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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 916 has weird spacing: '...Account newA...' == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: For this reason, it is RECOMMENDED that account key pairs be used for no other purpose besides ACME authentication. For example, the public key of an account key pair SHOULD NOT be included in a certificate. ACME clients and servers SHOULD verify that a CSR submitted in a finalize request does not contain a public key for any known account key pair. In particular, when a server receives a finalize request, it MUST verify that the public key in a CSR is not the same as the public key of the account key pair used to authenticate that request. This assures that vulnerabilities in the protocols with which the certificate is used (e.g., signing oracles in TLS [JSS15]) do not result in compromise of the ACME account. Because ACME accounts are uniquely identified by their account key pair (see Section 7.3.1) the server MUST not allow account key pair reuse across multiple accounts. -- The document date (October 12, 2018) is 2015 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. 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'REST' ** Obsolete normative reference: RFC 2818 (Obsoleted by RFC 9110) ** Downref: Normative reference to an Informational RFC: RFC 2985 ** Downref: Normative reference to an Informational RFC: RFC 2986 ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5751 (Obsoleted by RFC 8551) ** Obsolete normative reference: RFC 5988 (Obsoleted by RFC 8288) ** Obsolete normative reference: RFC 6844 (Obsoleted by RFC 8659) ** Obsolete normative reference: RFC 7159 (Obsoleted by RFC 8259) ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7807 (Obsoleted by RFC 9457) == Outdated reference: A later version (-10) exists of draft-ietf-acme-caa-05 == Outdated reference: A later version (-08) exists of draft-ietf-acme-ip-04 -- Obsolete informational reference (is this intentional?): RFC 5785 (Obsoleted by RFC 8615) -- Obsolete informational reference (is this intentional?): RFC 7525 (Obsoleted by RFC 9325) Summary: 12 errors (**), 0 flaws (~~), 8 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ACME Working Group R. Barnes 3 Internet-Draft Cisco 4 Intended status: Standards Track J. Hoffman-Andrews 5 Expires: April 15, 2019 EFF 6 D. McCarney 7 Let's Encrypt 8 J. Kasten 9 University of Michigan 10 October 12, 2018 12 Automatic Certificate Management Environment (ACME) 13 draft-ietf-acme-acme-16 15 Abstract 17 Public Key Infrastructure X.509 (PKIX) certificates are used for a 18 number of purposes, the most significant of which is the 19 authentication of domain names. Thus, certification authorities 20 (CAs) in the Web PKI are trusted to verify that an applicant for a 21 certificate legitimately represents the domain name(s) in the 22 certificate. Today, this verification is done through a collection 23 of ad hoc mechanisms. This document describes a protocol that a CA 24 and an applicant can use to automate the process of verification and 25 certificate issuance. The protocol also provides facilities for 26 other certificate management functions, such as certificate 27 revocation. 29 RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: The source for 30 this draft is maintained in GitHub. Suggested changes should be 31 submitted as pull requests at https://github.com/ietf-wg-acme/acme 32 [1]. Instructions are on that page as well. Editorial changes can 33 be managed in GitHub, but any substantive change should be discussed 34 on the ACME mailing list (acme@ietf.org). 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at https://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on April 15, 2019. 53 Copyright Notice 55 Copyright (c) 2018 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (https://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 71 2. Deployment Model and Operator Experience . . . . . . . . . . 5 72 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7 74 5. Character Encoding . . . . . . . . . . . . . . . . . . . . . 10 75 6. Message Transport . . . . . . . . . . . . . . . . . . . . . . 10 76 6.1. HTTPS Requests . . . . . . . . . . . . . . . . . . . . . 10 77 6.2. Request Authentication . . . . . . . . . . . . . . . . . 11 78 6.3. GET and POST-as-GET Requests . . . . . . . . . . . . . . 12 79 6.4. Request URL Integrity . . . . . . . . . . . . . . . . . . 13 80 6.4.1. "url" (URL) JWS Header Parameter . . . . . . . . . . 14 81 6.5. Replay protection . . . . . . . . . . . . . . . . . . . . 14 82 6.5.1. Replay-Nonce . . . . . . . . . . . . . . . . . . . . 14 83 6.5.2. "nonce" (Nonce) JWS Header Parameter . . . . . . . . 15 84 6.6. Rate Limits . . . . . . . . . . . . . . . . . . . . . . . 15 85 6.7. Errors . . . . . . . . . . . . . . . . . . . . . . . . . 15 86 6.7.1. Subproblems . . . . . . . . . . . . . . . . . . . . . 17 87 7. Certificate Management . . . . . . . . . . . . . . . . . . . 18 88 7.1. Resources . . . . . . . . . . . . . . . . . . . . . . . . 19 89 7.1.1. Directory . . . . . . . . . . . . . . . . . . . . . . 21 90 7.1.2. Account Objects . . . . . . . . . . . . . . . . . . . 23 91 7.1.3. Order Objects . . . . . . . . . . . . . . . . . . . . 24 92 7.1.4. Authorization Objects . . . . . . . . . . . . . . . . 27 93 7.1.5. Challenge Objects . . . . . . . . . . . . . . . . . . 29 94 7.1.6. Status Changes . . . . . . . . . . . . . . . . . . . 29 95 7.2. Getting a Nonce . . . . . . . . . . . . . . . . . . . . . 31 96 7.3. Account Creation . . . . . . . . . . . . . . . . . . . . 32 97 7.3.1. Finding an Account URL Given a Key . . . . . . . . . 34 98 7.3.2. Account Update . . . . . . . . . . . . . . . . . . . 35 99 7.3.3. Changes of Terms of Service . . . . . . . . . . . . . 35 100 7.3.4. External Account Binding . . . . . . . . . . . . . . 36 101 7.3.5. Account Key Roll-over . . . . . . . . . . . . . . . . 38 102 7.3.6. Account Deactivation . . . . . . . . . . . . . . . . 41 103 7.4. Applying for Certificate Issuance . . . . . . . . . . . . 42 104 7.4.1. Pre-Authorization . . . . . . . . . . . . . . . . . . 46 105 7.4.2. Downloading the Certificate . . . . . . . . . . . . . 48 106 7.5. Identifier Authorization . . . . . . . . . . . . . . . . 50 107 7.5.1. Responding to Challenges . . . . . . . . . . . . . . 52 108 7.5.2. Deactivating an Authorization . . . . . . . . . . . . 54 109 7.6. Certificate Revocation . . . . . . . . . . . . . . . . . 55 110 8. Identifier Validation Challenges . . . . . . . . . . . . . . 57 111 8.1. Key Authorizations . . . . . . . . . . . . . . . . . . . 59 112 8.2. Retrying Challenges . . . . . . . . . . . . . . . . . . . 59 113 8.3. HTTP Challenge . . . . . . . . . . . . . . . . . . . . . 60 114 8.4. DNS Challenge . . . . . . . . . . . . . . . . . . . . . . 62 115 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 64 116 9.1. MIME Type: application/pem-certificate-chain . . . . . . 64 117 9.2. Well-Known URI for the HTTP Challenge . . . . . . . . . . 65 118 9.3. Replay-Nonce HTTP Header . . . . . . . . . . . . . . . . 66 119 9.4. "url" JWS Header Parameter . . . . . . . . . . . . . . . 66 120 9.5. "nonce" JWS Header Parameter . . . . . . . . . . . . . . 66 121 9.6. URN Sub-namespace for ACME (urn:ietf:params:acme) . . . . 67 122 9.7. New Registries . . . . . . . . . . . . . . . . . . . . . 67 123 9.7.1. Fields in Account Objects . . . . . . . . . . . . . . 68 124 9.7.2. Fields in Order Objects . . . . . . . . . . . . . . . 68 125 9.7.3. Fields in Authorization Objects . . . . . . . . . . . 69 126 9.7.4. Error Types . . . . . . . . . . . . . . . . . . . . . 70 127 9.7.5. Resource Types . . . . . . . . . . . . . . . . . . . 71 128 9.7.6. Fields in the "meta" Object within a Directory Object 71 129 9.7.7. Identifier Types . . . . . . . . . . . . . . . . . . 72 130 9.7.8. Validation Methods . . . . . . . . . . . . . . . . . 73 131 10. Security Considerations . . . . . . . . . . . . . . . . . . . 74 132 10.1. Threat Model . . . . . . . . . . . . . . . . . . . . . . 74 133 10.2. Integrity of Authorizations . . . . . . . . . . . . . . 76 134 10.3. Denial-of-Service Considerations . . . . . . . . . . . . 79 135 10.4. Server-Side Request Forgery . . . . . . . . . . . . . . 80 136 10.5. CA Policy Considerations . . . . . . . . . . . . . . . . 80 137 11. Operational Considerations . . . . . . . . . . . . . . . . . 82 138 11.1. Key Selection . . . . . . . . . . . . . . . . . . . . . 82 139 11.2. DNS security . . . . . . . . . . . . . . . . . . . . . . 83 140 11.3. Token Entropy . . . . . . . . . . . . . . . . . . . . . 83 141 11.4. Malformed Certificate Chains . . . . . . . . . . . . . . 83 142 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 84 143 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 84 144 13.1. Normative References . . . . . . . . . . . . . . . . . . 85 145 13.2. Informative References . . . . . . . . . . . . . . . . . 88 146 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 89 147 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 89 149 1. Introduction 151 Certificates [RFC5280] in the Web PKI are most commonly used to 152 authenticate domain names. Thus, certification authorities (CAs) in 153 the Web PKI are trusted to verify that an applicant for a certificate 154 legitimately represents the domain name(s) in the certificate. 156 Different types of certificates reflect different kinds of CA 157 verification of information about the certificate subject. "Domain 158 Validation" (DV) certificates are by far the most common type. The 159 only validation the CA is required to perform in the DV issuance 160 process is to verify that the requester has effective control of the 161 domain [CABFBR]. The CA is not required to attempt to verify the 162 requester's real-world identity. (This is as opposed to 163 "Organization Validation" (OV) and "Extended Validation" (EV) 164 certificates, where the process is intended to also verify the real- 165 world identity of the requester.) 167 Existing Web PKI certificate authorities tend to use a set of ad hoc 168 protocols for certificate issuance and identity verification. In the 169 case of DV certificates, a typical user experience is something like: 171 o Generate a PKCS#10 [RFC2986] Certificate Signing Request (CSR). 173 o Cut-and-paste the CSR into a CA's web page. 175 o Prove ownership of the domain by one of the following methods: 177 * Put a CA-provided challenge at a specific place on the web 178 server. 180 * Put a CA-provided challenge in a DNS record corresponding to 181 the target domain. 183 * Receive a CA-provided challenge at a (hopefully) administrator- 184 controlled email address corresponding to the domain and then 185 respond to it on the CA's web page. 187 o Download the issued certificate and install it on their Web 188 Server. 190 With the exception of the CSR itself and the certificates that are 191 issued, these are all completely ad hoc procedures and are 192 accomplished by getting the human user to follow interactive natural- 193 language instructions from the CA rather than by machine-implemented 194 published protocols. In many cases, the instructions are difficult 195 to follow and cause significant frustration and confusion. Informal 196 usability tests by the authors indicate that webmasters often need 197 1-3 hours to obtain and install a certificate for a domain. Even in 198 the best case, the lack of published, standardized mechanisms 199 presents an obstacle to the wide deployment of HTTPS and other PKIX- 200 dependent systems because it inhibits mechanization of tasks related 201 to certificate issuance, deployment, and revocation. 203 This document describes an extensible framework for automating the 204 issuance and domain validation procedure, thereby allowing servers 205 and infrastructure software to obtain certificates without user 206 interaction. Use of this protocol should radically simplify the 207 deployment of HTTPS and the practicality of PKIX-based authentication 208 for other protocols based on Transport Layer Security (TLS) 209 [RFC5246]. 211 It should be noted that while the focus of this document is on 212 validating domain names for purposes of issuing certificates in the 213 Web PKI, ACME supports extensions for uses with other identifiers in 214 other PKI contexts. For example, as of this writing, there is 215 ongoing work to use ACME for issuance of Web PKI certificates 216 attesting to IP addresses [I-D.ietf-acme-ip] and STIR certificates 217 attesting to telephone numbers [I-D.ietf-acme-telephone]. 219 ACME can also be used to automate some aspects of certificate 220 management even where non-automated processes are still needed. For 221 example, the external account binding feature (see Section 7.3.4) can 222 allow an ACME account to use authorizations that have been granted to 223 an external, non-ACME account. This allows ACME to address issuance 224 scenarios that cannot yet be fully automated, such as the issuance of 225 Extended Validation certificates. 227 2. Deployment Model and Operator Experience 229 The guiding use case for ACME is obtaining certificates for websites 230 (HTTPS [RFC2818]). In this case, a web server is intended to speak 231 for one or more domains, and the process of certificate issuance is 232 intended to verify that this web server actually speaks for the 233 domain(s). 235 DV certificate validation commonly checks claims about properties 236 related to control of a domain name - properties that can be observed 237 by the certificate issuer in an interactive process that can be 238 conducted purely online. That means that under typical 239 circumstances, all steps in the request, verification, and issuance 240 process can be represented and performed by Internet protocols with 241 no out-of-band human intervention. 243 Prior to ACME, when deploying an HTTPS server, a server operator 244 typically gets a prompt to generate a self-signed certificate. If 245 the operator were instead deploying an HTTPS server using ACME, the 246 experience would be something like this: 248 o The operator's ACME client prompts the operator for the intended 249 domain name(s) that the web server is to stand for. 251 o The ACME client presents the operator with a list of CAs from 252 which it could get a certificate. (This list will change over 253 time based on the capabilities of CAs and updates to ACME 254 configuration.) The ACME client might prompt the operator for 255 payment information at this point. 257 o The operator selects a CA. 259 o In the background, the ACME client contacts the CA and requests 260 that it issue a certificate for the intended domain name(s). 262 o The CA verifies that the client controls the requested domain 263 name(s) by having the ACME client perform some action(s) that can 264 only be done with control of the domain name(s). For example, the 265 CA might require a client requesting example.com to provision DNS 266 record under example.com or an HTTP resource under 267 http://example.com. 269 o Once the CA is satisfied, it issues the certificate and the ACME 270 client automatically downloads and installs it, potentially 271 notifying the operator via email, SMS, etc. 273 o The ACME client periodically contacts the CA to get updated 274 certificates, stapled OCSP responses, or whatever else would be 275 required to keep the web server functional and its credentials up- 276 to-date. 278 In this way, it would be nearly as easy to deploy with a CA-issued 279 certificate as with a self-signed certificate. Furthermore, the 280 maintenance of that CA-issued certificate would require minimal 281 manual intervention. Such close integration of ACME with HTTPS 282 servers allows the immediate and automated deployment of certificates 283 as they are issued, sparing the human administrator from much of the 284 time-consuming work described in the previous section. 286 3. Terminology 288 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 289 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 290 "OPTIONAL" in this document are to be interpreted as described in BCP 291 14 [RFC2119] [RFC8174] when, and only when, they appear in all 292 capitals, as shown here. 294 The two main roles in ACME are "client" and "server". The ACME 295 client uses the protocol to request certificate management actions, 296 such as issuance or revocation. An ACME client may run on a web 297 server, mail server, or some other server system which requires valid 298 X.509 certificates. Or, it may run on a separate server that does 299 not consume the certificate, but is authorized to respond to a CA- 300 provided challenge. The ACME server runs at a certification 301 authority, and responds to client requests, performing the requested 302 actions if the client is authorized. 304 An ACME client authenticates to the server by means of an "account 305 key pair". The client uses the private key of this key pair to sign 306 all messages sent to the server. The server uses the public key to 307 verify the authenticity and integrity of messages from the client. 309 4. Protocol Overview 311 ACME allows a client to request certificate management actions using 312 a set of JavaScript Object Notation (JSON) messages carried over 313 HTTPS. Issuance using ACME resembles a traditional CA's issuance 314 process, in which a user creates an account, requests a certificate, 315 and proves control of the domain(s) in that certificate in order for 316 the CA to issue the requested certificate. 318 The first phase of ACME is for the client to request an account with 319 the ACME server. The client generates an asymmetric key pair and 320 requests a new account, optionally providing contact information, 321 agreeing to terms of service, and/or associating the account with an 322 existing account in another system. The creation request is signed 323 with the generated private key to prove that the client controls it. 325 Client Server 327 [Contact Information] 328 [ToS Agreement] 329 [Additional Data] 330 Signature -------> 331 Account URL 332 <------- Account Object 334 [] Information covered by request signatures 336 Account Creation 338 Once an account is registered, there are four major steps the client 339 needs to take to get a certificate: 341 1. Submit an order for a certificate to be issued 343 2. Prove control of any identifiers requested in the certificate 345 3. Finalize the order by submitting a CSR 347 4. Await issuance and download the issued certificate 349 The client's order for a certificate describes the desired 350 identifiers plus a few additional fields that capture semantics that 351 are not supported in the CSR format. If the server is willing to 352 consider issuing such a certificate, it responds with a list of 353 requirements that the client must satisfy before the certificate will 354 be issued. 356 For example, in most cases, the server will require the client to 357 demonstrate that it controls the identifiers in the requested 358 certificate. Because there are many different ways to validate 359 possession of different types of identifiers, the server will choose 360 from an extensible set of challenges that are appropriate for the 361 identifier being claimed. The client responds with a set of 362 responses that tell the server which challenges the client has 363 completed. The server then validates that the client has completed 364 the challenges. 366 Once the validation process is complete and the server is satisfied 367 that the client has met its requirements, the client finalizes the 368 order by submitting a PKCS#10 Certificate Signing Request (CSR). The 369 server will issue the requested certificate and make it available to 370 the client. 372 Client Server 374 [Order] 375 Signature -------> 376 <------- Required Authorizations 378 [Responses] 379 Signature -------> 381 <~~~~~~~~Validation~~~~~~~~> 383 [CSR] 384 Signature -------> 385 <------- Acknowledgement 387 <~~~~~~Await issuance~~~~~~> 389 GET request -------> 390 <------- Certificate 392 [] Information covered by request signatures 394 Certificate Issuance 396 To revoke a certificate, the client sends a signed revocation request 397 indicating the certificate to be revoked: 399 Client Server 401 [Revocation request] 402 Signature --------> 404 <-------- Result 406 [] Information covered by request signatures 408 Certificate Revocation 410 Note that while ACME is defined with enough flexibility to handle 411 different types of identifiers in principle, the primary use case 412 addressed by this document is the case where domain names are used as 413 identifiers. For example, all of the identifier validation 414 challenges described in Section 8 below address validation of domain 415 names. The use of ACME for other identifiers will require further 416 specification in order to describe how these identifiers are encoded 417 in the protocol and what types of validation challenges the server 418 might require. 420 5. Character Encoding 422 All requests and responses sent via HTTP by ACME clients, ACME 423 servers, and validation servers as well as any inputs for digest 424 computations MUST be encoded using the UTF-8 [RFC3629] character set. 425 Note that identifiers that appear in certificates may have their own 426 encoding considerations (e.g., DNS names containing non-ASCII 427 characters are expressed as A-labels rather than U-labels). Any such 428 encoding considerations are to be applied prior to the aforementioned 429 UTF-8 encoding. 431 6. Message Transport 433 Communications between an ACME client and an ACME server are done 434 over HTTPS, using JSON Web Signature (JWS) [RFC7515] to provide some 435 additional security properties for messages sent from the client to 436 the server. HTTPS provides server authentication and 437 confidentiality. With some ACME-specific extensions, JWS provides 438 authentication of the client's request payloads, anti-replay 439 protection, and integrity for the HTTPS request URL. 441 6.1. HTTPS Requests 443 Each ACME function is accomplished by the client sending a sequence 444 of HTTPS requests to the server, carrying JSON messages 445 [RFC2818][RFC7159]. Use of HTTPS is REQUIRED. Each subsection of 446 Section 7 below describes the message formats used by the function 447 and the order in which messages are sent. 449 In most HTTPS transactions used by ACME, the ACME client is the HTTPS 450 client and the ACME server is the HTTPS server. The ACME server acts 451 as a client when validating challenges: an HTTP client when 452 validating an 'http-01' challenge, a DNS client with 'dns-01', etc. 454 ACME servers SHOULD follow the recommendations of [RFC7525] when 455 configuring their TLS implementations. ACME servers that support TLS 456 1.3 MAY allow clients to send early data (0-RTT). This is safe 457 because the ACME protocol itself includes anti-replay protections 458 (see Section 6.5) in all cases where they are required. For this 459 reason, there are no restrictions on what ACME data can be carried in 460 0-RTT. 462 ACME clients MUST send a User-Agent header field, in accordance with 463 [RFC7231]. This header field SHOULD include the name and version of 464 the ACME software in addition to the name and version of the 465 underlying HTTP client software. 467 ACME clients SHOULD send an Accept-Language header field in 468 accordance with [RFC7231] to enable localization of error messages. 470 ACME servers that are intended to be generally accessible need to use 471 Cross-Origin Resource Sharing (CORS) in order to be accessible from 472 browser-based clients [W3C.REC-cors-20140116]. Such servers SHOULD 473 set the Access-Control-Allow-Origin header field to the value "*". 475 Binary fields in the JSON objects used by ACME are encoded using 476 base64url encoding described in [RFC4648] Section 5, according to the 477 profile specified in JSON Web Signature [RFC7515] Section 2. This 478 encoding uses a URL safe character set. Trailing '=' characters MUST 479 be stripped. Encoded values that include trailing '=' characters 480 MUST be rejected as improperly encoded. 482 6.2. Request Authentication 484 All ACME requests with a non-empty body MUST encapsulate their 485 payload in a JSON Web Signature (JWS) [RFC7515] object, signed using 486 the account's private key unless otherwise specified. The server 487 MUST verify the JWS before processing the request. Encapsulating 488 request bodies in JWS provides authentication of requests. 490 JWS objects sent in ACME requests MUST meet the following additional 491 criteria: 493 o The JWS MUST be in the Flattened JSON Serialization [RFC7515] 495 o The JWS MUST NOT have multiple signatures 497 o The JWS Unencoded Payload Option [RFC7797] MUST NOT be used 499 o The JWS Unprotected Header [RFC7515] MUST NOT be used 501 o The JWS Payload MUST NOT be detached 503 o The JWS Protected Header MUST include the following fields: 505 * "alg" (Algorithm) 507 + This field MUST NOT contain "none" or a Message 508 Authentication Code (MAC)-based algorithm (e.g. one in which 509 the algorithm registry description mentions MAC/HMAC). 511 * "nonce" (defined in Section 6.5 below) 513 * "url" (defined in Section 6.4 below) 514 * Either "jwk" (JSON Web Key) or "kid" (Key ID) as specified 515 below 517 An ACME server MUST implement the "ES256" signature algorithm 518 [RFC7518] and SHOULD implement the "EdDSA" signature algorithm using 519 the "Ed25519" variant (indicated by "crv") [RFC8037]. 521 The "jwk" and "kid" fields are mutually exclusive. Servers MUST 522 reject requests that contain both. 524 For newAccount requests, and for revokeCert requests authenticated by 525 a certificate key, there MUST be a "jwk" field. This field MUST 526 contain the public key corresponding to the private key used to sign 527 the JWS. 529 For all other requests, the request is signed using an existing 530 account and there MUST be a "kid" field. This field MUST contain the 531 account URL received by POSTing to the newAccount resource. 533 If the client sends a JWS signed with an algorithm that the server 534 does not support, then the server MUST return an error with status 535 code 400 (Bad Request) and type 536 "urn:ietf:params:acme:error:badSignatureAlgorithm". The problem 537 document returned with the error MUST include an "algorithms" field 538 with an array of supported "alg" values. See Section 6.7 for more 539 details on the structure of error responses. 541 Because client requests in ACME carry JWS objects in the Flattened 542 JSON Serialization, they must have the "Content-Type" header field 543 set to "application/jose+json". If a request does not meet this 544 requirement, then the server MUST return a response with status code 545 415 (Unsupported Media Type). 547 6.3. GET and POST-as-GET Requests 549 Note that authentication via signed JWS request bodies implies that 550 requests without an entity body are not authenticated, in particular 551 GET requests. Except for the cases described in this section, if the 552 server receives a GET request, it MUST return an error with status 553 code 405 "Method Not Allowed" and type "malformed". 555 If a client wishes to fetch a resource from the server (which would 556 otherwise be done with a GET), then it MUST send a POST request with 557 a JWS body as described above, where the payload of the JWS is a 558 zero-length octet string. In other words, the "payload" field of the 559 JWS object MUST be present and set to the empty string (""). 561 We will refer to these as "POST-as-GET" requests. On receiving a 562 request with a zero-length (and thus non-JSON) payload, the server 563 MUST authenticate the sender and verify any access control rules. 564 Otherwise, the server MUST treat this request as having the same 565 semantics as a GET request for the same resource. 567 The server MUST allow GET requests for the directory and newNonce 568 resources (see Section 7.1), in addition to POST-as-GET requests for 569 these resources. This enables clients to bootstrap into the ACME 570 authentication system. 572 6.4. Request URL Integrity 574 It is common in deployment for the entity terminating TLS for HTTPS 575 to be different from the entity operating the logical HTTPS server, 576 with a "request routing" layer in the middle. For example, an ACME 577 CA might have a content delivery network terminate TLS connections 578 from clients so that it can inspect client requests for denial-of- 579 service protection. 581 These intermediaries can also change values in the request that are 582 not signed in the HTTPS request, e.g., the request URL and header 583 fields. ACME uses JWS to provide an integrity mechanism, which 584 protects against an intermediary changing the request URL to another 585 ACME URL. 587 As noted in Section 6.2 above, all ACME request objects carry a "url" 588 header parameter in their protected header. This header parameter 589 encodes the URL to which the client is directing the request. On 590 receiving such an object in an HTTP request, the server MUST compare 591 the "url" header parameter to the request URL. If the two do not 592 match, then the server MUST reject the request as unauthorized. 594 Except for the directory resource, all ACME resources are addressed 595 with URLs provided to the client by the server. In requests sent to 596 these resources, the client MUST set the "url" header parameter to 597 the exact string provided by the server (rather than performing any 598 re-encoding on the URL). The server SHOULD perform the corresponding 599 string equality check, configuring each resource with the URL string 600 provided to clients and having the resource check that requests have 601 the same string in their "url" header parameter. The server MUST 602 reject the request as unauthorized if the string equality check 603 fails. 605 6.4.1. "url" (URL) JWS Header Parameter 607 The "url" header parameter specifies the URL [RFC3986] to which this 608 JWS object is directed. The "url" header parameter MUST be carried 609 in the protected header of the JWS. The value of the "url" header 610 parameter MUST be a string representing the target URL. 612 6.5. Replay protection 614 In order to protect ACME resources from any possible replay attacks, 615 ACME POST requests have a mandatory anti-replay mechanism. This 616 mechanism is based on the server maintaining a list of nonces that it 617 has issued, and requiring any signed request from the client to carry 618 such a nonce. 620 An ACME server provides nonces to clients using the HTTP Replay-Nonce 621 header field, as specified in Section 6.5.1 below. The server MUST 622 include a Replay-Nonce header field in every successful response to a 623 POST request and SHOULD provide it in error responses as well. 625 Every JWS sent by an ACME client MUST include, in its protected 626 header, the "nonce" header parameter, with contents as defined in 627 Section 6.5.2 below. As part of JWS verification, the ACME server 628 MUST verify that the value of the "nonce" header is a value that the 629 server previously provided in a Replay-Nonce header field. Once a 630 nonce value has appeared in an ACME request, the server MUST consider 631 it invalid, in the same way as a value it had never issued. 633 When a server rejects a request because its nonce value was 634 unacceptable (or not present), it MUST provide HTTP status code 400 635 (Bad Request), and indicate the ACME error type 636 "urn:ietf:params:acme:error:badNonce". An error response with the 637 "badNonce" error type MUST include a Replay-Nonce header with a fresh 638 nonce. On receiving such a response, a client SHOULD retry the 639 request using the new nonce. 641 The precise method used to generate and track nonces is up to the 642 server. For example, the server could generate a random 128-bit 643 value for each response, keep a list of issued nonces, and strike 644 nonces from this list as they are used. 646 6.5.1. Replay-Nonce 648 The "Replay-Nonce" header field includes a server-generated value 649 that the server can use to detect unauthorized replay in future 650 client requests. The server MUST generate the value provided in 651 Replay-Nonce in such a way that they are unique to each message, with 652 high probability, and unpredictable to anyone besides the server. 653 For instance, it is acceptable to generate Replay-Nonces randomly. 655 The value of the Replay-Nonce field MUST be an octet string encoded 656 according to the base64url encoding described in Section 2 of 657 [RFC7515]. Clients MUST ignore invalid Replay-Nonce values. The 658 ABNF [RFC5234] for the Replay-Nonce header field follows: 660 base64url = ALPHA / DIGIT / "-" / "_" 662 Replay-Nonce = 1*base64url 664 The Replay-Nonce header field SHOULD NOT be included in HTTP request 665 messages. 667 6.5.2. "nonce" (Nonce) JWS Header Parameter 669 The "nonce" header parameter provides a unique value that enables the 670 verifier of a JWS to recognize when replay has occurred. The "nonce" 671 header parameter MUST be carried in the protected header of the JWS. 673 The value of the "nonce" header parameter MUST be an octet string, 674 encoded according to the base64url encoding described in Section 2 of 675 [RFC7515]. If the value of a "nonce" header parameter is not valid 676 according to this encoding, then the verifier MUST reject the JWS as 677 malformed. 679 6.6. Rate Limits 681 Creation of resources can be rate limited by ACME servers to ensure 682 fair usage and prevent abuse. Once the rate limit is exceeded, the 683 server MUST respond with an error with the type 684 "urn:ietf:params:acme:error:rateLimited". Additionally, the server 685 SHOULD send a "Retry-After" header [RFC7231] indicating when the 686 current request may succeed again. If multiple rate limits are in 687 place, that is the time where all rate limits allow access again for 688 the current request with exactly the same parameters. 690 In addition to the human-readable "detail" field of the error 691 response, the server MAY send one or multiple link relations in the 692 "Link" header [RFC8288] pointing to documentation about the specific 693 rate limit that was hit, using the "help" link relation type. 695 6.7. Errors 697 Errors can be reported in ACME both at the HTTP layer and within 698 challenge objects as defined in Section 8. ACME servers can return 699 responses with an HTTP error response code (4XX or 5XX). For 700 example: If the client submits a request using a method not allowed 701 in this document, then the server MAY return status code 405 (Method 702 Not Allowed). 704 When the server responds with an error status, it SHOULD provide 705 additional information using a problem document [RFC7807]. To 706 facilitate automatic response to errors, this document defines the 707 following standard tokens for use in the "type" field (within the 708 ACME URN namespace "urn:ietf:params:acme:error:"): 710 +-------------------------+-----------------------------------------+ 711 | Type | Description | 712 +-------------------------+-----------------------------------------+ 713 | accountDoesNotExist | The request specified an account that | 714 | | does not exist | 715 | | | 716 | alreadyRevoked | The request specified a certificate to | 717 | | be revoked that has already been | 718 | | revoked | 719 | | | 720 | badCSR | The CSR is unacceptable (e.g., due to a | 721 | | short key) | 722 | | | 723 | badNonce | The client sent an unacceptable anti- | 724 | | replay nonce | 725 | | | 726 | badRevocationReason | The revocation reason provided is not | 727 | | allowed by the server | 728 | | | 729 | badSignatureAlgorithm | The JWS was signed with an algorithm | 730 | | the server does not support | 731 | | | 732 | caa | Certification Authority Authorization | 733 | | (CAA) records forbid the CA from | 734 | | issuing | 735 | | | 736 | compound | Specific error conditions are indicated | 737 | | in the "subproblems" array. | 738 | | | 739 | connection | The server could not connect to | 740 | | validation target | 741 | | | 742 | dns | There was a problem with a DNS query | 743 | | during identifier validation | 744 | | | 745 | externalAccountRequired | The request must include a value for | 746 | | the "externalAccountBinding" field | 747 | | | 748 | incorrectResponse | Response received didn't match the | 749 | | challenge's requirements | 750 | | | 751 | invalidContact | A contact URL for an account was | 752 | | invalid | 753 | | | 754 | malformed | The request message was malformed | 755 | | | 756 | rateLimited | The request exceeds a rate limit | 757 | | | 758 | rejectedIdentifier | The server will not issue for the | 759 | | identifier | 760 | | | 761 | serverInternal | The server experienced an internal | 762 | | error | 763 | | | 764 | tls | The server received a TLS error during | 765 | | validation | 766 | | | 767 | unauthorized | The client lacks sufficient | 768 | | authorization | 769 | | | 770 | unsupportedContact | A contact URL for an account used an | 771 | | unsupported protocol scheme | 772 | | | 773 | unsupportedIdentifier | An identifier is of an unsupported type | 774 | | | 775 | userActionRequired | Visit the "instance" URL and take | 776 | | actions specified there | 777 +-------------------------+-----------------------------------------+ 779 This list is not exhaustive. The server MAY return errors whose 780 "type" field is set to a URI other than those defined above. Servers 781 MUST NOT use the ACME URN namespace for errors not listed in the 782 appropriate IANA registry (see Section 9.6). Clients SHOULD display 783 the "detail" field of all errors. 785 In the remainder of this document, we use the tokens in the table 786 above to refer to error types, rather than the full URNs. For 787 example, an "error of type 'badCSR'" refers to an error document with 788 "type" value "urn:ietf:params:acme:error:badCSR". 790 6.7.1. Subproblems 792 Sometimes a CA may need to return multiple errors in response to a 793 request. Additionally, the CA may need to attribute errors to 794 specific identifiers. For instance, a new-order request may contain 795 multiple identifiers for which the CA cannot issue. In this 796 situation, an ACME problem document MAY contain the "subproblems" 797 field, containing a JSON array of problem documents, each of which 798 MAY contain an "identifier" field. If present, the "identifier" 799 field MUST contain an ACME identifier (Section 9.7.7). The 800 "identifier" field MUST NOT be present at the top level in ACME 801 problem documents. It can only be present in subproblems. 802 Subproblems need not all have the same type, and do not need to match 803 the top level type. 805 ACME clients may choose to use the "identifier" field of a subproblem 806 as a hint that an operation would succeed if that identifier were 807 omitted. For instance, if an order contains ten DNS identifiers, and 808 the new-order request returns a problem document with two 809 subproblems, referencing two of those identifiers, the ACME client 810 may choose to submit another order containing only the eight 811 identifiers not listed in the problem document. 813 HTTP/1.1 403 Forbidden 814 Content-Type: application/problem+json 816 { 817 "type": "urn:ietf:params:acme:error:malformed", 818 "detail": "Some of the identifiers requested were rejected", 819 "subproblems": [ 820 { 821 "type": "urn:ietf:params:acme:error:malformed", 822 "detail": "Invalid underscore in DNS name \"_example.com\"", 823 "identifier": { 824 "type": "dns", 825 "value": "_example.com" 826 } 827 }, 828 { 829 "type": "urn:ietf:params:acme:error:rejectedIdentifier", 830 "detail": "This CA will not issue for \"example.net\"", 831 "identifier": { 832 "type": "dns", 833 "value": "example.net" 834 } 835 } 836 ] 837 } 839 7. Certificate Management 841 In this section, we describe the certificate management functions 842 that ACME enables: 844 o Account Creation 846 o Ordering a Certificate 848 o Identifier Authorization 850 o Certificate Issuance 852 o Certificate Revocation 854 7.1. Resources 856 ACME is structured as a REST [REST] application with the following 857 types of resources: 859 o Account resources, representing information about an account 860 (Section 7.1.2, Section 7.3) 862 o Order resources, representing an account's requests to issue 863 certificates (Section 7.1.3) 865 o Authorization resources, representing an account's authorization 866 to act for an identifier (Section 7.1.4) 868 o Challenge resources, representing a challenge to prove control of 869 an identifier (Section 7.5, Section 8) 871 o Certificate resources, representing issued certificates 872 (Section 7.4.2) 874 o A "directory" resource (Section 7.1.1) 876 o A "newNonce" resource (Section 7.2) 878 o A "newAccount" resource (Section 7.3) 880 o A "newOrder" resource (Section 7.4) 882 o A "revokeCert" resource (Section 7.6) 884 o A "keyChange" resource (Section 7.3.5) 886 The server MUST provide "directory" and "newNonce" resources. 888 ACME uses different URLs for different management functions. Each 889 function is listed in a directory along with its corresponding URL, 890 so clients only need to be configured with the directory URL. These 891 URLs are connected by a few different link relations [RFC5988]. 893 The "up" link relation is used with challenge resources to indicate 894 the authorization resource to which a challenge belongs. It is also 895 used, with some media types, from certificate resources to indicate a 896 resource from which the client may fetch a chain of CA certificates 897 that could be used to validate the certificate in the original 898 resource. 900 The "index" link relation is present on all resources other than the 901 directory and indicates the URL of the directory. 903 The following diagram illustrates the relations between resources on 904 an ACME server. For the most part, these relations are expressed by 905 URLs provided as strings in the resources' JSON representations. 906 Lines with labels in quotes indicate HTTP link relations. 908 directory 909 | 910 +--> newNonce 911 | 912 +----------+----------+-----+-----+------------+ 913 | | | | | 914 | | | | | 915 V V V V V 916 newAccount newAuthz newOrder revokeCert keyChange 917 | | | 918 | | | 919 V | V 920 account | order --+--> finalize 921 | | | 922 | | +--> cert 923 | V 924 +---> authorization 925 | ^ 926 | | "up" 927 V | 928 challenge 930 ACME Resources and Relationships 932 The following table illustrates a typical sequence of requests 933 required to establish a new account with the server, prove control of 934 an identifier, issue a certificate, and fetch an updated certificate 935 some time after issuance. The "->" is a mnemonic for a Location 936 header pointing to a created resource. 938 +-------------------+--------------------------------+--------------+ 939 | Action | Request | Response | 940 +-------------------+--------------------------------+--------------+ 941 | Get directory | GET directory | 200 | 942 | | | | 943 | Get nonce | HEAD newNonce | 200 | 944 | | | | 945 | Create account | POST newAccount | 201 -> | 946 | | | account | 947 | | | | 948 | Submit order | POST newOrder | 201 -> order | 949 | | | | 950 | Fetch challenges | POST-as-GET order's | 200 | 951 | | authorization urls | | 952 | | | | 953 | Respond to | POST-as-GET authorization | 200 | 954 | challenges | challenge urls | | 955 | | | | 956 | Poll for status | POST-as-GET order | 200 | 957 | | | | 958 | Finalize order | POST order's finalize url | 200 | 959 | | | | 960 | Poll for status | POST-as-GET order | 200 | 961 | | | | 962 | Download | POST-as-GET order's | 200 | 963 | certificate | certificate url | | 964 +-------------------+--------------------------------+--------------+ 966 The remainder of this section provides the details of how these 967 resources are structured and how the ACME protocol makes use of them. 969 7.1.1. Directory 971 In order to help clients configure themselves with the right URLs for 972 each ACME operation, ACME servers provide a directory object. This 973 should be the only URL needed to configure clients. It is a JSON 974 object, whose field names are drawn from the resource registry 975 (Section 9.7.5) and whose values are the corresponding URLs. 977 +------------+--------------------+ 978 | Field | URL in value | 979 +------------+--------------------+ 980 | newNonce | New nonce | 981 | | | 982 | newAccount | New account | 983 | | | 984 | newOrder | New order | 985 | | | 986 | newAuthz | New authorization | 987 | | | 988 | revokeCert | Revoke certificate | 989 | | | 990 | keyChange | Key Change | 991 +------------+--------------------+ 993 There is no constraint on the URL of the directory except that it 994 should be different from the other ACME server resources' URLs, and 995 that it should not clash with other services. For instance: 997 o a host which functions as both an ACME and a Web server may want 998 to keep the root path "/" for an HTML "front page", and place the 999 ACME directory under the path "/acme". 1001 o a host which only functions as an ACME server could place the 1002 directory under the path "/". 1004 If the ACME server does not implement pre-authorization 1005 (Section 7.4.1) it MUST omit the "newAuthz" field of the directory. 1007 The object MAY additionally contain a field "meta". If present, it 1008 MUST be a JSON object; each field in the object is an item of 1009 metadata relating to the service provided by the ACME server. 1011 The following metadata items are defined (Section 9.7.6), all of 1012 which are OPTIONAL: 1014 termsOfService (optional, string): A URL identifying the current 1015 terms of service. 1017 website (optional, string): An HTTP or HTTPS URL locating a website 1018 providing more information about the ACME server. 1020 caaIdentities (optional, array of string): The hostnames that the 1021 ACME server recognizes as referring to itself for the purposes of 1022 CAA record validation as defined in [RFC6844]. Each string MUST 1023 represent the same sequence of ASCII code points that the server 1024 will expect to see as the "Issuer Domain Name" in a CAA issue or 1025 issuewild property tag. This allows clients to determine the 1026 correct issuer domain name to use when configuring CAA records. 1028 externalAccountRequired (optional, boolean): If this field is 1029 present and set to "true", then the CA requires that all new- 1030 account requests include an "externalAccountBinding" field 1031 associating the new account with an external account. 1033 Clients access the directory by sending a GET request to the 1034 directory URL. 1036 HTTP/1.1 200 OK 1037 Content-Type: application/json 1039 { 1040 "newNonce": "https://example.com/acme/new-nonce", 1041 "newAccount": "https://example.com/acme/new-account", 1042 "newOrder": "https://example.com/acme/new-order", 1043 "newAuthz": "https://example.com/acme/new-authz", 1044 "revokeCert": "https://example.com/acme/revoke-cert", 1045 "keyChange": "https://example.com/acme/key-change", 1046 "meta": { 1047 "termsOfService": "https://example.com/acme/terms/2017-5-30", 1048 "website": "https://www.example.com/", 1049 "caaIdentities": ["example.com"], 1050 "externalAccountRequired": false 1051 } 1052 } 1054 7.1.2. Account Objects 1056 An ACME account resource represents a set of metadata associated with 1057 an account. Account resources have the following structure: 1059 status (required, string): The status of this account. Possible 1060 values are: "valid", "deactivated", and "revoked". The value 1061 "deactivated" should be used to indicate client-initiated 1062 deactivation whereas "revoked" should be used to indicate server- 1063 initiated deactivation. (See Section 7.1.6) 1065 contact (optional, array of string): An array of URLs that the 1066 server can use to contact the client for issues related to this 1067 account. For example, the server may wish to notify the client 1068 about server-initiated revocation or certificate expiration. For 1069 information on supported URL schemes, see Section 7.3 1071 termsOfServiceAgreed (optional, boolean): Including this field in a 1072 new-account request, with a value of true, indicates the client's 1073 agreement with the terms of service. This field is not updateable 1074 by the client. 1076 orders (required, string): A URL from which a list of orders 1077 submitted by this account can be fetched via a POST-as-GET 1078 request, as described in Section 7.1.2.1. 1080 { 1081 "status": "valid", 1082 "contact": [ 1083 "mailto:cert-admin@example.com", 1084 "mailto:admin@example.com" 1085 ], 1086 "termsOfServiceAgreed": true, 1087 "orders": "https://example.com/acme/acct/evOfKhNU60wg/orders" 1088 } 1090 7.1.2.1. Orders List 1092 Each account object includes an "orders" URL from which a list of 1093 orders created by the account can be fetched via POST-as-GET request. 1094 The result of the request MUST be a JSON object whose "orders" field 1095 is an array of URLs, each identifying an order belonging to the 1096 account. The server SHOULD include pending orders, and SHOULD NOT 1097 include orders that are invalid in the array of URLs. The server MAY 1098 return an incomplete list, along with a Link header field with a 1099 "next" link relation indicating where further entries can be 1100 acquired. 1102 HTTP/1.1 200 OK 1103 Content-Type: application/json 1104 Link: ;rel="next" 1106 { 1107 "orders": [ 1108 "https://example.com/acme/order/TOlocE8rfgo", 1109 "https://example.com/acme/order/4E16bbL5iSw", 1110 /* more URLs not shown for example brevity */ 1111 "https://example.com/acme/order/neBHYLfw0mg" 1112 ] 1113 } 1115 7.1.3. Order Objects 1117 An ACME order object represents a client's request for a certificate 1118 and is used to track the progress of that order through to issuance. 1119 Thus, the object contains information about the requested 1120 certificate, the authorizations that the server requires the client 1121 to complete, and any certificates that have resulted from this order. 1123 status (required, string): The status of this order. Possible 1124 values are: "pending", "ready", "processing", "valid", and 1125 "invalid". (See Section 7.1.6) 1127 expires (optional, string): The timestamp after which the server 1128 will consider this order invalid, encoded in the format specified 1129 in RFC 3339 [RFC3339]. This field is REQUIRED for objects with 1130 "pending" or "valid" in the status field. 1132 identifiers (required, array of object): An array of identifier 1133 objects that the order pertains to. 1135 type (required, string): The type of identifier. This document 1136 defines the "dns" identifier type. See the registry defined in 1137 Section 9.7.7 for any others. 1139 value (required, string): The identifier itself. 1141 notBefore (optional, string): The requested value of the notBefore 1142 field in the certificate, in the date format defined in [RFC3339]. 1144 notAfter (optional, string): The requested value of the notAfter 1145 field in the certificate, in the date format defined in [RFC3339]. 1147 error (optional, object): The error that occurred while processing 1148 the order, if any. This field is structured as a problem document 1149 [RFC7807]. 1151 authorizations (required, array of string): For pending orders, the 1152 authorizations that the client needs to complete before the 1153 requested certificate can be issued (see Section 7.5), including 1154 unexpired authorizations that the client has completed in the past 1155 for identifiers specified in the order. The authorizations 1156 required are dictated by server policy and there may not be a 1:1 1157 relationship between the order identifiers and the authorizations 1158 required. For final orders (in the "valid" or "invalid" state), 1159 the authorizations that were completed. Each entry is a URL from 1160 which an authorization can be fetched with a POST-as-GET request. 1162 finalize (required, string): A URL that a CSR must be POSTed to once 1163 all of the order's authorizations are satisfied to finalize the 1164 order. The result of a successful finalization will be the 1165 population of the certificate URL for the order. 1167 certificate (optional, string): A URL for the certificate that has 1168 been issued in response to this order. 1170 { 1171 "status": "valid", 1172 "expires": "2015-03-01T14:09:07.99Z", 1174 "identifiers": [ 1175 { "type": "dns", "value": "example.com" }, 1176 { "type": "dns", "value": "www.example.com" } 1177 ], 1179 "notBefore": "2016-01-01T00:00:00Z", 1180 "notAfter": "2016-01-08T00:00:00Z", 1182 "authorizations": [ 1183 "https://example.com/acme/authz/PAniVnsZcis", 1184 "https://example.com/acme/authz/r4HqLzrSrpI" 1185 ], 1187 "finalize": "https://example.com/acme/order/TOlocE8rfgo/finalize", 1189 "certificate": "https://example.com/acme/cert/jWCdfHVGY2M" 1190 } 1192 Any identifier of type "dns" in a new-order request MAY have a 1193 wildcard domain name as its value. A wildcard domain name consists 1194 of a single asterisk character followed by a single full stop 1195 character ("*.") followed by a domain name as defined for use in the 1196 Subject Alternate Name Extension by RFC 5280 [RFC5280]. An 1197 authorization returned by the server for a wildcard domain name 1198 identifier MUST NOT include the asterisk and full stop ("*.") prefix 1199 in the authorization identifier value. The returned authorization 1200 MUST include the optional "wildcard" field, with a value of true. 1202 The elements of the "authorizations" and "identifiers" array are 1203 immutable once set. The server MUST NOT change the contents of 1204 either array after they are created. If a client observes a change 1205 in the contents of either array, then it SHOULD consider the order 1206 invalid. 1208 The "authorizations" array of the order SHOULD reflect all 1209 authorizations that the CA takes into account in deciding to issue, 1210 even if some authorizations were fulfilled in earlier orders or in 1211 pre-authorization transactions. For example, if a CA allows multiple 1212 orders to be fulfilled based on a single authorization transaction, 1213 then it SHOULD reflect that authorization in all of the orders. 1215 Note that just because an authorization URL is listed in the 1216 "authorizations" array of an order object doesn't mean that the 1217 client is required to take action. There are several reasons that 1218 the referenced authorizations may already be valid: 1220 o The client completed the authorization as part of a previous order 1222 o The client previously pre-authorized the identifier (see 1223 Section 7.4.1) 1225 o The server granted the client authorization based on an external 1226 account 1228 Clients SHOULD check the "status" field of an order to determine 1229 whether they need to take any action. 1231 7.1.4. Authorization Objects 1233 An ACME authorization object represents a server's authorization for 1234 an account to represent an identifier. In addition to the 1235 identifier, an authorization includes several metadata fields, such 1236 as the status of the authorization (e.g., "pending", "valid", or 1237 "revoked") and which challenges were used to validate possession of 1238 the identifier. 1240 The structure of an ACME authorization resource is as follows: 1242 identifier (required, object): The identifier that the account is 1243 authorized to represent 1245 type (required, string): The type of identifier. (See below and 1246 Section 9.7.7) 1248 value (required, string): The identifier itself. 1250 status (required, string): The status of this authorization. 1251 Possible values are: "pending", "valid", "invalid", "deactivated", 1252 "expired", and "revoked". (See Section 7.1.6) 1254 expires (optional, string): The timestamp after which the server 1255 will consider this authorization invalid, encoded in the format 1256 specified in RFC 3339 [RFC3339]. This field is REQUIRED for 1257 objects with "valid" in the "status" field. 1259 challenges (required, array of objects): For pending authorizations, 1260 the challenges that the client can fulfill in order to prove 1261 possession of the identifier. For valid authorizations, the 1262 challenge that was validated. For invalid authorizations, the 1263 challenge that was attempted and failed. Each array entry is an 1264 object with parameters required to validate the challenge. A 1265 client should attempt to fulfill one of these challenges, and a 1266 server should consider any one of the challenges sufficient to 1267 make the authorization valid. 1269 wildcard (optional, boolean): For authorizations created as a result 1270 of a newOrder request containing a DNS identifier with a value 1271 that contained a wildcard prefix this field MUST be present, and 1272 true. 1274 The only type of identifier defined by this specification is a fully- 1275 qualified domain name (type: "dns"). The domain name MUST be encoded 1276 in the form in which it would appear in a certificate. That is, it 1277 MUST be encoded according to the rules in Section 7 of [RFC5280]. 1278 Servers MUST verify any identifier values that begin with the ASCII 1279 Compatible Encoding prefix "xn--" as defined in [RFC5890] are 1280 properly encoded. Wildcard domain names (with "*" as the first 1281 label) MUST NOT be included in authorization objects. If an 1282 authorization object conveys authorization for the base domain of a 1283 newOrder DNS type identifier with a wildcard prefix then the optional 1284 authorizations "wildcard" field MUST be present with a value of true. 1286 Section 8 describes a set of challenges for domain name validation. 1288 { 1289 "status": "valid", 1290 "expires": "2015-03-01T14:09:07.99Z", 1292 "identifier": { 1293 "type": "dns", 1294 "value": "example.org" 1295 }, 1297 "challenges": [ 1298 { 1299 "url": "https://example.com/acme/chall/prV_B7yEyA4", 1300 "type": "http-01", 1301 "status": "valid", 1302 "token": "DGyRejmCefe7v4NfDGDKfA", 1303 "validated": "2014-12-01T12:05:58.16Z" 1304 } 1305 ], 1307 "wildcard": false 1308 } 1310 7.1.5. Challenge Objects 1312 An ACME challenge object represents a server's offer to validate a 1313 client's possession of an identifier in a specific way. Unlike the 1314 other objects listed above, there is not a single standard structure 1315 for a challenge object. The contents of a challenge object depend on 1316 the validation method being used. The general structure of challenge 1317 objects and an initial set of validation methods are described in 1318 Section 8. 1320 7.1.6. Status Changes 1322 Each ACME object type goes through a simple state machine over its 1323 lifetime. The "status" field of the object indicates which state the 1324 object is currently in. 1326 Challenge objects are created in the "pending" state. They 1327 transition to the "processing" state when the client responds to the 1328 challenge (see Section 7.5.1) and the server begins attempting to 1329 validate that the client has completed the challenge. Note that 1330 within the "processing" state, the server may attempt to validate the 1331 challenge multiple times (see Section 8.2). Likewise, client 1332 requests for retries do not cause a state change. If validation is 1333 successful, the challenge moves to the "valid" state; if there is an 1334 error, the challenge moves to the "invalid" state. 1336 pending 1337 | 1338 | Receive 1339 | response 1340 V 1341 processing <-+ 1342 | | | Server retry or 1343 | | | client retry request 1344 | +----+ 1345 | 1346 | 1347 Successful | Failed 1348 validation | validation 1349 +---------+---------+ 1350 | | 1351 V V 1352 valid invalid 1354 State Transitions for Challenge Objects 1356 Authorization objects are created in the "pending" state. If one of 1357 the challenges listed in the authorization transitions to the "valid" 1358 state, then the authorization also changes to the "valid" state. If 1359 the client attempts to fulfill a challenge and fails, or if there is 1360 an error while the authorization is still pending, then the 1361 authorization transitions to the "invalid" state. Once the 1362 authorization is in the valid state, it can expire ("expired"), be 1363 deactivated by the client ("deactivated", see Section 7.5.2), or 1364 revoked by the server ("revoked"). 1366 pending --------------------+ 1367 | | 1368 Challenge failure | | 1369 or | | 1370 Error | Challenge valid | 1371 +---------+---------+ | 1372 | | | 1373 V V | 1374 invalid valid | 1375 | | 1376 | | 1377 | | 1378 +--------------+--------------+ 1379 | | | 1380 | | | 1381 Server | Client | Time after | 1382 revoke | deactivate | "expires" | 1383 V V V 1384 revoked deactivated expired 1386 State Transitions for Authorization Objects 1388 Order objects are created in the "pending" state. Once all of the 1389 authorizations listed in the order object are in the "valid" state, 1390 the order transitions to the "ready" state. The order moves to the 1391 "processing" state after the client submits a request to the order's 1392 "finalize" URL and the CA begins the issuance process for the 1393 certificate. Once the certificate is issued, the order enters the 1394 "valid" state. If an error occurs at any of these stages, the order 1395 moves to the "invalid" state. The order also moves to the "invalid" 1396 state if it expires, or one of its authorizations enters a final 1397 state other than "valid" ("expired", "revoked", "deactivated"). 1399 pending --------------+ 1400 | | 1401 | All authz | 1402 | "valid" | 1403 V | 1404 ready ---------------+ 1405 | | 1406 | Receive | 1407 | finalize | 1408 | request | 1409 V | 1410 processing ------------+ 1411 | | 1412 | Certificate | Error or 1413 | issued | Authorization failure 1414 V V 1415 valid invalid 1417 State Transitions for Order Objects 1419 Account objects are created in the "valid" state, since no further 1420 action is required to create an account after a successful newAccount 1421 request. If the account is deactivated by the client or revoked by 1422 the server, it moves to the corresponding state. 1424 valid 1425 | 1426 | 1427 +-----------+-----------+ 1428 Client | Server | 1429 deactiv.| revoke | 1430 V V 1431 deactivated revoked 1433 State Transitions for Account Objects 1435 Note that some of these states may not ever appear in a "status" 1436 field, depending on server behavior. For example, a server that 1437 issues synchronously will never show an order in the "processing" 1438 state. A server that deletes expired authorizations immediately will 1439 never show an authorization in the "expired" state. 1441 7.2. Getting a Nonce 1443 Before sending a POST request to the server, an ACME client needs to 1444 have a fresh anti-replay nonce to put in the "nonce" header of the 1445 JWS. In most cases, the client will have gotten a nonce from a 1446 previous request. However, the client might sometimes need to get a 1447 new nonce, e.g., on its first request to the server or if an existing 1448 nonce is no longer valid. 1450 To get a fresh nonce, the client sends a HEAD request to the new- 1451 nonce resource on the server. The server's response MUST include a 1452 Replay-Nonce header field containing a fresh nonce, and SHOULD have 1453 status code 200 (OK). The server MUST also respond to GET requests 1454 for this resource, returning an empty body (while still providing a 1455 Replay-Nonce header) with a 204 (No Content) status. 1457 HEAD /acme/new-nonce HTTP/1.1 1458 Host: example.com 1460 HTTP/1.1 200 OK 1461 Replay-Nonce: oFvnlFP1wIhRlYS2jTaXbA 1462 Cache-Control: no-store 1464 Proxy caching of responses from the new-nonce resource can cause 1465 clients receive the same nonce repeatedly, leading to badNonce 1466 errors. The server MUST include a Cache-Control header field with 1467 the "no-store" directive in responses for the new-nonce resource, in 1468 order to prevent caching of this resource. 1470 7.3. Account Creation 1472 A client creates a new account with the server by sending a POST 1473 request to the server's new-account URL. The body of the request is 1474 a stub account object optionally containing the "contact" and 1475 "termsOfServiceAgreed" fields, and optionally the 1476 "onlyReturnExisting" and "externalAccountBinding" fields. 1478 contact (optional, array of string): Same meaning as the 1479 corresponding server field defined in Section 7.1.2 1481 termsOfServiceAgreed (optional, boolean): Same meaning as the 1482 corresponding server field defined in Section 7.1.2 1484 onlyReturnExisting (optional, boolean): If this field is present 1485 with the value "true", then the server MUST NOT create a new 1486 account if one does not already exist. This allows a client to 1487 look up an account URL based on an account key (see 1488 Section 7.3.1). 1490 externalAccountBinding (optional, object): An optional field for 1491 binding the new account with an existing non-ACME account (see 1492 Section 7.3.4). 1494 POST /acme/new-account HTTP/1.1 1495 Host: example.com 1496 Content-Type: application/jose+json 1498 { 1499 "protected": base64url({ 1500 "alg": "ES256", 1501 "jwk": {...}, 1502 "nonce": "6S8IqOGY7eL2lsGoTZYifg", 1503 "url": "https://example.com/acme/new-account" 1504 }), 1505 "payload": base64url({ 1506 "termsOfServiceAgreed": true, 1507 "contact": [ 1508 "mailto:cert-admin@example.com", 1509 "mailto:admin@example.com" 1510 ] 1511 }), 1512 "signature": "RZPOnYoPs1PhjszF...-nh6X1qtOFPB519I" 1513 } 1515 The server MUST ignore any values provided in the "orders" fields in 1516 account bodies sent by the client, as well as any other fields that 1517 it does not recognize. If new fields are specified in the future, 1518 the specification of those fields MUST describe whether they can be 1519 provided by the client. 1521 In general, the server MUST ignore any fields in the request object 1522 that it does not recognize. In particular, it MUST NOT reflect 1523 unrecognized fields in the resulting account object. This allows 1524 clients to detect when servers do not support an extension field. 1526 The server SHOULD validate that the contact URLs in the "contact" 1527 field are valid and supported by the server. If the server validates 1528 contact URLs it MUST support the "mailto" scheme. Clients MUST NOT 1529 provide a "mailto" URL in the "contact" field that contains "hfields" 1530 [RFC6068], or more than one "addr-spec" in the "to" component. If a 1531 server encounters a "mailto" contact URL that does not meet these 1532 criteria, then it SHOULD reject it as invalid. 1534 If the server rejects a contact URL for using an unsupported scheme 1535 it MUST return an error of type "unsupportedContact", with a 1536 description describing the error and what types of contact URLs the 1537 server considers acceptable. If the server rejects a contact URL for 1538 using a supported scheme but an invalid value then the server MUST 1539 return an error of type "invalidContact". 1541 If the server wishes to require the client to agree to terms under 1542 which the ACME service is to be used, it MUST indicate the URL where 1543 such terms can be accessed in the "termsOfService" subfield of the 1544 "meta" field in the directory object, and the server MUST reject new- 1545 account requests that do not have the "termsOfServiceAgreed" field 1546 set to "true". Clients SHOULD NOT automatically agree to terms by 1547 default. Rather, they SHOULD require some user interaction for 1548 agreement to terms. 1550 The server creates an account and stores the public key used to 1551 verify the JWS (i.e., the "jwk" element of the JWS header) to 1552 authenticate future requests from the account. The server returns 1553 this account object in a 201 (Created) response, with the account URL 1554 in a Location header field. The account URL is used as the "kid" 1555 value in the JWS authenticating subsequent requests by this account 1556 (See Section 6.2). 1558 HTTP/1.1 201 Created 1559 Content-Type: application/json 1560 Replay-Nonce: D8s4D2mLs8Vn-goWuPQeKA 1561 Location: https://example.com/acme/acct/evOfKhNU60wg 1562 Link: ;rel="index" 1564 { 1565 "status": "valid", 1567 "contact": [ 1568 "mailto:cert-admin@example.com", 1569 "mailto:admin@example.com" 1570 ], 1572 "orders": "https://example.com/acme/acct/evOfKhNU60wg/orders" 1573 } 1575 7.3.1. Finding an Account URL Given a Key 1577 If the server receives a newAccount request signed with a key for 1578 which it already has an account registered with the provided account 1579 key, then it MUST return a response with a 200 (OK) status code and 1580 provide the URL of that account in the Location header field. The 1581 body of this response represents the account object as it existed on 1582 the server before this request; any fields in the request object MUST 1583 be ignored. This allows a client that has an account key but not the 1584 corresponding account URL to recover the account URL. 1586 If a client wishes to find the URL for an existing account and does 1587 not want an account to be created if one does not already exist, then 1588 it SHOULD do so by sending a POST request to the new-account URL with 1589 a JWS whose payload has an "onlyReturnExisting" field set to "true" 1590 ({"onlyReturnExisting": true}). If a client sends such a request and 1591 an account does not exist, then the server MUST return an error 1592 response with status code 400 (Bad Request) and type 1593 "urn:ietf:params:acme:error:accountDoesNotExist". 1595 7.3.2. Account Update 1597 If the client wishes to update this information in the future, it 1598 sends a POST request with updated information to the account URL. 1599 The server MUST ignore any updates to the "orders" field, 1600 "termsOfServiceAgreed" field (see Section 7.3.3), the "status" field 1601 (except as allowed by Section 7.3.6), or any other fields it does not 1602 recognize. If the server accepts the update, it MUST return a 1603 response with a 200 (OK) status code and the resulting account 1604 object. 1606 For example, to update the contact information in the above account, 1607 the client could send the following request: 1609 POST /acme/acct/evOfKhNU60wg HTTP/1.1 1610 Host: example.com 1611 Content-Type: application/jose+json 1613 { 1614 "protected": base64url({ 1615 "alg": "ES256", 1616 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 1617 "nonce": "ax5RnthDqp_Yf4_HZnFLmA", 1618 "url": "https://example.com/acme/acct/evOfKhNU60wg" 1619 }), 1620 "payload": base64url({ 1621 "contact": [ 1622 "mailto:certificates@example.com", 1623 "mailto:admin@example.com" 1624 ] 1625 }), 1626 "signature": "hDXzvcj8T6fbFbmn...rDzXzzvzpRy64N0o" 1627 } 1629 7.3.3. Changes of Terms of Service 1631 As described above, a client can indicate its agreement with the CA's 1632 terms of service by setting the "termsOfServiceAgreed" field in its 1633 account object to "true". 1635 If the server has changed its terms of service since a client 1636 initially agreed, and the server is unwilling to process a request 1637 without explicit agreement to the new terms, then it MUST return an 1638 error response with status code 403 (Forbidden) and type 1639 "urn:ietf:params:acme:error:userActionRequired". This response MUST 1640 include a Link header field with link relation "terms-of-service" and 1641 the latest terms-of-service URL. 1643 The problem document returned with the error MUST also include an 1644 "instance" field, indicating a URL that the client should direct a 1645 human user to visit in order for instructions on how to agree to the 1646 terms. 1648 HTTP/1.1 403 Forbidden 1649 Replay-Nonce: T81bdZroZ2ITWSondpTmAw 1650 Link: ;rel="terms-of-service" 1651 Content-Type: application/problem+json 1652 Content-Language: en 1654 { 1655 "type": "urn:ietf:params:acme:error:userActionRequired", 1656 "detail": "Terms of service have changed", 1657 "instance": "https://example.com/acme/agreement/?token=W8Ih3PswD-8" 1658 } 1660 7.3.4. External Account Binding 1662 The server MAY require a value for the "externalAccountBinding" field 1663 to be present in "newAccount" requests. This can be used to 1664 associate an ACME account with an existing account in a non-ACME 1665 system, such as a CA customer database. 1667 To enable ACME account binding, the CA operating the ACME server 1668 needs to provide the ACME client with a MAC key and a key identifier, 1669 using some mechanism outside of ACME. The key identifier MUST be an 1670 ASCII string. The MAC key SHOULD be provided in base64url-encoded 1671 form, to maximize compatibility between non-ACME provisioning systems 1672 and ACME clients. 1674 The ACME client then computes a binding JWS to indicate the external 1675 account holder's approval of the ACME account key. The payload of 1676 this JWS is the ACME account key being registered, in JWK form. The 1677 protected header of the JWS MUST meet the following criteria: 1679 o The "alg" field MUST indicate a MAC-based algorithm 1681 o The "kid" field MUST contain the key identifier provided by the CA 1683 o The "nonce" field MUST NOT be present 1684 o The "url" field MUST be set to the same value as the outer JWS 1686 The "signature" field of the JWS will contain the MAC value computed 1687 with the MAC key provided by the CA. 1689 POST /acme/new-account HTTP/1.1 1690 Host: example.com 1691 Content-Type: application/jose+json 1693 { 1694 "protected": base64url({ 1695 "alg": "ES256", 1696 "jwk": /* account key */, 1697 "nonce": "K60BWPrMQG9SDxBDS_xtSw", 1698 "url": "https://example.com/acme/new-account" 1699 }), 1700 "payload": base64url({ 1701 "contact": ["mailto:example@anonymous.invalid"], 1702 "termsOfServiceAgreed": true, 1704 "externalAccountBinding": { 1705 "protected": base64url({ 1706 "alg": "HS256", 1707 "kid": /* key identifier from CA */, 1708 "url": "https://example.com/acme/new-account" 1709 }), 1710 "payload": base64url(/* same as in "jwk" above */), 1711 "signature": /* MAC using MAC key from CA */ 1712 } 1713 }), 1714 "signature": "5TWiqIYQfIDfALQv...x9C2mg8JGPxl5bI4" 1715 } 1717 If such a CA requires that new-account requests contain an 1718 "externalAccountBinding" field, then it MUST provide the value "true" 1719 in the "externalAccountRequired" subfield of the "meta" field in the 1720 directory object. If the CA receives a new-account request without 1721 an "externalAccountBinding" field, then it SHOULD reply with an error 1722 of type "externalAccountRequired". 1724 When a CA receives a new-account request containing an 1725 "externalAccountBinding" field, it decides whether or not to verify 1726 the binding. If the CA does not verify the binding, then it MUST NOT 1727 reflect the "externalAccountBinding" field in the resulting account 1728 object (if any). To verify the account binding, the CA MUST take the 1729 following steps: 1731 1. Verify that the value of the field is a well-formed JWS 1732 2. Verify that the JWS protected field meets the above criteria 1734 3. Retrieve the MAC key corresponding to the key identifier in the 1735 "kid" field 1737 4. Verify that the MAC on the JWS verifies using that MAC key 1739 5. Verify that the payload of the JWS represents the same key as was 1740 used to verify the outer JWS (i.e., the "jwk" field of the outer 1741 JWS) 1743 If all of these checks pass and the CA creates a new account, then 1744 the CA may consider the new account associated with the external 1745 account corresponding to the MAC key. The account object the CA 1746 returns MUST include an "externalAccountBinding" field with the same 1747 value as the field in the request. If any of these checks fail, then 1748 the CA MUST reject the new-account request. 1750 7.3.5. Account Key Roll-over 1752 A client may wish to change the public key that is associated with an 1753 account in order to recover from a key compromise or proactively 1754 mitigate the impact of an unnoticed key compromise. 1756 To change the key associated with an account, the client sends a 1757 request to the server containing signatures by both the old and new 1758 keys. The signature by the new key covers the account URL and the 1759 old key, signifying a request by the new key holder to take over the 1760 account from the old key holder. The signature by the old key covers 1761 this request and its signature, and indicates the old key holder's 1762 assent to the roll-over request. 1764 To create this request object, the client first constructs a key- 1765 change object describing the account to be updated and its account 1766 key: 1768 account (required, string): The URL for the account being modified. 1769 The content of this field MUST be the exact string provided in the 1770 Location header field in response to the new-account request that 1771 created the account. 1773 oldKey (required, JWK): The JWK representation of the old key 1775 The client then encapsulates the key-change object in an "inner" JWS, 1776 signed with the requested new account key. This "inner" JWS becomes 1777 the payload for the "outer" JWS that is the body of the ACME request. 1779 The outer JWS MUST meet the normal requirements for an ACME JWS (see 1780 Section 6.2). The inner JWS MUST meet the normal requirements, with 1781 the following differences: 1783 o The inner JWS MUST have a "jwk" header parameter, containing the 1784 public key of the new key pair. 1786 o The inner JWS MUST have the same "url" header parameter as the 1787 outer JWS. 1789 o The inner JWS MUST omit the "nonce" header parameter. 1791 This transaction has signatures from both the old and new keys so 1792 that the server can verify that the holders of the two keys both 1793 agree to the change. The signatures are nested to preserve the 1794 property that all signatures on POST messages are signed by exactly 1795 one key. The "inner" JWS effectively represents a request by the 1796 holder of the new key to take over the account form the holder of the 1797 old key. The "outer" JWS represents the current account holder's 1798 assent to this request. 1800 POST /acme/key-change HTTP/1.1 1801 Host: example.com 1802 Content-Type: application/jose+json 1804 { 1805 "protected": base64url({ 1806 "alg": "ES256", 1807 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 1808 "nonce": "S9XaOcxP5McpnTcWPIhYuB", 1809 "url": "https://example.com/acme/key-change" 1810 }), 1811 "payload": base64url({ 1812 "protected": base64url({ 1813 "alg": "ES256", 1814 "jwk": /* new key */, 1815 "url": "https://example.com/acme/key-change" 1816 }), 1817 "payload": base64url({ 1818 "account": "https://example.com/acme/acct/evOfKhNU60wg", 1819 "oldKey": /* old key */ 1820 }), 1821 "signature": "Xe8B94RD30Azj2ea...8BmZIRtcSKPSd8gU" 1822 }), 1823 "signature": "5TWiqIYQfIDfALQv...x9C2mg8JGPxl5bI4" 1824 } 1825 On receiving key-change request, the server MUST perform the 1826 following steps in addition to the typical JWS validation: 1828 1. Validate the POST request belongs to a currently active account, 1829 as described in Section 6. 1831 2. Check that the payload of the JWS is a well-formed JWS object 1832 (the "inner JWS"). 1834 3. Check that the JWS protected header of the inner JWS has a "jwk" 1835 field. 1837 4. Check that the inner JWS verifies using the key in its "jwk" 1838 field. 1840 5. Check that the payload of the inner JWS is a well-formed key- 1841 change object (as described above). 1843 6. Check that the "url" parameters of the inner and outer JWSs are 1844 the same. 1846 7. Check that the "account" field of the key-change object contains 1847 the URL for the account matching the old key (i.e., the "kid" 1848 field in the outer JWS). 1850 8. Check that the "oldKey" field of the key-change object is the 1851 same as the account key for the account in question. 1853 9. Check that no account exists whose account key is the same as the 1854 key in the "jwk" header parameter of the inner JWS. 1856 If all of these checks pass, then the server updates the 1857 corresponding account by replacing the old account key with the new 1858 public key and returns status code 200 (OK). Otherwise, the server 1859 responds with an error status code and a problem document describing 1860 the error. If there is an existing account with the new key 1861 provided, then the server SHOULD use status code 409 (Conflict) and 1862 provide the URL of that account in the Location header field. 1864 Note that changing the account key for an account SHOULD NOT have any 1865 other impact on the account. For example, the server MUST NOT 1866 invalidate pending orders or authorization transactions based on a 1867 change of account key. 1869 7.3.6. Account Deactivation 1871 A client can deactivate an account by posting a signed update to the 1872 account URL with a status field of "deactivated." Clients may wish 1873 to do this when the account key is compromised or decommissioned. A 1874 deactivated account can no longer request certificate issuance or 1875 access resources related to the account, such as orders or 1876 authorizations. If a server receives a POST or POST-as-GET from a 1877 deactivated account, it MUST return an error response with status 1878 code 401 (Unauthorized) and type 1879 "urn:ietf:params:acme:error:unauthorized". 1881 POST /acme/acct/evOfKhNU60wg HTTP/1.1 1882 Host: example.com 1883 Content-Type: application/jose+json 1885 { 1886 "protected": base64url({ 1887 "alg": "ES256", 1888 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 1889 "nonce": "ntuJWWSic4WVNSqeUmshgg", 1890 "url": "https://example.com/acme/acct/evOfKhNU60wg" 1891 }), 1892 "payload": base64url({ 1893 "status": "deactivated" 1894 }), 1895 "signature": "earzVLd3m5M4xJzR...bVTqn7R08AKOVf3Y" 1896 } 1898 The server MUST verify that the request is signed by the account key. 1899 If the server accepts the deactivation request, it replies with a 200 1900 (OK) status code and the current contents of the account object. 1902 Once an account is deactivated, the server MUST NOT accept further 1903 requests authorized by that account's key. The server SHOULD cancel 1904 any pending operations authorized by the account's key, such as 1905 certificate orders. A server may take a variety of actions in 1906 response to an account deactivation, e.g., deleting data related to 1907 that account or sending mail to the account's contacts. Servers 1908 SHOULD NOT revoke certificates issued by the deactivated account, 1909 since this could cause operational disruption for servers using these 1910 certificates. ACME does not provide a way to reactivate a 1911 deactivated account. 1913 7.4. Applying for Certificate Issuance 1915 The client begins the certificate issuance process by sending a POST 1916 request to the server's new-order resource. The body of the POST is 1917 a JWS object whose JSON payload is a subset of the order object 1918 defined in Section 7.1.3, containing the fields that describe the 1919 certificate to be issued: 1921 identifiers (required, array of object): An array of identifier 1922 objects that the client wishes to submit an order for. 1924 type (required, string): The type of identifier. 1926 value (required, string): The identifier itself. 1928 notBefore (optional, string): The requested value of the notBefore 1929 field in the certificate, in the date format defined in [RFC3339]. 1931 notAfter (optional, string): The requested value of the notAfter 1932 field in the certificate, in the date format defined in [RFC3339]. 1934 POST /acme/new-order HTTP/1.1 1935 Host: example.com 1936 Content-Type: application/jose+json 1938 { 1939 "protected": base64url({ 1940 "alg": "ES256", 1941 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 1942 "nonce": "5XJ1L3lEkMG7tR6pA00clA", 1943 "url": "https://example.com/acme/new-order" 1944 }), 1945 "payload": base64url({ 1946 "identifiers": [ 1947 { "type": "dns", "value": "example.com" } 1948 ], 1949 "notBefore": "2016-01-01T00:04:00+04:00", 1950 "notAfter": "2016-01-08T00:04:00+04:00" 1951 }), 1952 "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g" 1953 } 1955 The server MUST return an error if it cannot fulfill the request as 1956 specified, and MUST NOT issue a certificate with contents other than 1957 those requested. If the server requires the request to be modified 1958 in a certain way, it should indicate the required changes using an 1959 appropriate error type and description. 1961 If the server is willing to issue the requested certificate, it 1962 responds with a 201 (Created) response. The body of this response is 1963 an order object reflecting the client's request and any 1964 authorizations the client must complete before the certificate will 1965 be issued. 1967 HTTP/1.1 201 Created 1968 Replay-Nonce: MYAuvOpaoIiywTezizk5vw 1969 Location: https://example.com/acme/order/TOlocE8rfgo 1971 { 1972 "status": "pending", 1973 "expires": "2016-01-01T00:00:00Z", 1975 "notBefore": "2016-01-01T00:00:00Z", 1976 "notAfter": "2016-01-08T00:00:00Z", 1978 "identifiers": [ 1979 { "type": "dns", "value": "example.com" }, 1980 ], 1982 "authorizations": [ 1983 "https://example.com/acme/authz/PAniVnsZcis", 1984 ], 1986 "finalize": "https://example.com/acme/order/TOlocE8rfgo/finalize" 1987 } 1989 The order object returned by the server represents a promise that if 1990 the client fulfills the server's requirements before the "expires" 1991 time, then the server will be willing to finalize the order upon 1992 request and issue the requested certificate. In the order object, 1993 any authorization referenced in the "authorizations" array whose 1994 status is "pending" represents an authorization transaction that the 1995 client must complete before the server will issue the certificate 1996 (see Section 7.5). If the client fails to complete the required 1997 actions before the "expires" time, then the server SHOULD change the 1998 status of the order to "invalid" and MAY delete the order resource. 1999 Clients MUST NOT make any assumptions about the sort order of 2000 "identifiers" or "authorizations" elements in the returned order 2001 object. 2003 Once the client believes it has fulfilled the server's requirements, 2004 it should send a POST request to the order resource's finalize URL. 2005 The POST body MUST include a CSR: 2007 csr (required, string): A CSR encoding the parameters for the 2008 certificate being requested [RFC2986]. The CSR is sent in the 2009 base64url-encoded version of the DER format. (Note: Because this 2010 field uses base64url, and does not include headers, it is 2011 different from PEM.). 2013 POST /acme/order/TOlocE8rfgo/finalize HTTP/1.1 2014 Host: example.com 2015 Content-Type: application/jose+json 2017 { 2018 "protected": base64url({ 2019 "alg": "ES256", 2020 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2021 "nonce": "MSF2j2nawWHPxxkE3ZJtKQ", 2022 "url": "https://example.com/acme/order/TOlocE8rfgo/finalize" 2023 }), 2024 "payload": base64url({ 2025 "csr": "MIIBPTCBxAIBADBFMQ...FS6aKdZeGsysoCo4H9P", 2026 }), 2027 "signature": "uOrUfIIk5RyQ...nw62Ay1cl6AB" 2028 } 2030 The CSR encodes the client's requests with regard to the content of 2031 the certificate to be issued. The CSR MUST indicate the exact same 2032 set of requested identifiers as the initial new-order request. 2033 Identifiers of type "dns" MUST appear either in the commonName 2034 portion of the requested subject name, or in an extensionRequest 2035 attribute [RFC2985] requesting a subjectAltName extension. (These 2036 identifiers may appear in any sort order.) Specifications that 2037 define new identifier types must specify where in the certificate 2038 signing request these identifiers can appear. 2040 A request to finalize an order will result in error if the CA is 2041 unwilling to issue a certificate corresponding to the submitted CSR. 2042 For example: 2044 o If the order indicated does not have status "ready" 2046 o If the CSR and order identifiers differ 2048 o If the account is not authorized for the identifiers indicated in 2049 the CSR 2051 o If the CSR requests extensions that the CA is not willing to 2052 include 2054 In such cases, the problem document returned by the server SHOULD use 2055 error code "badCSR", and describe specific reasons the CSR was 2056 rejected in its "details" field. After returning such an error, the 2057 server SHOULD leave the order in the "ready" state, to allow the 2058 client to submit a new finalize request with an amended CSR. 2060 A request to finalize an order will return the order to be finalized. 2061 The client should begin polling the order by sending a POST-as-GET 2062 request to the order resource to obtain its current state. The 2063 status of the order will indicate what action the client should take: 2065 o "invalid": The certificate will not be issued. Consider this 2066 order process abandoned. 2068 o "pending": The server does not believe that the client has 2069 fulfilled the requirements. Check the "authorizations" array for 2070 entries that are still pending. 2072 o "ready": The server agrees that the requirements have been 2073 fulfilled, and is awaiting finalization. Submit a finalization 2074 request. 2076 o "processing": The certificate is being issued. Send a POST-as-GET 2077 request after the time given in the "Retry-After" header field of 2078 the response, if any. 2080 o "valid": The server has issued the certificate and provisioned its 2081 URL to the "certificate" field of the order. Download the 2082 certificate. 2084 HTTP/1.1 200 OK 2085 Replay-Nonce: CGf81JWBsq8QyIgPCi9Q9X 2086 Location: https://example.com/acme/order/TOlocE8rfgo 2088 { 2089 "status": "valid", 2090 "expires": "2015-12-31T00:17:00.00-09:00", 2092 "notBefore": "2015-12-31T00:17:00.00-09:00", 2093 "notAfter": "2015-12-31T00:17:00.00-09:00", 2095 "identifiers": [ 2096 { "type": "dns", "value": "example.com" }, 2097 { "type": "dns", "value": "www.example.com" } 2098 ], 2100 "authorizations": [ 2101 "https://example.com/acme/authz/PAniVnsZcis", 2102 "https://example.com/acme/authz/r4HqLzrSrpI" 2103 ], 2105 "finalize": "https://example.com/acme/order/TOlocE8rfgo/finalize", 2107 "certificate": "https://example.com/acme/cert/mAt3xBGaobw" 2108 } 2110 7.4.1. Pre-Authorization 2112 The order process described above presumes that authorization objects 2113 are created reactively, in response to a certificate order. Some 2114 servers may also wish to enable clients to obtain authorization for 2115 an identifier proactively, outside of the context of a specific 2116 issuance. For example, a client hosting virtual servers for a 2117 collection of names might wish to obtain authorization before any 2118 virtual servers are created and only create a certificate when a 2119 virtual server starts up. 2121 In some cases, a CA running an ACME server might have a completely 2122 external, non-ACME process for authorizing a client to issue 2123 certificates for an identifier. In these cases, the CA should 2124 provision its ACME server with authorization objects corresponding to 2125 these authorizations and reflect them as already valid in any orders 2126 submitted by the client. 2128 If a CA wishes to allow pre-authorization within ACME, it can offer a 2129 "new authorization" resource in its directory by adding the field 2130 "newAuthz" with a URL for the new authorization resource. 2132 To request authorization for an identifier, the client sends a POST 2133 request to the new-authorization resource specifying the identifier 2134 for which authorization is being requested. 2136 identifier (required, object): The identifier to appear in the 2137 resulting authorization object (see Section 7.1.4) 2139 type (required, string): The type of identifier. 2141 value (required, string): The identifier itself. 2143 POST /acme/new-authz HTTP/1.1 2144 Host: example.com 2145 Content-Type: application/jose+json 2147 { 2148 "protected": base64url({ 2149 "alg": "ES256", 2150 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2151 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2152 "url": "https://example.com/acme/new-authz" 2153 }), 2154 "payload": base64url({ 2155 "identifier": { 2156 "type": "dns", 2157 "value": "example.net" 2158 } 2159 }), 2160 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2161 } 2163 Note that because the identifier in a pre-authorization request is 2164 the exact identifier to be included in the authorization object, pre- 2165 authorization cannot be used to authorize issuance with wildcard DNS 2166 identifiers. 2168 Before processing the authorization request, the server SHOULD 2169 determine whether it is willing to issue certificates for the 2170 identifier. For example, the server should check that the identifier 2171 is of a supported type. Servers might also check names against a 2172 blacklist of known high-value identifiers. If the server is 2173 unwilling to issue for the identifier, it SHOULD return a 403 2174 (Forbidden) error, with a problem document describing the reason for 2175 the rejection. 2177 If the server is willing to proceed, it builds a pending 2178 authorization object from the inputs submitted by the client: 2180 o "identifier" the identifier submitted by the client 2182 o "status" MUST be "pending" unless the server has out-of-band 2183 information about the client's authorization status 2185 o "challenges" as selected by the server's policy for this 2186 identifier 2188 The server allocates a new URL for this authorization, and returns a 2189 201 (Created) response, with the authorization URL in the Location 2190 header field, and the JSON authorization object in the body. The 2191 client then follows the process described in Section 7.5 to complete 2192 the authorization process. 2194 7.4.2. Downloading the Certificate 2196 To download the issued certificate, the client simply sends a POST- 2197 as-GET request to the certificate URL. 2199 The default format of the certificate is application/pem-certificate- 2200 chain (see Section 9). 2202 The server MAY provide one or more link relation header fields 2203 [RFC5988] with relation "alternate". Each such field SHOULD express 2204 an alternative certificate chain starting with the same end-entity 2205 certificate. This can be used to express paths to various trust 2206 anchors. Clients can fetch these alternates and use their own 2207 heuristics to decide which is optimal. 2209 POST /acme/cert/mAt3xBGaobw HTTP/1.1 2210 Host: example.com 2211 Content-Type: application/jose+json 2212 Accept: application/pem-certificate-chain 2214 { 2215 "protected": base64url({ 2216 "alg": "ES256", 2217 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2218 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2219 "url": "https://example.com/acme/cert/mAt3xBGaobw" 2220 }), 2221 "payload": "", 2222 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2223 } 2225 HTTP/1.1 200 OK 2226 Content-Type: application/pem-certificate-chain 2227 Link: ;rel="index" 2229 -----BEGIN CERTIFICATE----- 2230 [End-entity certificate contents] 2231 -----END CERTIFICATE----- 2232 -----BEGIN CERTIFICATE----- 2233 [Issuer certificate contents] 2234 -----END CERTIFICATE----- 2235 -----BEGIN CERTIFICATE----- 2236 [Other certificate contents] 2237 -----END CERTIFICATE----- 2239 An ACME client MAY attempt to fetch the certificate with a GET 2240 request. If the server does not allow GET requests for certificate 2241 resources, then it will return an error as described in Section 6.3. 2242 On receiving such an error, the client SHOULD fall back to a POST-as- 2243 GET request. 2245 A certificate resource represents a single, immutable certificate. 2246 If the client wishes to obtain a renewed certificate, the client 2247 initiates a new order process to request one. 2249 Because certificate resources are immutable once issuance is 2250 complete, the server MAY enable the caching of the resource by adding 2251 Expires and Cache-Control header fields specifying a point in time in 2252 the distant future. These header fields have no relation to the 2253 certificate's period of validity. 2255 The ACME client MAY request other formats by including an Accept 2256 header field [RFC7231] in its request. For example, the client could 2257 use the media type "application/pkix-cert" [RFC2585] or "applicaiton/ 2258 pkcs7-mime" [RFC5751] to request the end-entity certificate in DER 2259 format. Server support for alternate formats is OPTIONAL. For 2260 formats that can only express a single certificate, the server SHOULD 2261 provide one or more "Link: rel="up"" header fields pointing to an 2262 issuer or issuers so that ACME clients can build a certificate chain 2263 as defined in TLS [RFC8446]. 2265 7.5. Identifier Authorization 2267 The identifier authorization process establishes the authorization of 2268 an account to manage certificates for a given identifier. This 2269 process assures the server of two things: 2271 1. That the client controls the private key of the account key pair, 2272 and 2274 2. That the client controls the identifier in question. 2276 This process may be repeated to associate multiple identifiers to a 2277 key pair (e.g., to request certificates with multiple identifiers), 2278 or to associate multiple accounts with an identifier (e.g., to allow 2279 multiple entities to manage certificates). 2281 Authorization resources are created by the server in response to 2282 certificate orders or authorization requests submitted by an account 2283 key holder; their URLs are provided to the client in the responses to 2284 these requests. The authorization object is implicitly tied to the 2285 account key used to sign the request. 2287 When a client receives an order from the server in reply to a new 2288 order request, it downloads the authorization resources by sending 2289 POST-as-GET requests to the indicated URLs. If the client initiates 2290 authorization using a request to the new authorization resource, it 2291 will have already received the pending authorization object in the 2292 response to that request. 2294 POST /acme/authz/PAniVnsZcis HTTP/1.1 2295 Host: example.com 2296 Content-Type: application/jose+json 2298 { 2299 "protected": base64url({ 2300 "alg": "ES256", 2301 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2302 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2303 "url": "https://example.com/acme/authz/1234" 2304 }), 2305 "payload": "", 2306 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2307 } 2309 HTTP/1.1 200 OK 2310 Content-Type: application/json 2311 Link: ;rel="index" 2313 { 2314 "status": "pending", 2315 "expires": "2018-03-03T14:09:30Z", 2317 "identifier": { 2318 "type": "dns", 2319 "value": "example.org" 2320 }, 2322 "challenges": [ 2323 { 2324 "type": "http-01", 2325 "url": "https://example.com/acme/chall/prV_B7yEyA4", 2326 "token": "DGyRejmCefe7v4NfDGDKfA" 2327 }, 2328 { 2329 "type": "dns-01", 2330 "url": "https://example.com/acme/chall/Rg5dV14Gh1Q", 2331 "token": "DGyRejmCefe7v4NfDGDKfA" 2332 } 2333 ], 2335 "wildcard": false 2336 } 2338 7.5.1. Responding to Challenges 2340 To prove control of the identifier and receive authorization, the 2341 client needs to provision the required challenge response based on 2342 the challenge type and indicate to the server that it is ready for 2343 the challenge validation to be attempted. 2345 The client indicates to the server it is ready for the challenge 2346 validation by sending an empty JSON body ("{}"), carried in a POST 2347 request to the challenge URL (not authorization URL). 2349 For example, if the client were to respond to the "http-01" challenge 2350 in the above authorization, it would send the following request: 2352 POST /acme/chall/prV_B7yEyA4 HTTP/1.1 2353 Host: example.com 2354 Content-Type: application/jose+json 2356 { 2357 "protected": base64url({ 2358 "alg": "ES256", 2359 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2360 "nonce": "Q_s3MWoqT05TrdkM2MTDcw", 2361 "url": "https://example.com/acme/chall/prV_B7yEyA4" 2362 }), 2363 "payload": base64url({}), 2364 "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ" 2365 } 2367 The server updates the authorization document by updating its 2368 representation of the challenge with the response object provided by 2369 the client. The server MUST ignore any fields in the response object 2370 that are not specified as response fields for this type of challenge. 2371 The server provides a 200 (OK) response with the updated challenge 2372 object as its body. 2374 If the client's response is invalid for any reason or does not 2375 provide the server with appropriate information to validate the 2376 challenge, then the server MUST return an HTTP error. On receiving 2377 such an error, the client SHOULD undo any actions that have been 2378 taken to fulfill the challenge, e.g., removing files that have been 2379 provisioned to a web server. 2381 The server is said to "finalize" the authorization when it has 2382 completed one of the validations, by assigning the authorization a 2383 status of "valid" or "invalid", corresponding to whether it considers 2384 the account authorized for the identifier. If the final state is 2385 "valid", then the server MUST include an "expires" field. When 2386 finalizing an authorization, the server MAY remove challenges other 2387 than the one that was completed, and may modify the "expires" field. 2388 The server SHOULD NOT remove challenges with status "invalid". 2390 Usually, the validation process will take some time, so the client 2391 will need to poll the authorization resource to see when it is 2392 finalized. For challenges where the client can tell when the server 2393 has validated the challenge (e.g., by seeing an HTTP or DNS request 2394 from the server), the client SHOULD NOT begin polling until it has 2395 seen the validation request from the server. 2397 To check on the status of an authorization, the client sends a POST- 2398 as-GET request to the authorization URL, and the server responds with 2399 the current authorization object. In responding to poll requests 2400 while the validation is still in progress, the server MUST return a 2401 200 (OK) response and MAY include a Retry-After header field to 2402 suggest a polling interval to the client. 2404 POST /acme/authz/PAniVnsZcis HTTP/1.1 2405 Host: example.com 2406 Content-Type: application/jose+json 2408 { 2409 "protected": base64url({ 2410 "alg": "ES256", 2411 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2412 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2413 "url": "https://example.com/acme/authz/PAniVnsZcis" 2414 }), 2415 "payload": "", 2416 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2417 } 2419 HTTP/1.1 200 OK 2420 Content-Type: application/json 2422 { 2423 "status": "valid", 2424 "expires": "2018-09-09T14:09:01.13Z", 2426 "identifier": { 2427 "type": "dns", 2428 "value": "example.org" 2429 }, 2431 "challenges": [ 2432 { 2433 "type": "http-01", 2434 "url": "https://example.com/acme/chall/prV_B7yEyA4", 2435 "status": "valid", 2436 "validated": "2014-12-01T12:05:13.72Z", 2437 "token": "IlirfxKKXAsHtmzK29Pj8A" 2438 } 2439 ], 2441 "wildcard": false 2442 } 2444 7.5.2. Deactivating an Authorization 2446 If a client wishes to relinquish its authorization to issue 2447 certificates for an identifier, then it may request that the server 2448 deactivates each authorization associated with it by sending POST 2449 requests with the static object {"status": "deactivated"} to each 2450 authorization URL. 2452 POST /acme/authz/PAniVnsZcis HTTP/1.1 2453 Host: example.com 2454 Content-Type: application/jose+json 2456 { 2457 "protected": base64url({ 2458 "alg": "ES256", 2459 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2460 "nonce": "xWCM9lGbIyCgue8di6ueWQ", 2461 "url": "https://example.com/acme/authz/PAniVnsZcis" 2462 }), 2463 "payload": base64url({ 2464 "status": "deactivated" 2465 }), 2466 "signature": "srX9Ji7Le9bjszhu...WTFdtujObzMtZcx4" 2467 } 2469 The server MUST verify that the request is signed by the account key 2470 corresponding to the account that owns the authorization. If the 2471 server accepts the deactivation, it should reply with a 200 (OK) 2472 status code and the updated contents of the authorization object. 2474 The server MUST NOT treat deactivated authorization objects as 2475 sufficient for issuing certificates. 2477 7.6. Certificate Revocation 2479 To request that a certificate be revoked, the client sends a POST 2480 request to the ACME server's revokeCert URL. The body of the POST is 2481 a JWS object whose JSON payload contains the certificate to be 2482 revoked: 2484 certificate (required, string): The certificate to be revoked, in 2485 the base64url-encoded version of the DER format. (Note: Because 2486 this field uses base64url, and does not include headers, it is 2487 different from PEM.) 2489 reason (optional, int): One of the revocation reasonCodes defined in 2490 Section 5.3.1 of [RFC5280] to be used when generating OCSP 2491 responses and CRLs. If this field is not set the server SHOULD 2492 omit the reasonCode CRL entry extension when generating OCSP 2493 responses and CRLs. The server MAY disallow a subset of 2494 reasonCodes from being used by the user. If a request contains a 2495 disallowed reasonCode the server MUST reject it with the error 2496 type "urn:ietf:params:acme:error:badRevocationReason". The 2497 problem document detail SHOULD indicate which reasonCodes are 2498 allowed. 2500 Revocation requests are different from other ACME requests in that 2501 they can be signed either with an account key pair or the key pair in 2502 the certificate. 2504 Example using an account key pair for the signature: 2506 POST /acme/revoke-cert HTTP/1.1 2507 Host: example.com 2508 Content-Type: application/jose+json 2510 { 2511 "protected": base64url({ 2512 "alg": "ES256", 2513 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2514 "nonce": "JHb54aT_KTXBWQOzGYkt9A", 2515 "url": "https://example.com/acme/revoke-cert" 2516 }), 2517 "payload": base64url({ 2518 "certificate": "MIIEDTCCAvegAwIBAgIRAP8...", 2519 "reason": 4 2520 }), 2521 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2522 } 2524 Example using the certificate key pair for the signature: 2526 POST /acme/revoke-cert HTTP/1.1 2527 Host: example.com 2528 Content-Type: application/jose+json 2530 { 2531 "protected": base64url({ 2532 "alg": "RS256", 2533 "jwk": /* certificate's public key */, 2534 "nonce": "JHb54aT_KTXBWQOzGYkt9A", 2535 "url": "https://example.com/acme/revoke-cert" 2536 }), 2537 "payload": base64url({ 2538 "certificate": "MIIEDTCCAvegAwIBAgIRAP8...", 2539 "reason": 1 2540 }), 2541 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2542 } 2544 Before revoking a certificate, the server MUST verify that the key 2545 used to sign the request is authorized to revoke the certificate. 2546 The server MUST consider at least the following accounts authorized 2547 for a given certificate: 2549 o the account that issued the certificate. 2551 o an account that holds authorizations for all of the identifiers in 2552 the certificate. 2554 The server MUST also consider a revocation request valid if it is 2555 signed with the private key corresponding to the public key in the 2556 certificate. 2558 If the revocation succeeds, the server responds with status code 200 2559 (OK). If the revocation fails, the server returns an error. For 2560 example, if the certificate has already been revoked the server 2561 returns an error response with status code 400 (Bad Request) and type 2562 "urn:ietf:params:acme:error:alreadyRevoked". 2564 HTTP/1.1 200 OK 2565 Replay-Nonce: IXVHDyxIRGcTE0VSblhPzw 2566 Content-Length: 0 2568 --- or --- 2570 HTTP/1.1 403 Forbidden 2571 Replay-Nonce: IXVHDyxIRGcTE0VSblhPzw 2572 Content-Type: application/problem+json 2573 Content-Language: en 2575 { 2576 "type": "urn:ietf:params:acme:error:unauthorized", 2577 "detail": "No authorization provided for name example.net" 2578 } 2580 8. Identifier Validation Challenges 2582 There are few types of identifiers in the world for which there is a 2583 standardized mechanism to prove possession of a given identifier. In 2584 all practical cases, CAs rely on a variety of means to test whether 2585 an entity applying for a certificate with a given identifier actually 2586 controls that identifier. 2588 Challenges provide the server with assurance that an account holder 2589 is also the entity that controls an identifier. For each type of 2590 challenge, it must be the case that in order for an entity to 2591 successfully complete the challenge the entity must both: 2593 o Hold the private key of the account key pair used to respond to 2594 the challenge 2596 o Control the identifier in question 2597 Section 10 documents how the challenges defined in this document meet 2598 these requirements. New challenges will need to document how they 2599 do. 2601 ACME uses an extensible challenge/response framework for identifier 2602 validation. The server presents a set of challenges in the 2603 authorization object it sends to a client (as objects in the 2604 "challenges" array), and the client responds by sending a response 2605 object in a POST request to a challenge URL. 2607 This section describes an initial set of challenge types. The 2608 definition of a challenge type includes: 2610 1. Content of challenge objects 2612 2. Content of response objects 2614 3. How the server uses the challenge and response to verify control 2615 of an identifier 2617 Challenge objects all contain the following basic fields: 2619 type (required, string): The type of challenge encoded in the 2620 object. 2622 url (required, string): The URL to which a response can be posted. 2624 status (required, string): The status of this challenge. Possible 2625 values are: "pending", "processing", "valid", and "invalid". (See 2626 Section 7.1.6) 2628 validated (optional, string): The time at which the server validated 2629 this challenge, encoded in the format specified in RFC 3339 2630 [RFC3339]. This field is REQUIRED if the "status" field is 2631 "valid". 2633 error (optional, object): Error that occurred while the server was 2634 validating the challenge, if any, structured as a problem document 2635 [RFC7807]. Multiple errors can be indicated by using subproblems 2636 Section 6.7.1. A challenge object with an error MUST have status 2637 equal to "invalid". 2639 All additional fields are specified by the challenge type. If the 2640 server sets a challenge's "status" to "invalid", it SHOULD also 2641 include the "error" field to help the client diagnose why the 2642 challenge failed. 2644 Different challenges allow the server to obtain proof of different 2645 aspects of control over an identifier. In some challenges, like HTTP 2646 and DNS, the client directly proves its ability to do certain things 2647 related to the identifier. The choice of which challenges to offer 2648 to a client under which circumstances is a matter of server policy. 2650 The identifier validation challenges described in this section all 2651 relate to validation of domain names. If ACME is extended in the 2652 future to support other types of identifiers, there will need to be 2653 new challenge types, and they will need to specify which types of 2654 identifier they apply to. 2656 8.1. Key Authorizations 2658 All challenges defined in this document make use of a key 2659 authorization string. A key authorization is a string that 2660 concatinates the token for the challenge with a key fingerprint, 2661 separated by a "." character: 2663 keyAuthorization = token || '.' || base64url(Thumbprint(accountKey)) 2665 The "Thumbprint" step indicates the computation specified in 2666 [RFC7638], using the SHA-256 digest [FIPS180-4]. As noted in 2667 [RFC7518] any prepended zero octets in the fields of a JWK object 2668 MUST be stripped before doing the computation. 2670 As specified in the individual challenges below, the token for a 2671 challenge is a string comprised entirely of characters in the URL- 2672 safe base64 alphabet. The "||" operator indicates concatenation of 2673 strings. 2675 8.2. Retrying Challenges 2677 ACME challenges typically require the client to set up some network- 2678 accessible resource that the server can query in order to validate 2679 that the client controls an identifier. In practice it is not 2680 uncommon for the server's queries to fail while a resource is being 2681 set up, e.g., due to information propagating across a cluster or 2682 firewall rules not being in place. 2684 Clients SHOULD NOT respond to challenges until they believe that the 2685 server's queries will succeed. If a server's initial validation 2686 query fails, the server SHOULD retry the query after some time, in 2687 order to account for delay in setting up responses such as DNS 2688 records or HTTP resources. The precise retry schedule is up to the 2689 server, but server operators should keep in mind the operational 2690 scenarios that the schedule is trying to accommodate. Given that 2691 retries are intended to address things like propagation delays in 2692 HTTP or DNS provisioning, there should not usually be any reason to 2693 retry more often than every 5 or 10 seconds. While the server is 2694 still trying, the status of the challenge remains "processing"; it is 2695 only marked "invalid" once the server has given up. 2697 The server MUST provide information about its retry state to the 2698 client via the "error" field in the challenge and the Retry-After 2699 HTTP header field in response to requests to the challenge resource. 2700 The server MUST add an entry to the "error" field in the challenge 2701 after each failed validation query. The server SHOULD set the Retry- 2702 After header field to a time after the server's next validation 2703 query, since the status of the challenge will not change until that 2704 time. 2706 Clients can explicitly request a retry by re-sending their response 2707 to a challenge in a new POST request (with a new nonce, etc.). This 2708 allows clients to request a retry when the state has changed (e.g., 2709 after firewall rules have been updated). Servers SHOULD retry a 2710 request immediately on receiving such a POST request. In order to 2711 avoid denial-of-service attacks via client-initiated retries, servers 2712 SHOULD rate-limit such requests. 2714 8.3. HTTP Challenge 2716 With HTTP validation, the client in an ACME transaction proves its 2717 control over a domain name by proving that it can provision HTTP 2718 resources on a server accessible under that domain name. The ACME 2719 server challenges the client to provision a file at a specific path, 2720 with a specific string as its content. 2722 As a domain may resolve to multiple IPv4 and IPv6 addresses, the 2723 server will connect to at least one of the hosts found in the DNS A 2724 and AAAA records, at its discretion. Because many web servers 2725 allocate a default HTTPS virtual host to a particular low-privilege 2726 tenant user in a subtle and non-intuitive manner, the challenge must 2727 be completed over HTTP, not HTTPS. 2729 type (required, string): The string "http-01" 2731 token (required, string): A random value that uniquely identifies 2732 the challenge. This value MUST have at least 128 bits of entropy. 2733 It MUST NOT contain any characters outside the base64url alphabet, 2734 and MUST NOT include base64 padding characters ("="). See 2735 [RFC4086] for additional information on randomness requirements. 2737 { 2738 "type": "http-01", 2739 "url": "https://example.com/acme/chall/prV_B7yEyA4", 2740 "status": "pending", 2741 "token": "LoqXcYV8q5ONbJQxbmR7SCTNo3tiAXDfowyjxAjEuX0" 2742 } 2744 A client fulfills this challenge by constructing a key authorization 2745 from the "token" value provided in the challenge and the client's 2746 account key. The client then provisions the key authorization as a 2747 resource on the HTTP server for the domain in question. 2749 The path at which the resource is provisioned is comprised of the 2750 fixed prefix "/.well-known/acme-challenge/", followed by the "token" 2751 value in the challenge. The value of the resource MUST be the ASCII 2752 representation of the key authorization. 2754 GET /.well-known/acme-challenge/LoqXcYV8...jxAjEuX0 2755 Host: example.org 2757 HTTP/1.1 200 OK 2758 Content-Type: application/octet-stream 2760 LoqXcYV8...jxAjEuX0.9jg46WB3...fm21mqTI 2762 (In the above, "..." indicates that the token and the JWK thumbprint 2763 in the key authorization have been truncated to fit on the page.) 2765 A client responds with an empty object ({}) to acknowledge that the 2766 challenge can be validated by the server. 2768 POST /acme/authz/PAniVnsZcis/0 2769 Host: example.com 2770 Content-Type: application/jose+json 2772 { 2773 "protected": base64url({ 2774 "alg": "ES256", 2775 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2776 "nonce": "UQI1PoRi5OuXzxuX7V7wL0", 2777 "url": "https://example.com/acme/chall/prV_B7yEyA4" 2778 }), 2779 "payload": base64url({}), 2780 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2781 } 2782 On receiving a response, the server constructs and stores the key 2783 authorization from the challenge "token" value and the current client 2784 account key. 2786 Given a challenge/response pair, the server verifies the client's 2787 control of the domain by verifying that the resource was provisioned 2788 as expected. 2790 1. Construct a URL by populating the URL template [RFC6570] 2791 "http://{domain}/.well-known/acme-challenge/{token}", where: 2793 * the domain field is set to the domain name being verified; and 2795 * the token field is set to the token in the challenge. 2797 2. Verify that the resulting URL is well-formed. 2799 3. Dereference the URL using an HTTP GET request. This request MUST 2800 be sent to TCP port 80 on the HTTP server. 2802 4. Verify that the body of the response is a well-formed key 2803 authorization. The server SHOULD ignore whitespace characters at 2804 the end of the body. 2806 5. Verify that key authorization provided by the HTTP server matches 2807 the key authorization stored by the server. 2809 The server SHOULD follow redirects when dereferencing the URL. 2810 Clients might use redirects, for example, so that the response can be 2811 provided by a centralized certificate management server. See 2812 Section 10.2 for security considerations related to redirects. 2814 If all of the above verifications succeed, then the validation is 2815 successful. If the request fails, or the body does not pass these 2816 checks, then it has failed. 2818 The client SHOULD de-provision the resource provisioned for this 2819 challenge once the challenge is complete, i.e., once the "status" 2820 field of the challenge has the value "valid" or "invalid". 2822 8.4. DNS Challenge 2824 When the identifier being validated is a domain name, the client can 2825 prove control of that domain by provisioning a TXT resource record 2826 containing a designated value for a specific validation domain name. 2828 type (required, string): The string "dns-01" 2829 token (required, string): A random value that uniquely identifies 2830 the challenge. This value MUST have at least 128 bits of entropy. 2831 It MUST NOT contain any characters outside the base64url alphabet, 2832 including padding characters ("="). See [RFC4086] for additional 2833 information on randomness requirements. 2835 { 2836 "type": "dns-01", 2837 "url": "https://example.com/acme/chall/Rg5dV14Gh1Q", 2838 "status": "pending", 2839 "token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA" 2840 } 2842 A client fulfills this challenge by constructing a key authorization 2843 from the "token" value provided in the challenge and the client's 2844 account key. The client then computes the SHA-256 digest [FIPS180-4] 2845 of the key authorization. 2847 The record provisioned to the DNS contains the base64url encoding of 2848 this digest. The client constructs the validation domain name by 2849 prepending the label "_acme-challenge" to the domain name being 2850 validated, then provisions a TXT record with the digest value under 2851 that name. For example, if the domain name being validated is 2852 "example.org", then the client would provision the following DNS 2853 record: 2855 _acme-challenge.example.org. 300 IN TXT "gfj9Xq...Rg85nM" 2857 A client responds with an empty object ({}) to acknowledge that the 2858 challenge can be validated by the server. 2860 POST /acme/chall/Rg5dV14Gh1Q 2861 Host: example.com 2862 Content-Type: application/jose+json 2864 { 2865 "protected": base64url({ 2866 "alg": "ES256", 2867 "kid": "https://example.com/acme/acct/evOfKhNU60wg", 2868 "nonce": "SS2sSl1PtspvFZ08kNtzKd", 2869 "url": "https://example.com/acme/chall/Rg5dV14Gh1Q" 2870 }), 2871 "payload": base64url({}), 2872 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2873 } 2874 On receiving a response, the server constructs and stores the key 2875 authorization from the challenge "token" value and the current client 2876 account key. 2878 To validate a DNS challenge, the server performs the following steps: 2880 1. Compute the SHA-256 digest [FIPS180-4] of the stored key 2881 authorization 2883 2. Query for TXT records for the validation domain name 2885 3. Verify that the contents of one of the TXT records match the 2886 digest value 2888 If all of the above verifications succeed, then the validation is 2889 successful. If no DNS record is found, or DNS record and response 2890 payload do not pass these checks, then the validation fails. 2892 The client SHOULD de-provision the resource record(s) provisioned for 2893 this challenge once the challenge is complete, i.e., once the 2894 "status" field of the challenge has the value "valid" or "invalid". 2896 9. IANA Considerations 2898 9.1. MIME Type: application/pem-certificate-chain 2900 A file of this type contains one or more certificates encoded with 2901 the PEM textual encoding, according to RFC 7468 [RFC7468]. The 2902 textual encoding of certificates in this file MUST use the strict 2903 encoding and MUST NOT include explanatory text. The ABNF for this 2904 format is as follows, where "stricttextualmsg" and "eol" are as 2905 defined in Section 3 of RFC 7468: 2907 certchain = stricttextualmsg *(eol stricttextualmsg) 2909 In order to provide easy interoperation with TLS, the first 2910 certificate MUST be an end-entity certificate. Each following 2911 certificate SHOULD directly certify the one preceding it. Because 2912 certificate validation requires that trust anchors be distributed 2913 independently, a certificate that represents a trust anchor MAY be 2914 omitted from the chain, provided that supported peers are known to 2915 possess any omitted certificates. 2917 The "Media Types" registry should be updated with the following 2918 additional value: 2920 MIME media type name: application 2921 MIME subtype name: pem-certificate-chain 2923 Required parameters: None 2925 Optional parameters: None 2927 Encoding considerations: 7bit 2929 Security considerations: Carries a cryptographic certificate and its 2930 associated certificate chain. This media type carries no active 2931 content. 2933 Interoperability considerations: None 2935 Published specification: draft-ietf-acme-acme [[ RFC EDITOR: Please 2936 replace draft-ietf-acme-acme above with the RFC number assigned to 2937 this ]] 2939 Applications which use this media type: ACME clients and servers, 2940 HTTP servers, other applications that need to be configured with a 2941 certificate chain 2943 Additional information: 2945 Deprecated alias names for this type: n/a Magic number(s): n/a File 2946 extension(s): .pem Macintosh file type code(s): n/a 2948 Person & email address to contact for further information: See 2949 Authors' Addresses section. 2951 Intended usage: COMMON 2953 Restrictions on usage: n/a 2955 Author: See Authors' Addresses section. 2957 Change controller: Internet Engineering Task Force iesg@ietf.org [2] 2959 9.2. Well-Known URI for the HTTP Challenge 2961 The "Well-Known URIs" registry should be updated with the following 2962 additional value (using the template from [RFC5785]): 2964 URI suffix: acme-challenge 2966 Change controller: IETF 2968 Specification document(s): This document, Section Section 8.3 2969 Related information: N/A 2971 9.3. Replay-Nonce HTTP Header 2973 The "Message Headers" registry should be updated with the following 2974 additional value: 2976 +------------------+----------+----------+--------------------------+ 2977 | Header Field | Protocol | Status | Reference | 2978 | Name | | | | 2979 +------------------+----------+----------+--------------------------+ 2980 | Replay-Nonce | http | standard | [[this-RFC, Section | 2981 | | | | 6.5.1] | 2982 +------------------+----------+----------+--------------------------+ 2984 9.4. "url" JWS Header Parameter 2986 The "JSON Web Signature and Encryption Header Parameters" registry 2987 should be updated with the following additional value: 2989 o Header Parameter Name: "url" 2991 o Header Parameter Description: URL 2993 o Header Parameter Usage Location(s): JWE, JWS 2995 o Change Controller: IESG 2997 o Specification Document(s): Section 6.4.1 of RFC XXXX 2999 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3000 to this document ]] 3002 9.5. "nonce" JWS Header Parameter 3004 The "JSON Web Signature and Encryption Header Parameters" registry 3005 should be updated with the following additional value: 3007 o Header Parameter Name: "nonce" 3009 o Header Parameter Description: Nonce 3011 o Header Parameter Usage Location(s): JWE, JWS 3013 o Change Controller: IESG 3015 o Specification Document(s): Section 6.5.2 of RFC XXXX 3017 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3018 to this document ]] 3020 9.6. URN Sub-namespace for ACME (urn:ietf:params:acme) 3022 The "IETF URN Sub-namespace for Registered Protocol Parameter 3023 Identifiers" registry should be updated with the following additional 3024 value, following the template in [RFC3553]: 3026 Registry name: acme 3028 Specification: RFC XXXX 3030 Repository: URL-TBD 3032 Index value: No transformation needed. 3034 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3035 to this document, and replace URL-TBD with the URL assigned by IANA 3036 for registries of ACME parameters. ]] 3038 9.7. New Registries 3040 This document requests that IANA create the following new registries: 3042 1. ACME Account Object Fields (Section 9.7.1) 3044 2. ACME Order Object Fields (Section 9.7.2) 3046 3. ACME Authorization Object Fields (Section 9.7.3) 3048 4. ACME Error Types (Section 9.7.4) 3050 5. ACME Resource Types (Section 9.7.5) 3052 6. ACME Directory Metadata Fields (Section 9.7.6) 3054 7. ACME Identifier Types (Section 9.7.7) 3056 8. ACME Validation Methods (Section 9.7.8) 3058 All of these registries are under a heading of "Automated Certificate 3059 Management Environment (ACME) Protocol" and are administered under a 3060 Specification Required policy [RFC8126]. 3062 9.7.1. Fields in Account Objects 3064 This registry lists field names that are defined for use in ACME 3065 account objects. Fields marked as "configurable" may be included in 3066 a new-account request. 3068 Template: 3070 o Field name: The string to be used as a field name in the JSON 3071 object 3073 o Field type: The type of value to be provided, e.g., string, 3074 boolean, array of string 3076 o Client configurable: Boolean indicating whether the server should 3077 accept values provided by the client 3079 o Reference: Where this field is defined 3081 Initial contents: The fields and descriptions defined in 3082 Section 7.1.2. 3084 +------------------------+---------------+--------------+-----------+ 3085 | Field Name | Field Type | Configurable | Reference | 3086 +------------------------+---------------+--------------+-----------+ 3087 | status | string | false | RFC XXXX | 3088 | | | | | 3089 | contact | array of | true | RFC XXXX | 3090 | | string | | | 3091 | | | | | 3092 | externalAccountBinding | object | true | RFC XXXX | 3093 | | | | | 3094 | termsOfServiceAgreed | boolean | true | RFC XXXX | 3095 | | | | | 3096 | orders | string | false | RFC XXXX | 3097 +------------------------+---------------+--------------+-----------+ 3099 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3100 to this document ]] 3102 9.7.2. Fields in Order Objects 3104 This registry lists field names that are defined for use in ACME 3105 order objects. Fields marked as "configurable" may be included in a 3106 new-order request. 3108 Template: 3110 o Field name: The string to be used as a field name in the JSON 3111 object 3113 o Field type: The type of value to be provided, e.g., string, 3114 boolean, array of string 3116 o Client configurable: Boolean indicating whether the server should 3117 accept values provided by the client 3119 o Reference: Where this field is defined 3121 Initial contents: The fields and descriptions defined in 3122 Section 7.1.3. 3124 +----------------+-----------------+--------------+-----------+ 3125 | Field Name | Field Type | Configurable | Reference | 3126 +----------------+-----------------+--------------+-----------+ 3127 | status | string | false | RFC XXXX | 3128 | | | | | 3129 | expires | string | false | RFC XXXX | 3130 | | | | | 3131 | identifiers | array of object | true | RFC XXXX | 3132 | | | | | 3133 | notBefore | string | true | RFC XXXX | 3134 | | | | | 3135 | notAfter | string | true | RFC XXXX | 3136 | | | | | 3137 | authorizations | array of string | false | RFC XXXX | 3138 | | | | | 3139 | finalize | string | false | RFC XXXX | 3140 | | | | | 3141 | certificate | string | false | RFC XXXX | 3142 +----------------+-----------------+--------------+-----------+ 3144 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3145 to this document ]] 3147 9.7.3. Fields in Authorization Objects 3149 This registry lists field names that are defined for use in ACME 3150 authorization objects. Fields marked as "configurable" may be 3151 included in a new-authorization request. 3153 Template: 3155 o Field name: The string to be used as a field name in the JSON 3156 object 3158 o Field type: The type of value to be provided, e.g., string, 3159 boolean, array of string 3161 o Client configurable: Boolean indicating whether the server should 3162 accept values provided by the client 3164 o Reference: Where this field is defined 3166 Initial contents: The fields and descriptions defined in 3167 Section 7.1.4. 3169 +------------+-----------------+--------------+-----------+ 3170 | Field Name | Field Type | Configurable | Reference | 3171 +------------+-----------------+--------------+-----------+ 3172 | identifier | object | true | RFC XXXX | 3173 | | | | | 3174 | status | string | false | RFC XXXX | 3175 | | | | | 3176 | expires | string | false | RFC XXXX | 3177 | | | | | 3178 | challenges | array of object | false | RFC XXXX | 3179 | | | | | 3180 | wildcard | boolean | false | RFC XXXX | 3181 +------------+-----------------+--------------+-----------+ 3183 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3184 to this document ]] 3186 9.7.4. Error Types 3188 This registry lists values that are used within URN values that are 3189 provided in the "type" field of problem documents in ACME. 3191 Template: 3193 o Type: The label to be included in the URN for this error, 3194 following "urn:ietf:params:acme:error:" 3196 o Description: A human-readable description of the error 3198 o Reference: Where the error is defined 3200 Initial contents: The types and descriptions in the table in 3201 Section 6.7 above, with the Reference field set to point to this 3202 specification. 3204 9.7.5. Resource Types 3206 This registry lists the types of resources that ACME servers may list 3207 in their directory objects. 3209 Template: 3211 o Field name: The value to be used as a field name in the directory 3212 object 3214 o Resource type: The type of resource labeled by the field 3216 o Reference: Where the resource type is defined 3218 Initial contents: 3220 +------------+--------------------+-----------+ 3221 | Field Name | Resource Type | Reference | 3222 +------------+--------------------+-----------+ 3223 | newNonce | New nonce | RFC XXXX | 3224 | | | | 3225 | newAccount | New account | RFC XXXX | 3226 | | | | 3227 | newOrder | New order | RFC XXXX | 3228 | | | | 3229 | newAuthz | New authorization | RFC XXXX | 3230 | | | | 3231 | revokeCert | Revoke certificate | RFC XXXX | 3232 | | | | 3233 | keyChange | Key change | RFC XXXX | 3234 | | | | 3235 | meta | Metadata object | RFC XXXX | 3236 +------------+--------------------+-----------+ 3238 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3239 to this document ]] 3241 9.7.6. Fields in the "meta" Object within a Directory Object 3243 This registry lists field names that are defined for use in the JSON 3244 object included in the "meta" field of an ACME directory object. 3246 Template: 3248 o Field name: The string to be used as a field name in the JSON 3249 object 3251 o Field type: The type of value to be provided, e.g., string, 3252 boolean, array of string 3254 o Reference: Where this field is defined 3256 Initial contents: The fields and descriptions defined in 3257 Section 7.1.1. 3259 +-------------------------+-----------------+-----------+ 3260 | Field Name | Field Type | Reference | 3261 +-------------------------+-----------------+-----------+ 3262 | termsOfService | string | RFC XXXX | 3263 | | | | 3264 | website | string | RFC XXXX | 3265 | | | | 3266 | caaIdentities | array of string | RFC XXXX | 3267 | | | | 3268 | externalAccountRequired | boolean | RFC XXXX | 3269 +-------------------------+-----------------+-----------+ 3271 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3272 to this document ]] 3274 9.7.7. Identifier Types 3276 This registry lists the types of identifiers that can be present in 3277 ACME authorization objects. 3279 Template: 3281 o Label: The value to be put in the "type" field of the identifier 3282 object 3284 o Reference: Where the identifier type is defined 3286 Initial contents: 3288 +-------+-----------+ 3289 | Label | Reference | 3290 +-------+-----------+ 3291 | dns | RFC XXXX | 3292 +-------+-----------+ 3294 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3295 to this document ]] 3297 9.7.8. Validation Methods 3299 This registry lists identifiers for the ways that CAs can validate 3300 control of identifiers. Each method's entry must specify whether it 3301 corresponds to an ACME challenge type. The "Identifier Type" field 3302 must be contained in the Label column of the ACME Identifier Types 3303 registry. 3305 Template: 3307 o Label: The identifier for this validation method 3309 o Identifier Type: The type of identifier that this method applies 3310 to 3312 o ACME: "Y" if the validation method corresponds to an ACME 3313 challenge type; "N" otherwise 3315 o Reference: Where the validation method is defined 3317 This registry may also contain reserved entries (e.g., to avoid 3318 collisions). Such entries should have the "ACME" field set to "N" 3319 and the "Identifier Type" set to "RESERVED". 3321 Initial Contents 3323 +------------+-----------------+------+-----------+ 3324 | Label | Identifier Type | ACME | Reference | 3325 +------------+-----------------+------+-----------+ 3326 | http-01 | dns | Y | RFC XXXX | 3327 | | | | | 3328 | dns-01 | dns | Y | RFC XXXX | 3329 | | | | | 3330 | tls-sni-01 | RESERVED | N | RFC XXXX | 3331 | | | | | 3332 | tls-sni-02 | RESERVED | N | RFC XXXX | 3333 +------------+-----------------+------+-----------+ 3335 When evaluating a request for an assignment in this registry, the 3336 designated expert should ensure that the method being registered has 3337 a clear, interoperable definition and does not overlap with existing 3338 validation methods. That is, it should not be possible for a client 3339 and server to follow the same set of actions to fulfill two different 3340 validation methods. 3342 The values "tls-sni-01" and "tls-sni-02" are reserved because they 3343 were used in pre-RFC versions of this specification to denote 3344 validation methods that were removed because they were found not to 3345 be secure in some cases. 3347 Validation methods do not have to be compatible with ACME in order to 3348 be registered. For example, a CA might wish to register a validation 3349 method in order to support its use with the ACME extensions to CAA 3350 [I-D.ietf-acme-caa]. 3352 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3353 to this document ]] 3355 10. Security Considerations 3357 ACME is a protocol for managing certificates that attest to 3358 identifier/key bindings. Thus the foremost security goal of ACME is 3359 to ensure the integrity of this process, i.e., to ensure that the 3360 bindings attested by certificates are correct and that only 3361 authorized entities can manage certificates. ACME identifies clients 3362 by their account keys, so this overall goal breaks down into two more 3363 precise goals: 3365 1. Only an entity that controls an identifier can get an 3366 authorization for that identifier 3368 2. Once authorized, an account key's authorizations cannot be 3369 improperly used by another account 3371 In this section, we discuss the threat model that underlies ACME and 3372 the ways that ACME achieves these security goals within that threat 3373 model. We also discuss the denial-of-service risks that ACME servers 3374 face, and a few other miscellaneous considerations. 3376 10.1. Threat Model 3378 As a service on the Internet, ACME broadly exists within the Internet 3379 threat model [RFC3552]. In analyzing ACME, it is useful to think of 3380 an ACME server interacting with other Internet hosts along two 3381 "channels": 3383 o An ACME channel, over which the ACME HTTPS requests are exchanged 3385 o A validation channel, over which the ACME server performs 3386 additional requests to validate a client's control of an 3387 identifier 3389 +------------+ 3390 | ACME | ACME Channel 3391 | Client |--------------------+ 3392 +------------+ | 3393 V 3394 +------------+ 3395 | ACME | 3396 | Server | 3397 +------------+ 3398 +------------+ | 3399 | Validation |<-------------------+ 3400 | Server | Validation Channel 3401 +------------+ 3403 Communications Channels Used by ACME 3405 In practice, the risks to these channels are not entirely separate, 3406 but they are different in most cases. Each channel, for example, 3407 uses a different communications pattern: the ACME channel will 3408 comprise inbound HTTPS connections to the ACME server and the 3409 validation channel outbound HTTP or DNS requests. 3411 Broadly speaking, ACME aims to be secure against active and passive 3412 attackers on any individual channel. Some vulnerabilities arise 3413 (noted below) when an attacker can exploit both the ACME channel and 3414 one of the others. 3416 On the ACME channel, in addition to network layer attackers, we also 3417 need to account for man-in-the-middle (MitM) attacks at the 3418 application layer, and for abusive use of the protocol itself. 3419 Protection against application layer MitM addresses potential 3420 attackers such as Content Distribution Networks (CDNs) and 3421 middleboxes with a TLS MitM function. Preventing abusive use of ACME 3422 means ensuring that an attacker with access to the validation channel 3423 can't obtain illegitimate authorization by acting as an ACME client 3424 (legitimately, in terms of the protocol). 3426 ACME does not protect against other types of abuse by a MitM on the 3427 ACME channel. For example, such an attacker could send a bogus 3428 "badSignatureAlgorithm" error response to downgrade a client to the 3429 lowest-quality signature algorithm that the server supports. A MitM 3430 that is present on all connections (such as a CDN), can cause denial- 3431 of-service conditions in a variety of ways. 3433 10.2. Integrity of Authorizations 3435 ACME allows anyone to request challenges for an identifier by 3436 registering an account key and sending a new-order request using that 3437 account key. The integrity of the authorization process thus depends 3438 on the identifier validation challenges to ensure that the challenge 3439 can only be completed by someone who both (1) holds the private key 3440 of the account key pair, and (2) controls the identifier in question. 3442 Validation responses need to be bound to an account key pair in order 3443 to avoid situations where a MitM on ACME HTTPS requests can switch 3444 out a legitimate domain holder's account key for one of his choosing. 3445 Such MitMs can arise, for example, if a CA uses a CDN or third-party 3446 reverse proxy in front of its ACME interface. An attack by such an 3447 MitM could have the following form: 3449 o Legitimate domain holder registers account key pair A 3451 o MitM registers account key pair B 3453 o Legitimate domain holder sends a new-order request signed using 3454 account key A 3456 o MitM suppresses the legitimate request but sends the same request 3457 signed using account key B 3459 o ACME server issues challenges and MitM forwards them to the 3460 legitimate domain holder 3462 o Legitimate domain holder provisions the validation response 3464 o ACME server performs validation query and sees the response 3465 provisioned by the legitimate domain holder 3467 o Because the challenges were issued in response to a message signed 3468 account key B, the ACME server grants authorization to account key 3469 B (the MitM) instead of account key A (the legitimate domain 3470 holder) 3472 Domain ACME 3473 Holder MitM Server 3474 | | | 3475 | newAccount(A) | | 3476 |--------------------->|--------------------->| 3477 | | | 3478 | | newAccount(B) | 3479 | |--------------------->| 3480 | newOrder(domain, A) | | 3481 |--------------------->| | 3482 | | newOrder(domain, B) | 3483 | |--------------------->| 3484 | | | 3485 | authz, challenges | authz, challenges | 3486 |<---------------------|<---------------------| 3487 | | | 3488 | response(chall, A) | response(chall, B) | 3489 |--------------------->|--------------------->| 3490 | | | 3491 | validation request | | 3492 |<--------------------------------------------| 3493 | | | 3494 | validation response | | 3495 |-------------------------------------------->| 3496 | | | 3497 | | | Considers challenge 3498 | | | fulfilled by B. 3499 | | | 3501 Man-in-the-Middle Attack Exploiting a Validation Method without 3502 Account Key Binding 3504 All of the challenges defined in this document have a binding between 3505 the account private key and the validation query made by the server, 3506 via the key authorization. The key authorization reflects the 3507 account public key and is provided to the server in the validation 3508 response over the validation channel. 3510 The association of challenges to identifiers is typically done by 3511 requiring the client to perform some action that only someone who 3512 effectively controls the identifier can perform. For the challenges 3513 in this document, the actions are: 3515 o HTTP: Provision files under .well-known on a web server for the 3516 domain 3518 o DNS: Provision DNS resource records for the domain 3519 There are several ways that these assumptions can be violated, both 3520 by misconfiguration and by attacks. For example, on a web server 3521 that allows non-administrative users to write to .well-known, any 3522 user can claim to own the web server's hostname by responding to an 3523 HTTP challenge. Similarly, if a server that can be used for ACME 3524 validation is compromised by a malicious actor, then that malicious 3525 actor can use that access to obtain certificates via ACME. 3527 The use of hosting providers is a particular risk for ACME 3528 validation. If the owner of the domain has outsourced operation of 3529 DNS or web services to a hosting provider, there is nothing that can 3530 be done against tampering by the hosting provider. As far as the 3531 outside world is concerned, the zone or website provided by the 3532 hosting provider is the real thing. 3534 More limited forms of delegation can also lead to an unintended party 3535 gaining the ability to successfully complete a validation 3536 transaction. For example, suppose an ACME server follows HTTP 3537 redirects in HTTP validation and a website operator provisions a 3538 catch-all redirect rule that redirects requests for unknown resources 3539 to a different domain. Then the target of the redirect could use 3540 that to get a certificate through HTTP validation since the 3541 validation path will not be known to the primary server. 3543 The DNS is a common point of vulnerability for all of these 3544 challenges. An entity that can provision false DNS records for a 3545 domain can attack the DNS challenge directly and can provision false 3546 A/AAAA records to direct the ACME server to send its HTTP validation 3547 query to a remote server of the attacker's choosing. There are a few 3548 different mitigations that ACME servers can apply: 3550 o Always querying the DNS using a DNSSEC-validating resolver 3551 (enhancing security for zones that are DNSSEC-enabled) 3553 o Querying the DNS from multiple vantage points to address local 3554 attackers 3556 o Applying mitigations against DNS off-path attackers, e.g., adding 3557 entropy to requests [I-D.vixie-dnsext-dns0x20] or only using TCP 3559 Given these considerations, the ACME validation process makes it 3560 impossible for any attacker on the ACME channel or a passive attacker 3561 on the validation channel to hijack the authorization process to 3562 authorize a key of the attacker's choice. 3564 An attacker that can only see the ACME channel would need to convince 3565 the validation server to provide a response that would authorize the 3566 attacker's account key, but this is prevented by binding the 3567 validation response to the account key used to request challenges. A 3568 passive attacker on the validation channel can observe the correct 3569 validation response and even replay it, but that response can only be 3570 used with the account key for which it was generated. 3572 An active attacker on the validation channel can subvert the ACME 3573 process, by performing normal ACME transactions and providing a 3574 validation response for his own account key. The risks due to 3575 hosting providers noted above are a particular case. 3577 Attackers can also exploit vulnerabilities in Internet routing 3578 protocols to gain access to the validation channel (see, e.g., 3579 [RFC7132]). In order to make such attacks more difficult, it is 3580 RECOMMENDED that the server perform DNS queries and make HTTP 3581 connections from multiple points in the network. Since routing 3582 attacks are often localized or dependent on the position of the 3583 attacker, forcing the attacker to attack multiple points (the 3584 server's validation vantage points) or a specific point (the DNS / 3585 HTTP server) makes it more difficult to subvert ACME validation using 3586 attacks on routing. 3588 10.3. Denial-of-Service Considerations 3590 As a protocol run over HTTPS, standard considerations for TCP-based 3591 and HTTP-based DoS mitigation also apply to ACME. 3593 At the application layer, ACME requires the server to perform a few 3594 potentially expensive operations. Identifier validation transactions 3595 require the ACME server to make outbound connections to potentially 3596 attacker-controlled servers, and certificate issuance can require 3597 interactions with cryptographic hardware. 3599 In addition, an attacker can also cause the ACME server to send 3600 validation requests to a domain of its choosing by submitting 3601 authorization requests for the victim domain. 3603 All of these attacks can be mitigated by the application of 3604 appropriate rate limits. Issues closer to the front end, like POST 3605 body validation, can be addressed using HTTP request limiting. For 3606 validation and certificate requests, there are other identifiers on 3607 which rate limits can be keyed. For example, the server might limit 3608 the rate at which any individual account key can issue certificates 3609 or the rate at which validation can be requested within a given 3610 subtree of the DNS. And in order to prevent attackers from 3611 circumventing these limits simply by minting new accounts, servers 3612 would need to limit the rate at which accounts can be registered. 3614 10.4. Server-Side Request Forgery 3616 Server-Side Request Forgery (SSRF) attacks can arise when an attacker 3617 can cause a server to perform HTTP requests to an attacker-chosen 3618 URL. In the ACME HTTP challenge validation process, the ACME server 3619 performs an HTTP GET request to a URL in which the attacker can 3620 choose the domain. This request is made before the server has 3621 verified that the client controls the domain, so any client can cause 3622 a query to any domain. 3624 Some ACME server implementations include information from the 3625 validation server's response (in order to facilitate debugging). 3626 Such implementations enable an attacker to extract this information 3627 from any web server that is accessible to the ACME server, even if it 3628 is not accessible to the ACME client. For example, the ACME server 3629 might be able to access servers behind a firewall that would prevent 3630 access by the ACME client. 3632 It might seem that the risk of SSRF through this channel is limited 3633 by the fact that the attacker can only control the domain of the URL, 3634 not the path. However, if the attacker first sets the domain to one 3635 they control, then they can send the server an HTTP redirect (e.g., a 3636 302 response) which will cause the server to query an arbitrary URL. 3638 In order to further limit the SSRF risk, ACME server operators should 3639 ensure that validation queries can only be sent to servers on the 3640 public Internet, and not, say, web services within the server 3641 operator's internal network. Since the attacker could make requests 3642 to these public servers himself, he can't gain anything extra through 3643 an SSRF attack on ACME aside from a layer of anonymization. 3645 10.5. CA Policy Considerations 3647 The controls on issuance enabled by ACME are focused on validating 3648 that a certificate applicant controls the identifier he claims. 3649 Before issuing a certificate, however, there are many other checks 3650 that a CA might need to perform, for example: 3652 o Has the client agreed to a subscriber agreement? 3654 o Is the claimed identifier syntactically valid? 3656 o For domain names: 3658 * If the leftmost label is a '*', then have the appropriate 3659 checks been applied? 3661 * Is the name on the Public Suffix List? 3662 * Is the name a high-value name? 3664 * Is the name a known phishing domain? 3666 o Is the key in the CSR sufficiently strong? 3668 o Is the CSR signed with an acceptable algorithm? 3670 o Has issuance been authorized or forbidden by a Certificate 3671 Authority Authorization (CAA) record? [RFC6844] 3673 CAs that use ACME to automate issuance will need to ensure that their 3674 servers perform all necessary checks before issuing. 3676 CAs using ACME to allow clients to agree to terms of service should 3677 keep in mind that ACME clients can automate this agreement, possibly 3678 not involving a human user. 3680 ACME does not specify how the server constructs the URLs that it uses 3681 to address resources. If the server operator uses URLs that are 3682 predictable to third parties, this can leak information about what 3683 URLs exist on the server, since an attacker can probe for whether 3684 POST-as-GET request to the URL returns "Not Found" or "Unauthorized". 3686 For example, suppose that the CA uses highly structured URLs with 3687 guessable fields: 3689 o Accounts: https://example.com/:accountID 3691 o Orders: https://example.com/:accountID/:domainName 3693 o Authorizations: https://example.com/:accountID/:domainName 3695 o Certificates: https://example.com/:accountID/:domainName 3697 Under that scheme, an attacker could probe for which domain names are 3698 associated with which accounts, which may allow correlation of 3699 ownership between domain names, if the CA does not otherwise permit 3700 it. 3702 To avoid leaking these correlations, CAs SHOULD assign URLs with an 3703 unpredictable component. For example, a CA might assign URLs for 3704 each resource type from an independent namespace, using unpredictable 3705 IDs for each resource: 3707 o Accounts: https://example.com/acct/:accountID 3709 o Orders: https://example.com/order/:orderID 3710 o Authorizations: https://example.com/authz/:authorizationID 3712 o Certificates: https://example.com/cert/:certID 3714 Such a scheme would leak only the type of resource, hiding the 3715 additional correlations revealed in the example above. 3717 11. Operational Considerations 3719 There are certain factors that arise in operational reality that 3720 operators of ACME-based CAs will need to keep in mind when 3721 configuring their services. For example: 3723 11.1. Key Selection 3725 ACME relies on two different classes of key pair: 3727 o Account key pairs, which are used to authenticate account holders 3729 o Certificate key pairs, which are used to sign and verify CSRs (and 3730 whose public keys are included in certificates) 3732 Compromise of the private key of an account key pair has more serious 3733 consequences than compromise of a private key corresponding to a 3734 certificate. While the compromise of a certificate key pair allows 3735 the attacker to impersonate the entities named in the certificate for 3736 the lifetime of the certificate, the compromise of an account key 3737 pair allows the attacker to take full control of the victim's ACME 3738 account, and take any action that the legitimate account holder could 3739 take within the scope of ACME: 3741 1. Issuing certificates using existing authorizations 3743 2. Revoking existing certificates 3745 3. Accessing and changing account information (e.g., contacts) 3747 4. Changing the account key pair for the account, locking out the 3748 legitimate account holder 3750 For this reason, it is RECOMMENDED that account key pairs be used for 3751 no other purpose besides ACME authentication. For example, the 3752 public key of an account key pair SHOULD NOT be included in a 3753 certificate. ACME clients and servers SHOULD verify that a CSR 3754 submitted in a finalize request does not contain a public key for any 3755 known account key pair. In particular, when a server receives a 3756 finalize request, it MUST verify that the public key in a CSR is not 3757 the same as the public key of the account key pair used to 3758 authenticate that request. This assures that vulnerabilities in the 3759 protocols with which the certificate is used (e.g., signing oracles 3760 in TLS [JSS15]) do not result in compromise of the ACME account. 3761 Because ACME accounts are uniquely identified by their account key 3762 pair (see Section 7.3.1) the server MUST not allow account key pair 3763 reuse across multiple accounts. 3765 11.2. DNS security 3767 As noted above, DNS forgery attacks against the ACME server can 3768 result in the server making incorrect decisions about domain control 3769 and thus mis-issuing certificates. Servers SHOULD perform DNS 3770 queries over TCP, which provides better resistance to some forgery 3771 attacks than DNS over UDP. 3773 An ACME-based CA will often need to make DNS queries, e.g., to 3774 validate control of DNS names. Because the security of such 3775 validations ultimately depends on the authenticity of DNS data, every 3776 possible precaution should be taken to secure DNS queries done by the 3777 CA. It is therefore RECOMMENDED that ACME-based CAs make all DNS 3778 queries via DNSSEC-validating stub or recursive resolvers. This 3779 provides additional protection to domains which choose to make use of 3780 DNSSEC. 3782 An ACME-based CA must use only a resolver if it trusts the resolver 3783 and every component of the network route by which it is accessed. It 3784 is therefore RECOMMENDED that ACME-based CAs operate their own 3785 DNSSEC-validating resolvers within their trusted network and use 3786 these resolvers both for both CAA record lookups and all record 3787 lookups in furtherance of a challenge scheme (A, AAAA, TXT, etc.). 3789 11.3. Token Entropy 3791 The http-01 and dns-01 validation methods mandate the usage of a 3792 random token value to uniquely identify the challenge. The value of 3793 the token is required to contain at least 128 bits of entropy for the 3794 following security properties. First, the ACME client should not be 3795 able to influence the ACME server's choice of token as this may allow 3796 an attacker to reuse a domain owner's previous challenge responses 3797 for a new validation request. Secondly, the entropy requirement 3798 prevents ACME clients from implementing a "naive" validation server 3799 that automatically replies to challenges by predicting the token. 3801 11.4. Malformed Certificate Chains 3803 ACME provides certificate chains in the widely-used format known 3804 colloquially as PEM (though it may diverge from the actual Privacy 3805 Enhanced Mail specifications [RFC1421], as noted in [RFC7468]). Some 3806 current software will allow the configuration of a private key and a 3807 certificate in one PEM file, by concatenating the textual encodings 3808 of the two objects. In the context of ACME, such software might be 3809 vulnerable to "key replacement" attacks. A malicious ACME server 3810 could cause a client to use a private key of its choosing by 3811 including the key in the PEM file returned in response to a query for 3812 a certificate URL. 3814 When processing an file of type "application/pem-certificate-chain", 3815 a client SHOULD verify that the file contains only encoded 3816 certificates. If anything other than a certificate is found (i.e., 3817 if the string "-----BEGIN" is ever followed by anything other than 3818 "CERTIFICATE"), then the client MUST reject the file as invalid. 3820 12. Acknowledgements 3822 In addition to the editors listed on the front page, this document 3823 has benefited from contributions from a broad set of contributors, 3824 all the way back to its inception. 3826 o Andrew Ayer, SSLMate 3828 o Karthik Bhargavan, INRIA 3830 o Peter Eckersley, EFF 3832 o Alex Halderman, University of Michigan 3834 o Sophie Herold, Hemio 3836 o Eric Rescorla, Mozilla 3838 o Seth Schoen, EFF 3840 o Martin Thomson, Mozilla 3842 o Jakub Warmuz, University of Oxford 3844 This document draws on many concepts established by Eric Rescorla's 3845 "Automated Certificate Issuance Protocol" draft. Martin Thomson 3846 provided helpful guidance in the use of HTTP. 3848 13. References 3849 13.1. Normative References 3851 [FIPS180-4] 3852 Department of Commerce, National., "NIST FIPS 180-4, 3853 Secure Hash Standard", March 2012, 3854 . 3857 [JSS15] Somorovsky, J., "On the Security of TLS 1.3 and QUIC 3858 Against Weaknesses in PKCS#1 v1.5 Encryption", n.d., 3859 . 3861 [REST] Fielding, R., "Architectural Styles and the Design of 3862 Network-based Software Architectures", 2000, 3863 . 3866 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3867 Requirement Levels", BCP 14, RFC 2119, 3868 DOI 10.17487/RFC2119, March 1997, 3869 . 3871 [RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key 3872 Infrastructure Operational Protocols: FTP and HTTP", 3873 RFC 2585, DOI 10.17487/RFC2585, May 1999, 3874 . 3876 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, 3877 DOI 10.17487/RFC2818, May 2000, 3878 . 3880 [RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object 3881 Classes and Attribute Types Version 2.0", RFC 2985, 3882 DOI 10.17487/RFC2985, November 2000, 3883 . 3885 [RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification 3886 Request Syntax Specification Version 1.7", RFC 2986, 3887 DOI 10.17487/RFC2986, November 2000, 3888 . 3890 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 3891 Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, 3892 . 3894 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 3895 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 3896 2003, . 3898 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 3899 Resource Identifier (URI): Generic Syntax", STD 66, 3900 RFC 3986, DOI 10.17487/RFC3986, January 2005, 3901 . 3903 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 3904 "Randomness Requirements for Security", BCP 106, RFC 4086, 3905 DOI 10.17487/RFC4086, June 2005, 3906 . 3908 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 3909 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 3910 . 3912 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 3913 Specifications: ABNF", STD 68, RFC 5234, 3914 DOI 10.17487/RFC5234, January 2008, 3915 . 3917 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3918 (TLS) Protocol Version 1.2", RFC 5246, 3919 DOI 10.17487/RFC5246, August 2008, 3920 . 3922 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 3923 Housley, R., and W. Polk, "Internet X.509 Public Key 3924 Infrastructure Certificate and Certificate Revocation List 3925 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 3926 . 3928 [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet 3929 Mail Extensions (S/MIME) Version 3.2 Message 3930 Specification", RFC 5751, DOI 10.17487/RFC5751, January 3931 2010, . 3933 [RFC5890] Klensin, J., "Internationalized Domain Names for 3934 Applications (IDNA): Definitions and Document Framework", 3935 RFC 5890, DOI 10.17487/RFC5890, August 2010, 3936 . 3938 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, 3939 DOI 10.17487/RFC5988, October 2010, 3940 . 3942 [RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' 3943 URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010, 3944 . 3946 [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., 3947 and D. Orchard, "URI Template", RFC 6570, 3948 DOI 10.17487/RFC6570, March 2012, 3949 . 3951 [RFC6844] Hallam-Baker, P. and R. Stradling, "DNS Certification 3952 Authority Authorization (CAA) Resource Record", RFC 6844, 3953 DOI 10.17487/RFC6844, January 2013, 3954 . 3956 [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 3957 Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 3958 2014, . 3960 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 3961 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 3962 DOI 10.17487/RFC7231, June 2014, 3963 . 3965 [RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, 3966 PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, 3967 April 2015, . 3969 [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 3970 Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 3971 2015, . 3973 [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, 3974 DOI 10.17487/RFC7518, May 2015, 3975 . 3977 [RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK) 3978 Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September 3979 2015, . 3981 [RFC7797] Jones, M., "JSON Web Signature (JWS) Unencoded Payload 3982 Option", RFC 7797, DOI 10.17487/RFC7797, February 2016, 3983 . 3985 [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP 3986 APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, 3987 . 3989 [RFC8037] Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH) 3990 and Signatures in JSON Object Signing and Encryption 3991 (JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017, 3992 . 3994 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 3995 Writing an IANA Considerations Section in RFCs", BCP 26, 3996 RFC 8126, DOI 10.17487/RFC8126, June 2017, 3997 . 3999 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 4000 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 4001 May 2017, . 4003 [RFC8288] Nottingham, M., "Web Linking", RFC 8288, 4004 DOI 10.17487/RFC8288, October 2017, 4005 . 4007 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4008 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4009 . 4011 13.2. Informative References 4013 [CABFBR] CA/Browser Forum, ., "CA/Browser Forum Baseline 4014 Requirements", September 2018, 4015 . 4017 [I-D.ietf-acme-caa] 4018 Landau, H., "CAA Record Extensions for Account URI and 4019 ACME Method Binding", draft-ietf-acme-caa-05 (work in 4020 progress), June 2018. 4022 [I-D.ietf-acme-ip] 4023 Shoemaker, R., "ACME IP Identifier Validation Extension", 4024 draft-ietf-acme-ip-04 (work in progress), July 2018. 4026 [I-D.ietf-acme-telephone] 4027 Peterson, J. and R. Barnes, "ACME Identifiers and 4028 Challenges for Telephone Numbers", draft-ietf-acme- 4029 telephone-01 (work in progress), October 2017. 4031 [I-D.vixie-dnsext-dns0x20] 4032 Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to 4033 Improve Transaction Identity", draft-vixie-dnsext- 4034 dns0x20-00 (work in progress), March 2008. 4036 [RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic 4037 Mail: Part I: Message Encryption and Authentication 4038 Procedures", RFC 1421, DOI 10.17487/RFC1421, February 4039 1993, . 4041 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 4042 Text on Security Considerations", BCP 72, RFC 3552, 4043 DOI 10.17487/RFC3552, July 2003, 4044 . 4046 [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An 4047 IETF URN Sub-namespace for Registered Protocol 4048 Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June 4049 2003, . 4051 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 4052 Uniform Resource Identifiers (URIs)", RFC 5785, 4053 DOI 10.17487/RFC5785, April 2010, 4054 . 4056 [RFC7132] Kent, S. and A. Chi, "Threat Model for BGP Path Security", 4057 RFC 7132, DOI 10.17487/RFC7132, February 2014, 4058 . 4060 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 4061 "Recommendations for Secure Use of Transport Layer 4062 Security (TLS) and Datagram Transport Layer Security 4063 (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 4064 2015, . 4066 [W3C.REC-cors-20140116] 4067 Kesteren, A., "Cross-Origin Resource Sharing", World Wide 4068 Web Consortium Recommendation REC-cors-20140116, January 4069 2014, . 4071 13.3. URIs 4073 [1] https://github.com/ietf-wg-acme/acme 4075 [2] mailto:iesg@ietf.org 4077 Authors' Addresses 4079 Richard Barnes 4080 Cisco 4082 Email: rlb@ipv.sx 4084 Jacob Hoffman-Andrews 4085 EFF 4087 Email: jsha@eff.org 4088 Daniel McCarney 4089 Let's Encrypt 4091 Email: cpu@letsencrypt.org 4093 James Kasten 4094 University of Michigan 4096 Email: jdkasten@umich.edu