[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 RFC 4985

INTERNET-DRAFT                                  S. Santesson (Microsoft)
Intended Category: Standards Track
Expires March 2006                                        September 2005

                Internet X.509 Public Key Infrastructure
        Subject Alternative Name for expression of service name
                    <draft-ietf-pkix-srvsan-00.txt>


Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than a "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


Abstract

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












Santesson                                                       [Page 1]

INTERNET DRAFT            DNS SRV RR otherName            September 2005


Table of Contents

   1  Introduction ................................................    2
   2  Name definitions ............................................    3
   3  Security Considerations .....................................    3
   4  IANA Considerations .........................................    4
   5  References ..................................................    4
   Appendix A. ASN.1 definitions ..................................    5
   Authors' Addresses .............................................    5
   Disclaimer .....................................................    6
   Copyright Statement ............................................    6

1.  Introduction

   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.

   Server discovery through a DNS query based on service/protocol
   relative to a domain is from an authentication perspective
   fundamentally different from when a client has prior trusted
   knowledge about the name and address of the server it attempts to
   connect. While authentication of the name and address of a server
   makes sense when the name and address of the server is prior
   knowledge, it typically has very little value if the name and address
   of the server is obtained from an untrusted source.

   Subsequent authentication of a server discovered through DNS RR
   lookup based on service name typically requires the client to
   authenticate that the connected server is authorized to provide the
   requested service rather than authenticating the servers host name.

   While DNS servers may have the capacity to provide trusted
   information, they may in many other situations not be trusted enough
   to do that, in which case the server may be required to provide
   verifiable credentials to support its due authorization to provide a
   requested service.

   One example where expression of such authorization can be very useful
   is when locating and authenticating a legitimate Kerberos KDC server.

   To support these scenarios, this standard defines a new name form for
   expression of service name relative to a domain in X.509
   certificates.

   Current dNSName GeneralName Subject Alternative name form only
   provide for DNS host names to be expressed in "preferred name



Santesson                                                       [Page 2]

INTERNET DRAFT            DNS SRV RR otherName            September 2005


   syntax," as specified by RFC 1034 [N4]. This definition therefore not
   broad enough to allow expression of a service related to that domain.

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-sRVName   OBJECT IDENTIFIER ::= { id-on ? }

      SRVName ::= UTF8String    (SIZE (1..MAX))

   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
         which 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.

   Example: _mail.example.com

   Even though this name form is based on the service resource record
   (SRV RR) definition in RFC 2782 [N3] and may be used to enhance
   subsequent authentication of DNS based service discovery, this
   standard does not define any new conditions or requirements regarding
   use of SRV RR for service discovery or where and when such use is
   appropriate.






Santesson                                                       [Page 3]

INTERNET DRAFT            DNS SRV RR otherName            September 2005


3  Security Considerations

   Assignment of services to hosts may be subject to change.
   Implementers should be aware of the need to revoke old certificates
   that no longer reflect the current assignment of services and thus
   make sure that all issued certificates are up to date.

   When X.509 certificates enhanced with the name form specified in this
   standard is used to enhance authentication of service discovery based
   on a SRV RR query to a DNS server, all security considerations of RFC
   2782 applies.

4  IANA Considerations

   This document has no actions for IANA.

5 References

   Normative references:

   [N1]        S. Bradner, "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [N2]        R. Housley, W. Polk, W. Ford, and D. Solo, "Internet
               X.509 Public Key Infrastructure: Certificate and
               Certificate Revocation List (CRL) Profile", RFC 3280,
               April 2002.

   [N3]        A. Gulbrandsen and P. Vixie, "A DNS RR for specifying the
               location of services (DNS SRV)", RFC 2782, February 2000.

   [N4]        P. Mockapetris, "DOMAIN NAMES - CONCEPTS AND FACILITIES",
               RFC 1034, November 1987

   [N5]        J. Reynolds, "Assigned Numbers: RFC 1700 is Replaced by
               an On-line Database", RFC 3232, January 2002.















Santesson                                                       [Page 4]

INTERNET DRAFT            DNS SRV RR otherName            September 2005


Appendix A. ASN.1 definitions

   TBD


Authors' Addresses


   Stefan Santesson
   Microsoft
   Tuborg Boulevard 12
   2900 Hellerup
   Denmark

   EMail: stefans@microsoft.com




































Santesson                                                       [Page 5]

INTERNET DRAFT            DNS SRV RR otherName            September 2005


Disclaimer

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.


Expires March 2006






























Santesson                                                       [Page 6]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/