gss_accept_sec_context(3)

NAME
gss_accept_sec_context - API function

SYNOPSIS
#include <gss.h>

OM_uint32 gss_accept_sec_context(OM_uint32 * minor_status, gss_ctx_id_t * context_handle, const gss_cred_id_t acceptor_cred_handle, const gss_buffer_t input_token_buffer, const gss_channel_bindings_t input_chan_bindings, gss_name_t * src_name, gss_OID * mech_type, gss_buffer_t output_token, OM_uint32 * ret_flags, OM_uint32 * time_rec, gss_cred_id_t * delegated_cred_handle);

ARGUMENTS

OM_uint32 * minor_status
    (Integer, modify) Mechanism specific status code.

gss_ctx_id_t * context_handle
    (gss_ctx_id_t, read/modify) Context handle for new
      context. Supply GSS_C_NO_CONTEXT for first call; use value
      returned in subsequent calls. Once gss_accept_sec_context() has
      returned a value via this parameter, resources have been assigned
      to the corresponding context, and must be freed by the
      application after use with a call to gss_delete_sec_context().

const gss_cred_id_t acceptor_cred_handle
    (gss_cred_id_t, read) Credential handle
      claimed by context acceptor. Specify GSS_C_NO_CREDENTIAL to
      accept the context as a default principal. If
      GSS_C_NO_CREDENTIAL is specified, but no default acceptor
      principal is defined, GSS_S_NO_CRED will be returned.

const gss_buffer_t input_token_buffer
    (buffer, opaque, read) Token obtained from
      remote application.

const gss_channel_bindings_t input_chan_bindings
    (channel bindings, read, optional)
      Application- specified bindings. Allows application to securely
      bind channel identification information to the security context.
      If channel bindings are not used, specify
      GSS_C_NO_CHANNEL_BINDINGS.

gss_name_t * src_name
    (gss_name_t, modify, optional) Authenticated name of
      context initiator. After use, this name should be deallocated by
      passing it to gss_release_name(). If not required, specify NULL.

gss_OID * mech_type
    (Object ID, modify, optional) Security mechanism used.
      The returned OID value will be a pointer into static storage, and
      should be treated as read-only by the caller (in particular, it
      does not need to be freed). If not required, specify NULL.

gss_buffer_t output_token
    (buffer, opaque, modify) Token to be passed to peer
      application. If the length field of the returned token buffer is
      0, then no token need be passed to the peer application. If a
      non- zero length field is returned, the associated storage must
      be freed after use by the application with a call to
      gss_release_buffer().

OM_uint32 * ret_flags
    (bit-mask, modify, optional) Contains various
      independent flags, each of which indicates that the context
      supports a specific service option. If not needed, specify NULL.
      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. See below for the flags.

OM_uint32 * time_rec
    (Integer, modify, optional) Number of seconds for which
      the context will remain valid. Specify NULL if not required.

gss_cred_id_t * delegated_cred_handle
    (gss_cred_id_t, modify, optional
      credential) Handle for credentials received from context
      initiator. Only valid if deleg_flag in ret_flags is true, in
      which case an explicit credential handle (i.e. not
      GSS_C_NO_CREDENTIAL) will be returned; if deleg_flag is false,
      gss_accept_sec_context() will set this parameter to
      GSS_C_NO_CREDENTIAL. If a credential handle is returned, the
      associated resources must be released by the application after
      use with a call to gss_release_cred(). Specify NULL if not
      required.

DESCRIPTION
Allows a remotely initiated security context between the application and a remote peer to be established. The routine may return a output_token which should be transferred to the peer application, where the peer application will present it to gss_init_sec_context. If no token need be sent, gss_accept_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_accept_sec_context will return a status flag of GSS_S_CONTINUE_NEEDED, in which case it should be called again when the reply token is received from the peer application, passing the token to gss_accept_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_accept_sec_context within a loop:

--------------------------------------------------- gss_ctx_id_t context_hdl = GSS_C_NO_CONTEXT;

do {
  receive_token_from_peer(input_token);
  maj_stat = gss_accept_sec_context(&min_stat,
                        &context_hdl,
                        cred_hdl,
                        input_token,
                        input_bindings,
                        &client_name,
                        &mech_type,
                        output_token,
                        &ret_flags,
                        &time_rec,
                        &deleg_cred);
  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;
  }; } while (maj_stat & GSS_S_CONTINUE_NEEDED); ---------------------------------------------------

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 mech_type parameter may be 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.

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_accept_sec_context returns, whether or not the context is fully established.

Although this requires that GSS-API implementations 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), applications should not rely on this behavior as the flag was not defined in Version 1 of the GSS-API. Instead, applications should be prepared to use per-message services 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. While the routine returns GSS_S_CONTINUE_NEEDED, the values returned via the ret_flags argument indicate the services that the implementation expects to be available from the established context.

If the initial call of gss_accept_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 (and the context_handle parameter) untouched for the application to delete (using gss_delete_sec_context).

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.

The `ret_flags` values:

`GSS_C_DELEG_FLAG`:: - True - Delegated credentials are available via the delegated_cred_handle parameter. - False - No credentials were delegated.

`GSS_C_MUTUAL_FLAG`:: - True - Remote peer asked for mutual authentication. - False - Remote peer did not ask for mutual authentication.

`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 the gss_wrap routine. - False - No confidentiality service (via gss_wrap) available. gss_wrap 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 or gss_wrap routines. - False - Per-message integrity service unavailable.

`GSS_C_ANON_FLAG`:: - True - The initiator does not wish to be authenticated; the src_name parameter (if requested) contains an anonymous internal name. - False - The initiator has been 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 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.

RETURN VALUE

`GSS_S_CONTINUE_NEEDED`: Indicates that a token from the peer application is required to complete the context, and that gss_accept_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 acceptance, 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_NO_CONTEXT`: Indicates that the supplied context handle did not refer to a valid context.

`GSS_S_BAD_SIG`: The input_token contains an invalid MIC.

`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_BAD_MECH`: The received token specified a mechanism that is not supported by the implementation or the provided credential.

REPORTING BUGS
Report bugs to <bug-gss@gnu.org>. GNU Generic Security Service home page: http://www.gnu.org/software/gss/ General help using GNU software: http://www.gnu.org/gethelp/

COPYRIGHT
Copyright © 2003-2022 Simon Josefsson.
Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.

SEE ALSO
The full documentation for gss is maintained as a Texinfo manual. If the info and gss programs are properly installed at your site, the command

    info gss

should give you access to the complete manual.