Automatic Certificate Management Environment (ACME)
RFC 8555

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Internet Engineering Task Force (IETF)                         R. Barnes
Request for Comments: 8555                                         Cisco
Category: Standards Track                             J. Hoffman-Andrews
ISSN: 2070-1721                                                      EFF
                                                             D. McCarney
                                                           Let's Encrypt
                                                               J. Kasten
                                                  University of Michigan
                                                              March 2019

          Automatic Certificate Management Environment (ACME)

Abstract

   Public Key Infrastructure using X.509 (PKIX) certificates are used
   for a number of purposes, the most significant of which is the
   authentication of domain names.  Thus, certification authorities
   (CAs) in the Web PKI are trusted to verify that an applicant for a
   certificate legitimately represents the domain name(s) in the
   certificate.  As of this writing, this verification is done through a
   collection of ad hoc mechanisms.  This document describes a protocol
   that a CA and an applicant can use to automate the process of
   verification and certificate issuance.  The protocol also provides
   facilities for other certificate management functions, such as
   certificate revocation.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8555.

Barnes, et al.               Standards Track                    [Page 1]
RFC 8555                          ACME                        March 2019

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................4
   2. Deployment Model and Operator Experience ........................5
   3. Terminology .....................................................7
   4. Protocol Overview ...............................................7
   5. Character Encoding .............................................10
   6. Message Transport ..............................................10
      6.1. HTTPS Requests ............................................10
      6.2. Request Authentication ....................................11
      6.3. GET and POST-as-GET Requests ..............................13
      6.4. Request URL Integrity .....................................13
           6.4.1. "url" (URL) JWS Header Parameter ...................14
      6.5. Replay Protection .........................................14
           6.5.1. Replay-Nonce .......................................15
           6.5.2. "nonce" (Nonce) JWS Header Parameter ...............16
      6.6. Rate Limits ...............................................16
      6.7. Errors ....................................................16
           6.7.1. Subproblems ........................................18
   7. Certificate Management .........................................20
      7.1. Resources .................................................20
           7.1.1. Directory ..........................................23
           7.1.2. Account Objects ....................................24
           7.1.3. Order Objects ......................................26
           7.1.4. Authorization Objects ..............................28
           7.1.5. Challenge Objects ..................................30
           7.1.6. Status Changes .....................................30
      7.2. Getting a Nonce ...........................................34
      7.3. Account Management ........................................34
           7.3.1. Finding an Account URL Given a Key .................36
           7.3.2. Account Update .....................................37