idnits 2.17.1 draft-ietf-acme-star-03.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 date (March 03, 2018) is 2240 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-18) exists of draft-ietf-acme-acme-09 ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7807 (Obsoleted by RFC 9457) == Outdated reference: A later version (-01) exists of draft-nir-saag-star-00 == Outdated reference: A later version (-02) exists of draft-sheffer-acme-star-request-01 -- Obsolete informational reference (is this intentional?): RFC 6962 (Obsoleted by RFC 9162) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ACME Working Group Y. Sheffer 3 Internet-Draft Intuit 4 Intended status: Standards Track D. Lopez 5 Expires: September 4, 2018 O. Gonzalez de Dios 6 A. Pastor Perales 7 Telefonica I+D 8 T. Fossati 9 Nokia 10 March 03, 2018 12 Support for Short-Term, Automatically-Renewed (STAR) Certificates in 13 Automated Certificate Management Environment (ACME) 14 draft-ietf-acme-star-03 16 Abstract 18 Public-key certificates need to be revoked when they are compromised, 19 that is, when the associated private key is exposed to an attacker. 20 However the revocation process is often unreliable. An alternative 21 to revocation is issuing a sequence of certificates, each with a 22 short validity period, and terminating this sequence upon compromise. 23 This memo proposes an ACME extension to enable the issuance of short- 24 term and automatically renewed (STAR) certificates. 26 [RFC Editor: please remove before publication] 28 While the draft is being developed, the editor's version can be found 29 at https://github.com/yaronf/I-D/tree/master/STAR. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on September 4, 2018. 48 Copyright Notice 50 Copyright (c) 2018 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 1.1. Name Delegation Use Case . . . . . . . . . . . . . . . . 4 67 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 68 1.3. Conventions used in this document . . . . . . . . . . . . 4 69 2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 4 70 2.1. Bootstrap . . . . . . . . . . . . . . . . . . . . . . . . 5 71 2.2. Refresh . . . . . . . . . . . . . . . . . . . . . . . . . 5 72 2.3. Termination . . . . . . . . . . . . . . . . . . . . . . . 6 73 3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 7 74 3.1. ACME Extensions . . . . . . . . . . . . . . . . . . . . . 7 75 3.1.1. Extending the Order Resource . . . . . . . . . . . . 7 76 3.1.2. Canceling a Recurrent Order . . . . . . . . . . . . . 8 77 3.2. Capability Discovery . . . . . . . . . . . . . . . . . . 9 78 3.3. Fetching the Certificates . . . . . . . . . . . . . . . . 10 79 4. Operational Considerations . . . . . . . . . . . . . . . . . 11 80 4.1. Short Term and the Impact of Skewed Clocks . . . . . . . 11 81 4.2. Impact on Certificate Transparency (CT) Logs . . . . . . 11 82 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 12 83 5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 12 84 5.1.1. ACME Server with STAR extension . . . . . . . . . . . 12 85 5.1.2. STAR Proxy . . . . . . . . . . . . . . . . . . . . . 13 86 5.2. Level of Maturity . . . . . . . . . . . . . . . . . . . . 13 87 5.3. Coverage . . . . . . . . . . . . . . . . . . . . . . . . 13 88 5.4. Version Compatibility . . . . . . . . . . . . . . . . . . 13 89 5.5. Licensing . . . . . . . . . . . . . . . . . . . . . . . . 14 90 5.6. Implementation experience . . . . . . . . . . . . . . . . 14 91 5.7. Contact Information . . . . . . . . . . . . . . . . . . . 14 92 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 93 6.1. New ACME Error Types . . . . . . . . . . . . . . . . . . 14 94 6.2. New ACME Order Object Fields . . . . . . . . . . . . . . 15 95 6.3. Not-Before and Not-After HTTP Headers . . . . . . . . . . 15 97 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 98 7.1. Denial of Service Considerations . . . . . . . . . . . . 16 99 7.2. Additional Considerations TBD . . . . . . . . . . . . . . 16 100 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 101 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 102 9.1. Normative References . . . . . . . . . . . . . . . . . . 17 103 9.2. Informative References . . . . . . . . . . . . . . . . . 17 104 Appendix A. Document History . . . . . . . . . . . . . . . . . . 19 105 A.1. draft-ietf-acme-star-03 . . . . . . . . . . . . . . . . . 19 106 A.2. draft-ietf-acme-star-02 . . . . . . . . . . . . . . . . . 19 107 A.3. draft-ietf-acme-star-01 . . . . . . . . . . . . . . . . . 19 108 A.4. draft-ietf-acme-star-00 . . . . . . . . . . . . . . . . . 19 109 A.5. draft-sheffer-acme-star-02 . . . . . . . . . . . . . . . 19 110 A.6. draft-sheffer-acme-star-01 . . . . . . . . . . . . . . . 19 111 A.7. draft-sheffer-acme-star-00 . . . . . . . . . . . . . . . 20 112 A.8. draft-sheffer-acme-star-lurk-00 . . . . . . . . . . . . . 20 113 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 115 1. Introduction 117 The ACME protocol [I-D.ietf-acme-acme] automates the process of 118 issuing a certificate to a named entity (an Identity Owner or IdO). 119 Typically, but not always, the identity is a domain name and we may 120 refer to the entity as a Domain Name Owner (DNO). 122 If the IdO wishes to obtain a string of short-term certificates 123 originating from the same private key (see [Topalovic] about why 124 using short-lived certificates might be preferable to explicit 125 revocation), she must go through the whole ACME protocol each time a 126 new short-term certificate is needed - e.g., every 2-3 days. If done 127 this way, the process would involve frequent interactions between the 128 registration function of the ACME Certification Authority (CA) and 129 the identity provider infrastructure (e.g.: DNS, web servers), 130 therefore making the issuance of short-term certificates exceedingly 131 dependent on the reliability of both. 133 This document presents an extension of the ACME protocol that 134 optimizes this process by making short-term certificates first class 135 objects in the ACME ecosystem. Once the order for a string of short- 136 term certificates is accepted, the CA is responsible for publishing 137 the next certificate at an agreed upon URL before the previous one 138 expires. The IdO can terminate the automatic renewal before the 139 natural deadline, if needed - e.g., on key compromise. 141 For a more generic treatment of STAR certificates, readers are 142 referred to [I-D.nir-saag-star]. 144 1.1. Name Delegation Use Case 146 The proposed mechanism can be used as a building block of an 147 efficient name-delegation protocol, for example one that exists 148 between a CDN or a cloud provider and its customers 149 [I-D.sheffer-acme-star-request]. At any time, the service customer 150 (i.e., the IdO) can terminate the delegation by simply instructing 151 the CA to stop the automatic renewal and letting the currently active 152 certificate expire shortly thereafter. 154 1.2. Terminology 156 IdO Identifier Owner, the owner of an identifier, e.g.: a domain 157 name, a telephone number. 158 DNO Domain Name Owner, a type of IdO whose identifier is a domain 159 name. 160 STAR Short-Term, Automatically Renewed X.509 certificates. 161 NDC Name Delegation Client, an entity to which the identifier owned 162 by the IdO is delegated for a limited time. Examples include a 163 CDN edge cache, a cloud provider's load balancer or Web 164 Application Firewall (WAF). 166 1.3. Conventions used in this document 168 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 169 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 170 "OPTIONAL" in this document are to be interpreted as described in 171 [RFC2119]. 173 2. Protocol Flow 175 The following subsections describe the three main phases of the 176 protocol: 178 o Bootstrap: the IdO asks an ACME CA to create a short-term and 179 automatically-renewed (STAR) certificate (Section 2.1); 180 o Auto-renewal: the ACME CA periodically re-issues the short-term 181 certificate and posts it to a public URL (Section 2.2); 182 o Termination: the IdO requests the ACME CA to discontinue the 183 automatic renewal of the certificate (Section 2.3). 185 This diagram presents the entities that are (or may be) involved in 186 the protocol and their interactions during the different phases. 188 Refresh 189 . . . . . . . . . . . . . . . . . . . . 190 . ' ` v 191 .-----. Bootstrap / Terminate .---------. 192 | IdO |------------------------------------->| ACME CA | 193 `-----' `---------' 194 ^ .- - -. ^ 195 ` . . . . . . . . : NDC : . . . . . . . . . ' 196 Request `- - -' Refresh 197 Delegation 199 Note that there might be a distinct NDC entity (e.g., a CDN edge 200 cache) that uses a separate channel to request the IdO to set up a 201 name delegation. The protocol described in 202 [I-D.sheffer-acme-star-request] may be used for this purpose. 204 2.1. Bootstrap 206 The IdO, in its role as an ACME client, requests the CA to issue a 207 STAR certificate, i.e., one that: 209 o Has a short validity, e.g., 24 to 72 hours. Note that the exact 210 definition of "short" depends on the use case; 211 o Is automatically renewed by the CA for a certain period of time; 212 o Is downloadable from a (highly available) public link without 213 requiring any special authorization. 215 Other than that, the ACME protocol flows as usual between IdO and CA. 216 In particular, IdO is responsible for satisfying the requested ACME 217 challenges until the CA is willing to issue the requested 218 certificate. Per normal ACME processing, the IdO is given back an 219 order URL for the issued STAR certificate to be used in subsequent 220 interaction with the CA (e.g., if the certificate needs to be 221 terminated.) 223 The bootstrap phase ends when the IdO obtains a confirmation from the 224 ACME CA that includes a certificate endpoint. 226 2.2. Refresh 228 The CA automatically re-issues the certificate using the same CSR 229 (and therefore the same identifier and public key) before it expires 230 and publishes it to the URL that was returned to the IdO at the end 231 of the bootstrap phase. The certificate user, which could be either 232 the IdO itself or a delegated third party, as described in 233 [I-D.sheffer-acme-star-request], obtains the certificate and uses it. 235 The refresh process (Figure 1) goes on until either: 237 o IdO explicitly terminates the automatic renewal (Section 2.3); or 238 o Automatic renewal expires. 240 Certificate ACME/STAR 241 User Server 242 | Retrieve cert | [...] 243 |---------------------->| | 244 | +------. / 245 | | | / 246 | | Automatic renewal : 247 | | | \ 248 | |<-----' \ 249 | Retrieve cert | | 250 |---------------------->| 72 hours 251 | | | 252 | +------. / 253 | | | / 254 | | Automatic renewal : 255 | | | \ 256 | |<-----' \ 257 | Retrieve cert | | 258 |---------------------->| 72 hours 259 | | | 260 | +------. / 261 | | | / 262 | | Automatic renewal : 263 | | | \ 264 | |<-----' \ 265 | | | 266 | [...] | [...] 268 Figure 1: Auto renewal 270 2.3. Termination 272 The IdO may request early termination of the STAR certificate by 273 sending a cancellation request to the order resource, as described in 274 Section 3.1.2. After the CA receives and verifies the request, it 275 shall: 277 o Cancel the automatic renewal process for the STAR certificate; 278 o Change the certificate publication resource to return an error 279 indicating the termination of the issuance; 280 o Change the status of the order to "canceled". 282 Note that it is not necessary to explicitly revoke the short-term 283 certificate. 285 Certificate ACME/STAR 286 User IdO Server 287 | | | 288 | | Terminate order | 289 | +---------------------->| 290 | | +-------. 291 | | | | 292 | | | End auto renewal 293 | | | Remove cert link 294 | | | etc. 295 | | | | 296 | | Done |<------' 297 | |<----------------------+ 298 | | | 299 | | 300 | Retrieve cert | 301 +---------------------------------------------->| 302 | Error: terminated | 303 |<----------------------------------------------+ 304 | | 306 Figure 2: Termination 308 3. Protocol Details 310 This section describes the protocol details, namely the extensions to 311 the ACME protocol required to issue STAR certificates. 313 3.1. ACME Extensions 315 This protocol extends the ACME protocol, to allow for recurrent 316 orders. 318 3.1.1. Extending the Order Resource 320 The order resource is extended with the following attributes: 322 { 323 "recurrent": true, 324 "recurrent-start-date": "2016-01-01T00:00:00Z", 325 "recurrent-end-date": "2017-01-01T00:00:00Z", 326 "recurrent-certificate-validity": 604800 327 } 329 o recurrent: MUST be true for STAR certificates. 330 o recurrent-start-date: the earliest date of validity of the first 331 certificate issued, in [RFC3339] format. This attribute is 332 optional. When omitted, the start date is as soon as 333 authorization is complete. 334 o recurrent-end-date: the latest date of validity of the last 335 certificate issued, in [RFC3339] format. 336 o recurrent-certificate-validity: the maximum validity period of 337 each STAR certificate, an integer that denotes a number of 338 seconds. 340 These attributes are included in a POST message when creating the 341 order, as part of the "payload" encoded object. They are returned 342 when the order has been created, and the ACME server MAY adjust them 343 at will, according to its local policy (see also Section 3.2). 345 The optional notBefore and notAfter fields MUST NOT be present in a 346 STAR order. 348 ACME defines the following values for the order resource's status: 349 "invalid", "pending", "processing", "valid". In the case of 350 recurrent orders, the status MUST be "valid" as long as STAR 351 certificates are being issued. We add a new status value: 352 "canceled", see Section 3.1.2. 354 3.1.2. Canceling a Recurrent Order 356 An important property of the recurrent order is that it can be 357 canceled by the IdO, with no need for certificate revocation. To 358 cancel the order, the ACME client sends a POST to the order URL: 360 POST /acme/order/1 HTTP/1.1 361 Host: acme-server.example.org 362 Content-Type: application/jose+json 364 { 365 "protected": base64url({ 366 "alg": "ES256", 367 "kid": "https://example.com/acme/acct/1", 368 "nonce": "5XJ1L3lEkMG7tR6pA00clA", 369 "url": "https://example.com/acme/order/1" 370 }), 371 "payload": base64url({ 372 "status": "canceled" 373 }), 374 "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g" 375 } 377 The server MUST NOT issue any additional certificates for this order, 378 beyond the certificate that is available for collection at the time 379 of deletion. 381 Immediately after the order is canceled, the server: 383 o MUST update the status of the order resource to "canceled" and 384 MUST set an appropriate "expires" date; 385 o MUST respond with 403 (Forbidden) to any requests to the 386 certificate endpoint. The response SHOULD provide additional 387 information using a problem document [RFC7807] with type 388 "urn:ietf:params:acme:error:recurrentOrderCanceled". 390 Issuing a cancellation for an order that is not in "valid" state has 391 undefined semantics. A client MUST NOT send such a request, and a 392 server MUST return an error response with status code 400 (Bad 393 Request) and type 394 "urn:ietf:params:acme:error:recurrentCancellationInvalid". 396 3.2. Capability Discovery 398 In order to support the discovery of STAR capabilities, The directory 399 object of an ACME STAR server MUST contain the following attributes 400 inside the "meta" field: 402 o star-enabled: boolean flag indicating STAR support. An ACME STAR 403 server MUST include this key, and MUST set it to true if the 404 feature is enabled. 405 o star-min-cert-validity: minimum acceptable value for recurrent- 406 certificate-validity, in seconds. 407 o star-max-renewal: maximum delta between recurrent-end-date and 408 recurrent-start-date, in seconds. 410 Example directory object advertising STAR support with one day star- 411 min-cert-validity and one year star-max-renewal: 413 { 414 "new-nonce": "https://example.com/acme/new-nonce", 415 "new-account": "https://example.com/acme/new-account", 416 "new-order": "https://example.com/acme/new-order", 417 "new-authz": "https://example.com/acme/new-authz", 418 "revoke-cert": "https://example.com/acme/revoke-cert", 419 "key-change": "https://example.com/acme/key-change", 420 "meta": { 421 "terms-of-service": "https://example.com/acme/terms/2017-5-30", 422 "website": "https://www.example.com/", 423 "caa-identities": ["example.com"], 424 "star-enabled": true, 425 "star-min-cert-validity": 86400, 426 "star-max-renewal": 31536000 427 } 428 } 430 3.3. Fetching the Certificates 432 The certificate is fetched from the certificate endpoint, as per 433 [I-D.ietf-acme-acme], Section 7.4.2. 435 GET /acme/cert/asdf HTTP/1.1 436 Host: acme-server.example.org 437 Accept: application/pkix-cert 439 HTTP/1.1 200 OK 440 Content-Type: application/pem-certificate-chain 441 Link: ;rel="index" 442 Not-Before: Mon, 1 Feb 2016 00:00:00 GMT 443 Not-After: Mon, 8 Feb 2016 00:00:00 GMT 445 -----BEGIN CERTIFICATE----- 446 [End-entity certificate contents] 447 -----END CERTIFICATE----- 448 -----BEGIN CERTIFICATE----- 449 [Issuer certificate contents] 450 -----END CERTIFICATE----- 451 -----BEGIN CERTIFICATE----- 452 [Other certificate contents] 453 -----END CERTIFICATE----- 455 The Server SHOULD include the "Not-Before" and "Not-After" HTTP 456 headers in the response. When they exist, they MUST be equal to the 457 respective fields inside the end-entity certificate. Their format is 458 "HTTP-date" as defined in Section 7.1.1.2 of [RFC7231]. Their 459 purpose is to enable client implementations that do not parse the 460 certificate. 462 To improve robustness, the next certificate MUST be made available by 463 the ACME CA at the latest halfway through the lifetime of the 464 currently active certificate. It is worth noting that this has an 465 implication in case of cancellation: in fact, from the time the next 466 certificate is made available, the cancellation is not completely 467 effective until the latter also expires. 469 The server MUST NOT issue any additional certificates for this order 470 beyond its recurrent-end-date. 472 Immediately after the order expires, the server MUST respond with 403 473 (Forbidden) to any requests to the certificate endpoint. The 474 response SHOULD provide additional information using a problem 475 document [RFC7807] with type 476 "urn:ietf:params:acme:error:recurrentOrderExpired". 478 4. Operational Considerations 480 4.1. Short Term and the Impact of Skewed Clocks 482 "Short Term" is a relative concept, therefore trying to define a cut- 483 off point that works in all cases would be a useless exercise. In 484 practice, the expected lifetime of a STAR certificate will be counted 485 in minutes, hours or days, depending on different factors: the 486 underlying requirements for revocation, how much clock 487 synchronization is expected among relying parties and the issuing CA, 488 etc. 490 Nevertheless, this section attempts to provide reasonable suggestions 491 for the Web use case, informed by current operational and research 492 experience. 494 Acer et al. [Acer] find that one of the main causes of "HTTPS error" 495 warnings in browers is misconfigured client clocks. In particular, 496 they observe that roughly 95% of the "severe" clock skews - the 6.7% 497 of clock-related breakage reports which account for clients that are 498 more than 24 hours behind - happen to be within 6-7 days. 500 In order to avoid these spurious warnings about a not (yet) valid 501 server certificate, it is RECOMMENDED that site owners pre-date their 502 Web facing certificates by 5 to 7 days. The exact number depends on 503 the percentage of the "clock-skewed" population that the site owner 504 expects to protect - 5 days cover 97.3%, 7 days cover 99.6%. Note 505 that exact choice is also likely to depend on the kind of clients 506 that is prevalent for a given site or app - for example, Android and 507 Mac OS clients are known to behave better than Windows clients. 508 These considerations are clearly out of scope of the present 509 document. 511 In terms of security, STAR certificates and certificates with OCSP 512 must-staple [RFC7633] can be considered roughly equivalent if the 513 STAR certificate's and the OCSP response's lifetimes are the same. 514 Given OCSP responses can be cached on average for 4 days [Stark], it 515 is RECOMMENDED that a STAR certificate that is used on the Web has an 516 "effective" lifetime (excluding any pre-dating to account for clock 517 skews) no longer than 4 days. 519 4.2. Impact on Certificate Transparency (CT) Logs 521 Provided that the recommendations in Section 4.1 are followed, the 522 increase in Certificate Transparency (CT) [RFC6962] log ingestion 523 should be one order of magnitude in the worst case compared to the 524 current state. 526 The input received from most members of the CT community when the 527 issue was raised was that this should not represent a problem for the 528 CT architecture. 530 5. Implementation Status 532 Note to RFC Editor: please remove this section before publication, 533 including the reference to [RFC7942]. 535 This section records the status of known implementations of the 536 protocol defined by this specification at the time of posting of this 537 Internet-Draft, and is based on a proposal described in [RFC7942]. 538 The description of implementations in this section is intended to 539 assist the IETF in its decision processes in progressing drafts to 540 RFCs. Please note that the listing of any individual implementation 541 here does not imply endorsement by the IETF. Furthermore, no effort 542 has been spent to verify the information presented here that was 543 supplied by IETF contributors. This is not intended as, and must not 544 be construed to be, a catalog of available implementations or their 545 features. Readers are advised to note that other implementations may 546 exist. 548 According to [RFC7942], "this will allow reviewers and working groups 549 to assign due consideration to documents that have the benefit of 550 running code, which may serve as evidence of valuable experimentation 551 and feedback that have made the implemented protocols more mature. 552 It is up to the individual working groups to use this information as 553 they see fit". 555 5.1. Overview 557 The implementation is constructed around 3 elements: STAR Client for 558 NDC, STAR Proxy for IdO and ACME Server for CA. The communication 559 between them is over an IP network and the HTTPS protocol. 561 The software of the implementation is available at: 562 https://github.com/mami-project/lurk 564 The following subsections offer a basic description, detailed 565 information is available in https://github.com/mami- 566 project/lurk/blob/master/proxySTAR_v2/README.md 568 5.1.1. ACME Server with STAR extension 570 This is a fork of the Let's Encrypt Boulder project that implements 571 an ACME compliant CA. It includes modifications to extend the ACME 572 protocol as it is specified in this draft, to support recurrent 573 orders and cancelling orders. 575 The implementation understands the new "recurrent" attributes as part 576 of the Certificate issuance in the POST request for a new resource. 577 An additional process "renewalManager.go" has been included in 578 parallel that reads the details of each recurrent request, 579 automatically produces a "cron" Linux based task that issues the 580 recurrent certificates, until the lifetime ends or the order is 581 canceled. This process is also in charge of maintaining a fixed URI 582 to enable the NDC to download certificates, unlike Boulder's regular 583 process of producing a unique URI per certificate. 585 5.1.2. STAR Proxy 587 The STAR Proxy has a double role as ACME client and STAR Server. The 588 former is a fork of the EFF Certbot project that implements an ACME 589 compliant client with the STAR extension. The latter is a basic HTTP 590 REST API server. 592 The STAR Proxy understands the basic API request with a server. The 593 current implementation of the API is defined in draft-ietf-acme-star- 594 01. Registration or order cancellation triggers the modified Certbot 595 client that requests, or cancels, the recurrent generation of 596 certificates using the STAR extension over ACME protocol. The URI 597 with the location of the recurrent certificate is delivered to the 598 STAR client as a response. 600 5.2. Level of Maturity 602 This is a prototype. 604 5.3. Coverage 606 A STAR Client is not included in this implementation, but done by 607 direct HTTP request with any open HTTP REST API tool. This is 608 expected to be covered as part of the [I-D.sheffer-acme-star-request] 609 implementation. 611 This implementation completely covers STAR Proxy and ACME Server with 612 STAR extension 614 5.4. Version Compatibility 616 The implementation is compatible with version draft-ietf-acme-star- 617 01. The implementation is based on the Boulder and Certbot code 618 release from 7-Aug-2017. 620 5.5. Licensing 622 This implementation inherits the Boulder license (Mozilla Public 623 License 2.0) and Certbot license (Apache License Version 2.0 ). 625 5.6. Implementation experience 627 To prove the concept all the implementation has been done with a 628 self-signed CA, to avoid impact on real domains. To be able to do it 629 we use the FAKE_DNS property of Boulder and static /etc/hosts entries 630 with domains names. Nonetheless this implementation should run with 631 real domains. 633 Most of the implementation has been made to avoid deep changes inside 634 of Boulder or Certbot, for example, the recurrent certificates 635 issuance by the CA is based on an external process that auto- 636 configures the standard Linux "cron" daemon in the ACME CA server. 638 The reference setup recommended is one physical host with 3 virtual 639 machines, one for each of the 3 components (client, proxy and server) 640 and the connectivity based on host bridge. 642 Network security is not enabled (iptables default policies are 643 "accept" and all rules removed) in this implementation to simplify 644 and test the protocol. 646 5.7. Contact Information 648 See author details below. 650 6. IANA Considerations 652 [[RFC Editor: please replace XXXX below by the RFC number.]] 654 6.1. New ACME Error Types 656 This document adds the following entries to the ACME Error Type 657 registry: 659 +------------------------------+------------------------+-----------+ 660 | Type | Description | Reference | 661 +------------------------------+------------------------+-----------+ 662 | recurrentOrderCanceled | The short-term | RFC XXXX | 663 | | certificate is no | | 664 | | longer available | | 665 | | because the recurrent | | 666 | | order has been | | 667 | | explicitly canceled by | | 668 | | the IdO | | 669 | recurrentOrderExpired | The short-term | RFC XXXX | 670 | | certificate is no | | 671 | | longer available | | 672 | | because the recurrent | | 673 | | order has expired | | 674 | recurrentCancellationInvalid | A request to cancel a | RFC XXXX | 675 | | recurrent order that | | 676 | | is not in state | | 677 | | "valid" has been | | 678 | | received | | 679 +------------------------------+------------------------+-----------+ 681 6.2. New ACME Order Object Fields 683 This document adds the following entries to the ACME Order Object 684 Fields registry: 686 +-------------------------------+--------+--------------+-----------+ 687 | Field Name | Field | Configurable | Reference | 688 | | Type | | | 689 +-------------------------------+--------+--------------+-----------+ 690 | recurrent | string | true | RFC XXXX | 691 | recurrent-start-date | string | true | RFC XXXX | 692 | recurrent-end-date | string | true | RFC XXXX | 693 | recurrent-certificate- | string | true | RFC XXXX | 694 | validity | | | | 695 +-------------------------------+--------+--------------+-----------+ 697 6.3. Not-Before and Not-After HTTP Headers 699 The "Message Headers" registry should be updated with the following 700 additional values: 702 +-------------------+----------+----------+-----------+ 703 | Header Field Name | Protocol | Status | Reference | 704 +-------------------+----------+----------+-----------+ 705 | Not-Before | http | standard | RFC XXXX | 706 | Not-After | http | standard | RFC XXXX | 707 +-------------------+----------+----------+-----------+ 709 7. Security Considerations 711 7.1. Denial of Service Considerations 713 STAR adds a new attack vector that increases the threat of denial of 714 service attacks, caused by the change to the CA's behavior. Each 715 STAR request amplifies the resource demands upon the CA, where one 716 order produces not one, but potentially dozens or hundreds of 717 certificates, depending on the "recurrent-certificate-validity" 718 parameter. An attacker can use this property to aggressively reduce 719 the "recurrent-certificate-validity" (e.g. 1 sec.) jointly with other 720 ACME attack vectors identified in Sec. 10 of [I-D.ietf-acme-acme]. 721 Other collateral impact is related to the certificate endpoint 722 resource where the client can retrieve the certificates periodically. 723 If this resource is external to the CA (e.g. a hosted web server), 724 the previous attack will be reflected to that resource. 726 Mitigation recommendations from ACME still apply, but some of them 727 need to be adjusted. For example, applying rate limiting to the 728 initial request, by the nature of the recurrent behavior cannot solve 729 the above problem. The CA server needs complementary mitigation and 730 specifically, it SHOULD enforce a minimum value on "recurrent- 731 certificate-validity". Alternatively, the CA can set an internal 732 certificate generation processes rate limit. 734 7.2. Additional Considerations TBD 736 8. Acknowledgments 738 This work is partially supported by the European Commission under 739 Horizon 2020 grant agreement no. 688421 Measurement and Architecture 740 for a Middleboxed Internet (MAMI). This support does not imply 741 endorsement. 743 Thanks to Jon Peterson and Martin Thomson for helpful comments and 744 discussions that have shaped this document. 746 9. References 748 9.1. Normative References 750 [I-D.ietf-acme-acme] 751 Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. 752 Kasten, "Automatic Certificate Management Environment 753 (ACME)", draft-ietf-acme-acme-09 (work in progress), 754 December 2017. 756 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 757 Requirement Levels", BCP 14, RFC 2119, 758 DOI 10.17487/RFC2119, March 1997, . 761 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 762 Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, 763 . 765 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 766 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 767 DOI 10.17487/RFC7231, June 2014, . 770 [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP 771 APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, 772 . 774 9.2. Informative References 776 [Acer] Acer, M., Stark, E., Felt, A., Fahl, S., Bhargava, R., 777 Dev, B., Braithwaite, M., Sleevi, R., and P. Tabriz, 778 "Where the Wild Warnings Are: Root Causes of Chrome HTTPS 779 Certificate Errors", DOI 10.1145/3133956.3134007, 2017, 780 . 782 [I-D.nir-saag-star] 783 Nir, Y., Fossati, T., and Y. Sheffer, "Considerations For 784 Using Short Term Certificates", draft-nir-saag-star-00 785 (work in progress), October 2017. 787 [I-D.sheffer-acme-star-request] 788 Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T. 789 Fossati, "Generating Certificate Requests for Short-Term, 790 Automatically-Renewed (STAR) Certificates", draft-sheffer- 791 acme-star-request-01 (work in progress), June 2017. 793 [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate 794 Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013, 795 . 797 [RFC7633] Hallam-Baker, P., "X.509v3 Transport Layer Security (TLS) 798 Feature Extension", RFC 7633, DOI 10.17487/RFC7633, 799 October 2015, . 801 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 802 Code: The Implementation Status Section", BCP 205, 803 RFC 7942, DOI 10.17487/RFC7942, July 2016, 804 . 806 [Stark] Stark, E., Huang, L., Israni, D., Jackson, C., and D. 807 Boneh, "The case for prefetching and prevalidating TLS 808 server certificates", 2012, 809 . 812 [Topalovic] 813 Topalovic, E., Saeta, B., Huang, L., Jackson, C., and D. 814 Boneh, "Towards Short-Lived Certificates", 2012, 815 . 817 Appendix A. Document History 819 [[Note to RFC Editor: please remove before publication.]] 821 A.1. draft-ietf-acme-star-03 823 o Clock skew considerations 824 o Recommendations for "short" in the Web use case 825 o CT log considerations 827 A.2. draft-ietf-acme-star-02 829 o Discovery of STAR capabilities via the directory object 830 o Use the more generic term Identifier Owner (IdO) instead of Domain 831 Name Owner (DNO) 832 o More precision about what goes in the order 833 o Detail server side behavior on cancellation 835 A.3. draft-ietf-acme-star-01 837 o Generalized the introduction, separating out the specifics of 838 CDNs. 839 o Clean out LURK-specific text. 840 o Using a POST to ensure cancellation is authenticated. 841 o First and last date of recurrent cert, as absolute dates. 842 Validity of certs in seconds. 843 o Use RFC7807 "Problem Details" in error responses. 844 o Add IANA considerations. 845 o Changed the document's title. 847 A.4. draft-ietf-acme-star-00 849 o Initial working group version. 850 o Removed the STAR interface, the protocol between NDC and DNO. 851 What remains is only the extended ACME protocol. 853 A.5. draft-sheffer-acme-star-02 855 o Using a more generic term for the delegation client, NDC. 856 o Added an additional use case: public cloud services. 857 o More detail on ACME authorization. 859 A.6. draft-sheffer-acme-star-01 861 o A terminology section. 862 o Some cleanup. 864 A.7. draft-sheffer-acme-star-00 866 o Renamed draft to prevent confusion with other work in this space. 867 o Added an initial STAR protocol: a REST API. 868 o Discussion of CDNI use cases. 870 A.8. draft-sheffer-acme-star-lurk-00 872 o Initial version. 874 Authors' Addresses 876 Yaron Sheffer 877 Intuit 879 EMail: yaronf.ietf@gmail.com 881 Diego Lopez 882 Telefonica I+D 884 EMail: diego.r.lopez@telefonica.com 886 Oscar Gonzalez de Dios 887 Telefonica I+D 889 EMail: oscar.gonzalezdedios@telefonica.com 891 Antonio Agustin Pastor Perales 892 Telefonica I+D 894 EMail: antonio.pastorperales@telefonica.com 896 Thomas Fossati 897 Nokia 899 EMail: thomas.fossati@nokia.com