GSS_INIT_SEC_CONTEXT(3)

NAME
gss_init_sec_context - Initiate a security context with a peer application

SYNOPSIS
#include <gssapi/gssapi.h>
OM_uint32
gss_init_sec_context(OM_uint32 *minor_status, const gss_cred_id_t initiator_cred_handle, gss_ctx_id_t *context_handle, const gss_name_t target_name, const gss_OID mech_type, OM_uint32 req_flags, OM_uint32 time_req, const gss_channel_bindings_t input_chan_bindings, const gss_buffer_t input_token, gss_OID *actual_mech_type, gss_buffer_t output_token, OM_uint32 *ret_flags, OM_uint32 *time_rec);

DESCRIPTION
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 whose length field contains the value zero. The routine may return a output_token which should be transferred to the peer application, where the peer application will present it to gss_accept_sec_context(3). 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 the context establishment, one or more reply tokens may be required from the peer application; if so, gss_init_sec_context() will return a status containing the supplementary information bit GSS_S_CONTINUE_NEEDED. In this case, gss_init_sec_context() should be called again when the reply token is received from the peer application, passing the reply token to gss_init_sec_context() via the input_token parameters.

Portable applications should be constructed to use the token length and return status to determine whether a token needs to be sent or waited for. Thus a typical portable caller should always invoke gss_init_sec_context() within a loop:

    int context_established = 0;
    gss_ctx_id_t context_hdl = GSS_C_NO_CONTEXT;
           ...
    input_token->length = 0;
    while (!context_established) {
      maj_stat = gss_init_sec_context(&min_stat,
    				  cred_hdl,
    				  &context_hdl,
    				  target_name,
    				  desired_mech,
    				  desired_services,
    				  desired_time,
    				  input_bindings,
    				  input_token,
    				  &actual_mech,
    				  output_token,
    				  &actual_services,
    				  &actual_time);
      if (GSS_ERROR(maj_stat)) {
        report_error(maj_stat, min_stat);
      };
      if (output_token->length != 0) {
        send_token_to_peer(output_token);
        gss_release_buffer(&min_stat, output_token)
      };
      if (GSS_ERROR(maj_stat)) {
        if (context_hdl != GSS_C_NO_CONTEXT)
          gss_delete_sec_context(&min_stat,
    			     &context_hdl,
    			     GSS_C_NO_BUFFER);
        break;
      };
      if (maj_stat & GSS_S_CONTINUE_NEEDED) {
        receive_token_from_peer(input_token);
      } else {
        context_established = 1;
      };
    };

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 via the time_rec parameter is undefined Unless the accompanying ret_flags parameter contains the bit GSS_C_PROT_READY_FLAG, indicating that per-message services may be applied in advance of a successful completion status, the value returned via 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 via the ret_flags parameter should contain the values that the implementation expects would be valid if context establishment were to succeed. In particular, if the application has requested a service such as delegation or anonymous authentication via the req_flags argument, and such a service is unavailable from the underlying mechanism, gss_init_sec_context() should generate a token that will not provide the service, and indicate via the ret_flags argument that the service will not be supported. The application may choose to abort the context establishment by calling gss_delete_sec_context(3) (if it cannot continue in the absence of the service), or it may choose to transmit the token and continue context establishment (if the service was merely desired but not mandatory).

•   The values of the GSS_C_PROT_READY_FLAG and GSS_C_TRANS_FLAG bits within ret_flags should indicate the actual state at the time gss_init_sec_context() returns, whether or not the context is fully established.

•   GSS-API implementations that support per-message protection are encouraged to set the GSS_C_PROT_READY_FLAG in the final ret_flags returned to a caller (i.e. 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 should be set to zero.

If the initial call of gss_init_sec_context() fails, the implementation should not create a context object, and should leave the value of the context_handle parameter set to GSS_C_NO_CONTEXT to indicate this. In the event of a failure on a subsequent call, the implementation is permitted to delete the "half-built" security context (in which case it should set the context_handle parameter to GSS_C_NO_CONTEXT ), but the preferred behavior is to leave the security context untouched for the application to delete (using gss_delete_sec_context(3) ).

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 routine error of GSS_S_FAILURE. This requirement for pairing did not exist in version 1 of the GSS-API specification, so applications that wish to run over version 1 implementations must special-case these codes.

PARAMETERS

minor_status
    Mechanism specific status code.

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

context_handle
    context handle for new context. Supply GSS_C_NO_CONTEXT for first call; use value returned by first call in continuation calls. Resources associated with this context-handle must be released by the application after use with a call to gss_delete_sec_context().

target_name
    Name of target

mech_type
    Object ID of desired mechanism. Supply GSS_C_NO_OID to obtain an implementation specific default

req_flags
    Contains various independent flags, each of which requests that the context support a specific service option. Symbolic names are provided for each flag, and the symbolic names corresponding to the required flags should be logically-ORed together to form the bit-mask value. The flags are:

    GSS_C_DELEG_FLAG

        True
            Delegate credentials to remote peer

        False
            Don't delegate

    GSS_C_MUTUAL_FLAG

        True
            Request that remote peer authenticate itself

        False
            Authenticate self to remote peer only

    GSS_C_REPLAY_FLAG

        True
            Enable replay detection for messages protected with gss_wrap(3) or gss_get_mic(3)

        False
            Don't attempt to detect replayed messages

    GSS_C_SEQUENCE_FLAG

        True
            Enable detection of out-of-sequence protected messages

        False
            Don't attempt to detect out-of-sequence messages

    GSS_C_CONF_FLAG

        True
            Request that confidentiality service be made available (via gss_wrap(3))

        False
            No per-message confidentiality service is required.

    GSS_C_INTEG_FLAG

        True
            Request that integrity service be made available (via gss_wrap(3) or gss_get_mic(3))

        False
            No per-message integrity service is required.

    GSS_C_ANON_FLAG

        True
            Do not reveal the initiator's identity to the acceptor.

        False
            Authenticate normally.

time_req
    Desired number of seconds for which context should remain valid. Supply 0 to request a default validity period.

input_chan_bindings
    Application-specified bindings. Allows application to securely bind channel identification information to the security context. Specify GSS_C_NO_CHANNEL_BINDINGS if channel bindings are not used.

input_token
    Token received from peer application. Supply GSS_C_NO_BUFFER, or a pointer to a buffer containing the value GSS_C_EMPTY_BUFFER on initial call.

actual_mech_type
    Actual mechanism used. The OID returned via this parameter will be a pointer to static storage that should be treated as read-only; In particular the application should not attempt to free it. Specify NULL if not required.

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

ret_flags
    Contains various independent flags, each of which indicates that the context supports a specific service option. Specify NULL if not required. Symbolic names are provided for each flag, and the symbolic names corresponding to the required flags should be logically-ANDed with the ret_flags value to test whether a given option is supported by the context. The flags are:

    GSS_C_DELEG_FLAG

        True
            Credentials were delegated to the remote peer

        False
            No credentials were delegated

    GSS_C_MUTUAL_FLAG

        True
            The remote peer has authenticated itself.

        False
            Remote peer has not authenticated itself.

    GSS_C_REPLAY_FLAG

        True
            Replay of protected messages will be detected

        False
            Replayed messages will not be detected

    GSS_C_SEQUENCE_FLAG

        True
            Out-of-sequence protected messages will be detected

        False
            Out-of-sequence messages will not be detected

    GSS_C_CONF_FLAG

        True
            Confidentiality service may be invoked by calling gss_wrap(3) routine

        False
            No confidentiality service (via gss_wrap(3)) available. gss_wrap(3) will provide message encapsulation, data-origin authentication and integrity services only.

    GSS_C_INTEG_FLAG

        True
            Integrity service may be invoked by calling either gss_get_mic(3) or gss_wrap(3) routines.

        False
            Per-message integrity service unavailable.

    GSS_C_ANON_FLAG

        True
            The initiator's identity has not been revealed, and will not be revealed if any emitted token is passed to the acceptor.

        False
            The initiator's identity has been or will be authenticated normally.

    GSS_C_PROT_READY_FLAG

        True
            Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available for use if the accompanying major status return value is either GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED.

        False
            Protection services (as specified by the states of the GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG) are available only if the accompanying major status return value is GSS_S_COMPLETE.

    GSS_C_TRANS_FLAG

        True
            The resultant security context may be transferred to other processes via a call to gss_export_sec_context().

        False
            The security context is not transferable.

    All other bits should be set to zero.

time_rec
    Number of seconds for which the context will remain valid. If the implementation does not support context expiration, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required.

RETURN VALUES

GSS_S_COMPLETE
    Successful completion

GSS_S_CONTINUE_NEEDED
    Indicates that a token from the peer application is required to complete the context, and that gss_init_sec_context must be called again with that token.

GSS_S_DEFECTIVE_TOKEN
    Indicates that consistency checks performed on the input_token failed

GSS_S_DEFECTIVE_CREDENTIAL
    Indicates that consistency checks performed on the credential failed.

GSS_S_NO_CRED
    The supplied credentials were not valid for context initiation, or the credential handle did not reference any credentials.

GSS_S_CREDENTIALS_EXPIRED
    The referenced credentials have expired

GSS_S_BAD_BINDINGS
    The input_token contains different channel bindings to those specified via the input_chan_bindings parameter

GSS_S_BAD_SIG
    The input_token contains an invalid MIC, or a MIC that could not be verified

GSS_S_OLD_TOKEN
    The input_token was too old. This is a fatal error during context establishment

GSS_S_DUPLICATE_TOKEN
    The input_token is valid, but is a duplicate of a token already processed. This is a fatal error during context establishment.

GSS_S_NO_CONTEXT
    Indicates that the supplied context handle did not refer to a valid context

GSS_S_BAD_NAMETYPE
    The provided target_name parameter contained an invalid or unsupported type of name

GSS_S_BAD_NAME
    The provided target_name parameter was ill-formed.

GSS_S_BAD_MECH
    The specified mechanism is not supported by the provided credential, or is unrecognized by the implementation.

SEE ALSO
gss_accept_sec_context(3), gss_delete_sec_context(3), gss_get_mic(3), gss_release_buffer(3), gss_wrap(3)

STANDARDS

RFC 2743
    Generic Security Service Application Program Interface Version 2, Update 1

RFC 2744
    Generic Security Service API Version 2 : C-bindings

HISTORY
The gss_init_sec_context function first appeared in FreeBSD 7.0.

AUTHORS
John Wray, Iris Associates

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

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