doc/standardisation/draft-ietf-kitten-gssapi-v3-guide-to-01.txt

NETWORK WORKING GROUP                                        N. Williams
Internet-Draft                                                       Sun
Expires: April 19, 2006                                 October 16, 2005


                         Guide to the GSS-APIv3
              draft-ietf-kitten-gssapi-v3-guide-to-01.txt

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   Extensions to the GSS-APIv2 are needed for a number of reasons.  This
   documents describes the extensions being proposed, the resons,
   possible future directions, and portability, IANA and security
   considerations.  This document does not define any protocol or
   interface and is purely informational.


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Table of Contents

   1.  Conventions used in this document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  A Pseudo-Mechanism OID for the GSS-API Itself  . . . . . . . .  6
   4.  Mechanism Attribute Inquiry Facilities . . . . . . . . . . . .  7
   5.  Security Context Extensibility Extensions  . . . . . . . . . .  8
   6.  Credential Extensibility Extensions  . . . . . . . . . . . . .  9
   7.  Credential Export/Import . . . . . . . . . . . . . . . . . . . 10
   8.  GSS_Store_cred() . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  Pseudo-Mechanism Stacking  . . . . . . . . . . . . . . . . . . 12
   10. Naming Extensions  . . . . . . . . . . . . . . . . . . . . . . 13
   11. Additional Name Types  . . . . . . . . . . . . . . . . . . . . 14
   12. GSS_Pseudo_random()  . . . . . . . . . . . . . . . . . . . . . 15
   13. Channel Bindings Specifications  . . . . . . . . . . . . . . . 16
   14. Semantic and Miscallaneous Extensions  . . . . . . . . . . . . 17
   15. Portability Considerations . . . . . . . . . . . . . . . . . . 18
   16. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   17. Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   18. Normative  . . . . . . . . . . . . . . . . . . . . . . . . . . 20
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 21
       Intellectual Property and Copyright Statements . . . . . . . . 22


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1.  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].


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2.  Introduction

   [NOTE: the references section is current fairly empty; the various
   KITTEN WG work items will be added to this I-D in a subsequent
   revision.]

   Since the advent of the GSS-APIv2 it has come to be used in a number
   of Internet (and other) protocols and a number of implementations
   exist.  In that time implementors and protocol designers have come to
   understand both, the GSS-API's strengths, and its shortcommings; we
   believe now that a number of extensions to the GSS-API are needed.
   Here these proposed extensions, forming what we may call the GSS-API
   version 3, are described at a high-level.;

   Some of these extensions are intended to facilitate further
   extensions, so that further major revisions to the GSS-API may not be
   necessary.  Others are intended to fill voids in the the GSS-APIv2.

   The extensions being proposed are:

      A pseudo-mechanism OID for the GSS-API itself

      Mechanism attribute inquiry facilities

      Security context extensibility extensions

      Credential extensibility extensions

      Credential export/import

      GSS_Store_cred(), for making delegated credentials available for
      acquisition

      Pseudo-mechanism stacking

      Naming extensions, to facilitate authorization by identifiers
      other than names

      Additional name types, specifically domain-based naming

      A pseudo-random function interface

      Channel bindings specifications

      Semantic extensions relating to thread- and/or fork-safety

      [Have I missed anything?  I have a feeling I have.  Re-keying?]


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      ...

   Additionally, because we foresee future minor extensions, including,
   specifically, extensions which may impact the various namespaces
   associated with APIs (symbol names, constant values, class names,
   etc...) we also propose the establishment of IANA registries for
   these namespaces.


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3.  A Pseudo-Mechanism OID for the GSS-API Itself

   A mechanism OID is assigned to identify and refer to the GSS-API
   iself.  This is necessary to enable the use of extended inquiry
   interfaces to inquire about features of a GSS-API implementation
   specifically, apart from actual mechanisms.

   But also, this OID is needed for better error handling, so that minor
   status codes produced in generic contexts that lack a mechanism OID
   can be distinguished from minor status codes for a "default"
   mechanism and properly displayed.


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4.  Mechanism Attribute Inquiry Facilities

   In the course of designing a pseudo-mechanism stacking facility, as
   well as while considering the impact of all of these extensions on
   portability, a need for interfaces through which to discover or
   inquire by features provided by GSS-API mechanisms was discovered.

   The proposed mechanism attribute inquiry interfaces consist of:

      GSS_Inquire_mech_attrs_for_mech()

      GSS_Indicate_mechs_by_mech_attrs()

      GSS_Display_mech_attr()

   These extensions facilitate portability by allowing GSS-APIv3
   applications to discover the features provided by a given
   implementation of the GSS-API or any mechanisms.  These extensions
   are also useful in facilitating stackable pseudo-mechanisms.


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5.  Security Context Extensibility Extensions

   In order to facilitate future security context options we introduce a
   GSS_Create_sec_context() interface that creates a security context
   object, for use with extensions and with GSS_Init_sec_context(),
   GSS_Accept_sec_context(), and GSS_Inquire_sec_context().  Such
   security contexts are in a non-established state until they are
   established through the use of GSS_Init_sec_context() or
   GSS_Accept_sec_context().


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6.  Credential Extensibility Extensions

   In order to facilitate future extensions to GSS credentials we
   introduce a GSS_Create_credential(), similar to
   GSS_Create_sec_context(), interface that creates an "empty"
   credential.


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7.  Credential Export/Import

   To allow for passing of credentials between different "session
   contexts," between different hosts, or for storage of post-dated
   credentials, we introduce a credential export/import facility, much
   like the security context export/import facility of the GSS-APIv2.

   Together with credential extensibility and other extensions this
   facility may allow for:

      Credential delegation at any time

      Post-dated credentials, and storage of the such for subsequent
      use.

      ...?


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8.  GSS_Store_cred()

   This extension fills a void in the GSS-APIv2 where delegated
   credentials could not be used except in the context of the same
   process that received them.  With this extension acceptor
   applications can now make delegated credentials available for use,
   with GSS_Acquire_cred() et. al., in other process contexts.

   [Manipulation of "credential stores" is (may be?) out of scope for
   this document.]


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9.  Pseudo-Mechanism Stacking

   A number of pseudo-mechanisms are being proposed which are designed
   to "stack" atop other mechanisms.  The possiblities are many,
   including: a compression mechanism, a perfect forward security
   mechanism, an many others.

   The GSS-APIv2 only had concrete mechanisms and one pseudo-mechanism
   (SPNEGO) available.  With this proposal the mechanism taxonomy is
   quite expanded:

      Concrete mechanisms (e.g., the Kerberos V mechanism)

      Composite mechanisms (a concrete mechanism composed with one or
      more stackable pseudo-mechanisms)

      Stackable pseudo-mechanisms

      Other pseudo-mechanisms (e.g., SPNEGO, the GSS-API itself)

   Although composed mechanisms may be made available for use by GSS-
   APIv2 applications without any further extensions, use of stackable
   pseudo-mechanisms can complicate mechanism negotiation; additionally,
   discovery of mechanisms appropriate for use in one or another context
   would require hard-coding information about them in GSS-APIv2
   applications.  Extensions to the GSS-APIv2 could facilitate use of
   composite.

   The mechanism attribute inquiry facilities, together with the
   forllowing additional interfaces, provide for a complete interface to
   mechanism composition and for managing the complexity of mechanism
   negotiation:

      GSS_Compose_oid()

      GSS_Decompose_oid()

      GSS_Release_oid()

      GSS_Indicate_negotiable_mechs()

      GSS_Negotiate_mechs()


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10.  Naming Extensions

   Some applications make use of exported names, as produced by
   GSS_Export_name(), to create/manage/evaluate access control lists; we
   call this name-based authorization.

   Exported names typically encode names that are meant for display to
   humans, not internal identifiers.

   In practice this creates a number of problems.  E.g., the referential
   integrity of such access control lists is hard to maintain as
   principals are added, removed, renamed or old principal names reused.

   Additionally, some mechanisms may lack a notion of a "canonical" name
   for some or all of their principals.  Such mechanisms cannot be used
   by applications that rely on name-based authorization.

   <Describe the proposed extensions in this area.>


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11.  Additional Name Types

   <Decribe domain-based names and the need for them.>


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12.  GSS_Pseudo_random()

   <Decribe GSS_Pseudo_random() and the need for it.>


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13.  Channel Bindings Specifications


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14.  Semantic and Miscallaneous Extensions

   The GSS-APIv2 specifications say nothing about the thread-safety,
   much less the fork-safety, of the GSS-API.  Thread-safety and fork-
   safety are, after all, platform- and/or language-specific matters.
   But as support for multi-threading spreads the matter of thread-
   safety cannot be avoided.  The matter of fork-safety is specific to
   platforms that provide a "fork()" function, or similar.

   <describe the GSS-APIv3's thread-safety requirements>

   <reference the portability considerations section>


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15.  Portability Considerations

   The potential for additional generic, mechanism-specific, language
   binding-specific and, most importantly, semantic extensions to the
   GSS-APIv3 may create application portability problems.  The mechanism
   attribute inquiry facilities of the GSS-APIv3 and the pseudo-
   mechanism OID for the GSS-API itself double as a run-time facility
   for discovery of feature availability.  Run-time feature discovery
   facilities, in turn, can be used at application build-time as well by
   building small applications to display the available features.

   <...>


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16.  IANA Considerations

   <Describe the namespace issues associated with future minor
   extensions to the GSS-APIv3 and the IANA registries to be created to
   cope with them.>


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17.  Security Considerations

   <...>

18.  Normative

   [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.

   [RFC2744]  Wray, J., "Generic Security Service API Version 2 :
              C-bindings", RFC 2744, January 2000.


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Author's Address

   Nicolas Williams
   Sun Microsystems
   5300 Riata Trace Ct
   Austin, TX  78727
   US

   Email: Nicolas.Williams@sun.com


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