RFC 5178

Generic Security Service Application Program Interface (GSS-API) Internationalization and Domain-Based Service Names and Name Type

📅 published May 2008, from ietf

RFC 5178 📜🎀 (Part 1 of 2)

Generic Security Service Application Program Interface (GSS-API) Internationalization and Domain-Based Service Names and Name Type

Written by: N. Williams (Sun) and A. Melnikov (Isode Ltd.) 👯‍♀️
Category: Standards Track 🛤️
Date: May 2008 📅
Obsoletes / Updates: nothing! This one doesn't obsolete or update any earlier RFC 💅

Status of This Memo ✨

okay so this document is an Internet standards track protocol for the Internet community 🌐. It's open for discussion and suggestions for improvements, so bring your ideas 💖. If you want the current standardization state and status of this protocol, check the current edition of "Internet Official Protocol Standards" (STD 1) 📚. And the distribution of this memo is unlimited, so share away 🦋.

Abstract 🌸

this doc is all about domain-name-based service principal names and their name type for the Generic Security Service Application Programming Interface (GSS-API) 🎀. It also covers internationalization of the GSS-API 🌍.

domain-based service names are kind of like host-based service names, except they use a domain name (which doesn't have to be an Internet domain name) on top of a hostname 🧚. The whole point is to protect applications that use insecure service discovery protocols 🛡️. It works by naming clustered services after the "domain" they serve, so clients can authorize the service's servers based on authenticating those service names 👑. Main character energy for sure 💅.

Table of Contents 🗂️

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.  Conventions Used in This Document . . . . . . . . . . . . . . . 4
3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
  3.1.  Name Type OID . . . . . . . . . . . . . . . . . . . . . . . 4
  3.2.  Name Type OID and Symbolic Name . . . . . . . . . . . . . . 4
4.  Query and Display Syntaxes  . . . . . . . . . . . . . . . . . . 4
  4.1.  Examples of Domain-Based Names  . . . . . . . . . . . . . . 5
5.  Internationalization (I18N) Considerations  . . . . . . . . . . 5
  5.1.  Importing Internationalized Names . . . . . . . . . . . . . 5
  5.2.  Displaying Internationalized Names  . . . . . . . . . . . . 5
6.  Application Protocol Examples . . . . . . . . . . . . . . . . . 6
  6.1.  NFSv4 Domain-Wide Namespace Root Server Discovery . . . . . 6
  6.2.  LDAP Server Discovery . . . . . . . . . . . . . . . . . . . 6
7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
  8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
  8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8

1. Introduction 🦋

okay so some apps need to figure out the names of servers for a specific resource 🔍. A lot of the usual ways to do server discovery are insecure 😬. Think queries for DNS [RFC1035] SRV resource records [RFC2782] without using DNSSEC [RFC4033]. Those can get attacked, and a client can be redirected to the wrong servers, or even sketchy malicious ones 💀. Worse, a client might get sent to a server that has credentials for itself and can totally authenticate to the client, and it could still be wrong or malicious (say it got compromised) 🙈.

so domain-based names let GSS-API [RFC2743] initiator apps (clients) authorize acceptor principals (servers) to serve the resource the client found through insecure discovery 🫶. And you don't need to secure the discovery method or add another protocol for server authorization, which is iconic 🔥. Basically a discovered server either has credentials for the domain-based service names it's supposed to answer, or it doesn't. Having valid credentials for those names is what authorizes a server for a domain-wide service 👑.

a domain-based name has three required elements 🎀:

a service name
a domain name
a hostname

the domain name and the hostname should be Domain Name System (DNS) names 💖, though domain-based names could also be used in non-DNS environments 🌈. Since we're using DNS names, we also have to cover internationalization of the GSS-API 🌍.

domain-based naming isn't brand new, btw 💅. According to a report to the KITTEN WG mailing list, at least one LDAP implementation already uses domain-based service naming ✨. Also the DIGEST-MD5 HTTP / Simple Authentication and Security Layer (SASL) mechanism [RFC2831] describes a similar idea 🧚. (See section 2.1.2 of [RFC2831] for the "serv-name" field of the digest-response 📚.)

2. 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 Considerations 🏛️

3.1. Name Type OID 🔢

IANA has recorded a 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 doc creates a new GSS-API name type with the symbolic name 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's a single name syntax for domain-based names 💅. It's written in ABNF [RFC5234] 🧠:

      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 in Section 4.1 of [RFC2743] 💖. Any other rules not defined above are defined in Appendix B.1 of [RFC5234] 📚.

4.1. Examples of Domain-Based Names 🧁

these examples are not normative 🙈:

ldap@somecompany.example@ds1.somecompany.example
nfs@somecompany.example@nfsroot1.somecompany.example

we're using the .example top-level domain here, following [RFC2606] 🍓.

5. Internationalization (I18N) Considerations 🌏

we're introducing new versions of GSS_Import_name() and GSS_Display_name() to support Unicode better 🌸. We also allow 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, 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() 🌈. It works exactly like GSS_Import_name() (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 through 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 follow 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() ✨. It works exactly like GSS_Display_name() (same input and output parameters and behavior), except that it outputs UTF-8 strings through its name_string output argument 🧚. GSS_Display_name_utf8() MUST NOT output ACE-encoded internationalized domain names 🙅‍♀️.

6. Application Protocol Examples 🎬

the following examples are not normative 💅. They show how the authors picture two applications using domain-based names ✨.

6.1. NFSv4 Domain-Wide Namespace Root Server Discovery 🗺️

work is ongoing to build domain-wide NFSv4 [RFC3530] filesystem namespaces 🌳. There's a single "root" with one or more servers (replicas), and multiple filesystems get glued into the namespace through "referrals" 🔗. Clients could then build a "global" namespace using the DNS domain hierarchy 🌐.

in this setup, clients would always know from context when they need to find the root servers for a given DNS domain 🧭. Root server discovery would use DNS SRV RR lookups, without DNSSEC where DNSSEC hasn't been deployed 🙃.

when using RPCSEC_GSS [RFC2203] for security, NFSv4 clients would use domain-based names to make sure the servers named in the SRV RRs are actually 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 domain-based names, protecting server discovery through insecure DNS SRV RR lookups, much like 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 found through SRV RR lookups. Switching those clients to domain-based naming when domain-based acceptor credentials haven't been deployed to LDAP servers, or when LDAP servers haven't been modified to allow domain-based naming, would break interoperability 💀. So this is a legacy server interoperability issue. 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 to allow use of domain-based names is not relevant to the theory of how domain-based naming would protect LDAP clients' server discovery 🙄.

7. Security Considerations 🔐

this section is SERIOUS, bestie 😭🚨

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 those cases, initiators are left to fall back on host-based names, so initiators MUST also verify that the acceptor's host-based name is authorized to provide the given service for the domain the initiator wanted 🛑.

the above security consideration also applies to all GSS-API initiators who lack support for domain-based service names 🫣.

also, as with all service names, the mere existence of a domain-based service name conveys meaningful information that initiators may use when making authorization decisions 👀. So administrators of distributed authentication services should be aware of how significant the service names are for which they create acceptor credentials 🧠. no cap, this matters a lot 💜.

8. References 📚

8.1. Normative References 📚

okay so these are the docs this spec literally can't function without, bestie 🫶 you have to read them to implement it

[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.

8.2. Informative References 🌸

these are the extra reads that are super helpful for the vibe check but aren't strictly required to get the spec working ✨

[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 💅

meet the people who wrote this 🦋 you can email them if you're curious

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.com

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