Network Working Group Nicolas Williams INTERNET-DRAFT Sun Microsystems November 2004 Stackable Generic Security Service Pseudo-Mechanisms Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC2026. 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 as "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 Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document defines and formalizes the concept of stackable pseudo- mechanisms for the Generic Security Service Application Programming Interface (GSS-API) and introduces a framework to support stackable pseudo-mechanisms and mechanism compositing. Stackable GSS-API pseudo-mechanisms allow for the composition of new mechanisms that combine features from multiple mechanisms. Stackable mechanisms that add support for Perfect Forward Security (PFS), data compression, additional authentication factors, etc... are facilitated by this document. Table of Contents 1. Introduction pg. 3 1.1. Glossary pg. 3 2. Issues with Mechanism Composition pg. 4 N. Williams [Page 1] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 3. Mechanism Composition pg. 5 3.1. Construction of Composed Mechanism OIDs pg. 5 3.2. Mechanism Composition Rules pg. 6 3.3. Interfacing with Composite Mechanisms pg. 6 3.4. Compatibility with the Basic GSS-API Interfaces pg. 7 3.5. Processing of Tokens for Composite Mechanisms pg. 7 4. New GSS-API Interfaces pg. 8 4.1. Mechanism Attributes and Attribute Sets pg. 8 4.1.1. Determination of Attribute Sets of Composite Mechs pg. 9 4.1.2. Initial Set of Known Mechanism Attributes pg. 9 4.1.3. Mechanism Attribute Sets of Existing Mechs pg. 11 4.2. New GSS-API Function Interfaces pg. 12 4.2.1. GSS_Indicate_mechs_by_mech_attrs() pg. 12 4.2.2. GSS_Inquire_mech_attrs_for_mech() pg. 13 4.2.3. GSS_Display_mech_attr() pg. 14 4.2.4. GSS_Compose_oid() pg. 15 4.2.5. GSS_Decompose_oid() pg. 15 4.2.6. GSS_Release_oid() pg. 16 4.2.7. GSS_Indicate_negotiable_mechs() pg. 16 4.2.8. GSS_Negotiate_mechs() pg. 17 4.3. New Major Status Values pg. 18 4.4. C-Bindings pg. 18 5. Negotiation of Composite Mechanisms pg. 19 5.1. Negotiation of Composite Mechanisms Through SPNEGO pg. 20 6. Requirements for Mechanism Designers pg. 20 7. IANA Considerations pg. 20 8. Security considerations pg. 20 9. References pg. 21 9.1. Informative references pg. 21 9.2. Normative references pg. 21 10. Author's Address pg. 21 N. Williams [Page 2] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 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]. 1. Introduction Recent discussions within the IETF have shown the need for a refactoring of the features that GSS-API mechanisms may provide and a way to compose new mechanisms from smaller components. Mechanism features are more formally referred to as "mechanism attributes" below. The terms "feature" and mechanism attribute" are sometimes used interchangeably. One way to do this is to "stack" multiple mechanisms on top of each other such that the features of all of them are summed into a new, composite mechanism. One existing GSS-API mechanism, LIPKEY [LIPKEY], is essentially stacked over another, SPKM-3 [LIPKEY], although LIPKEY does not conform to the stackable pseduo-mechanism framework described herein. The first truly stackable pseudo-mechanism proposed, CCM [CCM] was for signalling the willingness of an initiator and/or acceptor to utilize channel bindings as well as to correctly implement channel bindings. Since then other similar mechanism compositing needs and ideas have come up, along with problems such as "what combinations are possible, useful, reasonable and secure?" Problems which we believe are solved herein. Therefore the time has come to define the concept of GSS-API mechanism compositing through the use of stackable pseudo-mechanisms. 1.1. Glossary Concrete GSS-API mechanism A mechanism which can be used standalone. Examples include: the Kerberos V mechanism [CFX], SPKM-1/2 [SPKM] and SPKM-3 [LIPKEY]. GSS-API Pseudo-mechanism A mechanism which uses other mechanisms in the construction of its context and/or per-message tokens and security contexts. SPNEGO is an example of this. N. Williams [Page 3] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Stackable GSS-API pseudo-mechanism A mechanism which uses a single other mechanism in the construction of its tokens such that the OID of the composite result can be constructed by prepending the OID of the stackable pseudo-mechanism to the OID of the mechanism to be used by it. Mechanism-negotiation GSS-API pseudo-mechanism A GSS-API mechanism that negotiates the use of GSS-API mechanisms. SPNEGO [SPNEGO] is an example of this. 2. Issues with Mechanism Composition Interfacing with composite mechanisms through the existing GSS-API interfaces and the handling of composite mechanism tokens is straightforward enough and described in section 3. However, the concepts of stackable and composite mechanisms do give rise to several minor problems: - How to determine allowable combinations of mechanisms; - How to encode composite mechanism OIDs; - How to decompose the OID of a composite mechanism and process its tokens properly; - Application interfacing issues such as: - Whether and/or which composite mechanisms should be listed by GSS_Indicate_mechs(); - Whether and/or which composite mechanisms not listed by GSS_Indicate_mechs() may nonetheless be available for use by applications and how applications can detect their availability; - What additional interfaces should be provided to help applications select appropriate mechanisms; - Mechanism negotiation issues (related to the application interface issues listed above), such as: - Should applications advertise composite mechanisms in SPNEGO or other application-specific mechanism negotiation contexts? - Or should applications advertise concrete and stackable pseudo- mechanisms in SPNEGO or other application-specific mechanism negotiation contexts? N. Williams [Page 4] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Section 3 addresses the OID composition, decomposition and encoding issues, as well as basic interfacing and token handling issues. Section 4 addresses the application interfacing issues. Section 5 addresses the mechanism negotiation issues. 3. Mechanism Composition Mechanism composition by stacking pseudo-mechanisms on a concrete mechanism is conceptually simple: join the OIDs of the several mechanisms in question and process GSS-API tokens and routine calls through the top-most pseudo-mechanism in a stack, which can then, if necessary, do the same with the remainder of the stack. Some stackable pseudo-mechanisms may do nothing more than perform transformations on application data (e.g., compression); such pseudo-mechanisms will generally chain the processing of tokens and routine calls to the mechanisms below them in the stack. Other stackable pseudo-mechanisms may utilize the mechanisms below them only during security context setup. For example, a stackable pseudo-mechanism could perform a Diffie-Hellman key exchange and authenticate it by binding a security context established with the mechanism stacked below it; such a mechanism would provide its own per-message tokens. 3.1. Construction of Composed Mechanism OIDs Composition of mechanism OIDs is simple: prepend the OID of one pseudo-mechanism to the OID of another mechanism (composite or otherwise), but there MUST always be at least one final mechanism OID and it MUST be useful standalone (i.e., it MUST NOT be a pseudo-mechanism). A composite mechanism OID forms, essentially, a stack. The encoding of composed mechanism OIDs is not quite the concatenation of the component OIDs' encodings, however. This is because the first two arcs of ASN.1 OIDs are encoded differently from subsequent arcs (the first two arcs have a limited namespace and are encoded as a single octet), so were composite mechanism OIDs to be encoded as the concatenation of the component OIDs the result would not decode as the concatenation of the component OIDs. To avoid this problem the first two arcs of each component of a composite mechanism OID, other than the leading component, will be encoded as other arcs would. Decomposition of mechanism OIDs is similar, with each pseudo- mechanism in the stack being able to determine the OID suffix from knowledge of its own OID(s), from the composite mechanism OID in its OID or OID SET arguments and from the the composite OID from the initial context token for a given context. N. Williams [Page 5] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 New pseudo-mechanisms MAY be allocated OIDs from the prefix given below as follows by assignment of a sub-string of OID arcs to be appended to this prefix. This prefix OID is: [1.3.6.1.5.5.11 appears to be available, registration w/ IANA TBD] All OID allocations below this OID MUST be for stackable pseudo- mechanisms and MUST consist of a single arc. This will make it possible to decompose the OIDs of composite mechanisms without necessarily knowing a priori the OIDs of the component stackable pseudo-mechanisms. 3.2. Mechanism Composition Rules All new stackable pseudo-mechanisms MUST specify the rules for determining whether they can stack above a given mechanism, composite or otherwise. Such rules may be based on specific mechanism attribute sets and/or specific OIDs (composite and otherwise) of mechanisms stacked below them. All stackable pseudo-mechanisms MUST have the following mechanism composition rule relating to unknown mechanism attributes: - composition with mechanisms supporting unknown mechanism attributes MUST NOT be permitted. This rule protects against compositions which cannot be considered today but which might nonetheless arise due to the introduction of new mechanisms and which might turn out to be insecure or otherwise undesirable. Mechanism composition rules for stackable pseudo-mechanisms MAY and SHOULD be updated as new GSS-API mechanism attributes and mechanisms sporting them are introduced. The specifications of mechanisms that introduce new mechanism attributes or which otherwise should not be combined with others in ways which would be permitted under existing rules SHOULD also update the mechanism composition rules of affected pseudo-mechanisms. 3.3. Interfacing with Composite Mechanisms The basic GSS-API [RFC2743] interfaces MUST NOT accept as input or provide as output the OID of any stackable pseudo-mechanism. Composite mechanisms MUST be treated as concrete mechanisms by the basic GSS-API interfaces [RFC2743]. Thus the way in which a composite mechanism is used by applications with the basic GSS-API (version 2, update 1) is straightforward, exactly as if composite mechanisms were normal GSS-API mechanisms. This is facilitated by the fact that in all cases where the GSS-API N. Williams [Page 6] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 implementation might need to know how to process or create a token it has the necessary contextual information, the mechanism OID, available and can decompose composite mechanism OIDs as necessary. For example, for initial GSS_Init_sec_context() calls the implementation knows the desired mechanism OID, and if it should be left unspecified, it can pick a default mechanism given the initiator credentials provided by the application (and if none are provided other default mechanism and credential selections can still be made). For subsequent calls to GSS_Init_sec_context() the implementation knows which mechanism to use from the given [partially established] security context. Similarly for GSS_Accept_sec_context, where on initial calls the mechanism OID can be determined from the given initial context token's framing. The manner in which GSS-API implementations and the various mechanisms and pseudo-mechanisms interface with one another is more interesting; it is also left as an excercise to implementors. 3.4. Compatibility with the Basic GSS-API Interfaces In order to preserve backwards compatibility with applications that use only the basic GSS-API interfaces (version 2, update 1), several restrictions are imposed on the use of composite and stackable pseduo-mechanisms with the basic GSS-API interfaces: o GSS_Indicate_mechs() MUST NOT indicate support for any stackable pseduo-mechanisms under any circumstance. o GSS_Indicate_mechs() MAY indicate support for some, all or none of the available composite mechanisms. o Which composite mechanisms, if any, are indicated through GSS_Indicate_mechs() SHOULD be configurable. o GSS_Acquire_cred() and GSS_Add_cred() MUST NOT create credentials for composite mechanisms not explicitly requested or, if GSS_C_NULL_OID is given as a desired for composite mechanisms not indicated by GSS_Indicate_mechs(). o GSS_Acquire_cred() and GSS_Add_cred() MUST NOT (and truly cannot) create credentials for stackable pseudo-mechanisms. 3.5. Processing of Tokens for Composite Mechanisms The initial context token for any mechanism, composite or otherwise, MUST be encapsulated as described in section 3.1 of rfc2743 [RFC2743], and the OID used in that framing MUST be that of the mechanism, but in the case of composite mechanisms this OID MUST be the OID of the leading component of the composite mechanism. Note that this has implications for multi-mechanism implementations of the GSS-API, namely that acceptors MUST route initial context N. Williams [Page 7] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 tokens to the appropriate mechanism and they MUST allow that mechanism to determine the composite mechanism OID (such as by allowing that mechanism's GSS_Accept_sec_context() to output the actual mechanism to the application. In all other cases the mechanism that produced a given token can be determined by the given security context. 4. New GSS-API Interfaces GSS-API applications face, today, the problem of how to select from multiple GSS-API mechanisms that may be available. This problem is likely to be exacerbated by the introduction of stackable. To address this problem we introduce a new concept: that of mechanism attributes. By allowing applications to query the set of attributes associated with individual mechanisms and to find out which mechanisms support a given set of attributes we allow applications to select mechanisms based on their attributes yet without having to hardcode mechanism OIDs. Section 4.1 describes the mechanism mechanism attributes concept. Sections 4.2.1, 4.2.2 and 4.2.3 describe three new interfaces that deal in mechanisms and attribute sets: - GSS_Indicate_mechs_by_attrs() - GSS_Inquire_attrs_for_mech() - GSS_Display_mech_attr() Additional utility functions for mechanism OID composition and decomposition are given in sections 4.2.4, 4.2.5 and 4.2.6. Finally, two utility functions, GSS_Indicate_negotiable_mechs() and GSS_Negotiate_mechs(), to aid applications in mechanism negotiation are described in sections 4.2.7 and 4.2.8. These two interfaces may be implemented entirely in terms of the other interfaces described herein. 4.1. Mechanism Attributes and Attribute Sets An abstraction for the features provided by pseudo-mechanisms is needed in order to facilitate the programmatic composition of mechanisms. Two data types are needed: one for individual mechanism attributes and one for mechanism attribute sets. To simplify the mechanism attributes interfaces we reuse the 'OID' and 'OID set' data types and model individual mechanism attribute types as OIDs. To this end we define an open namespace of mechanism attributes and assign them arcs off of this OID: N. Williams [Page 8] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 [1.3.6.1.5.5.12 appears to be available, registration w/ IANA TBD] 4.1.1. Determination of Attribute Sets of Composite Mechs Each mechanism, composite or otherwise, has a set of mechanism attributes that it supports as specified. The mechanism attribute set of a composite mechanism is to be determined by the top-most stackable pseudo-mechanism of the composite according to its own attribute set and that of the mechanism stacked directly below it. It may well be that some composite mechanisms' attribute sets consist of the union of those of their every component, however this need not be the case and should not be assumed. Every stackable pseudo-mechanism's specification MUST specify the rules for determining the mechanism attribute set of mechanisms composed by it. 4.1.2. Initial Set of Known Mechanism Attributes Mech Attr name OID Arc Arc name -------------- ------- -------- GSS_C_MA_MECH_CONCRETE (1) concrete-mech GSS_C_MA_MECH_STACKABLE (2) pseudo-mech GSS_C_MA_MECH_COMPOSITE (3) composite-mech GSS_C_MA_MECH_NEGO (4) mech-negotiation-mech GSS_C_MA_MECH_GLUE (5) mech-glue GSS_C_MA_NOT_MECH (6) not-mech GSS_C_MA_DEPRECATED (7) mech-deprecated GSS_C_MA_NOT_DFLT_MECH (8) mech-not-default GSS_C_MA_ITOK_NOT_FRAMED (9) initial-token-not-framed GSS_C_MA_AUTH_INIT (10) auth-init-princ GSS_C_MA_AUTH_TARG (11) auth-targ-princ GSS_C_MA_AUTH_INIT_INIT (12) auth-init-princ-initial GSS_C_MA_AUTH_TARG_INIT (13) auth-targ-princ-initial GSS_C_MA_AUTH_INIT_ANON (14) auth-init-princ-anon GSS_C_MA_AUTH_TARG_ANON (15) auth-targ-princ-anon GSS_C_MA_DELEG_CRED (16) deleg-cred GSS_C_MA_INTEG_PROT (17) integ-prot GSS_C_MA_CONF_PROT (18) conf-prot GSS_C_MA_PROT_READY (19) prot-ready GSS_C_MA_REPLAY_DET (20) replay-detection GSS_C_MA_OOS_DET (21) oos-detection GSS_C_MA_CBINDINGS (22) channel-bindings GSS_C_MA_CBINDINGS_BIDI (23) channel-bindings-bidirectional GSS_C_MA_CBINDINGS_NEGO (24) channel-bindings-negotiate GSS_C_MA_PFS (25) pfs GSS_C_MA_COMPRESS (26) compress (27..) N. Williams [Page 9] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Mech Attr name Purpose -------------- ------- GSS_C_MA_MECH_CONCRETE Indicates that a mech is neither a pseudo- mechanism nor a composite mechanism. GSS_C_MA_MECH_STACKABLE Indicates that a mech is a pseudo-mechanism. GSS_C_MA_MECH_COMPOSITE Indicates that a mech is a composite mechanism. GSS_C_MA_MECH_NEGO Indicates that a mech negotiates other mechs (e.g., SPNEGO has this attribute). GSS_C_MA_MECH_GLUE Indicates that the OID is not for a mechanism but for the GSS-API itself. GSS_C_MA_NOT_MECH Indicates that the OID is known, yet also known not to be the OID of any GSS-API mechanism (or the GSS-API itself). GSS_C_MA_DEPRECATED Indicates that a mech (or its OID) is deprecated and MUST NOT be used as a default mechanism. GSS_C_MA_NOT_DFLT_MECH Indicates that a mech (or its OID) MUST NOT be used as a default mechanism. GSS_C_MA_ITOK_NOT_FRAMED Indicates that the given mechanism's initial context tokens are not properly framed as per-section 3.1 of rfc2743. GSS_C_MA_AUTH_INIT Indicates support for authentication of initiator to acceptor. GSS_C_MA_AUTH_TARG Indicates support for authentication of acceptor to initiator. GSS_C_MA_AUTH_INIT_INIT Indicates support for initial authentication of initiator to acceptor. GSS_C_MA_AUTH_TARG_INIT Indicates support for initial authentication of acceptor to initiator. GSS_C_MA_AUTH_INIT_ANON Indicates support for initiator anonymity. GSS_C_MA_AUTH_TARG_ANON Indicates support for acceptor anonymity. GSS_C_MA_DELEG_CRED Indicates support for credential delegation. GSS_C_MA_INTEG_PROT Indicates support for per-message integrity protection. GSS_C_MA_CONF_PROT Indicates support for per-message confidentiality protection. GSS_C_MA_PROT_READY Indicates support for per-message protection prior to full context establishment. N. Williams [Page 10] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 GSS_C_MA_REPLAY_DET Indicates support for replay detection. GSS_C_MA_OOS_DET Indicates support for out-of-sequence detection. GSS_C_MA_CBINDINGS Indicates support for channel bindings. GSS_C_MA_CBINDINGS_BIDI Indicates support for bidirectional channel bindings. GSS_C_MA_CBINDINGS_NEGO Indicates that the mech acts as a signal for application support for and willingness to use channel bindings. GSS_C_MA_PFS Indicates support for Perfect Forward Security. GSS_C_MA_COMPRESS Indicates support for compression of data inputs to GSS_Wrap(). 4.1.3. Mechanism Attribute Sets of Existing Mechs The Kerberos V mechanism [RFC1964] [CFX] provides the following mechanism attributes: GSS_C_MA_MECH_CONCRETE GSS_C_MA_AUTH_INIT GSS_C_MA_AUTH_TARG GSS_C_MA_DELEG_CRED GSS_C_MA_INTEG_PROT GSS_C_MA_CONF_PROT GSS_C_MA_PROT_READY (varies by initiator implementation) GSS_C_MA_REPLAY_DET GSS_C_MA_OOS_DET GSS_C_MA_CBINDINGS The Kerberos V mechanism also has a deprecated OID which has the same mechanism attributes as above, and GSS_C_MA_DEPRECATED. [The mechanism attributes of the SPKM family of mechanisms will be provided in a separate document as SPKM is current being reviewed for possibly significant changes due to problems in its specifications.] The LIPKEY mechanism offers the following attributes: GSS_C_MA_MECH_CONCRETE (should be stackable, but does not compose) GSS_C_MA_AUTH_INIT_INIT GSS_C_MA_AUTH_TARG (from SPKM-3) GSS_C_MA_AUTH_TARG_ANON (from SPKM-3) GSS_C_MA_INTEG_PROT GSS_C_MA_CONF_PROT GSS_C_MA_REPLAY_DET GSS_C_MA_OOS_DET (LIPKEY should also provide GSS_C_MA_CBINDINGS, but SPKM-3 N. Williams [Page 11] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 requires clarifications on this point.) The SPNEGO mechanism [SPNEGO] provides the following attribute: GSS_C_MA_MECH_NEGO All other mechanisms' attrivutes will be described elsewhere. 4.2. New GSS-API Function Interfaces Several new interfaces are given by which, for example, GSS-API applications may determine what features are provided by a given mechanism, what mechanisms provide what features and what compositions are legal. These new interfaces are all OPTIONAL. In order to preserve backwards compatibility with applications that do not use the new interfaces GSS_Indicate_mechs() MUST NOT indicate support for any stackable pseduo-mechanisms. GSS_Indicate_mechs() MAY indicate support for some, all or none of the available composite mechanisms; which composite mechanisms, if any, are indicated through GSS_Indicate_mechs() SHOULD be configurable. GSS_Acquire_cred() and GSS_Add_cred() MUST NOT create credentials for composite mechanisms not explicitly requested or, if no desired mechanism or mechanisms are given, for composite mechanisms not indicated by GSS_Indicate_mechs(). Applications SHOULD use GSS_Indicate_mechs_by_mech_attrs() instead of GSS_Indicate_mechs() wherever possible. Applications can use GSS_Indicate_mechs_by_mech_attrs() to determine what, if any, mechanisms provide a given set of features. GSS_Indicate_mechs_by_mech_attrs() can also be used to indicate (as in GSS_Indicate_mechs()) the set of available mechanisms of each type (concrete, mechanism negotiation pseudo-mechanism, stackable pseudo-mechanism and composite mechanisms). Applications may use GSS_Inquire_mech_attrs_for_mech() to test whether a given composite mechanism is available and the set of features that it offers. GSS_Negotiate_mechs() may be used to negotiate the use of mechanisms such that composite mechanisms need not be advertised but instead be implied by offering stackable pseudo-mechanisms. 4.2.1. GSS_Indicate_mechs_by_mech_attrs() Inputs: o desired_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_* -- OIDs that the mechanisms indicated in the mechs output parameter N. Williams [Page 12] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 -- MUST offer. o except_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_* -- OIDs that the mechanisms indicated in the mechs output parameter -- MUST NOT offer. Outputs: o major_status INTEGER, o minor_status INTEGER, o mechs SET OF OBJECT IDENTIFIER -- set of mechanisms that support -- the desired_mech_attrs but not the except_mech_attrs. Return major_status codes: o GSS_S_COMPLETE indicates success; the output mechs parameter MAY be the empty set (GSS_C_NO_OID_SET). o GSS_BAD_MECH_ATTR indicates that at least one mechanism attribute OID in desired_mech_attrs or except_mech_attrs is unknown to the implementation. o GSS_S_FAILURE indicates that the request failed for some other reason. GSS_Indicate_mechs_by_mech_attrs() returns the set of mechanism OIDs that offer at least the desired_mech_attrs but none of the except_mech_attrs. When desired_mech_attrs and except_mech_attrs are the empty set this function acts as a version of GSS_indicate_mechs() that outputs the set of all supported mechanisms of all types. By setting the desired_mechs input parameter to a set of a single GSS_C_MA_MECH* feature applications can obtain the list of all supported mechanisms of a given type (concrete, stackable, etc...). 4.2.2. GSS_Inquire_mech_attrs_for_mech() Inputs: o mech OBJECT IDENTIFIER -- mechanism OID Outputs: o major_status INTEGER, o minor_status INTEGER, o mech_attrs SET OF OBJECT IDENTIFIER -- set of mech_attrs OIDs -- (GSS_C_MA_*) N. Williams [Page 13] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Return major_status codes: o GSS_S_COMPLETE indicates success; the output mech_attrs parameter MAY be the empty set (GSS_C_NO_OID_SET). o GSS_S_BAD_MECH indicates that the mechanism named by the mech parameter does not exist or that mech is GSS_C_NO_OID and no default mechanism could be determined. o GSS_S_FAILURE indicates that the request failed for some other reason. GSS_Inquire_mech_attrs_for_mech() indicates the set of mechanism attributes supported by a given mechanism. Because the mechanism attribute sets of composite mechanisms need not be the union of their components', when called to obtain the feature set of a composite mechanism GSS_Inquire_mech_attrs_for_mech() obtains it by querying the mechanism at the top of the stack. See section 4.1. 4.2.3. GSS_Display_mech_attr() Inputs: o mech_attr OBJECT IDENTIFIER -- mechanism attribute OID Outputs: o major_status INTEGER, o minor_status INTEGER, o name OCTET STRING, -- name of mechanism attribute (e.g., -- GSS_C_MA_*) o short_desc OCTET STRING, -- a short description of the mechanism -- attribute o long_desc OCTET STRING -- a longer description of the mechanism -- attribute Return major_status codes: o GSS_S_COMPLETE indicates success. o GSS_S_BAD_MECH_ATTR indicates that the mechanism attribute referenced by the mech_attr parameter is unknown to the implementation. o GSS_S_FAILURE indicates that the request failed for some other reason. N. Williams [Page 14] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 This function can be used to obtain human-readable descriptions of GSS-API mechanism attributes. 4.2.4. GSS_Compose_oid() Inputs: o mech1 OBJECT IDENTIFIER, -- mechanism OID o mech2 OBJECT IDENTIFIER -- mechanism OID Outputs: o major_status INTEGER, o minor_status INTEGER, o composite OBJECT IDENTIFIER -- OID composition of mech1 with -- mech2 ({mech1 mech2}) Return major_status codes: o GSS_S_COMPLETE indicates success. o GSS_S_BAD_MECH indicates that mech1 is not supported. o GSS_S_FAILURE indicates that the request failed for some other reason. The minor status will be specific to mech1 and may provide further information. 4.2.5. GSS_Decompose_oid() Inputs: o input_mech OBJECT IDENTIFIER, -- mechanism OID. o mechs SET OF OBJECT IDENTIFIER -- mechanism OIDs (if -- GSS_C_NULL_OID_SET defaults to the set of stackable -- pseudo-mechanism OIDs indicated by -- GSS_Indicate_mechs_by_mech_attrs()). Outputs: o major_status INTEGER, o minor_status INTEGER, o lead_mech OBJECT IDENTIFIER, -- leading stackable pseudo- -- mechanism OID. o trail_mech OBJECT IDENTIFIER -- input_mech with lead_mech removed -- from the front. N. Williams [Page 15] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Return major_status codes: o GSS_S_COMPLETE indicates success. o GSS_S_BAD_MECH indicates that the input_mech could not be decomposed as no stackable pseudo-mechanism is available whose OID is a prefix of the input_mech. o GSS_S_FAILURE indicates that the request failed for some other reason. 4.2.6. GSS_Release_oid() The following text is adapted from the obsoleted rfc2078 [RFC2078]. Inputs: o oid OBJECT IDENTIFIER Outputs: o major_status INTEGER, o minor_status INTEGER Return major_status codes: o GSS_S_COMPLETE indicates successful completion o GSS_S_FAILURE indicates that the operation failed Allows the caller to release the storage associated with an OBJECT IDENTIFIER buffer allocated by another GSS-API call, specifically GSS_Compose_oid() and GSS_Decompose_oid(). This call's specific behavior depends on the language and programming environment within which a GSS-API implementation operates, and is therefore detailed within applicable bindings specifications; in particular, this call may be superfluous within bindings where memory management is automatic. 4.2.7. GSS_Indicate_negotiable_mechs() Inputs: o input_cred_handle CREDENTIAL HANDLE, -- credential handle to be -- used with GSS_Init_sec_context(); may be GSS_C_NO_CREDENTIAL. o peer_type_known BOOLEAN, -- indicates whether the peer is known -- to support or not supprot the stackable pseudo-mechanism -- framework. o peer_has_mech_stacking BOOLEAN -- indicates whether the peer -- supports the stackable pseudo-mechanism framework; ignore if N. Williams [Page 16] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 -- peer_type_known is FALSE. Outputs: o major_status INTEGER, o minor_status INTEGER, o offer_mechs SET OF OBJECT IDENTIFIER, -- mechanisms to offer. Return major_status codes: o GSS_S_COMPLETE indicates success. o GSS_S_NO_CREDENTIAL indicates that the caller's credentials are expired or, if input_cred_handle is GSS_C_NO_CREDENTIAL, that no credentials could be acquired for GSS_C_NO_NAME. o GSS_S_FAILURE indicates that the request failed for some other reason. This function produces a set of mechanism OIDs, optimized for space, that its caller should advertise to peers during mechanism negotiation. The output offer_mechs parameter will include all of the mechanisms for which the input_cred_handle has elements (as indicated by GSS_Inquire_cred()), but composite mechanisms will be included either implicitly or implicitly as per the following rules: - if peer_type_known is TRUE and peer_has_mech_stacking is FALSE then no composite mechanisms not indicated by GSS_Indicate_mechs() will be advertised, explictly or implicitly; - if peer_type_known is FALSE then all composite mechanisms indicated by GSS_Indicate_mechs() for which input_cred_handle has elements will be indicated in offer_mechs explicitly and all others may be indicated in offer_mechs implicitly, by including their component stackable pseduo-mechanism OIDs (see below); - if peer_type_known is TRUE and peer_has_mech_stacking is TRUE composite mechanisms will generally not be advertised explicitly, but will be advertised implicitly, by including their component stackable pseduo-mechanism OIDs (see below); no composite mechanisms will be advertised explicitly - if the input_cred_handle does not have elements for all of the possible composite mechanisms that could be constructed from the its elements' decomposed mechanisms, then all composite mechanisms for which the input_cred_handle does have elements will be advertised explicitly in offer_mechs. 4.2.8. GSS_Negotiate_mechs() N. Williams [Page 17] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Inputs: o input_credential_handle CREDENTIAL HANDLE, -- mechanisms offered -- by the caller. o peer_mechs SET OF OBJECT IDENTIFIER -- mechanisms offered by -- the caller's peer. Outputs: o major_status INTEGER, o minor_status INTEGER, o mechs SET OF OBJECT IDENTIFIER -- mechanisms common to the -- caller's credentials and the caller's peer. Return major_status codes: o GSS_S_COMPLETE indicates success; the output mechs parameter MAY be the empty set (GSS_C_NO_OID_SET). o GSS_S_NO_CREDENTIAL indicates that the caller's credentials are expired or, if input_cred_handle is GSS_C_NO_CREDENTIAL, that no credentials could be acquired for GSS_C_NO_NAME. o GSS_S_FAILURE indicates that the request failed for some other reason. This function matches the mechanisms for which the caller has credentials with the mechanisms offered by the caller's peer and returns the set of mechanisms in common to both, accounting for any composite mechanisms offered by the peer implicitly. 4.3. New Major Status Values A single new major status code is added for GSS_Display_mech_attr(): GSS_S_BAD_MECH_ATTR roughly corresponding to GSS_S_BAD_MECH, but applicable to mechanism attribute OIDs, rather than to mechanism OIDs. For the C-bindings GSS_S_BAD_MECH_ATTR shall have a routine error number of 19 (this is shifted to the left by GSS_C_ROUTINE_ERROR_OFFSET). 4.4. C-Bindings #define GSS_S_BAD_MECH_ATTR (19ul << GSS_C_ROUTINE_ERROR_OFFSET) OM_uint32 gss_inquire_mechs_for_mech_attrs( N. Williams [Page 18] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 OM_uint32 *minor_status, const gss_OID_set desired_mech_attrs, gss_OID_set *mechs); OM_uint32 gss_inquire_mech_attrs_for_mech( OM_uint32 *minor_status, const gss_OID mech, gss_OID_set *mech_attrs); OM_uint32 gss_display_mech_attr( OM_uint32 *minor_status, const gss_OID mech_attr, gss_buffer_t name, gss_buffer_t short_desc, gss_buffer_t long_desc); OM_uint32 gss_compose_oid( OM_uint32 *minor_status, const gss_OID mech1, const gss_OID mech2, gss_OID *composite); OM_uint32 gss_decompose_oid( OM_uint32 *minor_status, const gss_OID input_mech, const gss_OID_set mechs, gss_OID *lead_mech, gss_OID *trail_mech); OM_uint32 gss_release_oid( OM_uint32 *minor_status, gss_OID *oid); OM_uint32 GSS_Indicate_negotiable_mechs( OM_uint32 *minor_status, const gss_cred_id_t input_cred_handle, OM_uint32 peer_type_known, OM_uint32 peer_has_mech_stacking, gss_OID_set *offer_mechs); OM_uint32 gss_negotiate_mechs( OM_uint32 *minor_status, const gss_cred_id_t input_cred_handle, const gss_OID_set peer_mechs, const gss_OID_set *mechs); 5. Negotiation of Composite Mechanisms Where GSS-API implementations do not support the stackable mechanism framework interfaces applications may only negotiate explicitly from a set of concrete and composite mechanism OIDs as indicated by GSS_Indicate_mechs() and for which suitable credentials are available. GSS_Indicate_mechs(), as described in section 3.4, MUST N. Williams [Page 19] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 NOT indicate support for individual stackable pseudo-mechanisms, so there will not be any composite mechanisms implied but not explicitly offered in the mechanism negotiation. Applications that support the stackable mechanism framework SHOULD use GSS_Indicate_negotiable_mechs() to construct the set of mechanism OIDs to offer to their peers. GSS_Indicate_negotiable_mechs() optimizes for bandwidth consumption by using decomposed OIDs instead of composed OIDs, where possible. See section 4.2.7. Peers that support the stackable mechanism framework interfaces SHOULD use GSS_Negotiate_mechs() to select a mechanism as that routine accounts for composite mechanisms implicit in the mechanism offers. 5.1. Negotiation of Composite Mechanisms Through SPNEGO SPNEGO applications MUST advertise either the set of mechanism OIDs for which they have suitable credentials or the set of mechanism OIDs produced by calling GSS_Indicate_negotiable_mechs() with the available credentials and the peer_type_known parameter as FALSE. 6. Requirements for Mechanism Designers Stackable pseudo-mechanisms specifications MUST: - list the set of GSS-API mechanism attributes associated with them - list their initial mechanism composition rules - specify a mechanism for updating their mechanism composition rules All other mechanism specifications MUST: - list the set of GSS-API mechanism attributes associated with them 7. IANA Considerations The namsepace of programming language symbols with names beginning with GSS_C_MA_* is reserved for allocation by the IANA. Allocation of arcs in the namespace of OIDs relative to the base mechanism attribute OID specified in section 4 is reserved to the IANA. Allocation of arcs in the namespace of OIDs relative to the base stackable pseduo-mechanism OID specified in section 3 is reserved to the IANA. 8. Security considerations Some composite mechanisms may well not be secure. The mechanism composition rules of pseudo-mechanisms (including the default N. Williams [Page 20] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 composition rule given in section 3 for unknown mechanism attributes) should be used to prevent the use of unsafe composite mechanisms. Designers of pseudo-mechanisms should study the possible combinations of their mechanisms with others and design mechanism composition rules accordingly. Similarly, pseudo-mechanism designers MUST specify, and implementors MUST implement, composite mechanism attribute set determination rules appropriate to the subject pseduo-mechanism, as described in section 4.1.1. Failure to do so may lead to inappropriate composite mechanisms being deemed permissible by programmatic application of flawed mechanism composition rules or to by their application with incorrect mechanism attribute sets. 9. References 9.1. Informative references [?] ... 9.2. Normative references [RFC2026] S. Bradner, RFC2026: "The Internet Standard Process - Revision 3," October 1996, Obsoletes - RFC 1602, Status: Best Current Practice. [RFC2119] S. Bradner, RFC2119 (BCP14): "Key words for use in RFCs to Indicate Requirement Levels," March 1997, Status: Best Current Practice. [RFC2743] J. Linn, RFC2743: "Generic Security Service Application Program Interface Version 2, Update 1," January 2000, Status: Proposed Standard. [RFC2744] J. Wray, RFC2744: "Generic Security Service API Version 2 : C-bindings," January 2000, Status: Proposed Standard. [MUST add references to LIPKEY, SPKM, the Kerberos V mechanism, SPNEGO, CCM, etc...] ... 10. Author's Address Nicolas Williams Sun Microsystems 5300 Riata Trace Ct Austin, TX 78727 N. Williams [Page 21] DRAFT Stackable GSS-API Pseudo-Mechs Expires November 2004 Email: nicolas.williams@sun.com Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. N. Williams [Page 22]