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>
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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.
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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
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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.
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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.
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Appendix A. ASN.1 definitions
TBD
Authors' Addresses
Stefan Santesson
Microsoft
Tuborg Boulevard 12
2900 Hellerup
Denmark
EMail: stefans@microsoft.com
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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
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