutley Street, Suite 106 660 Farifax, VA 22031 661 US 663 Email: turners@ieca.com