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]
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]
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]
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] [N2] [N3] [N4] [N5] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 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. A. Gulbrandsen and P. Vixie, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. P. Mockapetris, "DOMAIN NAMES - CONCEPTS AND FACILITIES", RFC 1034, November 1987 J. Reynolds, "Assigned Numbers: RFC 1700 is Replaced by an On-line Database", RFC 3232, January 2002. Santesson [Page 4]
Appendix A. ASN.1 definitions TBD Authors Addresses Stefan Santesson Microsoft Tuborg Boulevard 12 2900 Hellerup Denmark EMail: stefans@microsoft.com Santesson [Page 5]
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]