Sun Microsystems

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Security NETWORK WORKING GROUP Internet-Draft This document introduces new application programming interfaces (APIs) to the Generic Security Services API (GSS-API) for extended mechanism attribute inquiry. These interfaces are primarily intended to reduce instances of hardcoding of mechanism identifiers in GSS applications. These interfaces include mechanism attributes and attribute sets, a function for inquiring the attributes of a mechanism, a function for indicating mechanisms that possess given attributes, and a function for displaying mechanism attributes.

GSS-API mechanisms have a number of properties that may be of interest to applications. The lack of APIs for inquiring about available mechanisms' properties has meant that many GSS-API applications must hardcode mechanism Object Identifiers (OIDs). Ongoing work may result in a variety of new GSS-API mechanisms. Applications should not have to hardcode their OIDs. For example, the Secure Shell version 2 (SSHv2) protocol supports the use of GSS-API mechanisms for authentication but explicitly prohibits the use of Simple and Protected GSS-API Negotiation (SPNEGO) . Future mechanisms that negotiate mechanisms would have to be forbidden as well, but there is no way to implement applications that inquire what mechanisms are available and then programmatically exclude mechanisms "like SPNEGO".

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 .

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 without having to hardcode mechanism OIDs. describes the mechanism attributes concept. Sections , , and 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()

An abstraction for the features provided by mechanisms and pseudo-mechanisms is needed in order to facilitate the programmatic selection of mechanisms. Pseudo-mechanisms are mechanisms that make reference to other mechanisms in order to provide their services. For example, SPNEGO is a pseudo-mechanism, for without other mechanisms SPNEGO is useless. Two data types are needed: one for individual mechanism attributes and one for mechanism attribute sets. To simplify the mechanism attribute 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: <1.3.6.1.5.5.13> Each mechanism has a set of mechanism attributes that it supports as described in its specification.

Mech Attr Name OID Arc Arc Name GSS_C_MA_MECH_CONCRETE (1) concrete-mech GSS_C_MA_MECH_PSEUDO (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_FRAMED (9) initial-is-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_MIC (19) mic GSS_C_MA_WRAP (20) wrap GSS_C_MA_PROT_READY (21) prot-ready GSS_C_MA_REPLAY_DET (22) replay-detection GSS_C_MA_OOS_DET (23) oos-detection GSS_C_MA_CBINDINGS (24) channel-bindings GSS_C_MA_PFS (25) pfs GSS_C_MA_COMPRESS (26) compress GSS_C_MA_CTX_TRANS (27) context-transfer <reserved> (28...) 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_PSEUDO Indicates that a mech is a pseudo-mechanism. GSS_C_MA_MECH_COMPOSITE Indicates that a mech is a composite of other mechanisms. This is reserved for a specification of "stackable" pseudo-mechanisms. 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 it is also known not to be the OID of any GSS-API mechanism (or of 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_FRAMED Indicates that the given mechanism's initial context tokens are properly framed as per Section 3.1 of . 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. "Initial authentication" refers to the use of passwords, or keys stored on tokens, for authentication. Whether a mechanism supports initial authentication may depend on IETF consensus (see Security Considerations). GSS_C_MA_AUTH_TARG_INIT Indicates support for initial authentication of acceptor to initiator. GSS_C_MA_AUTH_INIT_ANON Indicates support for GSS_C_NT_ANONYMOUS as an initiator principal name. GSS_C_MA_AUTH_TARG_ANON Indicates support for GSS_C_NT_ANONYMOUS as a target principal name. 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_MIC Indicates support for Message Integrity Code (MIC) tokens. GSS_C_MA_WRAP Indicates support for WRAP tokens. GSS_C_MA_PROT_READY Indicates support for per-message protection prior to full context establishment. 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_PFS Indicates support for Perfect Forward Security. GSS_C_MA_COMPRESS Indicates support for compression of data inputs to GSS_Wrap(). GSS_C_MA_CTX_TRANS Indicates support for security context export/import.

The Kerberos V mechanism provides the following mechanism attributes: GSS_C_MA_MECH_CONCRETE GSS_C_MA_ITOK_FRAMED 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_MIC GSS_C_MA_WRAP GSS_C_MA_PROT_READY GSS_C_MA_REPLAY_DET GSS_C_MA_OOS_DET GSS_C_MA_CBINDINGS GSS_C_MA_CTX_TRANS (some implementations, using implementation-specific exported context token formats) The Kerberos V mechanism also has a deprecated OID that has the same mechanism attributes as above as well as GSS_C_MA_DEPRECATED. The mechanism attributes of the Simple Public-Key GSS-API Mechanism (SPKM) family of mechanisms will be provided in a separate document, as SPKM is currently being reviewed for possibly significant changes due to problems in its specifications. The Low Infrastructure Public Key (LIPKEY) mechanism offers the following attributes: GSS_C_MA_MECH_CONCRETE GSS_C_MA_ITOK_FRAMED 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 GSS_C_MA_CTX_TRANS (some implementations, using implementation-specific exported context token formats) (LIPKEY should also provide GSS_C_MA_CBINDINGS, but SPKM-3 requires clarifications on this point.) The SPNEGO mechanism provides the following attributes: GSS_C_MA_MECH_NEGO GSS_C_MA_ITOK_FRAMED All other mechanisms' attributes will be described elsewhere.

Several new interfaces are given by which, for example, GSS-API applications may determine what features are provided by a given mechanism and what mechanisms provide what features. These new interfaces are all OPTIONAL. Applications should use GSS_Indicate_mechs_by_attrs() instead of GSS_Indicate_mechs() wherever possible. Applications can use GSS_Indicate_mechs_by_attrs() to determine what, if any, mechanisms provide a given set of features. GSS_Indicate_mechs_by_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, etc.).

Mechanism attributes may be added at any time. Not only may attributes be added to the list of known mechanism attributes at any time, but the set of mechanism attributes supported by a mechanism can be changed at any time. For example, new attributes might be added to reflect whether a mechanism's initiator must contact an online infrastructure and/or whether the acceptor must do so. In this example, the Kerberos V mechanism would gain a new attribute even though the mechanism itself is not modified. Applications making use of attributes not defined herein would then have no way of knowing whether a GSS-API implementation and its mechanisms know about new mechanism attributes. To address this problem, GSS_Indicate_mechs_by_attrs() and GSS_Inquire_attrs_for_mech() support a notion of critical mechanism attributes. Applications can search for mechanisms that understand mechanism attributes that are critical to the application, and the application may ask what mechanism attributes are understood by a given mechanism.

Inputs: desired_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_* OIDs that the mechanisms indicated in the mechs output parameter MUST offer. 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. critical_mech_attrs SET OF OBJECT IDENTIFIER -- set of GSS_C_MA_* OIDs that the mechanisms indicated in the mechs output parameter MUST understand (i.e., mechs must know whether critical attributes are or are not supported). Outputs: major_status INTEGER minor_status INTEGER mechs SET OF OBJECT IDENTIFIER -- set of mechanisms that support the given desired_mech_attrs but not the except_mech_attrs, and all of which understand the given critical_mech_attrs (the caller must release this output with GSS_Release_oid_set()). Return major_status codes: GSS_S_COMPLETE indicates success; the output mechs parameter MAY be the empty set (GSS_C_NO_OID_SET). GSS_S_FAILURE indicates that the request failed for some other reason. GSS_Indicate_mechs_by_attrs() returns the set of OIDs corresponding to mechanisms that offer at least the desired_mech_attrs but none of the except_mech_attrs, and that understand all of the attributes listed in critical_mech_attrs. When all three sets of OID input parameters are the empty set, this function acts as a version of GSS_indicate_mechs() that outputs the set of all supported mechanisms.

Inputs: mech OBJECT IDENTIFIER -- mechanism OID Outputs: major_status INTEGER minor_status INTEGER mech_attrs SET OF OBJECT IDENTIFIER -- set of mech_attrs OIDs (GSS_C_MA_*) supported by the mechanism (the caller must release this output with GSS_Release_oid_set()). known_mech_attrs SET OF OBJECT IDENTIFIER -- set of mech_attrs OIDs known to the mechanism implementation (the caller must release this output with GSS_Release_oid_set()). Return major_status codes: GSS_S_COMPLETE indicates success; the output mech_attrs parameter MAY be the empty set (GSS_C_NO_OID_SET). GSS_S_BAD_MECH indicates that the mechanism named by the mech parameter does not exist or that the mech is GSS_C_NO_OID and no default mechanism could be determined. GSS_S_FAILURE indicates that the request failed for some other reason. GSS_Inquire_attrs_for_mech() indicates the set of mechanism attributes supported by a given mechanism.

Inputs: mech_attr OBJECT IDENTIFIER -- mechanism attribute OID Outputs: major_status INTEGER minor_status INTEGER name OCTET STRING, -- name of mechanism attribute (e.g., GSS_C_MA_*). short_desc OCTET STRING, -- a short description of the mechanism attribute (the caller must release this output with GSS_Release_buffer()). long_desc OCTET STRING -- a longer description of the mechanism attribute (the caller must release this output with GSS_Release_buffer()). Return major_status codes: GSS_S_COMPLETE indicates success. GSS_S_BAD_MECH_ATTR indicates that the mechanism attribute referenced by the mech_attr parameter is unknown to the implementation. GSS_S_FAILURE indicates that the request failed for some other reason. This function can be used to obtain human-readable descriptions of GSS-API mechanism attributes.

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 of the GSS-API , 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).

Note that there is a bug in the C bindings of the GSS-APIv2u1 in that the C 'const' attribute is applied to types that are pointer typedefs. This is a bug because it declares that the pointer argument is 'const' rather than that the object pointed by it is const. To avoid this error, we hereby define new typedefs, which include const properly:

typedef const gss_buffer_desc * gss_const_buffer_t; typedef const struct gss_channel_bindings_struct * gss_const_channel_bindings_t; typedef const <platform-specific> gss_const_ctx_id_t; typedef const <platform-specific> gss_const_cred_id_t; typedef const <platform-specific> gss_const_name_t; typedef const gss_OID_desc * gss_const_OID; typedef const gss_OID_set_desc * gss_const_OID_set;

Note that only gss_const_OID and gss_const_OID_set are used below. We include the other const typedefs for convenience since the C bindings of the GSS-API do use const with pointer typedefs when it should often instead use the above typedefs instead.

#define GSS_S_BAD_MECH_ATTR (19ul << GSS_C_ROUTINE_ERROR_OFFSET) OM_uint32 gss_indicate_mechs_by_attrs( OM_uint32 *minor_status, gss_const_OID_set desired_mech_attrs, gss_const_OID_set except_mech_attrs, gss_const_OID_set critical_mech_attrs, gss_OID_set *mechs); OM_uint32 gss_inquire_attrs_for_mech( OM_uint32 *minor_status, gss_const_OID mech, gss_OID_set *mech_attrs, gss_OID_set *known_mech_attrs); OM_uint32 gss_display_mech_attr( OM_uint32 *minor_status, gss_const_OID mech_attr, gss_buffer_t name, gss_buffer_t short_desc, gss_buffer_t long_desc);

Note that output buffers must be released via gss_release_buffer(). Output OID sets must be released via gss_release_oid_set().

All future GSS-API mechanism specifications MUST: list the set of GSS-API mechanism attributes associated with them.

The namespace of programming-language symbols with names beginning with GSS_C_MA_* is reserved for allocation by IETF Consensus. IANA allocated a base OID, as an arc of 1.3.6.1.5.5, for the set of GSS_C_MA_* described herein, and registered all of the GSS_C_MA_* values described in .

This document specifies extensions to a security-related API. It imposes new requirements on future GSS-API mechanisms, and the specifications of future protocols that use the GSS-API should make reference to this document where applicable. The ability to inquire about specific properties of mechanisms should improve security. The semantics of each mechanism attribute may include a security component. Application developers must understand that mechanism attributes may be added at any time -- both to the set of known mechanism attributes as well as to existing mechanisms' sets of supported mechanism attributes. Therefore, application developers using the APIs described herein must understand what mechanism attributes their applications depend critically on, and must use the mechanism attribute criticality features of these APIs.