idnits 2.17.1 draft-ietf-acme-authority-token-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (July 2, 2018) is 2119 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'I-D.ietf-acme-service-provider' is defined on line 386, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-acme-star' is defined on line 391, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-stir-passport' is defined on line 413, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-stir-rfc4474bis' is defined on line 418, but no explicit reference was found in the text == Unused Reference: 'RFC7340' is defined on line 435, but no explicit reference was found in the text == Outdated reference: A later version (-18) exists of draft-ietf-acme-acme-12 == Outdated reference: A later version (-11) exists of draft-ietf-acme-star-03 Summary: 0 errors (**), 0 flaws (~~), 9 warnings (==), 1 comment (--). 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: Informational M. Barnes 5 Expires: January 3, 2019 iconectiv 6 D. Hancock 7 C. Wendt 8 Comcast 9 July 2, 2018 11 ACME Challenges Using an Authority Token 12 draft-ietf-acme-authority-token-00.txt 14 Abstract 16 A number of proposed challenges for the Automated Certificate 17 Management Environment (ACME) effectively rely on an external 18 authority issuing a token according to a particular policy. This 19 document specifies a generic Authority Token challenge for ACME which 20 supports subtype claims for different identifiers or namespaces that 21 can be defined separately for specific applications of this Authority 22 Token challenge. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on January 3, 2019. 41 Copyright Notice 43 Copyright (c) 2018 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 3. Challenges for an Authority Token . . . . . . . . . . . . . . 3 61 3.1. Token Type Requirements . . . . . . . . . . . . . . . . . 4 62 3.2. Authority Token Scope . . . . . . . . . . . . . . . . . . 4 63 3.3. Binding Challenges . . . . . . . . . . . . . . . . . . . 5 64 4. Registration . . . . . . . . . . . . . . . . . . . . . . . . 6 65 4.1. 'ATC' Token Type . . . . . . . . . . . . . . . . . . . . 7 66 5. Acquiring a Token . . . . . . . . . . . . . . . . . . . . . . 8 67 5.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 8 68 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 69 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 70 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 71 9. Informative References . . . . . . . . . . . . . . . . . . . 9 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 74 1. Introduction 76 ACME [I-D.ietf-acme-acme] is a mechanism for automating certificate 77 management on the Internet. It enables administrative entities to 78 prove effective control over resources like domain names, and 79 automates the process of generating and issuing certificates. 81 In some cases, proving effective control over an identifier requires 82 an attestation from a third party who has authority over the 83 resource, for example, an external policy administrator for a 84 namespace other than the DNS application ACME was originally designed 85 to support. In order to automate the process of issuing certificates 86 for those resources, this specification defines a generic Authority 87 Token challenge that ACME servers can issue in order to require 88 clients to return such a token. The challenge contains a type 89 indication that tells the client what sort of token it needs to 90 acquire. It is expected that the Authority Token challenge will be 91 usable for a variety of identifier types. 93 For example, the system of 94 [I-D.wendt-acme-authority-token-tnauthlist] provides a mechanism that 95 allows service providers to acquire certificates corresponding to a 96 Service Provider Code (SPC) as defined in 98 [I-D.ietf-stir-certificates] by consulting an external authority 99 responsible for those codes. Furthermore, Communications Service 100 Providers (CSPs) can delegate authority over numbers to their 101 customers, and those CSPs who support ACME can then help customers to 102 acquire certificates for those numbering resources with ACME. This 103 can permit number acquisition flows compatible with those shown in 104 [I-D.ietf-modern-problem-framework]. Another, similar example would 105 a mechanism that permits CSPs to delegate authority for particular 106 telephone numbers to customers, as described in 107 [I-D.ietf-acme-telephone]. 109 2. Terminology 111 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 112 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 113 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 114 described in [RFC2119]. 116 3. Challenges for an Authority Token 118 Proving that a device on the Internet has effective control over a 119 non-Internet resource is not as straightforward as proving control 120 over an Internet resources like a DNS zone or a web page. There has 121 been considerable interest in using ACME to issue certificates 122 associated with telephone numbers and service provider identifiers 123 used in the telephone network, for example. Provided that the issuer 124 of identifiers in a namespace, or someone acting on the issuer's 125 behalf, can implement a service that grants Authority Tokens to the 126 people to whom it has issued identifiers, a generic token could be 127 used as a response to an ACME challenge. This specification, 128 therefore, defines an Authority Token issued by authority over a 129 namespace to an ACME client for delivery to a CA in response to a 130 challenge. Authority over a hierarchical namespace can also be 131 delegated, so that delegates of a root authority can themselves act 132 as Token Authorities for certain types of names. 134 This architecture assumes a trust relationship between CAs and Token 135 Authorities: that CAs are willing to accept the attestation of Token 136 Authorities for particular types of identifiers as sufficient proof 137 to issue a credential. It furthermore assumes that ACME clients have 138 a relationship with Token Authorities which permits them to 139 authenticate and authorize the issuance of Authority Tokens to the 140 proper entities. This ACME challenge has no applicability to 141 identifiers or authorities where those pre-associations cannot be 142 assumed. 144 ACME challenges that support Authority Tokens therefore need to 145 specify the type of token they require; CAs can even provide a hint 146 in their challenges to ACME clients that tells them how to find a 147 Token Authority who can issue tokens for a given namespace. This 148 challenge type thus requires a new "tkauth-type" element, and may 149 optionally supply a "token-authority" designating a location where 150 tokens can be acquired. The set of "tkauth-type" values and the 151 semantic requirements for those tokens are tracked by an IANA 152 registry. 154 3.1. Token Type Requirements 156 The IANA will control a registry of tkauth-types under a policy of 157 Specification Required. In order to register a new tkauth-type, 158 specifications must address the following requirements. 160 While Authority Token types do not need to be specific to a 161 namespace, every token must carry enough information for a CA to 162 determine the name that it will issue a certificate for. Some types 163 of Authority Token types might be reusable for a number of different 164 namespaces; other might be specific to a particular type of name. 165 Therefore, in defining tkauth-types, future specifications must 166 indicate how a token conveys to the CA the name that the Token 167 Authority is attesting that the ACME client controls. 169 In most cases, an ACME client will need a protocol to request and 170 retrieve an Authority Token. The Token Authority will require 171 certain information from an ACME client in order to ascertain that it 172 is the right entity to request a certificate for a particular name. 173 The protocols used to request an Authority Token MUST convey to the 174 Token Authority the identifier type and value from the ACME 175 challenge, as well as the binding (see Section 3.3), and those MUST 176 be reflected in the Authority Token. A baseline mechanism for how 177 the Token Authority authenticates and authorizes ACME clients to 178 receive Authority Tokens is given in Section 5. 180 Because the assignment of resources can change over time, 181 demonstrations of authority must be regularly refreshed. Definitions 182 of a tkauth-type MUST specify how they manage the freshness of 183 authority assignments. Typically, a CA will expect a regular 184 refreshing of the token. 186 3.2. Authority Token Scope 188 An Authority Token is used to answer a challenge from an ACME server, 189 upon a request for the issuance of a certificate. An Token Authority 190 could grant to a client a Token that has the exact same scope as the 191 requested certificate; alternatively, an Authority Token could attest 192 all of resources that the client is eligible to receive certificates 193 for, which could be a superset of the scope of the requested 194 certificate. 196 For example, imagine a case where an Authority for DNS names knows 197 that a client is eligible to receive certificates for "example.com" 198 and "example.net". The client asks an ACME server for a certificate 199 for "example.com", the server directs the client to acquire an 200 Authority Token from the Authority. When the client sends an 201 acquisition request (see Section 5) to the Authority, the Authority 202 could issue a token scoped just to "example.com", or a token that 203 attests the client is eligible to receive certificates for both 204 "example.com" or "example.net". The advantage of the latter is that 205 if, at a later time (but one within the expiry of the JWT), the 206 client wanted to acquire a certificate for "example.net", it would 207 not have to return to the Authority, as the Token effectively pre- 208 authorized the issuance of that certificate. 210 Applications of the Authority Token to different identifier types 211 might require different scopes, so registrations of tkauth-types 212 should be clear if and how a scope greater than that of the requested 213 certificate would be conveyed in a token. 215 3.3. Binding Challenges 217 Applications that use the Authority Token need a way to correlate 218 tokens issued by an Authority with the proper ACME client, to prevent 219 replay or cut-and-paste attacks using a token issued for a different 220 purpose. To mitigate this, Authority Tokens contain a binding signed 221 by an Authority; an ACME server can use the binding to determine that 222 a Token presented by a client was in fact granted by the Authority 223 based on a request from the client, and not from some other entity. 225 Binding an Authority Token to a particular ACME account entails that 226 the Token could be reused up until its expiry for multiple challenges 227 issued by an ACME server. This might be a desirable property when 228 using short-lived certificates, for example, or in any cases where 229 the ACME server issues challenges more frequently that an Authority 230 Token can or should issue tokens, or in cases where the Authority 231 Token scope (see Section 3.2) is broad, so certificates with a more 232 narrow scope may periodically be issued. 234 For some identifier types, it may be more appropriate to bind the 235 Authority Token to a nonce specific to the challenge rather than to 236 an ACME account fingerprint. Any specification of the use of the 237 nonce for this purpose is left to the identifier type profile for the 238 Authority Token. 240 4. Registration 242 This draft registers a tkauth-type of "ATC", for the Authority Token 243 Challenge, a JWT usage which is further documented below. Taking the 244 identifier example of TNAuthList from 245 [I-D.wendt-acme-authority-token-tnauthlist], an ACME for this tkauth- 246 type challenge might for example look as follows: 248 HTTP/1.1 200 OK 249 Content-Type: application/json 250 Link: ;rel="directory" 252 { 253 "status": "pending", 255 "identifier": { 256 "type": "TNAuthList", 257 "value": "F83n2a...avn27DN3==" 258 }, 259 "challenges": [ 260 { 261 "type": "tkauth-01", 262 "tkauth-type": "ATC", 263 "token-authority": "https://authority.example.org/authz", 264 "url": "https://boulder.example.com/authz/asdf/0" 265 "token": "IlirfxKKXAsHtmzK29Pj8A" } 266 ], 267 } 269 Entities receiving this challenge know that they can, as a proof, 270 acquire a ATC token from the designated Token Authority (specified in 271 the "token-authority" field), and that this authority can provide 272 tokens corresponding to the identifier type of "TNAuthList". 274 Once the ATC has been acquired by the ACME Client, it can be posted 275 back to the URL given by the ACME challenge. 277 POST /acme/authz/asdf/0 HTTP/1.1 278 Host: boulder.example.com 279 Content-Type: application/jose+json 281 { 282 "protected": base64url({ 283 "alg": "ES256", 284 "kid": "https://boulder.example.com/acme/reg/asdf", 285 "nonce": "Q_s3MWoqT05TrdkM2MTDcw", 286 "url": "https://boulder.example.com/acme/authz/asdf/0" 287 }), 288 "payload": base64url({ 289 "ATC": "evaGxfADs...62jcerQ" 290 }), 291 "signature": "5wUrDI3eAaV4wl2Rfj3aC0Pp--XB3t4YYuNgacv_D3U" 292 } 294 The "ATC" field in this response contains the Authority Token. 296 4.1. 'ATC' Token Type 298 This specification pre-populates the tkauth-type registry with a type 299 for "ATC". 301 Here the "ATC" tkauth-type signifies a standard JWT token [RFC7519] 302 using a JWS-defined signature string [RFC7515]. This may be used for 303 any number of different identifier types given in ACME challenges. 305 For this ACME Authority Token usage of JWT, the payload of the JWT 306 OPTIONALLY contain an "iss" indicating the Token Authority that 307 generated the token, if the "x5u" element in the header does not 308 already convey that information; typically, this will be the same 309 location that appeared in the "token-authority" field of the ACME 310 challenge. In order to satisfy the requirement for replay prevention 311 the JWT MUST contain a "jti" element, and an "exp" claim. 313 The JWT payload must also contain a new JWT claim, "atc", for 314 Authority Token Challenge, which contains three elements in an array: 315 the identifier type, the identifier value, and the binding. The 316 identifier type and value are those given in the ACME challenge and 317 conveyed to the Token Authority by the ACME client. Again, following 318 the example of [I-D.wendt-acme-authority-token-tnauthlist], this 319 could be the TNAuthList, as defined in [RFC8226], that the Token 320 Authority is attesting. Practically speaking, that may contain a 321 list of Service Provider Code elements, telephone number range 322 elements, and/or individual telephone numbers. For the purposes of 323 the "ATC" tkauth-type, the binding is assumed to be a fingerprint of 324 the ACME credential for the account used to request the certificate, 325 but the specification of how the binding is generated is left to the 326 identifier type profile for the Authority Token. 328 So for example: 330 { "typ":"JWT", 331 "alg":"ES256", 332 "x5u":"https://authority.example.org/cert"} 333 { 334 "iss":"https://authority.example.org/authz", 335 "exp":1300819380, 336 "jti":"id6098364921", 337 "atc":{"TnAuthList","F83n2a...avn27DN3==", 338 "SHA256 56:3E:CF:AE:83:CA:4D:15:B0:29:FF:1B:71:D3:BA:B9:19:81:F8:50: 339 9B:DF:4A:D4:39:72:E2:B1:F0:B9:38:E3"} } 341 5. Acquiring a Token 343 [TBD. Show protocol flow for token acquisition.] 345 5.1. Example 347 [TBD.] 349 6. Acknowledgements 351 We would like to thank you for your contributions to this problem 352 statement and framework. 354 7. IANA Considerations 356 Future versions of this specification will include registrations for 357 the ACME Challenge type registries here. It will also create a 358 registry for "token types" as used in these challenges, following the 359 requirements in Section 3.1, pre-populated with the value for "ATC" 360 per Section 4.1. 362 8. Security Considerations 364 The capture of Authority Tokens by an adversary could enable an 365 attacker to acquire a certificate from a CA. Therefore, all 366 Authority Tokens MUST contain a field that identifies to the CA which 367 ACME client requested the token from the authority. All Authority 368 Tokens must specify an expiry (of the token itself as proof for a CA, 369 as opposed to the expiry of the name), and for some application, it 370 may make sense of that expiry to be quite short. Authority Tokens 371 must also contain a binding that will enable a CA to detect a 372 replayed Authority Token. Any protocol used to retrieve Authority 373 Tokens from an authority MUST use confidentiality to prevent 374 eavesdroppers from acquiring an Authority Token. 376 More TBD. 378 9. Informative References 380 [I-D.ietf-acme-acme] 381 Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. 382 Kasten, "Automatic Certificate Management Environment 383 (ACME)", draft-ietf-acme-acme-12 (work in progress), April 384 2018. 386 [I-D.ietf-acme-service-provider] 387 Barnes, M. and C. Wendt, "ACME Identifiers and Challenges 388 for VoIP Service Providers", draft-ietf-acme-service- 389 provider-02 (work in progress), October 2017. 391 [I-D.ietf-acme-star] 392 Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T. 393 Fossati, "Support for Short-Term, Automatically-Renewed 394 (STAR) Certificates in Automated Certificate Management 395 Environment (ACME)", draft-ietf-acme-star-03 (work in 396 progress), March 2018. 398 [I-D.ietf-acme-telephone] 399 Peterson, J. and R. Barnes, "ACME Identifiers and 400 Challenges for Telephone Numbers", draft-ietf-acme- 401 telephone-01 (work in progress), October 2017. 403 [I-D.ietf-modern-problem-framework] 404 Peterson, J. and T. McGarry, "Modern Problem Statement, 405 Use Cases, and Framework", draft-ietf-modern-problem- 406 framework-04 (work in progress), March 2018. 408 [I-D.ietf-stir-certificates] 409 Peterson, J. and S. Turner, "Secure Telephone Identity 410 Credentials: Certificates", draft-ietf-stir- 411 certificates-18 (work in progress), December 2017. 413 [I-D.ietf-stir-passport] 414 Wendt, C. and J. Peterson, "Personal Assertion Token 415 (PASSporT)", draft-ietf-stir-passport-11 (work in 416 progress), February 2017. 418 [I-D.ietf-stir-rfc4474bis] 419 Peterson, J., Jennings, C., Rescorla, E., and C. Wendt, 420 "Authenticated Identity Management in the Session 421 Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-16 422 (work in progress), February 2017. 424 [I-D.wendt-acme-authority-token-tnauthlist] 425 Wendt, C., Hancock, D., Barnes, M., and J. Peterson, 426 "TNAuthList profile of ACME Authority Token", draft-wendt- 427 acme-authority-token-tnauthlist-00 (work in progress), 428 March 2018. 430 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 431 Requirement Levels", BCP 14, RFC 2119, 432 DOI 10.17487/RFC2119, March 1997, 433 . 435 [RFC7340] Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure 436 Telephone Identity Problem Statement and Requirements", 437 RFC 7340, DOI 10.17487/RFC7340, September 2014, 438 . 440 [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 441 Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 442 2015, . 444 [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 445 (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, 446 . 448 [RFC8226] Peterson, J. and S. Turner, "Secure Telephone Identity 449 Credentials: Certificates", RFC 8226, 450 DOI 10.17487/RFC8226, February 2018, 451 . 453 Authors' Addresses 455 Jon Peterson 456 Neustar, Inc. 457 1800 Sutter St Suite 570 458 Concord, CA 94520 459 US 461 Email: jon.peterson@team.neustar 462 Mary Barnes 463 iconectiv 465 Email: mary.ietf.barnes@gmail.com 467 David Hancock 468 Comcast 470 Email: davidhancock.ietf@gmail.com 472 Chris Wendt 473 Comcast 474 One Comcast Center 475 Philadelphia, PA 19103 476 USA 478 Email: chris-ietf@chriswendt.net