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GSSAPI(3) Library Functions Manual GSSAPI(3)

gssapi — Generic Security Services API

GSS-API Library (libgssapi, -lgssapi)

#include <gssapi/gssapi.h>

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.

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 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.

This section lists the routines that make up the GSS-API, and offers a brief description of the purpose of each routine.

GSS-API Credential-management Routines:

gss_acquire_cred
Assume a global identity; Obtain a GSS-API credential handle for pre-existing credentials.
gss_add_cred
Construct credentials incrementally
gss_inquire_cred
Obtain information about a credential
gss_inquire_cred_by_mech
Obtain per-mechanism information about a credential.
gss_release_cred
Discard a credential handle.

GSS-API Context-Level Routines:

gss_init_sec_context
Initiate a security context with a peer application
gss_accept_sec_context
Accept a security context initiated by a peer application
gss_delete_sec_context
Discard a security context
gss_process_context_token
Process a token on a security context from a peer application
gss_context_time
Determine for how long a context will remain valid
gss_inquire_context
Obtain information about a security context
gss_wrap_size_limit
Determine token-size limit for gss_wrap(3) on a context
gss_export_sec_context
Transfer a security context to another process
gss_import_sec_context
Import a transferred context

GSS-API Per-message Routines:

gss_get_mic
Calculate a cryptographic message integrity code (MIC) for a message; integrity service
gss_verify_mic
Check a MIC against a message; verify integrity of a received message
gss_wrap
Attach a MIC to a message, and optionally encrypt the message content; confidentiality service
gss_unwrap
Verify a message with attached MIC, and decrypt message content if necessary.

GSS-API Name manipulation Routines:

gss_import_name
Convert a contiguous string name to internal-form
gss_display_name
Convert internal-form name to text
gss_compare_name
Compare two internal-form names
gss_release_name
Discard an internal-form name
gss_inquire_names_for_mech
List the name-types supported by the specified mechanism
gss_inquire_mechs_for_name
List mechanisms that support the specified name-type
gss_canonicalize_name
Convert an internal name to an MN
gss_export_name
Convert an MN to export form
gss_duplicate_name
Create a copy of an internal name

GSS-API Miscellaneous Routines

gss_add_oid_set_member
Add an object identifier to a set
gss_display_status
Convert a GSS-API status code to text
gss_indicate_mechs
Determine available underlying authentication mechanisms
gss_release_buffer
Discard a buffer
gss_release_oid_set
Discard a set of object identifiers
gss_create_empty_oid_set
Create a set containing no object identifiers
gss_test_oid_set_member
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.

RFC 2743
Generic Security Service Application Program Interface Version 2, Update 1
RFC 2744
Generic Security Service API Version 2 : C-bindings

The gssapi library first appeared in FreeBSD 7.0.

John Wray, Iris Associates

Copyright (C) The Internet Society (2000). All Rights Reserved.

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January 26, 2010 FreeBSD-12.0