Internet Security Research Group

roland@letsencrypt.org

Security ACME Working Group acme pki 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 .

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Table of Contents

• .  Introduction
• .  Terminology
• .  IP Identifier
• .  Identifier Validation Challenges
• .  HTTP Challenge
• .  TLS with Application-Layer Protocol Negotiation (TLS ALPN) Challenge
• .  DNS Challenge
• .  IANA Considerations
  • .  Identifier Types
  • .  Challenge Types
• .  Security Considerations
  • .  Certification Authority (CA) Policy Considerations
• . Normative References
• Acknowledgments
• Author's Address

Introduction The Automatic Certificate Management Environment (ACME) 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 can be used to validate IP identifiers.

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 when, and only when, they appear in all capitals, as shown here.

IP Identifier 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 for IPv4 and in for IPv6. An identifier for the IPv6 address 2001:db8::1 would be formatted like so: {"type": "ip", "value": "2001:db8::1"}

Identifier Validation Challenges IP identifiers MAY be used with the existing "http-01" (see ) and "tls-alpn-01" (see ). 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.

HTTP Challenge For the "http-01" challenge, the Host header field MUST be set to the IP address being used for validation per . The textual form of this address MUST be as defined in for IPv4 and in for IPv6.

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 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 or IP6.ARPA 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".

DNS Challenge The existing "dns-01" challenge MUST NOT be used to validate IP identifiers.

IANA Considerations

Identifier Types Per this document, a new type has been added to the "ACME Identifier Types" registry defined in with Label "ip" and Reference "RFC 8738".

Challenge Types Per this document, two new entries have been added to the "ACME Validation Methods" registry defined in . These entries are defined below:

Label	Identifier Type	ACME	Reference
http-01	ip	Y	RFC 8738
tls-alpn-01	ip	Y	RFC 8738

Security Considerations The extensions to ACME described in this document do not deviate from the broader threat model described in .

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.

Normative References This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them. This RFC is an official specification for the Internet community. It incorporates by reference, amends, corrects, and supplements the primary protocol standards documents relating to hosts. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document defines the changes that need to be made to the Domain Name System (DNS) to support hosts running IP version 6 (IPv6). The changes include a resource record type to store an IPv6 address, a domain to support lookups based on an IPv6 address, and updated definitions of existing query types that return Internet addresses as part of additional section processing. The extensions are designed to be compatible with existing applications and, in particular, DNS implementations themselves. [STANDARDS-TRACK] As IPv6 deployment increases, there will be a dramatic increase in the need to use IPv6 addresses in text. While the IPv6 address architecture in Section 2.2 of RFC 4291 describes a flexible model for text representation of an IPv6 address, this flexibility has been causing problems for operators, system engineers, and users. This document defines a canonical textual representation format. It does not define a format for internal storage, such as within an application or database. It is expected that the canonical format will be followed by humans and systems when representing IPv6 addresses as text, but all implementations must accept and be able to handle any legitimate RFC 4291 format. [STANDARDS-TRACK] This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK] The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. 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.

Acknowledgments The author would like to thank those who contributed to this document and offered editorial and technical input, especially and .

Author's Address Internet Security Research Group

roland@letsencrypt.org