Internet X.509 Public Key Infrastructure Subject Alternative Name for Expression of Service Name
RFC 4985

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Network Working Group                                       S. Santesson
Request for Comments: 4985                                     Microsoft
Category: Standards Track                                    August 2007

                Internet X.509 Public Key Infrastructure
        Subject Alternative Name for Expression of Service Name

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document defines a new name form for inclusion in the otherName
   field of an X.509 Subject Alternative Name extension that allows a
   certificate subject to be associated with the service name and domain
   name components of a DNS Service Resource Record.

Table of Contents

   1. Introduction ....................................................2
      1.1. Terminology ................................................2
   2. Name Definitions ................................................2
   3. Internationalized Domain Names ..................................4
   4. Name Constraints Matching Rules .................................5
   5. Security Considerations .........................................6
   6. Normative References ............................................6
   Appendix A. ASN.1 Syntax ...........................................7
      Appendix A.1. 1988 ASN.1 Module .................................7
      Appendix A.2. 1993 ASN.1 Module .................................8

Santesson                   Standards Track                     [Page 1]
RFC 4985                  DNS SRV RR otherName               August 2007

1.  Introduction

   This document specifies a name form for inclusion in X.509
   certificates that may be used by a certificate relying party to
   verify that a particular host is authorized to provide a specific
   service within a domain.

   RFC 2782 [N3] defines a DNS RR (Resource Record) for specifying the
   location of services (SRV RR), which allows clients to ask for a
   specific service/protocol for a specific domain and get back the
   names of any available servers.

   Existing name forms in X.509 certificates support authentication of a
   host name.  This is useful when the name of the host is known by the
   client prior to authentication.

   When a server host name is discovered through DNS RR lookup query
   based on service name, the client may need to authenticate the
   server's authorization to provide the requested service in addition
   to the server's host name.

   While DNS servers may have the capacity to provide trusted
   information, there may be many other situations where the binding
   between the name of the host and the provided service needs to be
   supported by additional credentials.

   Current dNSName GeneralName Subject Alternative name form only
   provides for DNS host names to be expressed in "preferred name
   syntax", as specified by RFC 1034 [N4].  This definition is therefore
   not broad enough to allow expression of a service related to that
   domain.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [N1].

2.  Name Definitions

   This section defines the SRVName name as a form of otherName from the
   GeneralName structure in SubjectAltName defined in RFC 3280 [N2].

      id-on-dnsSRV OBJECT IDENTIFIER ::= { id-on 7 }

      SRVName ::= IA5String (SIZE (1..MAX))

Santesson                   Standards Track                     [Page 2]
RFC 4985                  DNS SRV RR otherName               August 2007

   The SRVName, if present, MUST contain a service name and a domain
   name in the following form:

      _Service.Name

   The content of the components of this name form MUST be consistent
   with the corresponding definition of these components in an SRV RR
   according to RFC 2782 [N3].

   The content of these components are:

      Service
         The symbolic name of the desired service, as defined in
         Assigned Numbers [N5] or locally.  An underscore (_) is
         prepended to the service identifier to avoid collisions with
         DNS labels that occur in nature.  Some widely used services,
         notably POP, don't have a single universal name.  If Assigned
         Numbers names the service indicated, that name is the only name
         that is allowed in the service component of this name form.
         The Service is case insensitive.

      Name
         The DNS domain name of the domain where the specified service
         is located.

         If the domain name is an Internationalized Domain Name (IDN),