Automated Certificate Management Environment (ACME) IP Identifier Validation Extension
RFC 8738

Document Type RFC - Proposed Standard (February 2020; No errata)
Author Roland Shoemaker 
Last updated 2020-02-29
Replaces draft-shoemaker-acme-ip
Stream IETF
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Document shepherd Daniel McCarney
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IESG IESG state RFC 8738 (Proposed Standard)
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Responsible AD Roman Danyliw
Send notices to Daniel McCarney <cpu@letsencrypt.org>
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Internet Engineering Task Force (IETF)                    R.B. Shoemaker
Request for Comments: 8738                                          ISRG
Category: Standards Track                                  February 2020
ISSN: 2070-1721

   Automated Certificate Management Environment (ACME) IP Identifier
                          Validation Extension

Abstract

   This document specifies identifiers and challenges required to enable
   the Automated Certificate Management Environment (ACME) to issue
   certificates for IP addresses.

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/rfc8738.

Copyright Notice

   Copyright (c) 2020 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
   2.  Terminology
   3.  IP Identifier
   4.  Identifier Validation Challenges
   5.  HTTP Challenge
   6.  TLS with Application-Layer Protocol Negotiation (TLS ALPN)
           Challenge
   7.  DNS Challenge
   8.  IANA Considerations
     8.1.  Identifier Types
     8.2.  Challenge Types
   9.  Security Considerations
     9.1.  Certification Authority (CA) Policy Considerations
   10. Normative References
   Acknowledgments
   Author's Address

1.  Introduction

   The Automatic Certificate Management Environment (ACME) [RFC8555]
   only defines challenges for validating control of DNS host name
   identifiers, which limits its use to being used for issuing
   certificates for DNS identifiers.  In order to allow validation of
   IPv4 and IPv6 identifiers for inclusion in X.509 certificates, this
   document specifies how challenges defined in the original ACME
   specification and the TLS-ALPN extension specification [RFC8737] can
   be used to validate IP identifiers.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  IP Identifier

   [RFC8555] only defines the identifier type "dns", which is used to
   refer to fully qualified domain names.  If an ACME server wishes to
   request proof that a user controls an IPv4 or IPv6 address, it MUST
   create an authorization with the identifier type "ip".  The value
   field of the identifier MUST contain the textual form of the address
   as defined in Section 2.1 of [RFC1123] for IPv4 and in Section 4 of
   [RFC5952] for IPv6.

   An identifier for the IPv6 address 2001:db8::1 would be formatted
   like so:

   {"type": "ip", "value": "2001:db8::1"}

4.  Identifier Validation Challenges

   IP identifiers MAY be used with the existing "http-01" (see
   Section 8.3 of [RFC8555]) and "tls-alpn-01" (see Section 3 of
   [RFC8737]).  To use IP identifiers with these challenges, their
   initial DNS resolution step MUST be skipped, and the IP address used
   for validation MUST be the value of the identifier.

5.  HTTP Challenge

   For the "http-01" challenge, the Host header field MUST be set to the
   IP address being used for validation per [RFC7230].  The textual form
   of this address MUST be as defined in Section 2.1 of [RFC1123] for
   IPv4 and in Section 4 of [RFC5952] for IPv6.

6.  TLS with Application-Layer Protocol Negotiation (TLS ALPN) Challenge

   For the "tls-alpn-01" challenge, the subjectAltName extension in the
   validation certificate MUST contain a single iPAddress that matches
   the address being validated.  As [RFC6066] does not permit IP
   addresses to be used in the Server Name Indication (SNI) extension
   HostName field, the server MUST instead use the IN-ADDR.ARPA
   [RFC1034] or IP6.ARPA [RFC3596] reverse mapping of the IP address as
   the HostName field value instead of the IP address string
   representation itself.  For example, if the IP address being
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