The gss_init_sec_context() function initiates the establishment of a security context between the application and a remote peer. Initially, the input_token parameter should be specified either as GSS_C_NO_BUFFER, or as a pointer to a gss_buffer_desc object with a length field that contains a zero value. The routine may return a output_token, which should be transferred to the peer application, which will present it to gss_accept_sec_context(3GSS). If no token need be sent, gss_init_sec_context() will indicate this by setting the length field of the output_token argument to zero. To complete context establishment, one or more reply tokens may be required from the peer application; if so, gss_init_sec_context() will return a status code that contains the supplementary information bit GSS_S_CONTINUE_NEEDED. In this case, make another call to gss_init_sec_context() when the reply token is received from the peer application and pass the reply token to gss_init_sec_context() by means of the input_token parameter.

Construct portable applications to use the token length and return status to determine whether to send or wait for a token.

Whenever the routine returns a major status that includes the value GSS_S_CONTINUE_NEEDED, the context is not fully established, and the following restrictions apply to the output parameters:

• The value returned by means of the time_rec parameter is undefined. Unless the accompanying ret_flags parameter contains the bit GSS_C_PROT_READY_FLAG, which indicates that per-message services may be applied in advance of a successful completion status, the value returned by means of the actual_mech_type parameter is undefined until the routine returns a major status value of GSS_S_COMPLETE.
• The values of the GSS_C_DELEG_FLAG, GSS_C_MUTUAL_FLAG, GSS_C_REPLAY_FLAG, GSS_C_SEQUENCE_FLAG, GSS_C_CONF_FLAG, GSS_C_INTEG_FLAG and GSS_C_ANON_FLAG bits returned by the ret_flags parameter contain values that will be valid if context establishment succeeds. For example, if the application requests a service such as delegation or anonymous authentication by means of the req_flags argument, and the service is unavailable from the underlying mechanism, gss_init_sec_context() generates a token that will not provide the service, and it indicate by means of the ret_flags argument that the service will not be supported. The application may choose to abort context establishment by calling gss_delete_sec_context(3GSS) if it cannot continue without the service, or if the service was merely desired but not mandatory, it may transmit the token and continue context establishment.
• The values of the GSS_C_PROT_READY_FLAG and GSS_C_TRANS_FLAG bits within ret_flags indicate the actual state at the time gss_init_sec_context() returns, whether or not the context is fully established.
• The GSS-API sets the GSS_C_PROT_READY_FLAG in the final ret_flags returned to a caller, for example, when accompanied by a GSS_S_COMPLETE status code. However, applications should not rely on this behavior, as the flag was not defined in Version 1 of the GSS-API. Instead, applications should determine what per-message services are available after a successful context establishment according to the GSS_C_INTEG_FLAG and GSS_C_CONF_FLAG values.
• All other bits within the ret_flags argument are set to zero.

If the initial call of gss_init_sec_context() fails, the GSS-API does not create a context object; it leaves the value of the context_handle parameter set to GSS_C_NO_CONTEXT to indicate this. In the event of failure on a subsequent call, the GSS-API leaves the security context untouched for the application to delete using gss_delete_sec_context(3GSS).

During context establishment, the informational status bits GSS_S_OLD_TOKEN and GSS_S_DUPLICATE_TOKEN indicate fatal errors, and GSS-API mechanisms should always return them in association with a status code of GSS_S_FAILURE. This pairing requirement was not part of Version 1 of the GSS-API specification, so applications that wish to run on Version 1 implementations must special-case these codes.

The parameter descriptions for gss_init_sec_context() follow:

minor_status

A mechanism specific status code.

initiator_cred_handle

The handle for the credentials claimed. Supply GSS_C_NO_CREDENTIAL to act as a default initiator principal. If no default initiator is defined, the function returns GSS_S_NO_CRED.

context_handle

The context handle for a new context. Supply the value GSS_C_NO_CONTEXT for the first call, and use the value returned in any continuation calls. The resources associated with context_handle must be released by the application after use by a call to gss_delete_sec_context(3GSS).

target_name

The name of the target.

mech_type

The object ID of the desired mechanism. To obtain a specific default, supply the value GSS_C_NO_ID.

req_flags

Contains independent flags, each of which will request that the context support a specific service option. A symbolic name is provided for each flag. Logically-OR the symbolic name to the corresponding required flag to form the bit-mask value. req_flags may contain one of the following values:

GSS_C_DELEG_FLAG

If true, delegate credentials to a remote peer. Do not delegate the credentials if the value is false.

GSS_C_MUTUAL_FLAG

If true, request that the peer authenticate itself. If false, authenticate to the remote peer only.

GSS_C_REPLAY_FLAG

If true, enable replay detection for messages protected with gss_wrap(3GSS) or gss_get_mic(3GSS). Do not attempt to detect replayed messages if false.

GSS_C_SEQUENCE_FLAG

If true, enable detection of out-of-sequence protected messages. Do not attempt to detect out-of-sequence messages if false.

GSS_C_CONF_FLAG

If true, request that confidential service be made available by means of gss_wrap(3GSS). If false, no per-message confidential service is required.

GSS_C_INTEG_FLAG

If true, request that integrity service be made available by means of gss_wrap(3GSS) or gss_get_mic(3GSS). If false, no per-message integrity service is required.

GSS_C_ANON_FLAG

If true, do not reveal the initiator's identify to the acceptor. If false, authenticate normally.

time_req

The number of seconds for which the context will remain valid. Supply a zero value to time_req to request a default validity period.

input_chan_bindings

Optional application-specified bindings. Allows application to securely bind channel identification information to the security context. Set to GSS_C_NO_CHANNEL_BINDINGS if you do not want to use channel bindings.

input_token

Token received from the peer application. On the initial call, supply GSS_C_NO_BUFFER or a pointer to a buffer containing the value GSS_C_EMPTY_BUFFER.

actual_mech_type

The actual mechanism used. The OID returned by means of this parameter will be pointer to static storage that should be treated as read-only. The application should not attempt to free it. To obtain a specific default, supply the value GSS_C_NO_ID. Specify NULL if the parameter is not required.

output_token

The token to send to the peer application. If the length field of the returned buffer is zero, no token need be sent to the peer application. After use storage associated with this buffer must be freed by the application by a call to gss_release_buffer(3GSS).

ret_flags

Contains various independent flags, each of which indicates that the context supports a specific service option. If not needed, specify NULL. Test the returned bit-mask ret_flags value against its symbolic name to determine if the given option is supported by the context. ret_flags may contain one of the following values:

GSS_C_DELEG_FLAG

If true, credentials were delegated to the remote peer. If false, no credentials were delegated.

GSS_C_MUTUAL_FLAG

If true, the remote peer authenticated itself. If false, the remote peer did not authenticate itself.

GSS_C_REPLY_FLAG

If true, replay of protected messages will be detected. If false, replayed messages will not be detected.

GSS_C_SEQUENCE_FLAG

If true, out of sequence protected messages will be detected. If false, they will not be detected.

GSS_C_CONF_FLAG

If true, confidential service may be invoked by calling the gss_wrap() routine. If false, no confidentiality service is available by means of gss_wrap(3GSS). gss_wrap() will provide message encapsulation, data-origin authentication and integrity services only.

GSS_C_INTEG_FLAG

If true, integrity service may be invoked by calling either the gss_wrap(3GSS) or gss_get_mic(3GSS) routine. If false, per-message integrity service is not available.

GSS_C_ANON_FLAG

If true, the initiator's identity has not been revealed; it will not be revealed if any emitted token is passed to the acceptor. If false, the initiator has been or will be authenticated normally.

GSS_C_PROT_READY_FLAG

If true, the protection services specified by the states of GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG are available if the accompanying major status return value is either GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED. If false, the protection services are available only if the accompanying major status return value is GSS_S_COMPLETE.

GSS_C_TRANS_FLAG

If true, the resultant security context may be transferred to other processes by means of a call to gss_export_sec_context(3GSS). If false, the security context cannot be transferred.

time_rec

The number of seconds for which the context will remain valid. Specify NULL if the parameter is not required.

gss_init_sec_context() may return the following status codes:

GSS_S_COMPLETE

Successful completion.

GSS_S_CONTINUE_NEEDED

A token from the peer application is required to complete the context, and gss_init_sec_context() must be called again with that token.

GSS_S_DEFECTIVE_TOKEN

Consistency checks performed on the input_token failed.

GSS_S_DEFECTIVE_CREDENTIAL

Consistency checks performed on the credential failed.

GSS_S_NO_CRED

The supplied credentials are not valid for context acceptance, or the credential handle does not reference any credentials.

GSS_S_CREDENTIALS_EXPIRED

The referenced credentials have expired.

GSS_S_BAD_BINDINGS

The input_token contains different channel bindings than those specified by means of the input_chan_bindings parameter.

GSS_S_BAD_SIG

The input_token contains an invalid MIC or a MIC that cannot be verified.

GSS_S_OLD_TOKEN

The input_token is too old. This is a fatal error while establishing context.

GSS_S_DUPLICATE_TOKEN

The input_token is valid, but it is a duplicate of a token already processed. This is a fatal error while establishing context.

GSS_S_NO_CONTEXT

The supplied context handle does not refer to a valid context.

GSS_S_BAD_NAMETYPE

The provided target_name parameter contains an invalid or unsupported name type.

GSS_S_BAD_NAME

The supplied target_name parameter is ill-formed.

GSS_S_BAD_MECH

The token received specifies a mechanism that is not supported by the implementation or the provided credential.

GSS_S_FAILURE

The underlying mechanism detected an error for which no specific GSS status code is defined. The mechanism-specific status code reported by means of the minor_status parameter details the error condition.

See attributes(5) for descriptions of the following attributes:

gss_delete_sec_context(3GSS), gss_export_sec_context(3GSS), gss_get_mic(3GSS), gss_wrap(3GSS), attributes(5)

GSS-API Programming Guide