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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 925 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 (September 25, 2018) is 2039 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reference: RFC 7231 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7807 (Obsoleted by RFC 9457) == Outdated reference: A later version (-10) exists of draft-ietf-acme-caa-05 == Outdated reference: A later version (-08) exists of draft-ietf-acme-ip-04 == Outdated reference: A later version (-11) exists of draft-ietf-acme-star-03 -- Obsolete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: 11 errors (**), 0 flaws (~~), 9 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: March 29, 2019 EFF 6 D. McCarney 7 Let's Encrypt 8 J. Kasten 9 University of Michigan 10 September 25, 2018 12 Automatic Certificate Management Environment (ACME) 13 draft-ietf-acme-acme-15 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 March 29, 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 . . . . . . . . . . . . . . . . . . . . 15 83 6.5.2. "nonce" (Nonce) JWS Header Parameter . . . . . . . . 15 84 6.6. Rate Limits . . . . . . . . . . . . . . . . . . . . . . . 15 85 6.7. Errors . . . . . . . . . . . . . . . . . . . . . . . . . 16 86 6.7.1. Subproblems . . . . . . . . . . . . . . . . . . . . . 18 87 7. Certificate Management . . . . . . . . . . . . . . . . . . . 19 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 . . . . . . . . . . . . . . . . 49 107 7.5.1. Responding to Challenges . . . . . . . . . . . . . . 51 108 7.5.2. Deactivating an Authorization . . . . . . . . . . . . 53 109 7.6. Certificate Revocation . . . . . . . . . . . . . . . . . 54 110 8. Identifier Validation Challenges . . . . . . . . . . . . . . 56 111 8.1. Key Authorizations . . . . . . . . . . . . . . . . . . . 58 112 8.2. Retrying Challenges . . . . . . . . . . . . . . . . . . . 58 113 8.3. HTTP Challenge . . . . . . . . . . . . . . . . . . . . . 59 114 8.4. DNS Challenge . . . . . . . . . . . . . . . . . . . . . . 61 115 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63 116 9.1. MIME Type: application/pem-certificate-chain . . . . . . 63 117 9.2. Well-Known URI for the HTTP Challenge . . . . . . . . . . 64 118 9.3. Replay-Nonce HTTP Header . . . . . . . . . . . . . . . . 65 119 9.4. "url" JWS Header Parameter . . . . . . . . . . . . . . . 65 120 9.5. "nonce" JWS Header Parameter . . . . . . . . . . . . . . 65 121 9.6. URN Sub-namespace for ACME (urn:ietf:params:acme) . . . . 66 122 9.7. New Registries . . . . . . . . . . . . . . . . . . . . . 66 123 9.7.1. Fields in Account Objects . . . . . . . . . . . . . . 67 124 9.7.2. Fields in Order Objects . . . . . . . . . . . . . . . 67 125 9.7.3. Fields in Authorization Objects . . . . . . . . . . . 68 126 9.7.4. Error Types . . . . . . . . . . . . . . . . . . . . . 69 127 9.7.5. Resource Types . . . . . . . . . . . . . . . . . . . 70 128 9.7.6. Fields in the "meta" Object within a Directory Object 70 129 9.7.7. Identifier Types . . . . . . . . . . . . . . . . . . 71 130 9.7.8. Validation Methods . . . . . . . . . . . . . . . . . 72 131 10. Security Considerations . . . . . . . . . . . . . . . . . . . 73 132 10.1. Threat Model . . . . . . . . . . . . . . . . . . . . . . 73 133 10.2. Integrity of Authorizations . . . . . . . . . . . . . . 75 134 10.3. Denial-of-Service Considerations . . . . . . . . . . . . 78 135 10.4. Server-Side Request Forgery . . . . . . . . . . . . . . 79 136 10.5. CA Policy Considerations . . . . . . . . . . . . . . . . 79 137 11. Operational Considerations . . . . . . . . . . . . . . . . . 81 138 11.1. Key Selection . . . . . . . . . . . . . . . . . . . . . 81 139 11.2. DNS security . . . . . . . . . . . . . . . . . . . . . . 82 140 11.3. Token Entropy . . . . . . . . . . . . . . . . . . . . . 82 141 11.4. Malformed Certificate Chains . . . . . . . . . . . . . . 83 142 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 83 143 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 84 144 13.1. Normative References . . . . . . . . . . . . . . . . . . 84 145 13.2. Informative References . . . . . . . . . . . . . . . . . 87 146 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 "malformedRequest". 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 The server MAY allow GET requests for certificate resources in order 573 to allow certificates to be fetched by a lower-privileged process, 574 e.g., the web server that will use the referenced certificate chain. 575 (See [I-D.ietf-acme-star] for more advanced cases.) A server that 576 allows GET requests for certificate resources can still provide a 577 degree of access control by assigning them capability URLs 578 [W3C.WD-capability-urls-20140218]. As above, if the server does not 579 allow GET requests for a given resource, it MUST return an error with 580 status code 405 "Method Not Allowed" and type "malformedRequest". 582 6.4. Request URL Integrity 584 It is common in deployment for the entity terminating TLS for HTTPS 585 to be different from the entity operating the logical HTTPS server, 586 with a "request routing" layer in the middle. For example, an ACME 587 CA might have a content delivery network terminate TLS connections 588 from clients so that it can inspect client requests for denial-of- 589 service protection. 591 These intermediaries can also change values in the request that are 592 not signed in the HTTPS request, e.g., the request URL and header 593 fields. ACME uses JWS to provide an integrity mechanism, which 594 protects against an intermediary changing the request URL to another 595 ACME URL. 597 As noted in Section 6.2 above, all ACME request objects carry a "url" 598 header parameter in their protected header. This header parameter 599 encodes the URL to which the client is directing the request. On 600 receiving such an object in an HTTP request, the server MUST compare 601 the "url" header parameter to the request URL. If the two do not 602 match, then the server MUST reject the request as unauthorized. 604 Except for the directory resource, all ACME resources are addressed 605 with URLs provided to the client by the server. In requests sent to 606 these resources, the client MUST set the "url" header parameter to 607 the exact string provided by the server (rather than performing any 608 re-encoding on the URL). The server SHOULD perform the corresponding 609 string equality check, configuring each resource with the URL string 610 provided to clients and having the resource check that requests have 611 the same string in their "url" header parameter. The server MUST 612 reject the request as unauthorized if the string equality check 613 fails. 615 6.4.1. "url" (URL) JWS Header Parameter 617 The "url" header parameter specifies the URL [RFC3986] to which this 618 JWS object is directed. The "url" header parameter MUST be carried 619 in the protected header of the JWS. The value of the "url" header 620 parameter MUST be a string representing the target URL. 622 6.5. Replay protection 624 In order to protect ACME resources from any possible replay attacks, 625 ACME POST requests have a mandatory anti-replay mechanism. This 626 mechanism is based on the server maintaining a list of nonces that it 627 has issued, and requiring any signed request from the client to carry 628 such a nonce. 630 An ACME server provides nonces to clients using the HTTP Replay-Nonce 631 header field, as specified in Section 6.5.1 below. The server MUST 632 include a Replay-Nonce header field in every successful response to a 633 POST request and SHOULD provide it in error responses as well. 635 Every JWS sent by an ACME client MUST include, in its protected 636 header, the "nonce" header parameter, with contents as defined in 637 Section 6.5.2 below. As part of JWS verification, the ACME server 638 MUST verify that the value of the "nonce" header is a value that the 639 server previously provided in a Replay-Nonce header field. Once a 640 nonce value has appeared in an ACME request, the server MUST consider 641 it invalid, in the same way as a value it had never issued. 643 When a server rejects a request because its nonce value was 644 unacceptable (or not present), it MUST provide HTTP status code 400 645 (Bad Request), and indicate the ACME error type 646 "urn:ietf:params:acme:error:badNonce". An error response with the 647 "badNonce" error type MUST include a Replay-Nonce header with a fresh 648 nonce. On receiving such a response, a client SHOULD retry the 649 request using the new nonce. 651 The precise method used to generate and track nonces is up to the 652 server. For example, the server could generate a random 128-bit 653 value for each response, keep a list of issued nonces, and strike 654 nonces from this list as they are used. 656 6.5.1. Replay-Nonce 658 The "Replay-Nonce" header field includes a server-generated value 659 that the server can use to detect unauthorized replay in future 660 client requests. The server MUST generate the value provided in 661 Replay-Nonce in such a way that they are unique to each message, with 662 high probability, and unpredictable to anyone besides the server. 663 For instance, it is acceptable to generate Replay-Nonces randomly. 665 The value of the Replay-Nonce field MUST be an octet string encoded 666 according to the base64url encoding described in Section 2 of 667 [RFC7515]. Clients MUST ignore invalid Replay-Nonce values. The 668 ABNF [RFC5234] for the Replay-Nonce header field follows: 670 base64url = ALPHA / DIGIT / "-" / "_" 672 Replay-Nonce = 1*base64url 674 The Replay-Nonce header field SHOULD NOT be included in HTTP request 675 messages. 677 6.5.2. "nonce" (Nonce) JWS Header Parameter 679 The "nonce" header parameter provides a unique value that enables the 680 verifier of a JWS to recognize when replay has occurred. The "nonce" 681 header parameter MUST be carried in the protected header of the JWS. 683 The value of the "nonce" header parameter MUST be an octet string, 684 encoded according to the base64url encoding described in Section 2 of 685 [RFC7515]. If the value of a "nonce" header parameter is not valid 686 according to this encoding, then the verifier MUST reject the JWS as 687 malformed. 689 6.6. Rate Limits 691 Creation of resources can be rate limited by ACME servers to ensure 692 fair usage and prevent abuse. Once the rate limit is exceeded, the 693 server MUST respond with an error with the type 694 "urn:ietf:params:acme:error:rateLimited". Additionally, the server 695 SHOULD send a "Retry-After" header [RFC7231] indicating when the 696 current request may succeed again. If multiple rate limits are in 697 place, that is the time where all rate limits allow access again for 698 the current request with exactly the same parameters. 700 In addition to the human-readable "detail" field of the error 701 response, the server MAY send one or multiple link relations in the 702 "Link" header [RFC8288] pointing to documentation about the specific 703 rate limit that was hit, using the "help" link relation type. 705 6.7. Errors 707 Errors can be reported in ACME both at the HTTP layer and within 708 challenge objects as defined in Section 8. ACME servers can return 709 responses with an HTTP error response code (4XX or 5XX). For 710 example: If the client submits a request using a method not allowed 711 in this document, then the server MAY return status code 405 (Method 712 Not Allowed). 714 When the server responds with an error status, it SHOULD provide 715 additional information using a problem document [RFC7807]. To 716 facilitate automatic response to errors, this document defines the 717 following standard tokens for use in the "type" field (within the 718 ACME URN namespace "urn:ietf:params:acme:error:"): 720 +-------------------------+-----------------------------------------+ 721 | Type | Description | 722 +-------------------------+-----------------------------------------+ 723 | accountDoesNotExist | The request specified an account that | 724 | | does not exist | 725 | | | 726 | alreadyRevoked | The request specified a certificate to | 727 | | be revoked that has already been | 728 | | revoked | 729 | | | 730 | badCSR | The CSR is unacceptable (e.g., due to a | 731 | | short key) | 732 | | | 733 | badNonce | The client sent an unacceptable anti- | 734 | | replay nonce | 735 | | | 736 | badRevocationReason | The revocation reason provided is not | 737 | | allowed by the server | 738 | | | 739 | badSignatureAlgorithm | The JWS was signed with an algorithm | 740 | | the server does not support | 741 | | | 742 | caa | Certification Authority Authorization | 743 | | (CAA) records forbid the CA from | 744 | | issuing | 745 | | | 746 | compound | Specific error conditions are indicated | 747 | | in the "subproblems" array. | 748 | | | 749 | connection | The server could not connect to | 750 | | validation target | 751 | | | 752 | dns | There was a problem with a DNS query | 753 | | during identifier validation | 754 | | | 755 | externalAccountRequired | The request must include a value for | 756 | | the "externalAccountBinding" field | 757 | | | 758 | incorrectResponse | Response received didn't match the | 759 | | challenge's requirements | 760 | | | 761 | invalidContact | A contact URL for an account was | 762 | | invalid | 763 | | | 764 | malformed | The request message was malformed | 765 | | | 766 | rateLimited | The request exceeds a rate limit | 767 | | | 768 | rejectedIdentifier | The server will not issue for the | 769 | | identifier | 770 | | | 771 | serverInternal | The server experienced an internal | 772 | | error | 773 | | | 774 | tls | The server received a TLS error during | 775 | | validation | 776 | | | 777 | unauthorized | The client lacks sufficient | 778 | | authorization | 779 | | | 780 | unsupportedContact | A contact URL for an account used an | 781 | | unsupported protocol scheme | 782 | | | 783 | unsupportedIdentifier | An identifier is of an unsupported type | 784 | | | 785 | userActionRequired | Visit the "instance" URL and take | 786 | | actions specified there | 787 +-------------------------+-----------------------------------------+ 789 This list is not exhaustive. The server MAY return errors whose 790 "type" field is set to a URI other than those defined above. Servers 791 MUST NOT use the ACME URN namespace for errors not listed in the 792 appropriate IANA registry (see Section 9.6). Clients SHOULD display 793 the "detail" field of all errors. 795 In the remainder of this document, we use the tokens in the table 796 above to refer to error types, rather than the full URNs. For 797 example, an "error of type 'badCSR'" refers to an error document with 798 "type" value "urn:ietf:params:acme:error:badCSR". 800 6.7.1. Subproblems 802 Sometimes a CA may need to return multiple errors in response to a 803 request. Additionally, the CA may need to attribute errors to 804 specific identifiers. For instance, a new-order request may contain 805 multiple identifiers for which the CA cannot issue. In this 806 situation, an ACME problem document MAY contain the "subproblems" 807 field, containing a JSON array of problem documents, each of which 808 MAY contain an "identifier" field. If present, the "identifier" 809 field MUST contain an ACME identifier (Section 9.7.7). The 810 "identifier" field MUST NOT be present at the top level in ACME 811 problem documents. It can only be present in subproblems. 812 Subproblems need not all have the same type, and do not need to match 813 the top level type. 815 ACME clients may choose to use the "identifier" field of a subproblem 816 as a hint that an operation would succeed if that identifier were 817 omitted. For instance, if an order contains ten DNS identifiers, and 818 the new-order request returns a problem document with two 819 subproblems, referencing two of those identifiers, the ACME client 820 may choose to submit another order containing only the eight 821 identifiers not listed in the problem document. 823 HTTP/1.1 403 Forbidden 824 Content-Type: application/problem+json 826 { 827 "type": "urn:ietf:params:acme:error:malformed", 828 "detail": "Some of the identifiers requested were rejected", 829 "subproblems": [ 830 { 831 "type": "urn:ietf:params:acme:error:malformed", 832 "detail": "Invalid underscore in DNS name \"_example.com\"", 833 "identifier": { 834 "type": "dns", 835 "value": "_example.com" 836 } 837 }, 838 { 839 "type": "urn:ietf:params:acme:error:rejectedIdentifier", 840 "detail": "This CA will not issue for \"example.net\"", 841 "identifier": { 842 "type": "dns", 843 "value": "example.net" 844 } 845 } 846 ] 847 } 848 7. Certificate Management 850 In this section, we describe the certificate management functions 851 that ACME enables: 853 o Account Creation 855 o Ordering a Certificate 857 o Identifier Authorization 859 o Certificate Issuance 861 o Certificate Revocation 863 7.1. Resources 865 ACME is structured as a REST [REST] application with the following 866 types of resources: 868 o Account resources, representing information about an account 869 (Section 7.1.2, Section 7.3) 871 o Order resources, representing an account's requests to issue 872 certificates (Section 7.1.3) 874 o Authorization resources, representing an account's authorization 875 to act for an identifier (Section 7.1.4) 877 o Challenge resources, representing a challenge to prove control of 878 an identifier (Section 7.5, Section 8) 880 o Certificate resources, representing issued certificates 881 (Section 7.4.2) 883 o A "directory" resource (Section 7.1.1) 885 o A "newNonce" resource (Section 7.2) 887 o A "newAccount" resource (Section 7.3) 889 o A "newOrder" resource (Section 7.4) 891 o A "revokeCert" resource (Section 7.6) 893 o A "keyChange" resource (Section 7.3.5) 895 The server MUST provide "directory" and "newNonce" resources. 897 ACME uses different URLs for different management functions. Each 898 function is listed in a directory along with its corresponding URL, 899 so clients only need to be configured with the directory URL. These 900 URLs are connected by a few different link relations [RFC5988]. 902 The "up" link relation is used with challenge resources to indicate 903 the authorization resource to which a challenge belongs. It is also 904 used, with some media types, from certificate resources to indicate a 905 resource from which the client may fetch a chain of CA certificates 906 that could be used to validate the certificate in the original 907 resource. 909 The "index" link relation is present on all resources other than the 910 directory and indicates the URL of the directory. 912 The following diagram illustrates the relations between resources on 913 an ACME server. For the most part, these relations are expressed by 914 URLs provided as strings in the resources' JSON representations. 915 Lines with labels in quotes indicate HTTP link relations. 917 directory 918 | 919 +--> newNonce 920 | 921 +----------+----------+-----+-----+------------+ 922 | | | | | 923 | | | | | 924 V V V V V 925 newAccount newAuthz newOrder revokeCert keyChange 926 | | | 927 | | | 928 V | V 929 account | order --+--> finalize 930 | | | 931 | | +--> cert 932 | V 933 +---> authorization 934 | ^ 935 | | "up" 936 V | 937 challenge 939 ACME Resources and Relationships 941 The following table illustrates a typical sequence of requests 942 required to establish a new account with the server, prove control of 943 an identifier, issue a certificate, and fetch an updated certificate 944 some time after issuance. The "->" is a mnemonic for a Location 945 header pointing to a created resource. 947 +-------------------+--------------------------------+--------------+ 948 | Action | Request | Response | 949 +-------------------+--------------------------------+--------------+ 950 | Get directory | GET directory | 200 | 951 | | | | 952 | Get nonce | HEAD newNonce | 200 | 953 | | | | 954 | Create account | POST newAccount | 201 -> | 955 | | | account | 956 | | | | 957 | Submit order | POST newOrder | 201 -> order | 958 | | | | 959 | Fetch challenges | POST-as-GET order's | 200 | 960 | | authorization urls | | 961 | | | | 962 | Respond to | POST-as-GET authorization | 200 | 963 | challenges | challenge urls | | 964 | | | | 965 | Poll for status | POST-as-GET order | 200 | 966 | | | | 967 | Finalize order | POST order's finalize url | 200 | 968 | | | | 969 | Poll for status | POST-as-GET order | 200 | 970 | | | | 971 | Download | POST-as-GET order's | 200 | 972 | certificate | certificate url | | 973 +-------------------+--------------------------------+--------------+ 975 The remainder of this section provides the details of how these 976 resources are structured and how the ACME protocol makes use of them. 978 7.1.1. Directory 980 In order to help clients configure themselves with the right URLs for 981 each ACME operation, ACME servers provide a directory object. This 982 should be the only URL needed to configure clients. It is a JSON 983 object, whose field names are drawn from the resource registry 984 (Section 9.7.5) and whose values are the corresponding URLs. 986 +------------+--------------------+ 987 | Field | URL in value | 988 +------------+--------------------+ 989 | newNonce | New nonce | 990 | | | 991 | newAccount | New account | 992 | | | 993 | newOrder | New order | 994 | | | 995 | newAuthz | New authorization | 996 | | | 997 | revokeCert | Revoke certificate | 998 | | | 999 | keyChange | Key Change | 1000 +------------+--------------------+ 1002 There is no constraint on the URL of the directory except that it 1003 should be different from the other ACME server resources' URLs, and 1004 that it should not clash with other services. For instance: 1006 o a host which functions as both an ACME and a Web server may want 1007 to keep the root path "/" for an HTML "front page", and place the 1008 ACME directory under the path "/acme". 1010 o a host which only functions as an ACME server could place the 1011 directory under the path "/". 1013 If the ACME server does not implement pre-authorization 1014 (Section 7.4.1) it MUST omit the "newAuthz" field of the directory. 1016 The object MAY additionally contain a field "meta". If present, it 1017 MUST be a JSON object; each field in the object is an item of 1018 metadata relating to the service provided by the ACME server. 1020 The following metadata items are defined (Section 9.7.6), all of 1021 which are OPTIONAL: 1023 termsOfService (optional, string): A URL identifying the current 1024 terms of service. 1026 website (optional, string): An HTTP or HTTPS URL locating a website 1027 providing more information about the ACME server. 1029 caaIdentities (optional, array of string): The hostnames that the 1030 ACME server recognizes as referring to itself for the purposes of 1031 CAA record validation as defined in [RFC6844]. Each string MUST 1032 represent the same sequence of ASCII code points that the server 1033 will expect to see as the "Issuer Domain Name" in a CAA issue or 1034 issuewild property tag. This allows clients to determine the 1035 correct issuer domain name to use when configuring CAA records. 1037 externalAccountRequired (optional, boolean): If this field is 1038 present and set to "true", then the CA requires that all new- 1039 account requests include an "externalAccountBinding" field 1040 associating the new account with an external account. 1042 Clients access the directory by sending a GET request to the 1043 directory URL. 1045 HTTP/1.1 200 OK 1046 Content-Type: application/json 1048 { 1049 "newNonce": "https://example.com/acme/new-nonce", 1050 "newAccount": "https://example.com/acme/new-account", 1051 "newOrder": "https://example.com/acme/new-order", 1052 "newAuthz": "https://example.com/acme/new-authz", 1053 "revokeCert": "https://example.com/acme/revoke-cert", 1054 "keyChange": "https://example.com/acme/key-change", 1055 "meta": { 1056 "termsOfService": "https://example.com/acme/terms/2017-5-30", 1057 "website": "https://www.example.com/", 1058 "caaIdentities": ["example.com"], 1059 "externalAccountRequired": false 1060 } 1061 } 1063 7.1.2. Account Objects 1065 An ACME account resource represents a set of metadata associated with 1066 an account. Account resources have the following structure: 1068 status (required, string): The status of this account. Possible 1069 values are: "valid", "deactivated", and "revoked". The value 1070 "deactivated" should be used to indicate client-initiated 1071 deactivation whereas "revoked" should be used to indicate server- 1072 initiated deactivation. (See Section 7.1.6) 1074 contact (optional, array of string): An array of URLs that the 1075 server can use to contact the client for issues related to this 1076 account. For example, the server may wish to notify the client 1077 about server-initiated revocation or certificate expiration. For 1078 information on supported URL schemes, see Section 7.3 1080 termsOfServiceAgreed (optional, boolean): Including this field in a 1081 new-account request, with a value of true, indicates the client's 1082 agreement with the terms of service. This field is not updateable 1083 by the client. 1085 orders (required, string): A URL from which a list of orders 1086 submitted by this account can be fetched via a POST-as-GET 1087 request, as described in Section 7.1.2.1. 1089 { 1090 "status": "valid", 1091 "contact": [ 1092 "mailto:cert-admin@example.com", 1093 "mailto:admin@example.com" 1094 ], 1095 "termsOfServiceAgreed": true, 1096 "orders": "https://example.com/acme/acct/1/orders" 1097 } 1099 7.1.2.1. Orders List 1101 Each account object includes an "orders" URL from which a list of 1102 orders created by the account can be fetched via POST-as-GET request. 1103 The result of the request MUST be a JSON object whose "orders" field 1104 is an array of URLs, each identifying an order belonging to the 1105 account. The server SHOULD include pending orders, and SHOULD NOT 1106 include orders that are invalid in the array of URLs. The server MAY 1107 return an incomplete list, along with a Link header field with a 1108 "next" link relation indicating where further entries can be 1109 acquired. 1111 HTTP/1.1 200 OK 1112 Content-Type: application/json 1113 Link: ;rel="next" 1115 { 1116 "orders": [ 1117 "https://example.com/acme/acct/1/order/1", 1118 "https://example.com/acme/acct/1/order/2", 1119 /* 47 more URLs not shown for example brevity */ 1120 "https://example.com/acme/acct/1/order/50" 1121 ] 1122 } 1124 7.1.3. Order Objects 1126 An ACME order object represents a client's request for a certificate 1127 and is used to track the progress of that order through to issuance. 1128 Thus, the object contains information about the requested 1129 certificate, the authorizations that the server requires the client 1130 to complete, and any certificates that have resulted from this order. 1132 status (required, string): The status of this order. Possible 1133 values are: "pending", "ready", "processing", "valid", and 1134 "invalid". (See Section 7.1.6) 1136 expires (optional, string): The timestamp after which the server 1137 will consider this order invalid, encoded in the format specified 1138 in RFC 3339 [RFC3339]. This field is REQUIRED for objects with 1139 "pending" or "valid" in the status field. 1141 identifiers (required, array of object): An array of identifier 1142 objects that the order pertains to. 1144 type (required, string): The type of identifier. This document 1145 defines the "dns" identifier type. See the registry defined in 1146 Section 9.7.7 for any others. 1148 value (required, string): The identifier itself. 1150 notBefore (optional, string): The requested value of the notBefore 1151 field in the certificate, in the date format defined in [RFC3339]. 1153 notAfter (optional, string): The requested value of the notAfter 1154 field in the certificate, in the date format defined in [RFC3339]. 1156 error (optional, object): The error that occurred while processing 1157 the order, if any. This field is structured as a problem document 1158 [RFC7807]. 1160 authorizations (required, array of string): For pending orders, the 1161 authorizations that the client needs to complete before the 1162 requested certificate can be issued (see Section 7.5), including 1163 unexpired authorizations that the client has completed in the past 1164 for identifiers specified in the order. The authorizations 1165 required are dictated by server policy and there may not be a 1:1 1166 relationship between the order identifiers and the authorizations 1167 required. For final orders (in the "valid" or "invalid" state), 1168 the authorizations that were completed. Each entry is a URL from 1169 which an authorization can be fetched with a POST-as-GET request. 1171 finalize (required, string): A URL that a CSR must be POSTed to once 1172 all of the order's authorizations are satisfied to finalize the 1173 order. The result of a successful finalization will be the 1174 population of the certificate URL for the order. 1176 certificate (optional, string): A URL for the certificate that has 1177 been issued in response to this order. 1179 { 1180 "status": "valid", 1181 "expires": "2015-03-01T14:09:07.99Z", 1183 "identifiers": [ 1184 { "type": "dns", "value": "example.com" }, 1185 { "type": "dns", "value": "www.example.com" } 1186 ], 1188 "notBefore": "2016-01-01T00:00:00Z", 1189 "notAfter": "2016-01-08T00:00:00Z", 1191 "authorizations": [ 1192 "https://example.com/acme/authz/1234", 1193 "https://example.com/acme/authz/2345" 1194 ], 1196 "finalize": "https://example.com/acme/acct/1/order/1/finalize", 1198 "certificate": "https://example.com/acme/cert/1234" 1199 } 1201 Any identifier of type "dns" in a new-order request MAY have a 1202 wildcard domain name as its value. A wildcard domain name consists 1203 of a single asterisk character followed by a single full stop 1204 character ("*.") followed by a domain name as defined for use in the 1205 Subject Alternate Name Extension by RFC 5280 [RFC5280]. An 1206 authorization returned by the server for a wildcard domain name 1207 identifier MUST NOT include the asterisk and full stop ("*.") prefix 1208 in the authorization identifier value. The returned authorization 1209 MUST include the optional "wildcard" field, with a value of true. 1211 The elements of the "authorizations" and "identifiers" array are 1212 immutable once set. The server MUST NOT change the contents of 1213 either array after they are created. If a client observes a change 1214 in the contents of either array, then it SHOULD consider the order 1215 invalid. 1217 The "authorizations" array of the order SHOULD reflect all 1218 authorizations that the CA takes into account in deciding to issue, 1219 even if some authorizations were fulfilled in earlier orders or in 1220 pre-authorization transactions. For example, if a CA allows multiple 1221 orders to be fulfilled based on a single authorization transaction, 1222 then it SHOULD reflect that authorization in all of the orders. 1224 Note that just because an authorization URL is listed in the 1225 "authorizations" array of an order object doesn't mean that the 1226 client is required to take action. There are several reasons that 1227 the referenced authorizations may already be valid: 1229 o The client completed the authorization as part of a previous order 1231 o The client previously pre-authorized the identifier (see 1232 Section 7.4.1) 1234 o The server granted the client authorization based on an external 1235 account 1237 Clients SHOULD check the "status" field of an order to determine 1238 whether they need to take any action. 1240 7.1.4. Authorization Objects 1242 An ACME authorization object represents a server's authorization for 1243 an account to represent an identifier. In addition to the 1244 identifier, an authorization includes several metadata fields, such 1245 as the status of the authorization (e.g., "pending", "valid", or 1246 "revoked") and which challenges were used to validate possession of 1247 the identifier. 1249 The structure of an ACME authorization resource is as follows: 1251 identifier (required, object): The identifier that the account is 1252 authorized to represent 1254 type (required, string): The type of identifier. (See below and 1255 Section 9.7.7) 1257 value (required, string): The identifier itself. 1259 status (required, string): The status of this authorization. 1260 Possible values are: "pending", "valid", "invalid", "deactivated", 1261 "expired", and "revoked". (See Section 7.1.6) 1263 expires (optional, string): The timestamp after which the server 1264 will consider this authorization invalid, encoded in the format 1265 specified in RFC 3339 [RFC3339]. This field is REQUIRED for 1266 objects with "valid" in the "status" field. 1268 challenges (required, array of objects): For pending authorizations, 1269 the challenges that the client can fulfill in order to prove 1270 possession of the identifier. For valid authorizations, the 1271 challenge that was validated. For invalid authorizations, the 1272 challenge that was attempted and failed. Each array entry is an 1273 object with parameters required to validate the challenge. A 1274 client should attempt to fulfill one of these challenges, and a 1275 server should consider any one of the challenges sufficient to 1276 make the authorization valid. 1278 wildcard (optional, boolean): For authorizations created as a result 1279 of a newOrder request containing a DNS identifier with a value 1280 that contained a wildcard prefix this field MUST be present, and 1281 true. 1283 The only type of identifier defined by this specification is a fully- 1284 qualified domain name (type: "dns"). The domain name MUST be encoded 1285 in the form in which it would apper in a certificate. That is, it 1286 MUST be encoded according to the rules in Section 7 of [RFC5280]. 1287 Servers MUST verify any identifier values that begin with the ASCII 1288 Compatible Encoding prefix "xn--" as defined in [RFC5890] are 1289 properly encoded. Wildcard domain names (with "*" as the first 1290 label) MUST NOT be included in authorization objects. If an 1291 authorization object conveys authorization for the base domain of a 1292 newOrder DNS type identifier with a wildcard prefix then the optional 1293 authorizations "wildcard" field MUST be present with a value of true. 1295 Section 8 describes a set of challenges for domain name validation. 1297 { 1298 "status": "valid", 1299 "expires": "2015-03-01T14:09:07.99Z", 1301 "identifier": { 1302 "type": "dns", 1303 "value": "example.org" 1304 }, 1306 "challenges": [ 1307 { 1308 "url": "https://example.com/acme/authz/1234/0", 1309 "type": "http-01", 1310 "status": "valid", 1311 "token": "DGyRejmCefe7v4NfDGDKfA", 1312 "validated": "2014-12-01T12:05:58.16Z" 1313 } 1314 ], 1316 "wildcard": false 1317 } 1319 7.1.5. Challenge Objects 1321 An ACME challenge object represents a server's offer to validate a 1322 client's possession of an identifier in a specific way. Unlike the 1323 other objects listed above, there is not a single standard structure 1324 for a challenge object. The contents of a challenge object depend on 1325 the validation method being used. The general structure of challenge 1326 objects and an initial set of validation methods are described in 1327 Section 8. 1329 7.1.6. Status Changes 1331 Each ACME object type goes through a simple state machine over its 1332 lifetime. The "status" field of the object indicates which state the 1333 object is currently in. 1335 Challenge objects are created in the "pending" state. They 1336 transition to the "processing" state when the client responds to the 1337 challenge (see Section 7.5.1) and the server begins attempting to 1338 validate that the client has completed the challenge. Note that 1339 within the "processing" state, the server may attempt to validate the 1340 challenge multiple times (see Section 8.2). Likewise, client 1341 requests for retries do not cause a state change. If validation is 1342 successful, the challenge moves to the "valid" state; if there is an 1343 error, the challenge moves to the "invalid" state. 1345 pending 1346 | 1347 | Receive 1348 | response 1349 V 1350 processing <-+ 1351 | | | Server retry or 1352 | | | client retry request 1353 | +----+ 1354 | 1355 | 1356 Successful | Failed 1357 validation | validation 1358 +---------+---------+ 1359 | | 1360 V V 1361 valid invalid 1363 State Transitions for Challenge Objects 1365 Authorization objects are created in the "pending" state. If one of 1366 the challenges listed in the authorization transitions to the "valid" 1367 state, then the authorization also changes to the "valid" state. If 1368 the client attempts to fulfill a challenge and fails, or if there is 1369 an error while the authorization is still pending, then the 1370 authorization transitions to the "invalid" state. Once the 1371 authorization is in the valid state, it can expire ("expired"), be 1372 deactivated by the client ("deactivated", see Section 7.5.2), or 1373 revoked by the server ("revoked"). 1375 pending --------------------+ 1376 | | 1377 Challenge failure | | 1378 or | | 1379 Error | Challenge valid | 1380 +---------+---------+ | 1381 | | | 1382 V V | 1383 invalid valid | 1384 | | 1385 | | 1386 | | 1387 +--------------+--------------+ 1388 | | | 1389 | | | 1390 Server | Client | Time after | 1391 revoke | deactivate | "expires" | 1392 V V V 1393 revoked deactivated expired 1395 State Transitions for Authorization Objects 1397 Order objects are created in the "pending" state. Once all of the 1398 authorizations listed in the order object are in the "valid" state, 1399 the order transitions to the "ready" state. The order moves to the 1400 "processing" state after the client submits a request to the order's 1401 "finalize" URL and the CA begins the issuance process for the 1402 certificate. Once the certificate is issued, the order enters the 1403 "valid" state. If an error occurs at any of these stages, the order 1404 moves to the "invalid" state. The order also moves to the "invalid" 1405 state if it expires, or one of its authorizations enters a final 1406 state other than "valid" ("expired", "revoked", "deactivated"). 1408 pending --------------+ 1409 | | 1410 | All authz | 1411 | "valid" | 1412 V | 1413 ready ---------------+ 1414 | | 1415 | Receive | 1416 | finalize | 1417 | request | 1418 V | 1419 processing ------------+ 1420 | | 1421 | Certificate | Error or 1422 | issued | Authorization failure 1423 V V 1424 valid invalid 1426 State Transitions for Order Objects 1428 Account objects are created in the "valid" state, since no further 1429 action is required to create an account after a successful newAccount 1430 request. If the account is deactivated by the client or revoked by 1431 the server, it moves to the corresponding state. 1433 valid 1434 | 1435 | 1436 +-----------+-----------+ 1437 Client | Server | 1438 deactiv.| revoke | 1439 V V 1440 deactivated revoked 1442 State Transitions for Account Objects 1444 Note that some of these states may not ever appear in a "status" 1445 field, depending on server behavior. For example, a server that 1446 issues synchronously will never show an order in the "processing" 1447 state. A server that deletes expired authorizations immediately will 1448 never show an authorization in the "expired" state. 1450 7.2. Getting a Nonce 1452 Before sending a POST request to the server, an ACME client needs to 1453 have a fresh anti-replay nonce to put in the "nonce" header of the 1454 JWS. In most cases, the client will have gotten a nonce from a 1455 previous request. However, the client might sometimes need to get a 1456 new nonce, e.g., on its first request to the server or if an existing 1457 nonce is no longer valid. 1459 To get a fresh nonce, the client sends a HEAD request to the new- 1460 nonce resource on the server. The server's response MUST include a 1461 Replay-Nonce header field containing a fresh nonce, and SHOULD have 1462 status code 200 (OK). The server MUST also respond to GET requests 1463 for this resource, returning an empty body (while still providing a 1464 Replay-Nonce header) with a 204 (No Content) status. 1466 HEAD /acme/new-nonce HTTP/1.1 1467 Host: example.com 1469 HTTP/1.1 200 OK 1470 Replay-Nonce: oFvnlFP1wIhRlYS2jTaXbA 1471 Cache-Control: no-store 1473 Proxy caching of responses from the new-nonce resource can cause 1474 clients receive the same nonce repeatedly, leading to badNonce 1475 errors. The server MUST include a Cache-Control header field with 1476 the "no-store" directive in responses for the new-nonce resource, in 1477 order to prevent caching of this resource. 1479 7.3. Account Creation 1481 A client creates a new account with the server by sending a POST 1482 request to the server's new-account URL. The body of the request is 1483 a stub account object optionally containing the "contact" and 1484 "termsOfServiceAgreed" fields, and optionally the 1485 "onlyReturnExisting" and "externalAccountBinding" fields. 1487 contact (optional, array of string): Same meaning as the 1488 corresponding server field defined in Section 7.1.2 1490 termsOfServiceAgreed (optional, boolean): Same meaning as the 1491 corresponding server field defined in Section 7.1.2 1493 onlyReturnExisting (optional, boolean): If this field is present 1494 with the value "true", then the server MUST NOT create a new 1495 account if one does not already exist. This allows a client to 1496 look up an account URL based on an account key (see 1497 Section 7.3.1). 1499 externalAccountBinding (optional, object): An optional field for 1500 binding the new account with an existing non-ACME account (see 1501 Section 7.3.4). 1503 POST /acme/new-account HTTP/1.1 1504 Host: example.com 1505 Content-Type: application/jose+json 1507 { 1508 "protected": base64url({ 1509 "alg": "ES256", 1510 "jwk": {...}, 1511 "nonce": "6S8IqOGY7eL2lsGoTZYifg", 1512 "url": "https://example.com/acme/new-account" 1513 }), 1514 "payload": base64url({ 1515 "termsOfServiceAgreed": true, 1516 "contact": [ 1517 "mailto:cert-admin@example.com", 1518 "mailto:admin@example.com" 1519 ] 1520 }), 1521 "signature": "RZPOnYoPs1PhjszF...-nh6X1qtOFPB519I" 1522 } 1524 The server MUST ignore any values provided in the "orders" fields in 1525 account bodies sent by the client, as well as any other fields that 1526 it does not recognize. If new fields are specified in the future, 1527 the specification of those fields MUST describe whether they can be 1528 provided by the client. 1530 In general, the server MUST ignore any fields in the request object 1531 that it does not recognize. In particular, it MUST NOT reflect 1532 unrecognized fields in the resulting account object. This allows 1533 clients to detect when servers do not support an extension field. 1535 The server SHOULD validate that the contact URLs in the "contact" 1536 field are valid and supported by the server. If the server validates 1537 contact URLs it MUST support the "mailto" scheme. Clients MUST NOT 1538 provide a "mailto" URL in the "contact" field that contains "hfields" 1539 [RFC6068], or more than one "addr-spec" in the "to" component. If a 1540 server encounters a "mailto" contact URL that does not meet these 1541 criteria, then it SHOULD reject it as invalid. 1543 If the server rejects a contact URL for using an unsupported scheme 1544 it MUST return an error of type "unsupportedContact", with a 1545 description describing the error and what types of contact URLs the 1546 server considers acceptable. If the server rejects a contact URL for 1547 using a supported scheme but an invalid value then the server MUST 1548 return an error of type "invalidContact". 1550 If the server wishes to require the client to agree to terms under 1551 which the ACME service is to be used, it MUST indicate the URL where 1552 such terms can be accessed in the "termsOfService" subfield of the 1553 "meta" field in the directory object, and the server MUST reject new- 1554 account requests that do not have the "termsOfServiceAgreed" field 1555 set to "true". Clients SHOULD NOT automatically agree to terms by 1556 default. Rather, they SHOULD require some user interaction for 1557 agreement to terms. 1559 The server creates an account and stores the public key used to 1560 verify the JWS (i.e., the "jwk" element of the JWS header) to 1561 authenticate future requests from the account. The server returns 1562 this account object in a 201 (Created) response, with the account URL 1563 in a Location header field. The account URL is used as the "kid" 1564 value in the JWS authenticating subsequent requests by this account 1565 (See Section 6.2). 1567 HTTP/1.1 201 Created 1568 Content-Type: application/json 1569 Replay-Nonce: D8s4D2mLs8Vn-goWuPQeKA 1570 Location: https://example.com/acme/acct/1 1571 Link: ;rel="index" 1573 { 1574 "status": "valid", 1576 "contact": [ 1577 "mailto:cert-admin@example.com", 1578 "mailto:admin@example.com" 1579 ], 1581 "orders": "https://example.com/acme/acct/1/orders" 1582 } 1584 7.3.1. Finding an Account URL Given a Key 1586 If the server receives a newAccount request signed with a key for 1587 which it already has an account registered with the provided account 1588 key, then it MUST return a response with a 200 (OK) status code and 1589 provide the URL of that account in the Location header field. The 1590 body of this response represents the account object as it existed on 1591 the server before this request; any fields in the request object MUST 1592 be ignored. This allows a client that has an account key but not the 1593 corresponding account URL to recover the account URL. 1595 If a client wishes to find the URL for an existing account and does 1596 not want an account to be created if one does not already exist, then 1597 it SHOULD do so by sending a POST request to the new-account URL with 1598 a JWS whose payload has an "onlyReturnExisting" field set to "true" 1599 ({"onlyReturnExisting": true}). If a client sends such a request and 1600 an account does not exist, then the server MUST return an error 1601 response with status code 400 (Bad Request) and type 1602 "urn:ietf:params:acme:error:accountDoesNotExist". 1604 7.3.2. Account Update 1606 If the client wishes to update this information in the future, it 1607 sends a POST request with updated information to the account URL. 1608 The server MUST ignore any updates to the "orders" field, 1609 "termsOfServiceAgreed" field (see Section 7.3.3), the "status" field 1610 (except as allowed by Section 7.3.6), or any other fields it does not 1611 recognize. If the server accepts the update, it MUST return a 1612 response with a 200 (OK) status code and the resulting account 1613 object. 1615 For example, to update the contact information in the above account, 1616 the client could send the following request: 1618 POST /acme/acct/1 HTTP/1.1 1619 Host: example.com 1620 Content-Type: application/jose+json 1622 { 1623 "protected": base64url({ 1624 "alg": "ES256", 1625 "kid": "https://example.com/acme/acct/1", 1626 "nonce": "ax5RnthDqp_Yf4_HZnFLmA", 1627 "url": "https://example.com/acme/acct/1" 1628 }), 1629 "payload": base64url({ 1630 "contact": [ 1631 "mailto:certificates@example.com", 1632 "mailto:admin@example.com" 1633 ] 1634 }), 1635 "signature": "hDXzvcj8T6fbFbmn...rDzXzzvzpRy64N0o" 1636 } 1638 7.3.3. Changes of Terms of Service 1640 As described above, a client can indicate its agreement with the CA's 1641 terms of service by setting the "termsOfServiceAgreed" field in its 1642 account object to "true". 1644 If the server has changed its terms of service since a client 1645 initially agreed, and the server is unwilling to process a request 1646 without explicit agreement to the new terms, then it MUST return an 1647 error response with status code 403 (Forbidden) and type 1648 "urn:ietf:params:acme:error:userActionRequired". This response MUST 1649 include a Link header field with link relation "terms-of-service" and 1650 the latest terms-of-service URL. 1652 The problem document returned with the error MUST also include an 1653 "instance" field, indicating a URL that the client should direct a 1654 human user to visit in order for instructions on how to agree to the 1655 terms. 1657 HTTP/1.1 403 Forbidden 1658 Replay-Nonce: T81bdZroZ2ITWSondpTmAw 1659 Link: ;rel="terms-of-service" 1660 Content-Type: application/problem+json 1661 Content-Language: en 1663 { 1664 "type": "urn:ietf:params:acme:error:userActionRequired", 1665 "detail": "Terms of service have changed", 1666 "instance": "https://example.com/acme/agreement/?token=W8Ih3PswD-8" 1667 } 1669 7.3.4. External Account Binding 1671 The server MAY require a value for the "externalAccountBinding" field 1672 to be present in "newAccount" requests. This can be used to 1673 associate an ACME account with an existing account in a non-ACME 1674 system, such as a CA customer database. 1676 To enable ACME account binding, the CA operating the ACME server 1677 needs to provide the ACME client with a MAC key and a key identifier, 1678 using some mechanism outside of ACME. The key identifier MUST be an 1679 ASCII string. The MAC key SHOULD be provided in base64url-encoded 1680 form, to maximize compatibility between non-ACME provisioning systems 1681 and ACME clients. 1683 The ACME client then computes a binding JWS to indicate the external 1684 account holder's approval of the ACME account key. The payload of 1685 this JWS is the ACME account key being registered, in JWK form. The 1686 protected header of the JWS MUST meet the following criteria: 1688 o The "alg" field MUST indicate a MAC-based algorithm 1690 o The "kid" field MUST contain the key identifier provided by the CA 1692 o The "nonce" field MUST NOT be present 1693 o The "url" field MUST be set to the same value as the outer JWS 1695 The "signature" field of the JWS will contain the MAC value computed 1696 with the MAC key provided by the CA. 1698 POST /acme/new-account HTTP/1.1 1699 Host: example.com 1700 Content-Type: application/jose+json 1702 { 1703 "protected": base64url({ 1704 "alg": "ES256", 1705 "jwk": /* account key */, 1706 "nonce": "K60BWPrMQG9SDxBDS_xtSw", 1707 "url": "https://example.com/acme/new-account" 1708 }), 1709 "payload": base64url({ 1710 "contact": ["mailto:example@anonymous.invalid"], 1711 "termsOfServiceAgreed": true, 1713 "externalAccountBinding": { 1714 "protected": base64url({ 1715 "alg": "HS256", 1716 "kid": /* key identifier from CA */, 1717 "url": "https://example.com/acme/new-account" 1718 }), 1719 "payload": base64url(/* same as in "jwk" above */), 1720 "signature": /* MAC using MAC key from CA */ 1721 } 1722 }), 1723 "signature": "5TWiqIYQfIDfALQv...x9C2mg8JGPxl5bI4" 1724 } 1726 If such a CA requires that new-account requests contain an 1727 "externalAccountBinding" field, then it MUST provide the value "true" 1728 in the "externalAccountRequired" subfield of the "meta" field in the 1729 directory object. If the CA receives a new-account request without 1730 an "externalAccountBinding" field, then it SHOULD reply with an error 1731 of type "externalAccountRequired". 1733 When a CA receives a new-account request containing an 1734 "externalAccountBinding" field, it decides whether or not to verify 1735 the binding. If the CA does not verify the binding, then it MUST NOT 1736 reflect the "externalAccountBinding" field in the resulting account 1737 object (if any). To verify the account binding, the CA MUST take the 1738 following steps: 1740 1. Verify that the value of the field is a well-formed JWS 1741 2. Verify that the JWS protected field meets the above criteria 1743 3. Retrieve the MAC key corresponding to the key identifier in the 1744 "kid" field 1746 4. Verify that the MAC on the JWS verifies using that MAC key 1748 5. Verify that the payload of the JWS represents the same key as was 1749 used to verify the outer JWS (i.e., the "jwk" field of the outer 1750 JWS) 1752 If all of these checks pass and the CA creates a new account, then 1753 the CA may consider the new account associated with the external 1754 account corresponding to the MAC key. The account object the CA 1755 returns MUST include an "externalAccountBinding" field with the same 1756 value as the field in the request. If any of these checks fail, then 1757 the CA MUST reject the new-account request. 1759 7.3.5. Account Key Roll-over 1761 A client may wish to change the public key that is associated with an 1762 account in order to recover from a key compromise or proactively 1763 mitigate the impact of an unnoticed key compromise. 1765 To change the key associated with an account, the client sends a 1766 request to the server containing signatures by both the old and new 1767 keys. The signature by the new key covers the account URL and the 1768 old key, signifying a request by the new key holder to take over the 1769 account from the old key holder. The signature by the old key covers 1770 this request and its signature, and indicates the old key holder's 1771 assent to the roll-over request. 1773 To create this request object, the client first constructs a key- 1774 change object describing the account to be updated and its account 1775 key: 1777 account (required, string): The URL for the account being modified. 1778 The content of this field MUST be the exact string provided in the 1779 Location header field in response to the new-account request that 1780 created the account. 1782 oldKey (required, JWK): The JWK representation of the old key 1784 The client then encapsulates the key-change object in an "inner" JWS, 1785 signed with the requested new account key. This "inner" JWS becomes 1786 the payload for the "outer" JWS that is the body of the ACME request. 1788 The outer JWS MUST meet the normal requirements for an ACME JWS (see 1789 Section 6.2). The inner JWS MUST meet the normal requirements, with 1790 the following differences: 1792 o The inner JWS MUST have a "jwk" header parameter, containing the 1793 public key of the new key pair. 1795 o The inner JWS MUST have the same "url" header parameter as the 1796 outer JWS. 1798 o The inner JWS MAY omit the "nonce" header parameter. The server 1799 MUST ignore any value provided for the "nonce" header parameter. 1801 This transaction has signatures from both the old and new keys so 1802 that the server can verify that the holders of the two keys both 1803 agree to the change. The signatures are nested to preserve the 1804 property that all signatures on POST messages are signed by exactly 1805 one key. The "inner" JWS effectively represents a request by the 1806 holder of the new key to take over the account form the holder of the 1807 old key. The "outer" JWS represents the current account holder's 1808 assent to this request. 1810 POST /acme/key-change HTTP/1.1 1811 Host: example.com 1812 Content-Type: application/jose+json 1814 { 1815 "protected": base64url({ 1816 "alg": "ES256", 1817 "kid": "https://example.com/acme/acct/1", 1818 "nonce": "S9XaOcxP5McpnTcWPIhYuB", 1819 "url": "https://example.com/acme/key-change" 1820 }), 1821 "payload": base64url({ 1822 "protected": base64url({ 1823 "alg": "ES256", 1824 "jwk": /* new key */, 1825 "url": "https://example.com/acme/key-change" 1826 }), 1827 "payload": base64url({ 1828 "account": "https://example.com/acme/acct/1", 1829 "oldKey": /* old key */ 1830 }), 1831 "signature": "Xe8B94RD30Azj2ea...8BmZIRtcSKPSd8gU" 1832 }), 1833 "signature": "5TWiqIYQfIDfALQv...x9C2mg8JGPxl5bI4" 1834 } 1835 On receiving key-change request, the server MUST perform the 1836 following steps in addition to the typical JWS validation: 1838 1. Validate the POST request belongs to a currently active account, 1839 as described in Section 6. 1841 2. Check that the payload of the JWS is a well-formed JWS object 1842 (the "inner JWS"). 1844 3. Check that the JWS protected header of the inner JWS has a "jwk" 1845 field. 1847 4. Check that the inner JWS verifies using the key in its "jwk" 1848 field. 1850 5. Check that the payload of the inner JWS is a well-formed key- 1851 change object (as described above). 1853 6. Check that the "url" parameters of the inner and outer JWSs are 1854 the same. 1856 7. Check that the "account" field of the key-change object contains 1857 the URL for the account matching the old key (i.e., the "kid" 1858 field in the outer JWS). 1860 8. Check that the "oldKey" field of the key-change object is the 1861 same as the account key for the account in question. 1863 9. Check that no account exists whose account key is the same as the 1864 key in the "jwk" header parameter of the inner JWS. 1866 If all of these checks pass, then the server updates the 1867 corresponding account by replacing the old account key with the new 1868 public key and returns status code 200 (OK). Otherwise, the server 1869 responds with an error status code and a problem document describing 1870 the error. If there is an existing account with the new key 1871 provided, then the server SHOULD use status code 409 (Conflict) and 1872 provide the URL of that account in the Location header field. 1874 Note that changing the account key for an account SHOULD NOT have any 1875 other impact on the account. For example, the server MUST NOT 1876 invalidate pending orders or authorization transactions based on a 1877 change of account key. 1879 7.3.6. Account Deactivation 1881 A client can deactivate an account by posting a signed update to the 1882 account URL with a status field of "deactivated." Clients may wish 1883 to do this when the account key is compromised or decommissioned. A 1884 deactivated account can no longer request certificate issuance or 1885 access resources related to the account, such as orders or 1886 authorizations. If a server receives a POST or POST-as-GET from a 1887 deactivated account, it MUST return an error response with status 1888 code 401 (Unauthorized) and type 1889 "urn:ietf:params:acme:error:unauthorized". 1891 POST /acme/acct/1 HTTP/1.1 1892 Host: example.com 1893 Content-Type: application/jose+json 1895 { 1896 "protected": base64url({ 1897 "alg": "ES256", 1898 "kid": "https://example.com/acme/acct/1", 1899 "nonce": "ntuJWWSic4WVNSqeUmshgg", 1900 "url": "https://example.com/acme/acct/1" 1901 }), 1902 "payload": base64url({ 1903 "status": "deactivated" 1904 }), 1905 "signature": "earzVLd3m5M4xJzR...bVTqn7R08AKOVf3Y" 1906 } 1908 The server MUST verify that the request is signed by the account key. 1909 If the server accepts the deactivation request, it replies with a 200 1910 (OK) status code and the current contents of the account object. 1912 Once an account is deactivated, the server MUST NOT accept further 1913 requests authorized by that account's key. The server SHOULD cancel 1914 any pending operations authorized by the account's key, such as 1915 certificate orders. A server may take a variety of actions in 1916 response to an account deactivation, e.g., deleting data related to 1917 that account or sending mail to the account's contacts. Servers 1918 SHOULD NOT revoke certificates issued by the deactivated account, 1919 since this could cause operational disruption for servers using these 1920 certificates. ACME does not provide a way to reactivate a 1921 deactivated account. 1923 7.4. Applying for Certificate Issuance 1925 The client begins the certificate issuance process by sending a POST 1926 request to the server's new-order resource. The body of the POST is 1927 a JWS object whose JSON payload is a subset of the order object 1928 defined in Section 7.1.3, containing the fields that describe the 1929 certificate to be issued: 1931 identifiers (required, array of object): An array of identifier 1932 objects that the client wishes to submit an order for. 1934 type (required, string): The type of identifier. 1936 value (required, string): The identifier itself. 1938 notBefore (optional, string): The requested value of the notBefore 1939 field in the certificate, in the date format defined in [RFC3339]. 1941 notAfter (optional, string): The requested value of the notAfter 1942 field in the certificate, in the date format defined in [RFC3339]. 1944 POST /acme/new-order HTTP/1.1 1945 Host: example.com 1946 Content-Type: application/jose+json 1948 { 1949 "protected": base64url({ 1950 "alg": "ES256", 1951 "kid": "https://example.com/acme/acct/1", 1952 "nonce": "5XJ1L3lEkMG7tR6pA00clA", 1953 "url": "https://example.com/acme/new-order" 1954 }), 1955 "payload": base64url({ 1956 "identifiers": [ 1957 { "type": "dns", "value": "example.com" } 1958 ], 1959 "notBefore": "2016-01-01T00:04:00+04:00", 1960 "notAfter": "2016-01-08T00:04:00+04:00" 1961 }), 1962 "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g" 1963 } 1965 The server MUST return an error if it cannot fulfill the request as 1966 specified, and MUST NOT issue a certificate with contents other than 1967 those requested. If the server requires the request to be modified 1968 in a certain way, it should indicate the required changes using an 1969 appropriate error type and description. 1971 If the server is willing to issue the requested certificate, it 1972 responds with a 201 (Created) response. The body of this response is 1973 an order object reflecting the client's request and any 1974 authorizations the client must complete before the certificate will 1975 be issued. 1977 HTTP/1.1 201 Created 1978 Replay-Nonce: MYAuvOpaoIiywTezizk5vw 1979 Location: https://example.com/acme/order/asdf 1981 { 1982 "status": "pending", 1983 "expires": "2016-01-01T00:00:00Z", 1985 "notBefore": "2016-01-01T00:00:00Z", 1986 "notAfter": "2016-01-08T00:00:00Z", 1988 "identifiers": [ 1989 { "type": "dns", "value": "example.com" }, 1990 ], 1992 "authorizations": [ 1993 "https://example.com/acme/authz/1234", 1994 ], 1996 "finalize": "https://example.com/acme/order/asdf/finalize" 1997 } 1999 The order object returned by the server represents a promise that if 2000 the client fulfills the server's requirements before the "expires" 2001 time, then the server will be willing to finalize the order upon 2002 request and issue the requested certificate. In the order object, 2003 any authorization referenced in the "authorizations" array whose 2004 status is "pending" represents an authorization transaction that the 2005 client must complete before the server will issue the certificate 2006 (see Section 7.5). If the client fails to complete the required 2007 actions before the "expires" time, then the server SHOULD change the 2008 status of the order to "invalid" and MAY delete the order resource. 2009 Clients MUST NOT make any assumptions about the sort order of 2010 "identifiers" or "authorizations" elements in the returned order 2011 object. 2013 Once the client believes it has fulfilled the server's requirements, 2014 it should send a POST request to the order resource's finalize URL. 2015 The POST body MUST include a CSR: 2017 csr (required, string): A CSR encoding the parameters for the 2018 certificate being requested [RFC2986]. The CSR is sent in the 2019 base64url-encoded version of the DER format. (Note: Because this 2020 field uses base64url, and does not include headers, it is 2021 different from PEM.). 2023 POST /acme/order/asdf/finalize HTTP/1.1 2024 Host: example.com 2025 Content-Type: application/jose+json 2027 { 2028 "protected": base64url({ 2029 "alg": "ES256", 2030 "kid": "https://example.com/acme/acct/1", 2031 "nonce": "MSF2j2nawWHPxxkE3ZJtKQ", 2032 "url": "https://example.com/acme/order/asdf/finalize" 2033 }), 2034 "payload": base64url({ 2035 "csr": "MIIBPTCBxAIBADBFMQ...FS6aKdZeGsysoCo4H9P", 2036 }), 2037 "signature": "uOrUfIIk5RyQ...nw62Ay1cl6AB" 2038 } 2040 The CSR encodes the client's requests with regard to the content of 2041 the certificate to be issued. The CSR MUST indicate the exact same 2042 set of requested identifiers as the initial new-order request. 2043 Identifiers of type "dns" MUST appear either in the commonName 2044 portion of the requested subject name, or in an extensionRequest 2045 attribute [RFC2985] requesting a subjectAltName extension. (These 2046 identifiers may appear in any sort order.) Specifications that 2047 define new identifier types must specify where in the certificate 2048 signing request these identifiers can appear. 2050 A request to finalize an order will result in error if the CA is 2051 unwilling to issue a certificate corresponding to the submitted CSR. 2052 For example: 2054 o If the order indicated does not have status "ready" 2056 o If the CSR and order identifiers differ 2058 o If the account is not authorized for the identifiers indicated in 2059 the CSR 2061 o If the CSR requests extensions that the CA is not willing to 2062 include 2064 In such cases, the problem document returned by the server SHOULD use 2065 error code "badCSR", and describe specific reasons the CSR was 2066 rejected in its "details" field. After returning such an error, the 2067 server SHOULD leave the order in the "ready" state, to allow the 2068 client to submit a new finalize request with an amended CSR. 2070 A request to finalize an order will return the order to be finalized. 2071 The client should begin polling the order by sending a POST-as-GET 2072 request to the order resource to obtain its current state. The 2073 status of the order will indicate what action the client should take: 2075 o "invalid": The certificate will not be issued. Consider this 2076 order process abandoned. 2078 o "pending": The server does not believe that the client has 2079 fulfilled the requirements. Check the "authorizations" array for 2080 entries that are still pending. 2082 o "ready": The server agrees that the requirements have been 2083 fulfilled, and is awaiting finalization. Submit a finalization 2084 request. 2086 o "processing": The certificate is being issued. Send a POST-as-GET 2087 request after the time given in the "Retry-After" header field of 2088 the response, if any. 2090 o "valid": The server has issued the certificate and provisioned its 2091 URL to the "certificate" field of the order. Download the 2092 certificate. 2094 HTTP/1.1 200 OK 2095 Replay-Nonce: CGf81JWBsq8QyIgPCi9Q9X 2096 Location: https://example.com/acme/order/asdf 2098 { 2099 "status": "valid", 2100 "expires": "2015-12-31T00:17:00.00-09:00", 2102 "notBefore": "2015-12-31T00:17:00.00-09:00", 2103 "notAfter": "2015-12-31T00:17:00.00-09:00", 2105 "identifiers": [ 2106 { "type": "dns", "value": "example.com" }, 2107 { "type": "dns", "value": "www.example.com" } 2108 ], 2110 "authorizations": [ 2111 "https://example.com/acme/authz/1234", 2112 "https://example.com/acme/authz/2345" 2113 ], 2115 "finalize": "https://example.com/acme/order/asdf/finalize", 2117 "certificate": "https://example.com/acme/cert/asdf" 2118 } 2120 7.4.1. Pre-Authorization 2122 The order process described above presumes that authorization objects 2123 are created reactively, in response to a certificate order. Some 2124 servers may also wish to enable clients to obtain authorization for 2125 an identifier proactively, outside of the context of a specific 2126 issuance. For example, a client hosting virtual servers for a 2127 collection of names might wish to obtain authorization before any 2128 virtual servers are created and only create a certificate when a 2129 virtual server starts up. 2131 In some cases, a CA running an ACME server might have a completely 2132 external, non-ACME process for authorizing a client to issue 2133 certificates for an identifier. In these cases, the CA should 2134 provision its ACME server with authorization objects corresponding to 2135 these authorizations and reflect them as already valid in any orders 2136 submitted by the client. 2138 If a CA wishes to allow pre-authorization within ACME, it can offer a 2139 "new authorization" resource in its directory by adding the field 2140 "newAuthz" with a URL for the new authorization resource. 2142 To request authorization for an identifier, the client sends a POST 2143 request to the new-authorization resource specifying the identifier 2144 for which authorization is being requested. 2146 identifier (required, object): The identifier to appear in the 2147 resulting authorization object (see Section 7.1.4) 2149 type (required, string): The type of identifier. 2151 value (required, string): The identifier itself. 2153 POST /acme/new-authz HTTP/1.1 2154 Host: example.com 2155 Content-Type: application/jose+json 2157 { 2158 "protected": base64url({ 2159 "alg": "ES256", 2160 "kid": "https://example.com/acme/acct/1", 2161 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2162 "url": "https://example.com/acme/new-authz" 2163 }), 2164 "payload": base64url({ 2165 "identifier": { 2166 "type": "dns", 2167 "value": "example.net" 2168 } 2169 }), 2170 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2171 } 2173 Note that because the identifier in a pre-authorization request is 2174 the exact identifier to be included in the authorization object, pre- 2175 authorization cannot be used to authorize issuance with wildcard DNS 2176 identifiers. 2178 Before processing the authorization request, the server SHOULD 2179 determine whether it is willing to issue certificates for the 2180 identifier. For example, the server should check that the identifier 2181 is of a supported type. Servers might also check names against a 2182 blacklist of known high-value identifiers. If the server is 2183 unwilling to issue for the identifier, it SHOULD return a 403 2184 (Forbidden) error, with a problem document describing the reason for 2185 the rejection. 2187 If the server is willing to proceed, it builds a pending 2188 authorization object from the inputs submitted by the client: 2190 o "identifier" the identifier submitted by the client 2192 o "status" MUST be "pending" unless the server has out-of-band 2193 information about the client's authorization status 2195 o "challenges" as selected by the server's policy for this 2196 identifier 2198 The server allocates a new URL for this authorization, and returns a 2199 201 (Created) response, with the authorization URL in the Location 2200 header field, and the JSON authorization object in the body. The 2201 client then follows the process described in Section 7.5 to complete 2202 the authorization process. 2204 7.4.2. Downloading the Certificate 2206 To download the issued certificate, the client simply sends a POST- 2207 as-GET request to the certificate URL. 2209 The default format of the certificate is application/pem-certificate- 2210 chain (see Section 9). 2212 The server MAY provide one or more link relation header fields 2213 [RFC5988] with relation "alternate". Each such field SHOULD express 2214 an alternative certificate chain starting with the same end-entity 2215 certificate. This can be used to express paths to various trust 2216 anchors. Clients can fetch these alternates and use their own 2217 heuristics to decide which is optimal. 2219 GET /acme/cert/asdf HTTP/1.1 2220 Host: example.com 2221 Accept: application/pem-certificate-chain 2223 HTTP/1.1 200 OK 2224 Content-Type: application/pem-certificate-chain 2225 Link: ;rel="index" 2227 -----BEGIN CERTIFICATE----- 2228 [End-entity certificate contents] 2229 -----END CERTIFICATE----- 2230 -----BEGIN CERTIFICATE----- 2231 [Issuer certificate contents] 2232 -----END CERTIFICATE----- 2233 -----BEGIN CERTIFICATE----- 2234 [Other certificate contents] 2235 -----END CERTIFICATE----- 2236 A certificate resource represents a single, immutable certificate. 2237 If the client wishes to obtain a renewed certificate, the client 2238 initiates a new order process to request one. 2240 Because certificate resources are immutable once issuance is 2241 complete, the server MAY enable the caching of the resource by adding 2242 Expires and Cache-Control header fields specifying a point in time in 2243 the distant future. These header fields have no relation to the 2244 certificate's period of validity. 2246 The ACME client MAY request other formats by including an Accept 2247 header field [RFC7231] in its request. For example, the client could 2248 use the media type "application/pkix-cert" [RFC2585] or "applicaiton/ 2249 pkcs7-mime" [RFC5751] to request the end-entity certificate in DER 2250 format. Server support for alternate formats is OPTIONAL. For 2251 formats that can only express a single certificate, the server SHOULD 2252 provide one or more "Link: rel="up"" header fields pointing to an 2253 issuer or issuers so that ACME clients can build a certificate chain 2254 as defined in TLS [RFC8446]. 2256 7.5. Identifier Authorization 2258 The identifier authorization process establishes the authorization of 2259 an account to manage certificates for a given identifier. This 2260 process assures the server of two things: 2262 1. That the client controls the private key of the account key pair, 2263 and 2265 2. That the client controls the identifier in question. 2267 This process may be repeated to associate multiple identifiers to a 2268 key pair (e.g., to request certificates with multiple identifiers), 2269 or to associate multiple accounts with an identifier (e.g., to allow 2270 multiple entities to manage certificates). 2272 Authorization resources are created by the server in response to 2273 certificate orders or authorization requests submitted by an account 2274 key holder; their URLs are provided to the client in the responses to 2275 these requests. The authorization object is implicitly tied to the 2276 account key used to sign the request. 2278 When a client receives an order from the server in reply to a new 2279 order request, it downloads the authorization resources by sending 2280 POST-as-GET requests to the indicated URLs. If the client initiates 2281 authorization using a request to the new authorization resource, it 2282 will have already received the pending authorization object in the 2283 response to that request. 2285 POST /acme/authz/1234 HTTP/1.1 2286 Host: example.com 2287 Content-Type: application/jose+json 2288 Accept: application/pkix-cert 2290 { 2291 "protected": base64url({ 2292 "alg": "ES256", 2293 "kid": "https://example.com/acme/acct/1", 2294 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2295 "url": "https://example.com/acme/authz/1234", 2296 }), 2297 "payload": "", 2298 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2299 } 2301 HTTP/1.1 200 OK 2302 Content-Type: application/json 2303 Link: ;rel="index" 2305 { 2306 "status": "pending", 2307 "expires": "2018-03-03T14:09:30Z", 2309 "identifier": { 2310 "type": "dns", 2311 "value": "example.org" 2312 }, 2314 "challenges": [ 2315 { 2316 "type": "http-01", 2317 "url": "https://example.com/acme/authz/1234/0", 2318 "token": "DGyRejmCefe7v4NfDGDKfA" 2319 }, 2320 { 2321 "type": "dns-01", 2322 "url": "https://example.com/acme/authz/1234/2", 2323 "token": "DGyRejmCefe7v4NfDGDKfA" 2324 } 2325 ], 2327 "wildcard": false 2328 } 2330 7.5.1. Responding to Challenges 2332 To prove control of the identifier and receive authorization, the 2333 client needs to provision the required challenge response based on 2334 the challenge type and indicate to the server that it is ready for 2335 the challenge validation to be attempted. 2337 The client indicates to the server it is ready for the challenge 2338 validation by sending an empty JSON body ("{}"), carried in a POST 2339 request to the challenge URL (not authorization URL). 2341 For example, if the client were to respond to the "http-01" challenge 2342 in the above authorization, it would send the following request: 2344 POST /acme/authz/1234/0 HTTP/1.1 2345 Host: example.com 2346 Content-Type: application/jose+json 2348 { 2349 "protected": base64url({ 2350 "alg": "ES256", 2351 "kid": "https://example.com/acme/acct/1", 2352 "nonce": "Q_s3MWoqT05TrdkM2MTDcw", 2353 "url": "https://example.com/acme/authz/1234/0" 2354 }), 2355 "payload": base64url({}), 2356 "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ" 2357 } 2359 The server updates the authorization document by updating its 2360 representation of the challenge with the response object provided by 2361 the client. The server MUST ignore any fields in the response object 2362 that are not specified as response fields for this type of challenge. 2363 The server provides a 200 (OK) response with the updated challenge 2364 object as its body. 2366 If the client's response is invalid for any reason or does not 2367 provide the server with appropriate information to validate the 2368 challenge, then the server MUST return an HTTP error. On receiving 2369 such an error, the client SHOULD undo any actions that have been 2370 taken to fulfill the challenge, e.g., removing files that have been 2371 provisioned to a web server. 2373 The server is said to "finalize" the authorization when it has 2374 completed one of the validations, by assigning the authorization a 2375 status of "valid" or "invalid", corresponding to whether it considers 2376 the account authorized for the identifier. If the final state is 2377 "valid", then the server MUST include an "expires" field. When 2378 finalizing an authorization, the server MAY remove challenges other 2379 than the one that was completed, and may modify the "expires" field. 2380 The server SHOULD NOT remove challenges with status "invalid". 2382 Usually, the validation process will take some time, so the client 2383 will need to poll the authorization resource to see when it is 2384 finalized. For challenges where the client can tell when the server 2385 has validated the challenge (e.g., by seeing an HTTP or DNS request 2386 from the server), the client SHOULD NOT begin polling until it has 2387 seen the validation request from the server. 2389 To check on the status of an authorization, the client sends a POST- 2390 as-GET request to the authorization URL, and the server responds with 2391 the current authorization object. In responding to poll requests 2392 while the validation is still in progress, the server MUST return a 2393 200 (OK) response and MAY include a Retry-After header field to 2394 suggest a polling interval to the client. 2396 POST /acme/authz/1234 HTTP/1.1 2397 Host: example.com 2398 Content-Type: application/jose+json 2399 Accept: application/pkix-cert 2401 { 2402 "protected": base64url({ 2403 "alg": "ES256", 2404 "kid": "https://example.com/acme/acct/1", 2405 "nonce": "uQpSjlRb4vQVCjVYAyyUWg", 2406 "url": "https://example.com/acme/authz/1234", 2407 }), 2408 "payload": "", 2409 "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" 2410 } 2412 HTTP/1.1 200 OK 2413 Content-Type: application/json 2415 { 2416 "status": "valid", 2417 "expires": "2018-09-09T14:09:01.13Z", 2419 "identifier": { 2420 "type": "dns", 2421 "value": "example.org" 2422 }, 2424 "challenges": [ 2425 { 2426 "type": "http-01", 2427 "url": "https://example.com/acme/authz/1234/0", 2428 "status": "valid", 2429 "validated": "2014-12-01T12:05:13.72Z", 2430 "token": "IlirfxKKXAsHtmzK29Pj8A" 2431 } 2432 ], 2434 "wildcard": false 2435 } 2437 7.5.2. Deactivating an Authorization 2439 If a client wishes to relinquish its authorization to issue 2440 certificates for an identifier, then it may request that the server 2441 deactivates each authorization associated with it by sending POST 2442 requests with the static object {"status": "deactivated"} to each 2443 authorization URL. 2445 POST /acme/authz/1234 HTTP/1.1 2446 Host: example.com 2447 Content-Type: application/jose+json 2449 { 2450 "protected": base64url({ 2451 "alg": "ES256", 2452 "kid": "https://example.com/acme/acct/1", 2453 "nonce": "xWCM9lGbIyCgue8di6ueWQ", 2454 "url": "https://example.com/acme/authz/1234" 2455 }), 2456 "payload": base64url({ 2457 "status": "deactivated" 2458 }), 2459 "signature": "srX9Ji7Le9bjszhu...WTFdtujObzMtZcx4" 2460 } 2462 The server MUST verify that the request is signed by the account key 2463 corresponding to the account that owns the authorization. If the 2464 server accepts the deactivation, it should reply with a 200 (OK) 2465 status code and the updated contents of the authorization object. 2467 The server MUST NOT treat deactivated authorization objects as 2468 sufficient for issuing certificates. 2470 7.6. Certificate Revocation 2472 To request that a certificate be revoked, the client sends a POST 2473 request to the ACME server's revokeCert URL. The body of the POST is 2474 a JWS object whose JSON payload contains the certificate to be 2475 revoked: 2477 certificate (required, string): The certificate to be revoked, in 2478 the base64url-encoded version of the DER format. (Note: Because 2479 this field uses base64url, and does not include headers, it is 2480 different from PEM.) 2482 reason (optional, int): One of the revocation reasonCodes defined in 2483 Section 5.3.1 of [RFC5280] to be used when generating OCSP 2484 responses and CRLs. If this field is not set the server SHOULD 2485 omit the reasonCode CRL entry extension when generating OCSP 2486 responses and CRLs. The server MAY disallow a subset of 2487 reasonCodes from being used by the user. If a request contains a 2488 disallowed reasonCode the server MUST reject it with the error 2489 type "urn:ietf:params:acme:error:badRevocationReason". The 2490 problem document detail SHOULD indicate which reasonCodes are 2491 allowed. 2493 Revocation requests are different from other ACME requests in that 2494 they can be signed either with an account key pair or the key pair in 2495 the certificate. 2497 Example using an account key pair for the signature: 2499 POST /acme/revoke-cert HTTP/1.1 2500 Host: example.com 2501 Content-Type: application/jose+json 2503 { 2504 "protected": base64url({ 2505 "alg": "ES256", 2506 "kid": "https://example.com/acme/acct/1", 2507 "nonce": "JHb54aT_KTXBWQOzGYkt9A", 2508 "url": "https://example.com/acme/revoke-cert" 2509 }), 2510 "payload": base64url({ 2511 "certificate": "MIIEDTCCAvegAwIBAgIRAP8...", 2512 "reason": 4 2513 }), 2514 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2515 } 2517 Example using the certificate key pair for the signature: 2519 POST /acme/revoke-cert HTTP/1.1 2520 Host: example.com 2521 Content-Type: application/jose+json 2523 { 2524 "protected": base64url({ 2525 "alg": "RS256", 2526 "jwk": /* certificate's public key */, 2527 "nonce": "JHb54aT_KTXBWQOzGYkt9A", 2528 "url": "https://example.com/acme/revoke-cert" 2529 }), 2530 "payload": base64url({ 2531 "certificate": "MIIEDTCCAvegAwIBAgIRAP8...", 2532 "reason": 1 2533 }), 2534 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2535 } 2537 Before revoking a certificate, the server MUST verify that the key 2538 used to sign the request is authorized to revoke the certificate. 2539 The server MUST consider at least the following accounts authorized 2540 for a given certificate: 2542 o the account that issued the certificate. 2544 o an account that holds authorizations for all of the identifiers in 2545 the certificate. 2547 The server MUST also consider a revocation request valid if it is 2548 signed with the private key corresponding to the public key in the 2549 certificate. 2551 If the revocation succeeds, the server responds with status code 200 2552 (OK). If the revocation fails, the server returns an error. For 2553 example, if the certificate has already been revoked the server 2554 returns an error response with status code 400 (Bad Request) and type 2555 "urn:ietf:params:acme:error:alreadyRevoked". 2557 HTTP/1.1 200 OK 2558 Replay-Nonce: IXVHDyxIRGcTE0VSblhPzw 2559 Content-Length: 0 2561 --- or --- 2563 HTTP/1.1 403 Forbidden 2564 Replay-Nonce: IXVHDyxIRGcTE0VSblhPzw 2565 Content-Type: application/problem+json 2566 Content-Language: en 2568 { 2569 "type": "urn:ietf:params:acme:error:unauthorized", 2570 "detail": "No authorization provided for name example.net" 2571 } 2573 8. Identifier Validation Challenges 2575 There are few types of identifiers in the world for which there is a 2576 standardized mechanism to prove possession of a given identifier. In 2577 all practical cases, CAs rely on a variety of means to test whether 2578 an entity applying for a certificate with a given identifier actually 2579 controls that identifier. 2581 Challenges provide the server with assurance that an account holder 2582 is also the entity that controls an identifier. For each type of 2583 challenge, it must be the case that in order for an entity to 2584 successfully complete the challenge the entity must both: 2586 o Hold the private key of the account key pair used to respond to 2587 the challenge 2589 o Control the identifier in question 2590 Section 10 documents how the challenges defined in this document meet 2591 these requirements. New challenges will need to document how they 2592 do. 2594 ACME uses an extensible challenge/response framework for identifier 2595 validation. The server presents a set of challenges in the 2596 authorization object it sends to a client (as objects in the 2597 "challenges" array), and the client responds by sending a response 2598 object in a POST request to a challenge URL. 2600 This section describes an initial set of challenge types. The 2601 definition of a challenge type includes: 2603 1. Content of challenge objects 2605 2. Content of response objects 2607 3. How the server uses the challenge and response to verify control 2608 of an identifier 2610 Challenge objects all contain the following basic fields: 2612 type (required, string): The type of challenge encoded in the 2613 object. 2615 url (required, string): The URL to which a response can be posted. 2617 status (required, string): The status of this challenge. Possible 2618 values are: "pending", "processing", "valid", and "invalid". (See 2619 Section 7.1.6) 2621 validated (optional, string): The time at which the server validated 2622 this challenge, encoded in the format specified in RFC 3339 2623 [RFC3339]. This field is REQUIRED if the "status" field is 2624 "valid". 2626 error (optional, object): Error that occurred while the server was 2627 validating the challenge, if any, structured as a problem document 2628 [RFC7807]. Multiple errors can be indicated by using subproblems 2629 Section 6.7.1. A challenge object with an error MUST have status 2630 equal to "invalid". 2632 All additional fields are specified by the challenge type. If the 2633 server sets a challenge's "status" to "invalid", it SHOULD also 2634 include the "error" field to help the client diagnose why the 2635 challenge failed. 2637 Different challenges allow the server to obtain proof of different 2638 aspects of control over an identifier. In some challenges, like HTTP 2639 and DNS, the client directly proves its ability to do certain things 2640 related to the identifier. The choice of which challenges to offer 2641 to a client under which circumstances is a matter of server policy. 2643 The identifier validation challenges described in this section all 2644 relate to validation of domain names. If ACME is extended in the 2645 future to support other types of identifiers, there will need to be 2646 new challenge types, and they will need to specify which types of 2647 identifier they apply to. 2649 8.1. Key Authorizations 2651 All challenges defined in this document make use of a key 2652 authorization string. A key authorization is a string that 2653 concatinates the token for the challenge with a key fingerprint, 2654 separated by a "." character: 2656 keyAuthorization = token || '.' || base64url(Thumbprint(accountKey)) 2658 The "Thumbprint" step indicates the computation specified in 2659 [RFC7638], using the SHA-256 digest [FIPS180-4]. As noted in 2660 [RFC7518] any prepended zero octets in the fields of a JWK object 2661 MUST be stripped before doing the computation. 2663 As specified in the individual challenges below, the token for a 2664 challenge is a string comprised entirely of characters in the URL- 2665 safe base64 alphabet. The "||" operator indicates concatenation of 2666 strings. 2668 8.2. Retrying Challenges 2670 ACME challenges typically require the client to set up some network- 2671 accessible resource that the server can query in order to validate 2672 that the client controls an identifier. In practice it is not 2673 uncommon for the server's queries to fail while a resource is being 2674 set up, e.g., due to information propagating across a cluster or 2675 firewall rules not being in place. 2677 Clients SHOULD NOT respond to challenges until they believe that the 2678 server's queries will succeed. If a server's initial validation 2679 query fails, the server SHOULD retry the query after some time, in 2680 order to account for delay in setting up responses such as DNS 2681 records or HTTP resources. The precise retry schedule is up to the 2682 server, but server operators should keep in mind the operational 2683 scenarios that the schedule is trying to accommodate. Given that 2684 retries are intended to address things like propagation delays in 2685 HTTP or DNS provisioning, there should not usually be any reason to 2686 retry more often than every 5 or 10 seconds. While the server is 2687 still trying, the status of the challenge remains "processing"; it is 2688 only marked "invalid" once the server has given up. 2690 The server MUST provide information about its retry state to the 2691 client via the "error" field in the challenge and the Retry-After 2692 HTTP header field in response to requests to the challenge resource. 2693 The server MUST add an entry to the "error" field in the challenge 2694 after each failed validation query. The server SHOULD set the Retry- 2695 After header field to a time after the server's next validation 2696 query, since the status of the challenge will not change until that 2697 time. 2699 Clients can explicitly request a retry by re-sending their response 2700 to a challenge in a new POST request (with a new nonce, etc.). This 2701 allows clients to request a retry when the state has changed (e.g., 2702 after firewall rules have been updated). Servers SHOULD retry a 2703 request immediately on receiving such a POST request. In order to 2704 avoid denial-of-service attacks via client-initiated retries, servers 2705 SHOULD rate-limit such requests. 2707 8.3. HTTP Challenge 2709 With HTTP validation, the client in an ACME transaction proves its 2710 control over a domain name by proving that it can provision HTTP 2711 resources on a server accessible under that domain name. The ACME 2712 server challenges the client to provision a file at a specific path, 2713 with a specific string as its content. 2715 As a domain may resolve to multiple IPv4 and IPv6 addresses, the 2716 server will connect to at least one of the hosts found in the DNS A 2717 and AAAA records, at its discretion. Because many web servers 2718 allocate a default HTTPS virtual host to a particular low-privilege 2719 tenant user in a subtle and non-intuitive manner, the challenge must 2720 be completed over HTTP, not HTTPS. 2722 type (required, string): The string "http-01" 2724 token (required, string): A random value that uniquely identifies 2725 the challenge. This value MUST have at least 128 bits of entropy. 2726 It MUST NOT contain any characters outside the base64url alphabet, 2727 and MUST NOT include base64 padding characters ("="). See 2728 [RFC4086] for additional information on randomness requirements. 2730 { 2731 "type": "http-01", 2732 "url": "https://example.com/acme/authz/0", 2733 "status": "pending", 2734 "token": "LoqXcYV8q5ONbJQxbmR7SCTNo3tiAXDfowyjxAjEuX0" 2735 } 2737 A client fulfills this challenge by constructing a key authorization 2738 from the "token" value provided in the challenge and the client's 2739 account key. The client then provisions the key authorization as a 2740 resource on the HTTP server for the domain in question. 2742 The path at which the resource is provisioned is comprised of the 2743 fixed prefix "/.well-known/acme-challenge/", followed by the "token" 2744 value in the challenge. The value of the resource MUST be the ASCII 2745 representation of the key authorization. 2747 GET /.well-known/acme-challenge/LoqXcYV8...jxAjEuX0 2748 Host: example.org 2750 HTTP/1.1 200 OK 2751 Content-Type: application/octet-stream 2753 LoqXcYV8...jxAjEuX0.9jg46WB3...fm21mqTI 2755 (In the above, "..." indicates that the token and the JWK thumbprint 2756 in the key authorization have been truncated to fit on the page.) 2758 A client responds with an empty object ({}) to acknowledge that the 2759 challenge can be validated by the server. 2761 POST /acme/authz/1234/0 2762 Host: example.com 2763 Content-Type: application/jose+json 2765 { 2766 "protected": base64url({ 2767 "alg": "ES256", 2768 "kid": "https://example.com/acme/acct/1", 2769 "nonce": "UQI1PoRi5OuXzxuX7V7wL0", 2770 "url": "https://example.com/acme/authz/1234/0" 2771 }), 2772 "payload": base64url({}), 2773 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2774 } 2775 On receiving a response, the server constructs and stores the key 2776 authorization from the challenge "token" value and the current client 2777 account key. 2779 Given a challenge/response pair, the server verifies the client's 2780 control of the domain by verifying that the resource was provisioned 2781 as expected. 2783 1. Construct a URL by populating the URL template [RFC6570] 2784 "http://{domain}/.well-known/acme-challenge/{token}", where: 2786 * the domain field is set to the domain name being verified; and 2788 * the token field is set to the token in the challenge. 2790 2. Verify that the resulting URL is well-formed. 2792 3. Dereference the URL using an HTTP GET request. This request MUST 2793 be sent to TCP port 80 on the HTTP server. 2795 4. Verify that the body of the response is a well-formed key 2796 authorization. The server SHOULD ignore whitespace characters at 2797 the end of the body. 2799 5. Verify that key authorization provided by the HTTP server matches 2800 the key authorization stored by the server. 2802 The server SHOULD follow redirects when dereferencing the URL. 2803 Clients might use redirects, for example, so that the response can be 2804 provided by a centralized certificate management server. See 2805 Section 10.2 for security considerations related to redirects. 2807 If all of the above verifications succeed, then the validation is 2808 successful. If the request fails, or the body does not pass these 2809 checks, then it has failed. 2811 The client SHOULD de-provision the resource provisioned for this 2812 challenge once the challenge is complete, i.e., once the "status" 2813 field of the challenge has the value "valid" or "invalid". 2815 8.4. DNS Challenge 2817 When the identifier being validated is a domain name, the client can 2818 prove control of that domain by provisioning a TXT resource record 2819 containing a designated value for a specific validation domain name. 2821 type (required, string): The string "dns-01" 2822 token (required, string): A random value that uniquely identifies 2823 the challenge. This value MUST have at least 128 bits of entropy. 2824 It MUST NOT contain any characters outside the base64url alphabet, 2825 including padding characters ("="). See [RFC4086] for additional 2826 information on randomness requirements. 2828 { 2829 "type": "dns-01", 2830 "url": "https://example.com/acme/authz/1234/2", 2831 "status": "pending", 2832 "token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA" 2833 } 2835 A client fulfills this challenge by constructing a key authorization 2836 from the "token" value provided in the challenge and the client's 2837 account key. The client then computes the SHA-256 digest [FIPS180-4] 2838 of the key authorization. 2840 The record provisioned to the DNS contains the base64url encoding of 2841 this digest. The client constructs the validation domain name by 2842 prepending the label "_acme-challenge" to the domain name being 2843 validated, then provisions a TXT record with the digest value under 2844 that name. For example, if the domain name being validated is 2845 "example.org", then the client would provision the following DNS 2846 record: 2848 _acme-challenge.example.org. 300 IN TXT "gfj9Xq...Rg85nM" 2850 A client responds with an empty object ({}) to acknowledge that the 2851 challenge can be validated by the server. 2853 POST /acme/authz/1234/2 2854 Host: example.com 2855 Content-Type: application/jose+json 2857 { 2858 "protected": base64url({ 2859 "alg": "ES256", 2860 "kid": "https://example.com/acme/acct/1", 2861 "nonce": "SS2sSl1PtspvFZ08kNtzKd", 2862 "url": "https://example.com/acme/authz/1234/2" 2863 }), 2864 "payload": base64url({}), 2865 "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4" 2866 } 2867 On receiving a response, the server constructs and stores the key 2868 authorization from the challenge "token" value and the current client 2869 account key. 2871 To validate a DNS challenge, the server performs the following steps: 2873 1. Compute the SHA-256 digest [FIPS180-4] of the stored key 2874 authorization 2876 2. Query for TXT records for the validation domain name 2878 3. Verify that the contents of one of the TXT records match the 2879 digest value 2881 If all of the above verifications succeed, then the validation is 2882 successful. If no DNS record is found, or DNS record and response 2883 payload do not pass these checks, then the validation fails. 2885 The client SHOULD de-provision the resource record(s) provisioned for 2886 this challenge once the challenge is complete, i.e., once the 2887 "status" field of the challenge has the value "valid" or "invalid". 2889 9. IANA Considerations 2891 9.1. MIME Type: application/pem-certificate-chain 2893 A file of this type contains one or more certificates encoded with 2894 the PEM textual encoding, according to RFC 7468 [RFC7468]. The 2895 textual encoding of certificates in this file MUST use the strict 2896 encoding and MUST NOT include explanatory text. The ABNF for this 2897 format is as follows, where "stricttextualmsg" and "eol" are as 2898 defined in Section 3 of RFC 7468: 2900 certchain = stricttextualmsg *(eol stricttextualmsg) 2902 In order to provide easy interoperation with TLS, the first 2903 certificate MUST be an end-entity certificate. Each following 2904 certificate SHOULD directly certify the one preceding it. Because 2905 certificate validation requires that trust anchors be distributed 2906 independently, a certificate that represents a trust anchor MAY be 2907 omitted from the chain, provided that supported peers are known to 2908 possess any omitted certificates. 2910 The "Media Types" registry should be updated with the following 2911 additional value: 2913 MIME media type name: application 2914 MIME subtype name: pem-certificate-chain 2916 Required parameters: None 2918 Optional parameters: None 2920 Encoding considerations: 7bit 2922 Security considerations: Carries a cryptographic certificate and its 2923 associated certificate chain. This media type carries no active 2924 content. 2926 Interoperability considerations: None 2928 Published specification: draft-ietf-acme-acme [[ RFC EDITOR: Please 2929 replace draft-ietf-acme-acme above with the RFC number assigned to 2930 this ]] 2932 Applications which use this media type: ACME clients and servers, 2933 HTTP servers, other applications that need to be configured with a 2934 certificate chain 2936 Additional information: 2938 Deprecated alias names for this type: n/a Magic number(s): n/a File 2939 extension(s): .pem Macintosh file type code(s): n/a 2941 Person & email address to contact for further information: See 2942 Authors' Addresses section. 2944 Intended usage: COMMON 2946 Restrictions on usage: n/a 2948 Author: See Authors' Addresses section. 2950 Change controller: Internet Engineering Task Force iesg@ietf.org [2] 2952 9.2. Well-Known URI for the HTTP Challenge 2954 The "Well-Known URIs" registry should be updated with the following 2955 additional value (using the template from [RFC5785]): 2957 URI suffix: acme-challenge 2959 Change controller: IETF 2961 Specification document(s): This document, Section Section 8.3 2962 Related information: N/A 2964 9.3. Replay-Nonce HTTP Header 2966 The "Message Headers" registry should be updated with the following 2967 additional value: 2969 +------------------+----------+----------+--------------------------+ 2970 | Header Field | Protocol | Status | Reference | 2971 | Name | | | | 2972 +------------------+----------+----------+--------------------------+ 2973 | Replay-Nonce | http | standard | [[this-RFC, Section | 2974 | | | | 6.5.1] | 2975 +------------------+----------+----------+--------------------------+ 2977 9.4. "url" JWS Header Parameter 2979 The "JSON Web Signature and Encryption Header Parameters" registry 2980 should be updated with the following additional value: 2982 o Header Parameter Name: "url" 2984 o Header Parameter Description: URL 2986 o Header Parameter Usage Location(s): JWE, JWS 2988 o Change Controller: IESG 2990 o Specification Document(s): Section 6.4.1 of RFC XXXX 2992 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 2993 to this document ]] 2995 9.5. "nonce" JWS Header Parameter 2997 The "JSON Web Signature and Encryption Header Parameters" registry 2998 should be updated with the following additional value: 3000 o Header Parameter Name: "nonce" 3002 o Header Parameter Description: Nonce 3004 o Header Parameter Usage Location(s): JWE, JWS 3006 o Change Controller: IESG 3008 o Specification Document(s): Section 6.5.2 of RFC XXXX 3010 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3011 to this document ]] 3013 9.6. URN Sub-namespace for ACME (urn:ietf:params:acme) 3015 The "IETF URN Sub-namespace for Registered Protocol Parameter 3016 Identifiers" registry should be updated with the following additional 3017 value, following the template in [RFC3553]: 3019 Registry name: acme 3021 Specification: RFC XXXX 3023 Repository: URL-TBD 3025 Index value: No transformation needed. 3027 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3028 to this document, and replace URL-TBD with the URL assigned by IANA 3029 for registries of ACME parameters. ]] 3031 9.7. New Registries 3033 This document requests that IANA create the following new registries: 3035 1. ACME Account Object Fields (Section 9.7.1) 3037 2. ACME Order Object Fields (Section 9.7.2) 3039 3. ACME Authorization Object Fields (Section 9.7.3) 3041 4. ACME Error Types (Section 9.7.4) 3043 5. ACME Resource Types (Section 9.7.5) 3045 6. ACME Directory Metadata Fields (Section 9.7.6) 3047 7. ACME Identifier Types (Section 9.7.7) 3049 8. ACME Validation Methods (Section 9.7.8) 3051 All of these registries are under a heading of "Automated Certificate 3052 Management Environment (ACME) Protocol" and are administered under a 3053 Specification Required policy [RFC8126]. 3055 9.7.1. Fields in Account Objects 3057 This registry lists field names that are defined for use in ACME 3058 account objects. Fields marked as "configurable" may be included in 3059 a new-account request. 3061 Template: 3063 o Field name: The string to be used as a field name in the JSON 3064 object 3066 o Field type: The type of value to be provided, e.g., string, 3067 boolean, array of string 3069 o Client configurable: Boolean indicating whether the server should 3070 accept values provided by the client 3072 o Reference: Where this field is defined 3074 Initial contents: The fields and descriptions defined in 3075 Section 7.1.2. 3077 +------------------------+---------------+--------------+-----------+ 3078 | Field Name | Field Type | Configurable | Reference | 3079 +------------------------+---------------+--------------+-----------+ 3080 | status | string | false | RFC XXXX | 3081 | | | | | 3082 | contact | array of | true | RFC XXXX | 3083 | | string | | | 3084 | | | | | 3085 | externalAccountBinding | object | true | RFC XXXX | 3086 | | | | | 3087 | termsOfServiceAgreed | boolean | true | RFC XXXX | 3088 | | | | | 3089 | orders | string | false | RFC XXXX | 3090 +------------------------+---------------+--------------+-----------+ 3092 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3093 to this document ]] 3095 9.7.2. Fields in Order Objects 3097 This registry lists field names that are defined for use in ACME 3098 order objects. Fields marked as "configurable" may be included in a 3099 new-order request. 3101 Template: 3103 o Field name: The string to be used as a field name in the JSON 3104 object 3106 o Field type: The type of value to be provided, e.g., string, 3107 boolean, array of string 3109 o Client configurable: Boolean indicating whether the server should 3110 accept values provided by the client 3112 o Reference: Where this field is defined 3114 Initial contents: The fields and descriptions defined in 3115 Section 7.1.3. 3117 +----------------+-----------------+--------------+-----------+ 3118 | Field Name | Field Type | Configurable | Reference | 3119 +----------------+-----------------+--------------+-----------+ 3120 | status | string | false | RFC XXXX | 3121 | | | | | 3122 | expires | string | false | RFC XXXX | 3123 | | | | | 3124 | identifiers | array of object | true | RFC XXXX | 3125 | | | | | 3126 | notBefore | string | true | RFC XXXX | 3127 | | | | | 3128 | notAfter | string | true | RFC XXXX | 3129 | | | | | 3130 | authorizations | array of string | false | RFC XXXX | 3131 | | | | | 3132 | finalize | string | false | RFC XXXX | 3133 | | | | | 3134 | certificate | string | false | RFC XXXX | 3135 +----------------+-----------------+--------------+-----------+ 3137 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3138 to this document ]] 3140 9.7.3. Fields in Authorization Objects 3142 This registry lists field names that are defined for use in ACME 3143 authorization objects. Fields marked as "configurable" may be 3144 included in a new-authorization request. 3146 Template: 3148 o Field name: The string to be used as a field name in the JSON 3149 object 3151 o Field type: The type of value to be provided, e.g., string, 3152 boolean, array of string 3154 o Client configurable: Boolean indicating whether the server should 3155 accept values provided by the client 3157 o Reference: Where this field is defined 3159 Initial contents: The fields and descriptions defined in 3160 Section 7.1.4. 3162 +------------+-----------------+--------------+-----------+ 3163 | Field Name | Field Type | Configurable | Reference | 3164 +------------+-----------------+--------------+-----------+ 3165 | identifier | object | true | RFC XXXX | 3166 | | | | | 3167 | status | string | false | RFC XXXX | 3168 | | | | | 3169 | expires | string | false | RFC XXXX | 3170 | | | | | 3171 | challenges | array of object | false | RFC XXXX | 3172 | | | | | 3173 | wildcard | boolean | false | RFC XXXX | 3174 +------------+-----------------+--------------+-----------+ 3176 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3177 to this document ]] 3179 9.7.4. Error Types 3181 This registry lists values that are used within URN values that are 3182 provided in the "type" field of problem documents in ACME. 3184 Template: 3186 o Type: The label to be included in the URN for this error, 3187 following "urn:ietf:params:acme:error:" 3189 o Description: A human-readable description of the error 3191 o Reference: Where the error is defined 3193 Initial contents: The types and descriptions in the table in 3194 Section 6.7 above, with the Reference field set to point to this 3195 specification. 3197 9.7.5. Resource Types 3199 This registry lists the types of resources that ACME servers may list 3200 in their directory objects. 3202 Template: 3204 o Field name: The value to be used as a field name in the directory 3205 object 3207 o Resource type: The type of resource labeled by the field 3209 o Reference: Where the resource type is defined 3211 Initial contents: 3213 +------------+--------------------+-----------+ 3214 | Field Name | Resource Type | Reference | 3215 +------------+--------------------+-----------+ 3216 | newNonce | New nonce | RFC XXXX | 3217 | | | | 3218 | newAccount | New account | RFC XXXX | 3219 | | | | 3220 | newOrder | New order | RFC XXXX | 3221 | | | | 3222 | newAuthz | New authorization | RFC XXXX | 3223 | | | | 3224 | revokeCert | Revoke certificate | RFC XXXX | 3225 | | | | 3226 | keyChange | Key change | RFC XXXX | 3227 | | | | 3228 | meta | Metadata object | RFC XXXX | 3229 +------------+--------------------+-----------+ 3231 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3232 to this document ]] 3234 9.7.6. Fields in the "meta" Object within a Directory Object 3236 This registry lists field names that are defined for use in the JSON 3237 object included in the "meta" field of an ACME directory object. 3239 Template: 3241 o Field name: The string to be used as a field name in the JSON 3242 object 3244 o Field type: The type of value to be provided, e.g., string, 3245 boolean, array of string 3247 o Reference: Where this field is defined 3249 Initial contents: The fields and descriptions defined in 3250 Section 7.1.2. 3252 +-------------------------+-----------------+-----------+ 3253 | Field Name | Field Type | Reference | 3254 +-------------------------+-----------------+-----------+ 3255 | termsOfService | string | RFC XXXX | 3256 | | | | 3257 | website | string | RFC XXXX | 3258 | | | | 3259 | caaIdentities | array of string | RFC XXXX | 3260 | | | | 3261 | externalAccountRequired | boolean | RFC XXXX | 3262 +-------------------------+-----------------+-----------+ 3264 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3265 to this document ]] 3267 9.7.7. Identifier Types 3269 This registry lists the types of identifiers that can be present in 3270 ACME authorization objects. 3272 Template: 3274 o Label: The value to be put in the "type" field of the identifier 3275 object 3277 o Reference: Where the identifier type is defined 3279 Initial contents: 3281 +-------+-----------+ 3282 | Label | Reference | 3283 +-------+-----------+ 3284 | dns | RFC XXXX | 3285 +-------+-----------+ 3287 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3288 to this document ]] 3290 9.7.8. Validation Methods 3292 This registry lists identifiers for the ways that CAs can validate 3293 control of identifiers. Each method's entry must specify whether it 3294 corresponds to an ACME challenge type. The "Identifier Type" field 3295 must be contained in the Label column of the ACME Identifier Types 3296 registry. 3298 Template: 3300 o Label: The identifier for this validation method 3302 o Identifier Type: The type of identifier that this method applies 3303 to 3305 o ACME: "Y" if the validation method corresponds to an ACME 3306 challenge type; "N" otherwise 3308 o Reference: Where the validation method is defined 3310 This registry may also contain reserved entries (e.g., to avoid 3311 collisions). Such entries should have the "ACME" field set to "N" 3312 and the "Identifier Type" set to "RESERVED". 3314 Initial Contents 3316 +------------+-----------------+------+-----------+ 3317 | Label | Identifier Type | ACME | Reference | 3318 +------------+-----------------+------+-----------+ 3319 | http-01 | dns | Y | RFC XXXX | 3320 | | | | | 3321 | dns-01 | dns | Y | RFC XXXX | 3322 | | | | | 3323 | tls-sni-01 | RESERVED | N | RFC XXXX | 3324 | | | | | 3325 | tls-sni-02 | RESERVED | N | RFC XXXX | 3326 +------------+-----------------+------+-----------+ 3328 When evaluating a request for an assignment in this registry, the 3329 designated expert should ensure that the method being registered has 3330 a clear, interoperable definition and does not overlap with existing 3331 validation methods. That is, it should not be possible for a client 3332 and server to follow the same set of actions to fulfill two different 3333 validation methods. 3335 The values "tls-sni-01" and "tls-sni-02" are reserved because they 3336 were used in pre-RFC versions of this specification to denote 3337 validation methods that were removed because they were found not to 3338 be secure in some cases. 3340 Validation methods do not have to be compatible with ACME in order to 3341 be registered. For example, a CA might wish to register a validation 3342 method in order to support its use with the ACME extensions to CAA 3343 [I-D.ietf-acme-caa]. 3345 [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned 3346 to this document ]] 3348 10. Security Considerations 3350 ACME is a protocol for managing certificates that attest to 3351 identifier/key bindings. Thus the foremost security goal of ACME is 3352 to ensure the integrity of this process, i.e., to ensure that the 3353 bindings attested by certificates are correct and that only 3354 authorized entities can manage certificates. ACME identifies clients 3355 by their account keys, so this overall goal breaks down into two more 3356 precise goals: 3358 1. Only an entity that controls an identifier can get an 3359 authorization for that identifier 3361 2. Once authorized, an account key's authorizations cannot be 3362 improperly used by another account 3364 In this section, we discuss the threat model that underlies ACME and 3365 the ways that ACME achieves these security goals within that threat 3366 model. We also discuss the denial-of-service risks that ACME servers 3367 face, and a few other miscellaneous considerations. 3369 10.1. Threat Model 3371 As a service on the Internet, ACME broadly exists within the Internet 3372 threat model [RFC3552]. In analyzing ACME, it is useful to think of 3373 an ACME server interacting with other Internet hosts along two 3374 "channels": 3376 o An ACME channel, over which the ACME HTTPS requests are exchanged 3378 o A validation channel, over which the ACME server performs 3379 additional requests to validate a client's control of an 3380 identifier 3382 +------------+ 3383 | ACME | ACME Channel 3384 | Client |--------------------+ 3385 +------------+ | 3386 V 3387 +------------+ 3388 | ACME | 3389 | Server | 3390 +------------+ 3391 +------------+ | 3392 | Validation |<-------------------+ 3393 | Server | Validation Channel 3394 +------------+ 3396 Communications Channels Used by ACME 3398 In practice, the risks to these channels are not entirely separate, 3399 but they are different in most cases. Each channel, for example, 3400 uses a different communications pattern: the ACME channel will 3401 comprise inbound HTTPS connections to the ACME server and the 3402 validation channel outbound HTTP or DNS requests. 3404 Broadly speaking, ACME aims to be secure against active and passive 3405 attackers on any individual channel. Some vulnerabilities arise 3406 (noted below) when an attacker can exploit both the ACME channel and 3407 one of the others. 3409 On the ACME channel, in addition to network layer attackers, we also 3410 need to account for man-in-the-middle (MitM) attacks at the 3411 application layer, and for abusive use of the protocol itself. 3412 Protection against application layer MitM addresses potential 3413 attackers such as Content Distribution Networks (CDNs) and 3414 middleboxes with a TLS MitM function. Preventing abusive use of ACME 3415 means ensuring that an attacker with access to the validation channel 3416 can't obtain illegitimate authorization by acting as an ACME client 3417 (legitimately, in terms of the protocol). 3419 ACME does not protect against other types of abuse by a MitM on the 3420 ACME channel. For example, such an attacker could send a bogus 3421 "badSignatureAlgorithm" error response to downgrade a client to the 3422 lowest-quality signature algorithm that the server supports. A MitM 3423 that is present on all connections (such as a CDN), can cause denial- 3424 of-service conditions in a variety of ways. 3426 10.2. Integrity of Authorizations 3428 ACME allows anyone to request challenges for an identifier by 3429 registering an account key and sending a new-order request using that 3430 account key. The integrity of the authorization process thus depends 3431 on the identifier validation challenges to ensure that the challenge 3432 can only be completed by someone who both (1) holds the private key 3433 of the account key pair, and (2) controls the identifier in question. 3435 Validation responses need to be bound to an account key pair in order 3436 to avoid situations where a MitM on ACME HTTPS requests can switch 3437 out a legitimate domain holder's account key for one of his choosing. 3438 Such MitMs can arise, for example, if a CA uses a CDN or third-party 3439 reverse proxy in front of its ACME interface. An attack by such an 3440 MitM could have the following form: 3442 o Legitimate domain holder registers account key pair A 3444 o MitM registers account key pair B 3446 o Legitimate domain holder sends a new-order request signed using 3447 account key A 3449 o MitM suppresses the legitimate request but sends the same request 3450 signed using account key B 3452 o ACME server issues challenges and MitM forwards them to the 3453 legitimate domain holder 3455 o Legitimate domain holder provisions the validation response 3457 o ACME server performs validation query and sees the response 3458 provisioned by the legitimate domain holder 3460 o Because the challenges were issued in response to a message signed 3461 account key B, the ACME server grants authorization to account key 3462 B (the MitM) instead of account key A (the legitimate domain 3463 holder) 3465 Domain ACME 3466 Holder MitM Server 3467 | | | 3468 | newAccount(A) | | 3469 |--------------------->|--------------------->| 3470 | | | 3471 | | newAccount(B) | 3472 | |--------------------->| 3473 | newOrder(domain, A) | | 3474 |--------------------->| | 3475 | | newOrder(domain, B) | 3476 | |--------------------->| 3477 | | | 3478 | authz, challenges | authz, challenges | 3479 |<---------------------|<---------------------| 3480 | | | 3481 | response(chall, A) | response(chall, B) | 3482 |--------------------->|--------------------->| 3483 | | | 3484 | validation request | | 3485 |<--------------------------------------------| 3486 | | | 3487 | validation response | | 3488 |-------------------------------------------->| 3489 | | | 3490 | | | Considers challenge 3491 | | | fulfilled by B. 3492 | | | 3494 Man-in-the-Middle Attack Exploiting a Validation Method without 3495 Account Key Binding 3497 All of the challenges defined in this document have a binding between 3498 the account private key and the validation query made by the server, 3499 via the key authorization. The key authorization reflects the 3500 account public key and is provided to the server in the validation 3501 response over the validation channel. 3503 The association of challenges to identifiers is typically done by 3504 requiring the client to perform some action that only someone who 3505 effectively controls the identifier can perform. For the challenges 3506 in this document, the actions are: 3508 o HTTP: Provision files under .well-known on a web server for the 3509 domain 3511 o DNS: Provision DNS resource records for the domain 3512 There are several ways that these assumptions can be violated, both 3513 by misconfiguration and by attacks. For example, on a web server 3514 that allows non-administrative users to write to .well-known, any 3515 user can claim to own the web server's hostname by responding to an 3516 HTTP challenge. Similarly, if a server that can be used for ACME 3517 validation is compromised by a malicious actor, then that malicious 3518 actor can use that access to obtain certificates via ACME. 3520 The use of hosting providers is a particular risk for ACME 3521 validation. If the owner of the domain has outsourced operation of 3522 DNS or web services to a hosting provider, there is nothing that can 3523 be done against tampering by the hosting provider. As far as the 3524 outside world is concerned, the zone or website provided by the 3525 hosting provider is the real thing. 3527 More limited forms of delegation can also lead to an unintended party 3528 gaining the ability to successfully complete a validation 3529 transaction. For example, suppose an ACME server follows HTTP 3530 redirects in HTTP validation and a website operator provisions a 3531 catch-all redirect rule that redirects requests for unknown resources 3532 to a different domain. Then the target of the redirect could use 3533 that to get a certificate through HTTP validation since the 3534 validation path will not be known to the primary server. 3536 The DNS is a common point of vulnerability for all of these 3537 challenges. An entity that can provision false DNS records for a 3538 domain can attack the DNS challenge directly and can provision false 3539 A/AAAA records to direct the ACME server to send its HTTP validation 3540 query to a remote server of the attacker's choosing. There are a few 3541 different mitigations that ACME servers can apply: 3543 o Always querying the DNS using a DNSSEC-validating resolver 3544 (enhancing security for zones that are DNSSEC-enabled) 3546 o Querying the DNS from multiple vantage points to address local 3547 attackers 3549 o Applying mitigations against DNS off-path attackers, e.g., adding 3550 entropy to requests [I-D.vixie-dnsext-dns0x20] or only using TCP 3552 Given these considerations, the ACME validation process makes it 3553 impossible for any attacker on the ACME channel or a passive attacker 3554 on the validation channel to hijack the authorization process to 3555 authorize a key of the attacker's choice. 3557 An attacker that can only see the ACME channel would need to convince 3558 the validation server to provide a response that would authorize the 3559 attacker's account key, but this is prevented by binding the 3560 validation response to the account key used to request challenges. A 3561 passive attacker on the validation channel can observe the correct 3562 validation response and even replay it, but that response can only be 3563 used with the account key for which it was generated. 3565 An active attacker on the validation channel can subvert the ACME 3566 process, by performing normal ACME transactions and providing a 3567 validation response for his own account key. The risks due to 3568 hosting providers noted above are a particular case. 3570 Attackers can also exploit vulnerabilities in Internet routing 3571 protocols to gain access to the validation channel (see, e.g., 3572 [RFC7132]). In order to make such attacks more difficult, it is 3573 RECOMMENDED that the server perform DNS queries and make HTTP 3574 connections from multiple points in the network. Since routing 3575 attacks are often localized or dependent on the position of the 3576 attacker, forcing the attacker to attack multiple points (the 3577 server's validation vantage points) or a specific point (the DNS / 3578 HTTP server) makes it more difficult to subvert ACME validation using 3579 attacks on routing. 3581 10.3. Denial-of-Service Considerations 3583 As a protocol run over HTTPS, standard considerations for TCP-based 3584 and HTTP-based DoS mitigation also apply to ACME. 3586 At the application layer, ACME requires the server to perform a few 3587 potentially expensive operations. Identifier validation transactions 3588 require the ACME server to make outbound connections to potentially 3589 attacker-controlled servers, and certificate issuance can require 3590 interactions with cryptographic hardware. 3592 In addition, an attacker can also cause the ACME server to send 3593 validation requests to a domain of its choosing by submitting 3594 authorization requests for the victim domain. 3596 All of these attacks can be mitigated by the application of 3597 appropriate rate limits. Issues closer to the front end, like POST 3598 body validation, can be addressed using HTTP request limiting. For 3599 validation and certificate requests, there are other identifiers on 3600 which rate limits can be keyed. For example, the server might limit 3601 the rate at which any individual account key can issue certificates 3602 or the rate at which validation can be requested within a given 3603 subtree of the DNS. And in order to prevent attackers from 3604 circumventing these limits simply by minting new accounts, servers 3605 would need to limit the rate at which accounts can be registered. 3607 10.4. Server-Side Request Forgery 3609 Server-Side Request Forgery (SSRF) attacks can arise when an attacker 3610 can cause a server to perform HTTP requests to an attacker-chosen 3611 URL. In the ACME HTTP challenge validation process, the ACME server 3612 performs an HTTP GET request to a URL in which the attacker can 3613 choose the domain. This request is made before the server has 3614 verified that the client controls the domain, so any client can cause 3615 a query to any domain. 3617 Some ACME server implementations include information from the 3618 validation server's response (in order to facilitate debugging). 3619 Such implementations enable an attacker to extract this information 3620 from any web server that is accessible to the ACME server, even if it 3621 is not accessible to the ACME client. For example, the ACME server 3622 might be able to access servers behind a firewall that would prevent 3623 access by the ACME client. 3625 It might seem that the risk of SSRF through this channel is limited 3626 by the fact that the attacker can only control the domain of the URL, 3627 not the path. However, if the attacker first sets the domain to one 3628 they control, then they can send the server an HTTP redirect (e.g., a 3629 302 response) which will cause the server to query an arbitrary URL. 3631 In order to further limit the SSRF risk, ACME server operators should 3632 ensure that validation queries can only be sent to servers on the 3633 public Internet, and not, say, web services within the server 3634 operator's internal network. Since the attacker could make requests 3635 to these public servers himself, he can't gain anything extra through 3636 an SSRF attack on ACME aside from a layer of anonymization. 3638 10.5. CA Policy Considerations 3640 The controls on issuance enabled by ACME are focused on validating 3641 that a certificate applicant controls the identifier he claims. 3642 Before issuing a certificate, however, there are many other checks 3643 that a CA might need to perform, for example: 3645 o Has the client agreed to a subscriber agreement? 3647 o Is the claimed identifier syntactically valid? 3649 o For domain names: 3651 * If the leftmost label is a '*', then have the appropriate 3652 checks been applied? 3654 * Is the name on the Public Suffix List? 3655 * Is the name a high-value name? 3657 * Is the name a known phishing domain? 3659 o Is the key in the CSR sufficiently strong? 3661 o Is the CSR signed with an acceptable algorithm? 3663 o Has issuance been authorized or forbidden by a Certificate 3664 Authority Authorization (CAA) record? [RFC6844] 3666 CAs that use ACME to automate issuance will need to ensure that their 3667 servers perform all necessary checks before issuing. 3669 CAs using ACME to allow clients to agree to terms of service should 3670 keep in mind that ACME clients can automate this agreement, possibly 3671 not involving a human user. 3673 ACME does not specify how the server constructs the URLs that it uses 3674 to address resources. If the server operator uses URLs that are 3675 predictable to third parties, this can leak information about what 3676 URLs exist on the server, since an attacker can probe for whether 3677 POST-as-GET request to the URL returns "Not Found" or "Unauthorized". 3679 For example, suppose that the CA uses highly structured URLs with 3680 several low-entropy fields: 3682 o Accounts: https://example.com/:accountID 3684 o Orders: https://example.com/:accountID/:orderID 3686 o Authorizations: https://example.com/:accountID/:authorizationID 3688 o Certificates: https://example.com/:accountID/:certID 3690 If the ID fields have low entropy, then an attacker can find out how 3691 many users a CA has, how many authorizations each account has, etc. 3693 In order to avoid leaking these correlations, servers SHOULD assign 3694 capability URLs for dynamically-created resources 3695 [W3C.WD-capability-urls-20140218]. These URLs incorporate large 3696 unpredictable components to prevent third parties from guessing them. 3697 These URLs SHOULD NOT have a structure that would enable a third 3698 party to infer correlations between resources. 3700 For example, a CA might assign URLs for each resource type from an 3701 independent namespace, using unpredictable IDs for each resource: 3703 o Accounts: https://example.com/acct/:accountID 3705 o Orders: https://example.com/order/:orderID 3707 o Authorizations: https://example.com/authz/:authorizationID 3709 o Certificates: https://example.com/cert/:certID 3711 Such a scheme would leak only the type of resource, hiding the 3712 additional correlations revealed in the example above. 3714 11. Operational Considerations 3716 There are certain factors that arise in operational reality that 3717 operators of ACME-based CAs will need to keep in mind when 3718 configuring their services. For example: 3720 11.1. Key Selection 3722 ACME relies on two different classes of key pair: 3724 o Account key pairs, which are used to authenticate account holders 3726 o Certificate key pairs, which are used to sign and verify CSRs (and 3727 whose public keys are included in certificates) 3729 Compromise of the private key of an account key pair has more serious 3730 consequences than compromise of a private key corresponding to a 3731 certificate. While the compromise of a certificate key pair allows 3732 the attacker to impersonate the entities named in the certificate for 3733 the lifetime of the certificate, the compromise of an account key 3734 pair allows the attacker to take full control of the victim's ACME 3735 account, and take any action that the legitimate account holder could 3736 take within the scope of ACME: 3738 1. Issuing certificates using existing authorizations 3740 2. Revoking existing certificates 3742 3. Accessing and changing account information (e.g., contacts) 3744 4. Changing the account key pair for the account, locking out the 3745 legitimate account holder 3747 For this reason, it is RECOMMENDED that account key pairs be used for 3748 no other purpose besides ACME authentication. For example, the 3749 public key of an account key pair SHOULD NOT be included in a 3750 certificate. ACME clients and servers SHOULD verify that a CSR 3751 submitted in a finalize request does not contain a public key for any 3752 known account key pair. In particular, when a server receives a 3753 finalize request, it MUST verify that the public key in a CSR is not 3754 the same as the public key of the account key pair used to 3755 authenticate that request. This assures that vulnerabilities in the 3756 protocols with which the certificate is used (e.g., signing oracles 3757 in TLS [JSS15]) do not result in compromise of the ACME account. 3758 Because ACME accounts are uniquely identified by their account key 3759 pair (see Section 7.3.1) the server MUST not allow account key pair 3760 reuse across multiple accounts. 3762 11.2. DNS security 3764 As noted above, DNS forgery attacks against the ACME server can 3765 result in the server making incorrect decisions about domain control 3766 and thus mis-issuing certificates. Servers SHOULD perform DNS 3767 queries over TCP, which provides better resistance to some forgery 3768 attacks than DNS over UDP. 3770 An ACME-based CA will often need to make DNS queries, e.g., to 3771 validate control of DNS names. Because the security of such 3772 validations ultimately depends on the authenticity of DNS data, every 3773 possible precaution should be taken to secure DNS queries done by the 3774 CA. It is therefore RECOMMENDED that ACME-based CAs make all DNS 3775 queries via DNSSEC-validating stub or recursive resolvers. This 3776 provides additional protection to domains which choose to make use of 3777 DNSSEC. 3779 An ACME-based CA must use only a resolver if it trusts the resolver 3780 and every component of the network route by which it is accessed. It 3781 is therefore RECOMMENDED that ACME-based CAs operate their own 3782 DNSSEC-validating resolvers within their trusted network and use 3783 these resolvers both for both CAA record lookups and all record 3784 lookups in furtherance of a challenge scheme (A, AAAA, TXT, etc.). 3786 11.3. Token Entropy 3788 The http-01 and dns-01 validation methods mandate the usage of a 3789 random token value to uniquely identify the challenge. The value of 3790 the token is required to contain at least 128 bits of entropy for the 3791 following security properties. First, the ACME client should not be 3792 able to influence the ACME server's choice of token as this may allow 3793 an attacker to reuse a domain owner's previous challenge responses 3794 for a new validation request. Secondly, the entropy requirement 3795 prevents ACME clients from implementing a "naive" validation server 3796 that automatically replies to challenges by predicting the token. 3798 11.4. Malformed Certificate Chains 3800 ACME provides certificate chains in the widely-used format known 3801 colloquially as PEM (though it may diverge from the actual Privacy 3802 Enhanced Mail specifications [RFC1421], as noted in [RFC7468]). Some 3803 current software will allow the configuration of a private key and a 3804 certificate in one PEM file, by concatenating the textual encodings 3805 of the two objects. In the context of ACME, such software might be 3806 vulnerable to "key replacement" attacks. A malicious ACME server 3807 could cause a client to use a private key of its choosing by 3808 including the key in the PEM file returned in response to a query for 3809 a certificate URL. 3811 When processing an file of type "application/pem-certificate-chain", 3812 a client SHOULD verify that the file contains only encoded 3813 certificates. If anything other than a certificate is found (i.e., 3814 if the string "-----BEGIN" is ever followed by anything other than 3815 "CERTIFICATE"), then the client MUST reject the file as invalid. 3817 12. Acknowledgements 3819 In addition to the editors listed on the front page, this document 3820 has benefited from contributions from a broad set of contributors, 3821 all the way back to its inception. 3823 o Andrew Ayer, SSLMate 3825 o Karthik Bhargavan, INRIA 3827 o Peter Eckersley, EFF 3829 o Alex Halderman, University of Michigan 3831 o Sophie Herold, Hemio 3833 o Eric Rescorla, Mozilla 3835 o Seth Schoen, EFF 3837 o Martin Thomson, Mozilla 3839 o Jakub Warmuz, University of Oxford 3841 This document draws on many concepts established by Eric Rescorla's 3842 "Automated Certificate Issuance Protocol" draft. Martin Thomson 3843 provided helpful guidance in the use of HTTP. 3845 13. References 3847 13.1. Normative References 3849 [FIPS180-4] 3850 Department of Commerce, National., "NIST FIPS 180-4, 3851 Secure Hash Standard", March 2012, 3852 . 3855 [JSS15] Somorovsky, J., "On the Security of TLS 1.3 and QUIC 3856 Against Weaknesses in PKCS#1 v1.5 Encryption", n.d., 3857 . 3859 [REST] Fielding, R., "Architectural Styles and the Design of 3860 Network-based Software Architectures", 2000, 3861 . 3864 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3865 Requirement Levels", BCP 14, RFC 2119, 3866 DOI 10.17487/RFC2119, March 1997, 3867 . 3869 [RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key 3870 Infrastructure Operational Protocols: FTP and HTTP", 3871 RFC 2585, DOI 10.17487/RFC2585, May 1999, 3872 . 3874 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, 3875 DOI 10.17487/RFC2818, May 2000, 3876 . 3878 [RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object 3879 Classes and Attribute Types Version 2.0", RFC 2985, 3880 DOI 10.17487/RFC2985, November 2000, 3881 . 3883 [RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification 3884 Request Syntax Specification Version 1.7", RFC 2986, 3885 DOI 10.17487/RFC2986, November 2000, 3886 . 3888 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 3889 Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, 3890 . 3892 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 3893 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 3894 2003, . 3896 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 3897 Resource Identifier (URI): Generic Syntax", STD 66, 3898 RFC 3986, DOI 10.17487/RFC3986, January 2005, 3899 . 3901 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 3902 "Randomness Requirements for Security", BCP 106, RFC 4086, 3903 DOI 10.17487/RFC4086, June 2005, 3904 . 3906 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 3907 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 3908 . 3910 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 3911 Specifications: ABNF", STD 68, RFC 5234, 3912 DOI 10.17487/RFC5234, January 2008, 3913 . 3915 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3916 (TLS) Protocol Version 1.2", RFC 5246, 3917 DOI 10.17487/RFC5246, August 2008, 3918 . 3920 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 3921 Housley, R., and W. Polk, "Internet X.509 Public Key 3922 Infrastructure Certificate and Certificate Revocation List 3923 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 3924 . 3926 [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet 3927 Mail Extensions (S/MIME) Version 3.2 Message 3928 Specification", RFC 5751, DOI 10.17487/RFC5751, January 3929 2010, . 3931 [RFC5890] Klensin, J., "Internationalized Domain Names for 3932 Applications (IDNA): Definitions and Document Framework", 3933 RFC 5890, DOI 10.17487/RFC5890, August 2010, 3934 . 3936 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, 3937 DOI 10.17487/RFC5988, October 2010, 3938 . 3940 [RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' 3941 URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010, 3942 . 3944 [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., 3945 and D. Orchard, "URI Template", RFC 6570, 3946 DOI 10.17487/RFC6570, March 2012, 3947 . 3949 [RFC6844] Hallam-Baker, P. and R. Stradling, "DNS Certification 3950 Authority Authorization (CAA) Resource Record", RFC 6844, 3951 DOI 10.17487/RFC6844, January 2013, 3952 . 3954 [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 3955 Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 3956 2014, . 3958 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 3959 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 3960 DOI 10.17487/RFC7231, June 2014, 3961 . 3963 [RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, 3964 PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, 3965 April 2015, . 3967 [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 3968 Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 3969 2015, . 3971 [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, 3972 DOI 10.17487/RFC7518, May 2015, 3973 . 3975 [RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK) 3976 Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September 3977 2015, . 3979 [RFC7797] Jones, M., "JSON Web Signature (JWS) Unencoded Payload 3980 Option", RFC 7797, DOI 10.17487/RFC7797, February 2016, 3981 . 3983 [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP 3984 APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, 3985 . 3987 [RFC8037] Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH) 3988 and Signatures in JSON Object Signing and Encryption 3989 (JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017, 3990 . 3992 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 3993 Writing an IANA Considerations Section in RFCs", BCP 26, 3994 RFC 8126, DOI 10.17487/RFC8126, June 2017, 3995 . 3997 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3998 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3999 May 2017, . 4001 [RFC8288] Nottingham, M., "Web Linking", RFC 8288, 4002 DOI 10.17487/RFC8288, October 2017, 4003 . 4005 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4006 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4007 . 4009 13.2. Informative References 4011 [CABFBR] CA/Browser Forum, ., "CA/Browser Forum Baseline 4012 Requirements", September 2018, 4013 . 4015 [I-D.ietf-acme-caa] 4016 Landau, H., "CAA Record Extensions for Account URI and 4017 ACME Method Binding", draft-ietf-acme-caa-05 (work in 4018 progress), June 2018. 4020 [I-D.ietf-acme-ip] 4021 Shoemaker, R., "ACME IP Identifier Validation Extension", 4022 draft-ietf-acme-ip-04 (work in progress), July 2018. 4024 [I-D.ietf-acme-star] 4025 Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T. 4026 Fossati, "Support for Short-Term, Automatically-Renewed 4027 (STAR) Certificates in Automated Certificate Management 4028 Environment (ACME)", draft-ietf-acme-star-03 (work in 4029 progress), March 2018. 4031 [I-D.ietf-acme-telephone] 4032 Peterson, J. and R. Barnes, "ACME Identifiers and 4033 Challenges for Telephone Numbers", draft-ietf-acme- 4034 telephone-01 (work in progress), October 2017. 4036 [I-D.vixie-dnsext-dns0x20] 4037 Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to 4038 Improve Transaction Identity", draft-vixie-dnsext- 4039 dns0x20-00 (work in progress), March 2008. 4041 [RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic 4042 Mail: Part I: Message Encryption and Authentication 4043 Procedures", RFC 1421, DOI 10.17487/RFC1421, February 4044 1993, . 4046 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 4047 Text on Security Considerations", BCP 72, RFC 3552, 4048 DOI 10.17487/RFC3552, July 2003, 4049 . 4051 [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An 4052 IETF URN Sub-namespace for Registered Protocol 4053 Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June 4054 2003, . 4056 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 4057 Uniform Resource Identifiers (URIs)", RFC 5785, 4058 DOI 10.17487/RFC5785, April 2010, 4059 . 4061 [RFC7132] Kent, S. and A. Chi, "Threat Model for BGP Path Security", 4062 RFC 7132, DOI 10.17487/RFC7132, February 2014, 4063 . 4065 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 4066 "Recommendations for Secure Use of Transport Layer 4067 Security (TLS) and Datagram Transport Layer Security 4068 (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 4069 2015, . 4071 [W3C.REC-cors-20140116] 4072 Kesteren, A., "Cross-Origin Resource Sharing", World Wide 4073 Web Consortium Recommendation REC-cors-20140116, January 4074 2014, . 4076 [W3C.WD-capability-urls-20140218] 4077 Tennison, J., "Good Practices for Capability URLs", World 4078 Wide Web Consortium WD WD-capability-urls-20140218, 4079 February 2014, 4080 . 4082 13.3. URIs 4084 [1] https://github.com/ietf-wg-acme/acme 4086 [2] mailto:iesg@ietf.org 4088 Authors' Addresses 4090 Richard Barnes 4091 Cisco 4093 Email: rlb@ipv.sx 4095 Jacob Hoffman-Andrews 4096 EFF 4098 Email: jsha@eff.org 4100 Daniel McCarney 4101 Let's Encrypt 4103 Email: cpu@letsencrypt.org 4105 James Kasten 4106 University of Michigan 4108 Email: jdkasten@umich.edu