RFC 2744
Generic Security Service API Version 2 : C-bindings
Network Working Group J. Wray Request for Comments: 2744 Iris Associates Obsoletes: 1509 January 2000 Category: Standards Track Generic Security Service API Version 2 : C-bindings Status 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. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved.Abstract
This document specifies C language bindings for Version 2, Update 1 of the Generic Security Service Application Program Interface (GSS- API), which is described at a language-independent conceptual level in RFC-2743 [GSSAPI]. It obsoletes RFC-1509, making specific incremental changes in response to implementation experience and liaison requests. It is intended, therefore, that this memo or a successor version thereof will become the basis for subsequent progression of the GSS-API specification on the standards track. The Generic Security Service Application Programming Interface provides security services to its callers, and is intended for implementation atop a variety of underlying cryptographic mechanisms. Typically, GSS-API callers will be application protocols into which security enhancements are integrated through invocation of services provided by the GSS-API. The GSS-API allows a caller application to authenticate a principal identity associated with a peer application, to delegate rights to a peer, and to apply security services such as confidentiality and integrity on a per-message basis.
1. Introduction
The Generic Security Service Application Programming Interface [GSSAPI] provides security services to calling applications. It allows a communicating application to authenticate the user associated with another application, to delegate rights to another application, and to apply security services such as confidentiality and integrity on a per-message basis. There are four stages to using the GSS-API: a) The application acquires a set of credentials with which it may prove its identity to other processes. The application's credentials vouch for its global identity, which may or may not be related to any local username under which it may be running. b) A pair of communicating applications establish a joint security context using their credentials. The security context is a pair of GSS-API data structures that contain shared state information, which is required in order that per-message security services may be provided. Examples of state that might be shared between applications as part of a security context are cryptographic keys, and message sequence numbers. As part of the establishment of a security context, the context initiator is authenticated to the responder, and may require that the responder is authenticated in turn. The initiator may optionally give the responder the right to initiate further security contexts, acting as an agent or delegate of the initiator. This transfer of rights is termed delegation, and is achieved by creating a set of credentials, similar to those used by the initiating application, but which may be used by the responder. To establish and maintain the shared information that makes up the security context, certain GSS-API calls will return a token data structure, which is an opaque data type that may contain cryptographically protected data. The caller of such a GSS-API routine is responsible for transferring the token to the peer application, encapsulated if necessary in an application- application protocol. On receipt of such a token, the peer application should pass it to a corresponding GSS-API routine which will decode the token and extract the information, updating the security context state information accordingly.
c) Per-message services are invoked to apply either:
integrity and data origin authentication, or confidentiality,
integrity and data origin authentication to application data,
which are treated by GSS-API as arbitrary octet-strings. An
application transmitting a message that it wishes to protect will
call the appropriate GSS-API routine (gss_get_mic or gss_wrap) to
apply protection, specifying the appropriate security context, and
send the resulting token to the receiving application. The
receiver will pass the received token (and, in the case of data
protected by gss_get_mic, the accompanying message-data) to the
corresponding decoding routine (gss_verify_mic or gss_unwrap) to
remove the protection and validate the data.
d) At the completion of a communications session (which may extend
across several transport connections), each application calls a
GSS-API routine to delete the security context. Multiple contexts
may also be used (either successively or simultaneously) within a
single communications association, at the option of the
applications.
2. GSS-API Routines
This section lists the routines that make up the GSS-API, and
offers a brief description of the purpose of each routine.
Detailed descriptions of each routine are listed in alphabetical
order in section 5.
Table 2-1 GSS-API Credential-management Routines
Routine Section Function
------- ------- --------
gss_acquire_cred 5.2 Assume a global identity; Obtain
a GSS-API credential handle for
pre-existing credentials.
gss_add_cred 5.3 Construct credentials
incrementally
gss_inquire_cred 5.21 Obtain information about a
credential
gss_inquire_cred_by_mech 5.22 Obtain per-mechanism information
about a credential.
gss_release_cred 5.27 Discard a credential handle.
Table 2-2 GSS-API Context-Level Routines Routine Section Function ------- ------- -------- gss_init_sec_context 5.19 Initiate a security context with a peer application gss_accept_sec_context 5.1 Accept a security context initiated by a peer application gss_delete_sec_context 5.9 Discard a security context gss_process_context_token 5.25 Process a token on a security context from a peer application gss_context_time 5.7 Determine for how long a context will remain valid gss_inquire_context 5.20 Obtain information about a security context gss_wrap_size_limit 5.34 Determine token-size limit for gss_wrap on a context gss_export_sec_context 5.14 Transfer a security context to another process gss_import_sec_context 5.17 Import a transferred context Table 2-3 GSS-API Per-message Routines Routine Section Function ------- ------- -------- gss_get_mic 5.15 Calculate a cryptographic message integrity code (MIC) for a message; integrity service gss_verify_mic 5.32 Check a MIC against a message; verify integrity of a received message gss_wrap 5.33 Attach a MIC to a message, and optionally encrypt the message content; confidentiality service gss_unwrap 5.31 Verify a message with attached MIC, and decrypt message content if necessary.
Table 2-4 GSS-API Name manipulation Routines Routine Section Function ------- ------- -------- gss_import_name 5.16 Convert a contiguous string name to internal-form gss_display_name 5.10 Convert internal-form name to text gss_compare_name 5.6 Compare two internal-form names gss_release_name 5.28 Discard an internal-form name gss_inquire_names_for_mech 5.24 List the name-types supported by the specified mechanism gss_inquire_mechs_for_name 5.23 List mechanisms that support the specified name-type gss_canonicalize_name 5.5 Convert an internal name to an MN gss_export_name 5.13 Convert an MN to export form gss_duplicate_name 5.12 Create a copy of an internal name Table 2-5 GSS-API Miscellaneous Routines Routine Section Function ------- ------- -------- gss_add_oid_set_member 5.4 Add an object identifier to a set gss_display_status 5.11 Convert a GSS-API status code to text gss_indicate_mechs 5.18 Determine available underlying authentication mechanisms gss_release_buffer 5.26 Discard a buffer gss_release_oid_set 5.29 Discard a set of object identifiers gss_create_empty_oid_set 5.8 Create a set containing no object identifiers gss_test_oid_set_member 5.30 Determines whether an object identifier is a member of a set. Individual GSS-API implementations may augment these routines by providing additional mechanism-specific routines if required functionality is not available from the generic forms. Applications are encouraged to use the generic routines wherever possible on portability grounds.
3. Data Types and Calling Conventions
The following conventions are used by the GSS-API C-language bindings:3.1. Integer types
GSS-API uses the following integer data type: OM_uint32 32-bit unsigned integer Where guaranteed minimum bit-count is important, this portable data type is used by the GSS-API routine definitions. Individual GSS-API implementations will include appropriate typedef definitions to map this type onto a built-in data type. If the platform supports the X/Open xom.h header file, the OM_uint32 definition contained therein should be used; the GSS-API header file in Appendix A contains logic that will detect the prior inclusion of xom.h, and will not attempt to re-declare OM_uint32. If the X/Open header file is not available on the platform, the GSS-API implementation should use the smallest natural unsigned integer type that provides at least 32 bits of precision.3.2. String and similar data
Many of the GSS-API routines take arguments and return values that describe contiguous octet-strings. All such data is passed between the GSS-API and the caller using the gss_buffer_t data type. This data type is a pointer to a buffer descriptor, which consists of a length field that contains the total number of bytes in the datum, and a value field which contains a pointer to the actual datum: typedef struct gss_buffer_desc_struct { size_t length; void *value; } gss_buffer_desc, *gss_buffer_t; Storage for data returned to the application by a GSS-API routine using the gss_buffer_t conventions is allocated by the GSS-API routine. The application may free this storage by invoking the gss_release_buffer routine. Allocation of the gss_buffer_desc object is always the responsibility of the application; unused gss_buffer_desc objects may be initialized to the value GSS_C_EMPTY_BUFFER.
3.2.1. Opaque data types
Certain multiple-word data items are considered opaque data types at the GSS-API, because their internal structure has no significance either to the GSS-API or to the caller. Examples of such opaque data types are the input_token parameter to gss_init_sec_context (which is opaque to the caller), and the input_message parameter to gss_wrap (which is opaque to the GSS-API). Opaque data is passed between the GSS-API and the application using the gss_buffer_t datatype.3.2.2. Character strings
Certain multiple-word data items may be regarded as simple ISO Latin-1 character strings. Examples are the printable strings passed to gss_import_name via the input_name_buffer parameter. Some GSS-API routines also return character strings. All such character strings are passed between the application and the GSS-API implementation using the gss_buffer_t datatype, which is a pointer to a gss_buffer_desc object. When a gss_buffer_desc object describes a printable string, the length field of the gss_buffer_desc should only count printable characters within the string. In particular, a trailing NUL character should NOT be included in the length count, nor should either the GSS-API implementation or the application assume the presence of an uncounted trailing NUL.3.3. Object Identifiers
Certain GSS-API procedures take parameters of the type gss_OID, or Object identifier. This is a type containing ISO-defined tree- structured values, and is used by the GSS-API caller to select an underlying security mechanism and to specify namespaces. A value of type gss_OID has the following structure: typedef struct gss_OID_desc_struct { OM_uint32 length; void *elements; } gss_OID_desc, *gss_OID; The elements field of this structure points to the first byte of an octet string containing the ASN.1 BER encoding of the value portion of the normal BER TLV encoding of the gss_OID. The length field contains the number of bytes in this value. For example, the gss_OID value corresponding to {iso(1) identified-organization(3) icd- ecma(12) member-company(2) dec(1011) cryptoAlgorithms(7) DASS(5)}, meaning the DASS X.509 authentication mechanism, has a length field of 7 and an elements field pointing to seven octets containing the
following octal values: 53,14,2,207,163,7,5. GSS-API implementations should provide constant gss_OID values to allow applications to request any supported mechanism, although applications are encouraged on portability grounds to accept the default mechanism. gss_OID values should also be provided to allow applications to specify particular name types (see section 3.10). Applications should treat gss_OID_desc values returned by GSS-API routines as read-only. In particular, the application should not attempt to deallocate them with free(). The gss_OID_desc datatype is equivalent to the X/Open OM_object_identifier datatype[XOM].3.4. Object Identifier Sets
Certain GSS-API procedures take parameters of the type gss_OID_set. This type represents one or more object identifiers (section 2.3). A gss_OID_set object has the following structure: typedef struct gss_OID_set_desc_struct { size_t count; gss_OID elements; } gss_OID_set_desc, *gss_OID_set; The count field contains the number of OIDs within the set. The elements field is a pointer to an array of gss_OID_desc objects, each of which describes a single OID. gss_OID_set values are used to name the available mechanisms supported by the GSS-API, to request the use of specific mechanisms, and to indicate which mechanisms a given credential supports. All OID sets returned to the application by GSS-API are dynamic objects (the gss_OID_set_desc, the "elements" array of the set, and the "elements" array of each member OID are all dynamically allocated), and this storage must be deallocated by the application using the gss_release_oid_set() routine.3.5. Credentials
A credential handle is a caller-opaque atomic datum that identifies a GSS-API credential data structure. It is represented by the caller- opaque type gss_cred_id_t, which should be implemented as a pointer or arithmetic type. If a pointer implementation is chosen, care must be taken to ensure that two gss_cred_id_t values may be compared with the == operator. GSS-API credentials can contain mechanism-specific principal authentication data for multiple mechanisms. A GSS-API credential is composed of a set of credential-elements, each of which is applicable to a single mechanism. A credential may contain at most one
credential-element for each supported mechanism. A credential-element
identifies the data needed by a single mechanism to authenticate a
single principal, and conceptually contains two credential-references
that describe the actual mechanism-specific authentication data, one
to be used by GSS-API for initiating contexts, and one to be used
for accepting contexts. For mechanisms that do not distinguish
between acceptor and initiator credentials, both references would
point to the same underlying mechanism-specific authentication data.
Credentials describe a set of mechanism-specific principals, and give
their holder the ability to act as any of those principals. All
principal identities asserted by a single GSS-API credential should
belong to the same entity, although enforcement of this property is
an implementation-specific matter. The GSS-API does not make the
actual credentials available to applications; instead a credential
handle is used to identify a particular credential, held internally
by GSS-API. The combination of GSS-API credential handle and
mechanism identifies the principal whose identity will be asserted by
the credential when used with that mechanism.
The gss_init_sec_context and gss_accept_sec_context routines allow
the value GSS_C_NO_CREDENTIAL to be specified as their credential
handle parameter. This special credential-handle indicates a desire
by the application to act as a default principal. While individual
GSS-API implementations are free to determine such default behavior
as appropriate to the mechanism, the following default behavior by
these routines is recommended for portability:
gss_init_sec_context
1) If there is only a single principal capable of initiating
security contexts for the chosen mechanism that the application
is authorized to act on behalf of, then that principal shall be
used, otherwise
2) If the platform maintains a concept of a default network-
identity for the chosen mechanism, and if the application is
authorized to act on behalf of that identity for the purpose of
initiating security contexts, then the principal corresponding
to that identity shall be used, otherwise
3) If the platform maintains a concept of a default local
identity, and provides a means to map local identities into
network-identities for the chosen mechanism, and if the
application is authorized to act on behalf of the network-
identity image of the default local identity for the purpose of
initiating security contexts using the chosen mechanism, then
the principal corresponding to that identity shall be used,
otherwise
4) A user-configurable default identity should be used.
gss_accept_sec_context
1) If there is only a single authorized principal identity capable
of accepting security contexts for the chosen mechanism, then
that principal shall be used, otherwise
2) If the mechanism can determine the identity of the target
principal by examining the context-establishment token, and if
the accepting application is authorized to act as that
principal for the purpose of accepting security contexts using
the chosen mechanism, then that principal identity shall be
used, otherwise
3) If the mechanism supports context acceptance by any principal,
and if mutual authentication was not requested, any principal
that the application is authorized to accept security contexts
under using the chosen mechanism may be used, otherwise
4)A user-configurable default identity shall be used.
The purpose of the above rules is to allow security contexts to be
established by both initiator and acceptor using the default behavior
wherever possible. Applications requesting default behavior are
likely to be more portable across mechanisms and platforms than ones
that use gss_acquire_cred to request a specific identity.
3.6. Contexts
The gss_ctx_id_t data type contains a caller-opaque atomic value that
identifies one end of a GSS-API security context. It should be
implemented as a pointer or arithmetic type. If a pointer type is
chosen, care should be taken to ensure that two gss_ctx_id_t values
may be compared with the == operator.
The security context holds state information about each end of a peer
communication, including cryptographic state information.
3.7. Authentication tokens
A token is a caller-opaque type that GSS-API uses to maintain synchronization between the context data structures at each end of a GSS-API security context. The token is a cryptographically protected octet-string, generated by the underlying mechanism at one end of a GSS-API security context for use by the peer mechanism at the other end. Encapsulation (if required) and transfer of the token are the responsibility of the peer applications. A token is passed between the GSS-API and the application using the gss_buffer_t conventions.3.8. Interprocess tokens
Certain GSS-API routines are intended to transfer data between processes in multi-process programs. These routines use a caller- opaque octet-string, generated by the GSS-API in one process for use by the GSS-API in another process. The calling application is responsible for transferring such tokens between processes in an OS- specific manner. Note that, while GSS-API implementors are encouraged to avoid placing sensitive information within interprocess tokens, or to cryptographically protect them, many implementations will be unable to avoid placing key material or other sensitive data within them. It is the application's responsibility to ensure that interprocess tokens are protected in transit, and transferred only to processes that are trustworthy. An interprocess token is passed between the GSS-API and the application using the gss_buffer_t conventions.3.9. Status values
Every GSS-API routine returns two distinct values to report status information to the caller: GSS status codes and Mechanism status codes.3.9.1. GSS status codes
GSS-API routines return GSS status codes as their OM_uint32 function value. These codes indicate errors that are independent of the underlying mechanism(s) used to provide the security service. The errors that can be indicated via a GSS status code are either generic API routine errors (errors that are defined in the GSS-API specification) or calling errors (errors that are specific to these language bindings). A GSS status code can indicate a single fatal generic API error from the routine and a single calling error. In addition, supplementary status information may be indicated via the setting of bits in the supplementary info field of a GSS status code.
These errors are encoded into the 32-bit GSS status code as follows:
MSB LSB
|------------------------------------------------------------|
| Calling Error | Routine Error | Supplementary Info |
|------------------------------------------------------------|
Bit 31 24 23 16 15 0
Hence if a GSS-API routine returns a GSS status code whose upper 16
bits contain a non-zero value, the call failed. If the calling error
field is non-zero, the invoking application's call of the routine was
erroneous. Calling errors are defined in table 5-1. If the routine
error field is non-zero, the routine failed for one of the routine-
specific reasons listed below in table 5-2. Whether or not the upper
16 bits indicate a failure or a success, the routine may indicate
additional information by setting bits in the supplementary info
field of the status code. The meaning of individual bits is listed
below in table 5-3.
Table 3-1 Calling Errors
Name Value in field Meaning
---- -------------- -------
GSS_S_CALL_INACCESSIBLE_READ 1 A required input parameter
could not be read
GSS_S_CALL_INACCESSIBLE_WRITE 2 A required output parameter
could not be written.
GSS_S_CALL_BAD_STRUCTURE 3 A parameter was malformed
Table 3-2 Routine Errors
Name Value in field Meaning
---- -------------- -------
GSS_S_BAD_MECH 1 An unsupported mechanism
was requested
GSS_S_BAD_NAME 2 An invalid name was
supplied
GSS_S_BAD_NAMETYPE 3 A supplied name was of an
unsupported type
GSS_S_BAD_BINDINGS 4 Incorrect channel bindings
were supplied
GSS_S_BAD_STATUS 5 An invalid status code was
supplied
GSS_S_BAD_MIC GSS_S_BAD_SIG 6 A token had an invalid MIC
GSS_S_NO_CRED 7 No credentials were
supplied, or the
credentials were
unavailable or
inaccessible.
GSS_S_NO_CONTEXT 8 No context has been
established
GSS_S_DEFECTIVE_TOKEN 9 A token was invalid
GSS_S_DEFECTIVE_CREDENTIAL 10 A credential was invalid
GSS_S_CREDENTIALS_EXPIRED 11 The referenced credentials
have expired
GSS_S_CONTEXT_EXPIRED 12 The context has expired
GSS_S_FAILURE 13 Miscellaneous failure (see
text)
GSS_S_BAD_QOP 14 The quality-of-protection
requested could not be
provided
GSS_S_UNAUTHORIZED 15 The operation is forbidden
by local security policy
GSS_S_UNAVAILABLE 16 The operation or option is
unavailable
GSS_S_DUPLICATE_ELEMENT 17 The requested credential
element already exists
GSS_S_NAME_NOT_MN 18 The provided name was not a
mechanism name
Table 3-3 Supplementary Status Bits
Name Bit Number Meaning
---- ---------- -------
GSS_S_CONTINUE_NEEDED 0 (LSB) Returned only by
gss_init_sec_context or
gss_accept_sec_context. The
routine must be called again
to complete its function.
See routine documentation for
detailed description
GSS_S_DUPLICATE_TOKEN 1 The token was a duplicate of
an earlier token
GSS_S_OLD_TOKEN 2 The token's validity period
has expired
GSS_S_UNSEQ_TOKEN 3 A later token has already been
processed
GSS_S_GAP_TOKEN 4 An expected per-message token
was not received
The routine documentation also uses the name GSS_S_COMPLETE, which is
a zero value, to indicate an absence of any API errors or
supplementary information bits.
All GSS_S_xxx symbols equate to complete OM_uint32 status codes,
rather than to bitfield values. For example, the actual value of the
symbol GSS_S_BAD_NAMETYPE (value 3 in the routine error field) is
3<<16. The macros GSS_CALLING_ERROR(), GSS_ROUTINE_ERROR() and
GSS_SUPPLEMENTARY_INFO() are provided, each of which takes a GSS
status code and removes all but the relevant field. For example, the
value obtained by applying GSS_ROUTINE_ERROR to a status code removes
the calling errors and supplementary info fields, leaving only the
routine errors field. The values delivered by these macros may be
directly compared with a GSS_S_xxx symbol of the appropriate type.
The macro GSS_ERROR() is also provided, which when applied to a GSS
status code returns a non-zero value if the status code indicated a
calling or routine error, and a zero value otherwise. All macros
defined by GSS-API evaluate their argument(s) exactly once.
A GSS-API implementation may choose to signal calling errors in a
platform-specific manner instead of, or in addition to the routine
value; routine errors and supplementary info should be returned via
major status values only.
The GSS major status code GSS_S_FAILURE is used to indicate that the
underlying mechanism detected an error for which no specific GSS
status code is defined. The mechanism-specific status code will
provide more details about the error.
3.9.2. Mechanism-specific status codes
GSS-API routines return a minor_status parameter, which is used to indicate specialized errors from the underlying security mechanism. This parameter may contain a single mechanism-specific error, indicated by a OM_uint32 value. The minor_status parameter will always be set by a GSS-API routine, even if it returns a calling error or one of the generic API errors indicated above as fatal, although most other output parameters may remain unset in such cases. However, output parameters that are expected to return pointers to storage allocated by a routine must always be set by the routine, even in the event of an error, although in such cases the GSS-API routine may elect to set the returned parameter value to NULL to indicate that no storage was actually allocated. Any length field associated with such pointers (as in a gss_buffer_desc structure) should also be set to zero in such cases.3.10. Names
A name is used to identify a person or entity. GSS-API authenticates the relationship between a name and the entity claiming the name. Since different authentication mechanisms may employ different namespaces for identifying their principals, GSSAPI's naming support is necessarily complex in multi-mechanism environments (or even in some single-mechanism environments where the underlying mechanism supports multiple namespaces). Two distinct representations are defined for names: An internal form. This is the GSS-API "native" format for names, represented by the implementation-specific gss_name_t type. It is opaque to GSS-API callers. A single gss_name_t object may contain multiple names from different namespaces, but all names should refer to the same entity. An example of such an internal name would be the name returned from a call to the gss_inquire_cred routine, when applied to a credential containing credential elements for multiple authentication mechanisms employing different namespaces. This gss_name_t object will contain a distinct name for the entity for each authentication mechanism. For GSS-API implementations supporting multiple namespaces, objects of type gss_name_t must contain sufficient information to determine the namespace to which each primitive name belongs.
Mechanism-specific contiguous octet-string forms. A format
capable of containing a single name (from a single namespace).
Contiguous string names are always accompanied by an object
identifier specifying the namespace to which the name belongs, and
their format is dependent on the authentication mechanism that
employs the name. Many, but not all, contiguous string names will
be printable, and may therefore be used by GSS-API applications
for communication with their users.
Routines (gss_import_name and gss_display_name) are provided to
convert names between contiguous string representations and the
internal gss_name_t type. gss_import_name may support multiple
syntaxes for each supported namespace, allowing users the freedom to
choose a preferred name representation. gss_display_name should use
an implementation-chosen printable syntax for each supported name-
type.
If an application calls gss_display_name(), passing the internal name
resulting from a call to gss_import_name(), there is no guarantee the
the resulting contiguous string name will be the same as the original
imported string name. Nor do name-space identifiers necessarily
survive unchanged after a journey through the internal name-form. An
example of this might be a mechanism that authenticates X.500 names,
but provides an algorithmic mapping of Internet DNS names into X.500.
That mechanism's implementation of gss_import_name() might, when
presented with a DNS name, generate an internal name that contained
both the original DNS name and the equivalent X.500 name.
Alternatively, it might only store the X.500 name. In the latter
case, gss_display_name() would most likely generate a printable X.500
name, rather than the original DNS name.
The process of authentication delivers to the context acceptor an
internal name. Since this name has been authenticated by a single
mechanism, it contains only a single name (even if the internal name
presented by the context initiator to gss_init_sec_context had
multiple components). Such names are termed internal mechanism
names, or "MN"s and the names emitted by gss_accept_sec_context() are
always of this type. Since some applications may require MNs without
wanting to incur the overhead of an authentication operation, a
second function, gss_canonicalize_name(), is provided to convert a
general internal name into an MN.
Comparison of internal-form names may be accomplished via the
gss_compare_name() routine, which returns true if the two names being
compared refer to the same entity. This removes the need for the
application program to understand the syntaxes of the various
printable names that a given GSS-API implementation may support.
Since GSS-API assumes that all primitive names contained within a
given internal name refer to the same entity, gss_compare_name() can return true if the two names have at least one primitive name in common. If the implementation embodies knowledge of equivalence relationships between names taken from different namespaces, this knowledge may also allow successful comparison of internal names containing no overlapping primitive elements. When used in large access control lists, the overhead of invoking gss_import_name() and gss_compare_name() on each name from the ACL may be prohibitive. As an alternative way of supporting this case, GSS-API defines a special form of the contiguous string name which may be compared directly (e.g. with memcmp()). Contiguous names suitable for comparison are generated by the gss_export_name() routine, which requires an MN as input. Exported names may be re- imported by the gss_import_name() routine, and the resulting internal name will also be an MN. The gss_OID constant GSS_C_NT_EXPORT_NAME indentifies the "export name" type, and the value of this constant is given in Appendix A. Structurally, an exported name object consists of a header containing an OID identifying the mechanism that authenticated the name, and a trailer containing the name itself, where the syntax of the trailer is defined by the individual mechanism specification. The precise format of an export name is defined in the language-independent GSS-API specification [GSSAPI]. Note that the results obtained by using gss_compare_name() will in general be different from those obtained by invoking gss_canonicalize_name() and gss_export_name(), and then comparing the exported names. The first series of operation determines whether two (unauthenticated) names identify the same principal; the second whether a particular mechanism would authenticate them as the same principal. These two operations will in general give the same results only for MNs. The gss_name_t datatype should be implemented as a pointer type. To allow the compiler to aid the application programmer by performing type-checking, the use of (void *) is discouraged. A pointer to an implementation-defined type is the preferred choice. Storage is allocated by routines that return gss_name_t values. A procedure, gss_release_name, is provided to free storage associated with an internal-form name.
3.11. Channel Bindings
GSS-API supports the use of user-specified tags to identify a given context to the peer application. These tags are intended to be used to identify the particular communications channel that carries the context. Channel bindings are communicated to the GSS-API using the following structure: typedef struct gss_channel_bindings_struct { OM_uint32 initiator_addrtype; gss_buffer_desc initiator_address; OM_uint32 acceptor_addrtype; gss_buffer_desc acceptor_address; gss_buffer_desc application_data; } *gss_channel_bindings_t; The initiator_addrtype and acceptor_addrtype fields denote the type of addresses contained in the initiator_address and acceptor_address buffers. The address type should be one of the following: GSS_C_AF_UNSPEC Unspecified address type GSS_C_AF_LOCAL Host-local address type GSS_C_AF_INET Internet address type (e.g. IP) GSS_C_AF_IMPLINK ARPAnet IMP address type GSS_C_AF_PUP pup protocols (eg BSP) address type GSS_C_AF_CHAOS MIT CHAOS protocol address type GSS_C_AF_NS XEROX NS address type GSS_C_AF_NBS nbs address type GSS_C_AF_ECMA ECMA address type GSS_C_AF_DATAKIT datakit protocols address type GSS_C_AF_CCITT CCITT protocols GSS_C_AF_SNA IBM SNA address type GSS_C_AF_DECnet DECnet address type GSS_C_AF_DLI Direct data link interface address type GSS_C_AF_LAT LAT address type GSS_C_AF_HYLINK NSC Hyperchannel address type GSS_C_AF_APPLETALK AppleTalk address type GSS_C_AF_BSC BISYNC 2780/3780 address type GSS_C_AF_DSS Distributed system services address type GSS_C_AF_OSI OSI TP4 address type GSS_C_AF_X25 X.25 GSS_C_AF_NULLADDR No address specified Note that these symbols name address families rather than specific addressing formats. For address families that contain several alternative address forms, the initiator_address and acceptor_address fields must contain sufficient information to determine which address
form is used. When not otherwise specified, addresses should be specified in network byte-order (that is, native byte-ordering for the address family). Conceptually, the GSS-API concatenates the initiator_addrtype, initiator_address, acceptor_addrtype, acceptor_address and application_data to form an octet string. The mechanism calculates a MIC over this octet string, and binds the MIC to the context establishment token emitted by gss_init_sec_context. The same bindings are presented by the context acceptor to gss_accept_sec_context, and a MIC is calculated in the same way. The calculated MIC is compared with that found in the token, and if the MICs differ, gss_accept_sec_context will return a GSS_S_BAD_BINDINGS error, and the context will not be established. Some mechanisms may include the actual channel binding data in the token (rather than just a MIC); applications should therefore not use confidential data as channel-binding components. Individual mechanisms may impose additional constraints on addresses and address types that may appear in channel bindings. For example, a mechanism may verify that the initiator_address field of the channel bindings presented to gss_init_sec_context contains the correct network address of the host system. Portable applications should therefore ensure that they either provide correct information for the address fields, or omit addressing information, specifying GSS_C_AF_NULLADDR as the address-types.3.12. Optional parameters
Various parameters are described as optional. This means that they follow a convention whereby a default value may be requested. The following conventions are used for omitted parameters. These conventions apply only to those parameters that are explicitly documented as optional.3.12.1. gss_buffer_t types
Specify GSS_C_NO_BUFFER as a value. For an input parameter this signifies that default behavior is requested, while for an output parameter it indicates that the information that would be returned via the parameter is not required by the application.3.12.2. Integer types (input)
Individual parameter documentation lists values to be used to indicate default actions.
3.12.3. Integer types (output)
Specify NULL as the value for the pointer.3.12.4. Pointer types
Specify NULL as the value.3.12.5. Object IDs
Specify GSS_C_NO_OID as the value.3.12.6. Object ID Sets
Specify GSS_C_NO_OID_SET as the value.3.12.7. Channel Bindings
Specify GSS_C_NO_CHANNEL_BINDINGS to indicate that channel bindings are not to be used.
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