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Network Working Group                                        N. WilliamsRequest for Comments: 5178                                           SunCategory: Standards Track                                    A. Melnikov                                                              Isode Ltd.                                                                May 2008Generic Security Service Application Program Interface (GSS-API)Internationalization and Domain-Based Service Names and Name TypeStatus 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 describes domain-name-based service principal names and   the corresponding name type for the Generic Security Service   Application Programming Interface (GSS-API).  Internationalization of   the GSS-API is also covered.   Domain-based service names are similar to host-based service names,   but using a domain name (not necessarily an Internet domain name) in   addition to a hostname.  The primary purpose of domain-based names is   to provide a measure of protection to applications that utilize   insecure service discovery protocols.  This is achieved by providing   a way to name clustered services after the "domain" which they   service, thereby allowing their clients to authorize the service's   servers based on authentication of their service names.Williams & Melnikov         Standards Track                     [Page 1]

RFC 5178                 GSS Domain-Based Names                 May 2008Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .32.  Conventions Used in This Document . . . . . . . . . . . . . . .43.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .43.1.  Name Type OID . . . . . . . . . . . . . . . . . . . . . . .43.2.  Name Type OID and Symbolic Name . . . . . . . . . . . . . .44.  Query and Display Syntaxes  . . . . . . . . . . . . . . . . . .44.1.  Examples of Domain-Based Names  . . . . . . . . . . . . . .55.  Internationalization (I18N) Considerations  . . . . . . . . . .55.1.  Importing Internationalized Names . . . . . . . . . . . . .55.2.  Displaying Internationalized Names  . . . . . . . . . . . .56.  Application Protocol Examples . . . . . . . . . . . . . . . . .66.1.  NFSv4 Domain-Wide Namespace Root Server Discovery . . . . .66.2.  LDAP Server Discovery . . . . . . . . . . . . . . . . . . .67.  Security Considerations . . . . . . . . . . . . . . . . . . . .78.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .78.1.  Normative References  . . . . . . . . . . . . . . . . . . .78.2.  Informative References  . . . . . . . . . . . . . . . . . .8Williams & Melnikov         Standards Track                     [Page 2]

RFC 5178                 GSS Domain-Based Names                 May 20081.  Introduction   Some applications need to discover the names of servers for a   specific resource.  Some common methods for server discovery are   insecure, e.g., queries for DNS [RFC1035] SRV resource records   [RFC2782] without using DNSSEC [RFC4033], and are subject to attacks   whereby a client can be re-directed to incorrect and possibly   malicious servers.  A client may even be re-directed to a server that   has credentials for itself and thus may authenticate itself to the   client, and yet it could be incorrect or malicious (because it has   been compromised, say).   Domain-based names allow for GSS-API [RFC2743] initiator applications   (clients) to authorize acceptor principals (servers) to serve the   resource for which the client used insecure server discovery without   either securing the server discovery method or requiring an   additional protocol for server authorization.  That is, either a   discovered server has credentials for authenticating the domain-based   service names that it is intended to respond to, or it does not.   Availability of valid credentials for authenticating domain-based   names embodies the authorization of a given server to a domain-wide   service.   A domain-based name consists of three required elements:   o  a service name   o  a domain name   o  a hostname   The domain name and the hostname should be Domain Name System (DNS)   names, though domain-based names could be used in non-DNS   environments.  Because of the use of DNS names we must also provide   for internationalization of the GSS-API.   Note that domain-based naming isn't new.  According to a report to   the KITTEN WG mailing list, there exists at least one implementation   of LDAP which uses domain-based service naming, and the DIGEST-MD5   HTTP / Simple Authentication and Security Layer (SASL) mechanism   [RFC2831] describes a similar notion.  (Seesection 2.1.2 of   [RFC2831] for a description of the "serv-name" field of the digest-   response.)Williams & Melnikov         Standards Track                     [Page 3]

RFC 5178                 GSS Domain-Based Names                 May 20082.  Conventions Used in This Document   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 [RFC2119].3.  IANA Considerations3.1.  Name Type OID   The IANA has recorded the following new name-type OID in IANA's "SMI   Security for Name System Designators Codes (nametypes)" registry:   5 gss-domain-based-services [RFC5178]3.2.  Name Type OID and Symbolic Name   This document creates a new GSS-API name-type, with a symbolic name   of "GSS_C_NT_DOMAINBASED_SERVICE" and this OID:   {iso(1) org(3) dod(6) internet(1) security(5) nametypes(6) gss-   domain-based(5)}4.  Query and Display Syntaxes   There is a single name syntax for domain-based names.  It is   expressed using the ABNF [RFC5234].   The syntax is:         domain-based-name = service "@" domain "@" hostname         hostname          = domain         domain            = sub-domain 1*("." sub-domain)         sub-domain        = Let-dig [Ldh-str]         Let-dig           = ALPHA / DIGIT         Ldh-str           = *( ALPHA / DIGIT / "-" ) Let-dig   Where <service> is defined inSection 4.1 of [RFC2743].  Other rules   not defined above are defined inAppendix B.1 of [RFC5234].Williams & Melnikov         Standards Track                     [Page 4]

RFC 5178                 GSS Domain-Based Names                 May 20084.1.  Examples of Domain-Based Names   These examples are not normative:   o  ldap@somecompany.example@ds1.somecompany.example   o  nfs@somecompany.example@nfsroot1.somecompany.example   The .example top-level domain is used here in accordance with   [RFC2606].5.  Internationalization (I18N) Considerations   We introduce new versions of GSS_Import_name() and GSS_Display_name()   to better support Unicode.  Additionally, we provide for the use of   ASCII Compatible Encoding (ACE)-encoded DNS in the non-   internationalized interfaces [RFC3490].5.1.  Importing Internationalized Names   When the input_name_type parameter is the   GSS_C_NT_DOMAINBASED_SERVICE OID, then GSS_Import_name()   implementations and GSS-API mechanisms MUST accept ACE-encoded   internationalized domain names in the hostname and domain name slots   of the given domain-based name string.   Support for non-ASCII internationalized domain names SHOULD also be   provided through a new function, GSS_Import_name_utf8(), that   operates exactly like GSS_Import_name() (with the same input and   output parameters and behavior), except that it MUST accept   internationalized domain names both as UTF-8 strings and as ACE-   encoded strings via its input_name_string argument.5.2.  Displaying Internationalized Names   Implementations of GSS_Display_name() MUST only output US-ASCII or   ACE-encoded internationalized domain names in the hostname and domain   name slots of domain-based names (or mechanism names (MN) that   conform to the mechanism's form for domain-based names).   Support for non-ASCII internationalized domain names SHOULD also be   provided through a new function, GSS_Display_name_utf8(), that   operates exactly like GSS_Display_name() (with the same input and   output parameters and behavior), except that it outputs UTF-8 strings   via its name_string output argument.  GSS_Display_name_utf8() MUST   NOT output ACE-encoded internationalized domain names.Williams & Melnikov         Standards Track                     [Page 5]

RFC 5178                 GSS Domain-Based Names                 May 20086.  Application Protocol Examples   The following examples are not normative.  They describe how the   authors envision two applications' use of domain-based names.6.1.  NFSv4 Domain-Wide Namespace Root Server Discovery   Work is ongoing to provide a method for constructing domain-wide   NFSv4 [RFC3530] filesystem namespaces where there is a single "root"   with one or more servers (replicas) and multiple filesystems glued   into the namespace through use of "referrals".  Clients could then   construct a "global" namespace through use of the DNS domain   hierarchy.   Here, clients would always know, from context, when they need to find   the root servers for a given DNS domain.  Root server discovery would   be performed using DNS SRV RR lookups, without using DNSSEC where   DNSSEC has not been deployed.   When using RPCSEC_GSS [RFC2203] for security, NFSv4 clients would use   domain-based names to ensure that the servers named in the SRV RRs   are in fact authorized to be the NFSv4 root servers for the target   domain.6.2.  LDAP Server Discovery   LDAP clients using the GSS-API through SASL would also benefit from   use of domain-based names to protect server discovery through   insecure DNS SRV RR lookups, much as described above.   Unlike NFSv4 clients, not all LDAP clients always know from context   when they should use domain-based names.  That's because existing   clients may use host-based naming to authenticate servers discovered   through SRV RR lookups.  Changing such clients to use domain-based   naming when domain-based acceptor credentials have not been deployed   to LDAP servers, or when LDAP servers have not been modified to allow   use of domain-based naming, would break interoperability.  That is,   there is a legacy server interoperability issue here.  Therefore,   LDAP clients may require additional configuration at deployment time   to enable (or disable) use of domain-based naming.   Note: whether SASL [RFC4422] or its GSS-API bridges [RFC4752] [GS2]   require updates in order allow use of domain-based names is not   relevant to the theory of how domain-based naming would protect LDAP   clients' server discovery.Williams & Melnikov         Standards Track                     [Page 6]

RFC 5178                 GSS Domain-Based Names                 May 20087.  Security Considerations   Use of GSS-API domain-based names may not be negotiable by some GSS-   API mechanisms, and some acceptors may not support GSS-API domain-   based names.  In such cases, the initiators are left to fall back on   the use of host-based names, so the initiators MUST also verify that   the acceptor's host-based name is authorized to provide the given   service for the domain that the initiator had wanted.   The above security consideration also applies to all GSS-API   initiators who lack support for domain-based service names.   Note that, as with all service names, the mere existence of a domain-   based service name conveys meaningful information that may be used by   initiators for making authorization decisions; therefore,   administrators of distributed authentication services should be aware   of the significance of the service names for which they create   acceptor credentials.8.  References8.1.  Normative References   [RFC1035]  Mockapetris, P., "Domain names - implementation and              specification", STD 13,RFC 1035, November 1987.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2743]  Linn, J., "Generic Security Service Application Program              Interface Version 2, Update 1",RFC 2743, January 2000.   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for              specifying the location of services (DNS SRV)",RFC 2782,              February 2000.   [RFC2831]  Leach, P. and C. Newman, "Using Digest Authentication as a              SASL Mechanism",RFC 2831, May 2000.   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,              "Internationalizing Domain Names in Applications (IDNA)",RFC 3490, March 2003.   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234, January 2008.Williams & Melnikov         Standards Track                     [Page 7]

RFC 5178                 GSS Domain-Based Names                 May 20088.2.  Informative References   [GS2]      Josefsson, S., "Using GSS-API Mechanisms in SASL: The GS2              Mechanism Family", Work in Progress, October 2007.   [RFC2203]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol              Specification",RFC 2203, September 1997.   [RFC2606]  Eastlake, D. and A. Panitz, "Reserved Top Level DNS              Names",BCP 32,RFC 2606, June 1999.   [RFC3530]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,              Beame, C., Eisler, M., and D. Noveck, "Network File System              (NFS) version 4 Protocol",RFC 3530, April 2003.   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.              Rose, "DNS Security Introduction and Requirements",RFC 4033, March 2005.   [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and              Security Layer (SASL)",RFC 4422, June 2006.   [RFC4752]  Melnikov, A., "The Kerberos V5 ("GSSAPI") Simple              Authentication and Security Layer (SASL) Mechanism",RFC 4752, November 2006.Authors' Addresses   Nicolas Williams   Sun Microsystems   5300 Riata Trace Ct.   Austin, TX  78727   US   EMail: Nicolas.Williams@sun.com   Alexey Melnikov   Isode Ltd.   5 Castle Business Village,   36 Station Road   Hampton, Middlesex  TW12 2BX   United Kingdom   EMail: Alexey.Melnikov@isode.comWilliams & Melnikov         Standards Track                     [Page 8]

RFC 5178                 GSS Domain-Based Names                 May 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   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, THE IETF TRUST 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.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Williams & Melnikov         Standards Track                     [Page 9]