libgss - shared library for GSSAPI (Generic Security Service
Application Programming Interface)
libgss is a shared library which contains all the GSSAPIs as per the
RFC 2743 and implemented as C-language interfaces as defined in the
RFC 2744, Generic Security Service API : C-bindings.
GSSAPI provides security services for applications independent of the
various underlying security mechanisms. The services include
authentication, integrity and/or confidentiality services. GSSAPI
provides secure communication between two peers with a data structure
called a security context. A GSSAPI caller is responsible for
transfer of token between peers. GSSAPI is independent of the
underlying communication protocols.
The application that establishes the secure connection is called the
context initiator or simply initiator. The application that accepts
the secure connection is the context acceptor or simply acceptor.
An application developer who uses GSSAPI C-binding interfaces can link
an application with libgss.sl. The underlying security mechanism can
be specified at runtime in a configuration file called /etc/gss/mech
and the library will dynamically load the corresponding mechanism
specific shared library (for example, libgssapi_krb5.sl in the case of
Kerberos), from the path specified in the configuration file.
The /etc/gss/mech file has the following format:
first column contains the names of the backend security mechanism
which support GSSAPI.
second column contains the object identifier (OID).
third column contains the name of the shared library which
implements the backend security mechanism for GSSAPI.
(The backend library has to be placed in /usr/lib/gss
path for 32bit and /usr/lib/pa20_64/gss path for 64bit
The default path of the mechanism file (/etc/gss/mech) can be changed
by GSSAPI_MECH_CONF environment variable.
Example /etc/gss/mech file
# Mechanism Name Object Identifier Shared Library
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krb5_mech 1.2.840.1135184.108.40.206 libgssapi_krb5.sl
Besides this configuration file, there are two other configuration
files /etc/gss/qop and /etc/gss/gsscred.conf, which can be used in
association with libgss.sl.
The /etc/gss/qop file contains information about the GSSAPI-based
quality of protection (QOP) for each underlying security mechanisms.
The /etc/gss/qop file has the following format:
first column specifies the string name of QOP.
second column contains its QOP value (32-bit integer).
third column contains names of the security mechanism.
Example /etc/gss/qop file
# QOP string QOP Value Mechanism Name
GSS_KRB5_INTEG_C_QOP_DES_MD5 0 kerberos_v5
The /etc/gss/gsscred.conf is a configuration file that selects the
underlying mechanism used to store the gsscred table. The gsscred
table is used to store the mapping between a security principal and
the UNIX uid. The supported gsscred backend mechanism is only flat
files. Therefore, the entry "files" must be specified in
/etc/gss/gsscred.conf for the successful operation of the library.
Example /etc/gss/gsscred.conf file
# gsscred configuration file
# Valid gsscred backend mechanisms are:
Using the GSSAPI framework
Applications communicating using the GSSAPI framework go through the
following main stages:
1. The communicating applications acquire a set of credentials to
prove their identity to other applications. The applications'
credentials vouch for their global identities.
2. The applications establish a joint security context using their
credentials. This information is used to provide per message
security services like integrity and confidentiality.
Establishing the security context is done as follows. One
application (client) initiates the context setup. The other
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application (server) accepts it after exchanging zero or more
number of tokens. The number of exchanges depends upon the
underlying security mechanism.
3. Per message services apply confidentiality and integrity. An
application transmitting a message that it wishes to protect will
call the GSSAPI routine (gss_get_mic or gss_wrap calls) to apply
protection. The transmitting application specifies the
appropriate security context and sends this to the receiving
application. The receiver will pass the data to the
corresponding decoding routine (gss_verify_mic or gss_unwrap
calls ) to respectively remove the protection and validate the
4. At the completion of a communication session, the peer
applications call GSSAPI routines to delete the security context.
The names of the APIs implemented in the libgss.sl library and a
very brief description for each of them are given below. For
details about using these APIs, refer to the respective man
Credential Manipulation APIs
Credentials are used to prove the identity of an application to
another application. GSSAPIs assume that credentials of the
applications are already in place. The following GSSAPIs are used to
inquire and manipulate them.
gss_acquire_cred: Allows an application to acquire a handle for a
pre-existing credential by name.
gss_release_cred: Informs GSSAPI that the specified credential is no
longer required by the process. When all the processes have released
a credential, it will be deleted.
gss_inquire_cred: Obtain information about a credential.
gss_inquire_cred_by_mech: Obtain per mechanism information about a
gss_add_cred: Construct credentials by adding incrementally.
Context Manipulation APIs
For the applications to establish a joint security context and use it
for security services the following GSSAPIs are required.
gss_init_sec_context: Initiate a security context with a peer
gss_accept_sec_context: Accept a security context initiated by a peer
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gss_delete_sec_context: Discard a security context (release the memory
of the context structure).
gss_inquire_context: Obtain information about a security context.
gss_process_context_token: Process a token from a peer application.
gss_export_sec_context: Transfer a security context to another
gss_import_sec_context: Import a transferred context.
gss_context_time: Determine for how long a context will remain valid.
gss_wrap_size_limit: Determine token size limit for gss_wrap on a
Per Message Operation APIs
To perform per message operations like data integrity and data privacy
services the following GSSAPIs could be used:
gss_get_mic: To calculate a cryptographic Message Integrity Code
(MIC) for a message (Integrity Service).
gss_verify_mic: To verify message integrity.
gss_wrap: To encrypt a message for Confidentiality Service.
gss_unwrap: To decrypt a message for Confidentiality Service.
Name Manipulation APIs
Names identify principals. Names are represented in printable form
(for presentation to an application) or in internal for (canonical
form) that is used by the API and is opaque to applications. The
following are the APIs that are used manipulate the names:
gss_import_name: Convert a contiguous string name to a internal form.
gss_display_name: Convert a internal form name to a 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 a
gss_inquire_mechs_for_name: List mechanisms that support the specified
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gss_canonicalize_name: Convert an internal name to a mechanism
specific Mechanism Name (MN).
gss_export_name: Convert an MN to flat name representation suitable
for bitwise comparison.
gss_duplicate_name: Create a copy of an internal name.
Miscellaneous Operation APIs
Besides the above mentioned category of APIs, there are APIs which are
used for miscellaneous operations like creating and deleting list of
mechanism OIDs, display the GSSAPI error status codes in text format,
releasing the memory for the buffer etc. as given below: as
gss_add_oid_set_member: Add object identifier to a set of OIDs.
gss_release_oid_set: Release the memory of a set of OID's.
gss_create_empty_oid_set: Create an OID set with no OID's.
gss_test_oid_set_member: Determine whether an OID is a member of a
gss_release_buffer: Release the memory of a buffer.
gss_release_oid: Release the memory of an OID structure.
gss_release_name: Release the memory of a nametype.
gss_display_status: Convert GSSAPI status code to text.
gss_indicate_mechs: Determine available underlying security
libgss.sl was developed by Sun Microsystems, Inc.
The manpages for DCE-GSSAPI are included with the DCE-CoreTools
product. To see those manpages add /opt/dce/share/man to MANPATH.
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