GSS-API Programming Guide



See Access Control List (ACL).

Access Control List (ACL)

A file containing a list of principals with certain access permissions. Typically, a server consults an access control list to verify that a client has permission to use its services. Note that a principal authenticated by GSS-API can still be denied services if an ACL does not permit them.


A security service that verifies the claimed identity of a principal.


The process of determining whether a principal can use a service, which objects the principal is allowed to access, and the type of access allowed for each.


Narrowly, a process that makes use of a network service on behalf of a user; for example, an application that uses rlogin. In some cases, a server can itself be a client of some other server or service. Informally, a principal that makes use of a service.


A security service that encrypts data; confidentiality also includes integrity and authentication services. See also authentication, integrity, service.


A “state of trust” between two applications. When a context has successfully been established between two peers, the context acceptor is aware that the context initiator is who it claims to be, and can verify and decrypt messages sent to it. If the context includes mutual authentication, then initiator knows the acceptor's identity is valid and can also verify and/or decrypt messages from it.

context-level token

See token.


An information package that identifies a principal; a principal's “identification badge,” specifying who the principal is and, often, what privileges it has. Credentials are produced by security mechanisms.

credential cache

A storage space (usually a file) containing credentials stored by a given mechanism.

data replay

Data replay is said to occur when a single message in a message stream is received more than once. Many security mechanisms support data replay detection. Replay detection, if available, must be requested at context-establishment time.

data type

(Also data type) The form that a given piece of data takes — for example, an int, a string, a gss_name_t structure, or a gss_OID_set structure.


If permitted by the underlying security mechanism, a principal (generally the context initiator) can designate a peer principal (usually the context acceptor) as a proxy by delegating its credentials to it. The delegated credentials can be used by the recipient to make requests on behalf of the original principal, as might be the case when a principal uses rlogin from machine to machine to machine.

exported name

A name that has been converted from the GSS-API internal-name format (specifically, a Mechanism Name) to the GSS-API Exported Name format by gss_export_name(). An exported name can be compared with names that are in non-GSS-API string format with memcmp(). See also Mechanism Name (MN), name.


Historically, security flavor and authentication flavor were equivalent terms, as a flavor indicated a type of authentication (AUTH_UNIX, AUTH_DES, AUTH_KERB). RPCSEC_GSS is also a security flavor, even though it provides integrity and confidentiality services in addition to authentication.


The Generic Security Service Application Programming Interface. A network layer providing support for various modular security services. GSS-API provides for security authentication, integrity, and confidentiality services, and allows maximum portability of applications with regard to security. See also authentication, confidentiality, integrity.


A machine accessible over a network.


A security service that, in addition to user authentication, provides proof of the validity of transmitted data through cryptographic tagging. See also authentication, confidentiality, Message Integrity Code (MIC).


A software package that specifies cryptographic techniques to achieve data authentication or confidentiality. Examples include Kerberos v5 and Diffie-Hellman public key.

Mechanism Name (MN)

A special instance of a GSS-API internal-format name. A normal internal-format GSS-API name may contain several instances of a name, each in the format of an underlying mechanism; a Mechanism Name, however, is unique to a particular mechanism. Mechanism Names are generated by gss_canonicalize_name().


Data in the form of a gss_buffer_t object sent from one GSS-API-based application to its peer. An example of a message is “ls” sent to a remote ftp server.

A message can contain more than just the user-provided data. For example, gss_wrap() takes an unwrapped message and produces a wrapped one to be sent; the wrapped message includes both the original message and an accompanying MIC. GSS-API-generated information that does not include a message is a token — see token for more.

Message Integrity Code (MIC)

A cryptographic “tag” attached to transmitted data to ensure the data's validity. The recipient of the data generates its own MIC and compares it to the one that was sent; if they're equal, the message is valid. Some MICs, such as those generated by gss_get_mic(), are visible to the application, while others, such as those generated by gss_wrap() or gss_init_sec_context(), are not.

message–level token

See token.


See Message Integrity Code (MIC).


See Mechanism Name (MN).

mutual authentication

When a context is established, a context initiator must authenticate itself to the context acceptor. In some cases the initiator might request that the acceptor authenticate itself back. If the acceptor does so, the two are said to be mutually authenticated.


The name of a principal, such as “joe@machine.” Names in the GSS-API are handled through the gss_name_t structure, which is opaque to applications. See also exported name, Mechanism Name (MN), name type, principal.

name type

The particular form that a name is given in. Name types are stored as gss_OID types and are used to indicate the format used for a name. For example, the name “joe@machine” would have a name type of GSS_C_NT_HOSTBASED_SERVICE. See also exported name, Mechanism Name (MN), name.


See opaque.


A particular piece of data is said to be opaque if its value or format is not normally visible to functions that use it. For example, the input_token parameter to gss_init_sec_context() is opaque to the application, but significant to the GSS-API; similarly, the input_message parameter to gss_wrap() is opaque to the GSS-API but important to the application doing the wrapping.

out-of-sequence detection

Many security mechanisms can detect if messages in a message stream are received out of their proper order. Message detection, if available, must be requested at context-establishment time.

per-message token

See token.


A uniquely named client/user or server/service instance that participates in a network communication; GSS–API–based transactions involve interactions between principals. Examples of principal names include:

  • joe

  • joe@machine

  • nfs@machine

  • 123.45.678.9


See also name, name type.


See confidentiality.


See Quality of Protection (QOP).

Quality of Protection (QOP)

A parameter used to select the cryptographic algorithms to be used in conjunction with the integrity or confidentiality service. With integrity, the QOP specifies the algorithm for producing a Message Integrity Code (MIC); with confidentiality, it specifies the algorithm for both the MIC and message encryption.

replay detection

Many security mechanisms can detect if a message in a message stream has been incorrectly repeated. Message replay detection, if available, must be requested at context-establishment time.

security flavor

See flavor.

security mechanism

See mechanism.

security service

See service.


A principal that provides a resource to network clients. For example, if you rlogin to the machine, then that machine is the server providing the rlogin service.


1. (Also, network service) A resource provided to network clients; often provided by more than one server. For example, if you rlogin to the machine, then that machine is the server providing the rlogin service.

2. A security service can be either integrity or confidentiality, providing a level of protection beyond authentication. See also authentication, integrity and confidentiality.


A data packet in the form of a GSS-API gss_buffer_t structure. Tokens are produced by GSS-API functions for transfer to peer applications.

Tokens come in two types. Context-level tokens contain information used to establish or manage a security context. For example, gss_init_sec_context() bundles a context initiator's credential handle, the target machine's name, flags for various requested services, and more into a token to be sent to the context acceptor.

Message tokens (also known as per-message tokens or message-level tokens) contain information generated by a GSS-API function from messages to be sent to a peer application. For example, gss_get_mic() produces an identifying cryptographic tag for a given message and stores it in a token to be sent to a peer with the message. (Technically, a token is considered to be separate from a message, which is why gss_wrap() is said to produce an output_message and not an output_token.)

See also message.