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.
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Table of Contents
1. Introduction
2. Terminology
3. IP Identifier
4. Identifier Validation Challenges
5. HTTP Challenge
6. TLS with Application Level 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 Level 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
validated is 2001:db8::1, the SNI HostName field should contain "1.0.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa"
.
7. DNS Challenge
The existing "dns-01" challenge MUST NOT be used to validate IP
identifiers.
8. IANA Considerations
8.1. Identifier Types
Per this document, a new type has been added to the "ACME Identifier
Types" registry defined in Section 9.7.7 of [RFC8555] with Label "ip"
and Reference "RFC 8738".
8.2. Challenge Types
Per this document, two new entries have been added to the "ACME
Validation Methods" registry defined in Section 9.7.8 of [RFC8555].
These entries are defined below:
+-------------+-----------------+------+-----------+
| Label | Identifier Type | ACME | Reference |
+=============+=================+======+===========+
| http-01 | ip | Y | RFC 8738 |
+-------------+-----------------+------+-----------+
| tls-alpn-01 | ip | Y | RFC 8738 |
+-------------+-----------------+------+-----------+
Table 1
9. Security Considerations
The extensions to ACME described in this document do not deviate from
the broader threat model described in Section 10.1 of [RFC8555].
9.1. Certification Authority (CA) Policy Considerations
This document only specifies how an ACME server may validate that a
certificate applicant controls an IP identifier at the time of
validation. The CA may wish to perform additional checks not
specified in this document. For example, if the CA believes an IP
identifier belongs to an ISP or cloud service provider with short
delegation periods, they may wish to impose additional restrictions
on certificates requested for that identifier.
10. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/info/rfc3596>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
[RFC8737] Shoemaker, R.B., "Automated Certificate Management
Environment (ACME) TLS Application-Layer Protocol
Negotiation (ALPN) Challenge Extension", RFC 8737,
DOI 10.17487/RFC8737, February 2020,
<https://www.rfc-editor.org/info/rfc8737>.
Acknowledgments
The author would like to thank those who contributed to this document
and offered editorial and technical input, especially Jacob Hoffman-
Andrews and Daniel McCarney.
Author's Address
Roland Bracewell Shoemaker
Internet Security Research Group
Email: roland@letsencrypt.org