gss_init_sec_context.3

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.Dd January 26, 2010
.Dt GSS_INIT_SEC_CONTEXT 3 PRM
.Os
.Sh NAME
.Nm gss_init_sec_context
.Nd Initiate a security context with a peer application
.\" This next command is for sections 2 and 3 only.
.\" .Sh LIBRARY
.Sh SYNOPSIS
.In "gssapi/gssapi.h"
.Ft OM_uint32
.Fo gss_init_sec_context
.Fa "OM_uint32 *minor_status"
.Fa "const gss_cred_id_t initiator_cred_handle"
.Fa "gss_ctx_id_t *context_handle"
.Fa "const gss_name_t target_name"
.Fa "const gss_OID mech_type"
.Fa "OM_uint32 req_flags"
.Fa "OM_uint32 time_req"
.Fa "const gss_channel_bindings_t input_chan_bindings"
.Fa "const gss_buffer_t input_token"
.Fa "gss_OID *actual_mech_type"
.Fa "gss_buffer_t output_token"
.Fa "OM_uint32 *ret_flags"
.Fa "OM_uint32 *time_rec"
.Fc
.Sh 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
.Dv 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
.Xr gss_accept_sec_context 3 . If no token need be sent,
.Fn gss_init_sec_context
will indicate this by setting the
.Dv 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,
.Fn gss_init_sec_context
will return a status
containing the supplementary information bit
.Dv GSS_S_CONTINUE_NEEDED.
In this case,
.Fn gss_init_sec_context
should be called again when the reply token is received from the peer
application, passing the reply token to
.Fn gss_init_sec_context
via the input_token parameters.
.Pp
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
.Fn gss_init_sec_context
within a loop:
.Bd -literal
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;
  };
};
.Ed
.Pp
Whenever the routine returns a major status that includes the value
.Dv GSS_S_CONTINUE_NEEDED, the context is not fully established and the
following restrictions apply to the output parameters:
.Bl -bullet
.It
The value returned via the
.Fa time_rec
parameter is undefined Unless
the accompanying
.Fa ret_flags
parameter contains the bit
.Dv 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
.Fa actual_mech_type
parameter is undefined until the
routine returns a major status value of
.Dv GSS_S_COMPLETE.
.It
The values of the
.Dv GSS_C_DELEG_FLAG ,
.Dv GSS_C_MUTUAL_FLAG ,
.Dv GSS_C_REPLAY_FLAG ,
.Dv GSS_C_SEQUENCE_FLAG ,
.Dv GSS_C_CONF_FLAG ,
.Dv GSS_C_INTEG_FLAG and
.Dv GSS_C_ANON_FLAG bits returned via the
.Fa 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
.Fa req_flags
argument, and such a service is unavailable from the
underlying mechanism,
.Fn gss_init_sec_context
should generate a token
that will not provide the service, and indicate via the
.Fa ret_flags
argument that the service will not be supported.  The application
may choose to abort the context establishment by calling
.Xr 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).
.It
The values of the
.Dv GSS_C_PROT_READY_FLAG and
.Dv GSS_C_TRANS_FLAG bits
within
.Fa ret_flags
should indicate the actual state at the time
.Fn gss_init_sec_context
returns, whether or not the context is fully established.
.It
GSS-API implementations that support per-message protection are
encouraged to set the
.Dv GSS_C_PROT_READY_FLAG in the final
.Fa ret_flags
returned to a caller (i.e. when accompanied by a
.Dv 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
.Dv GSS_C_INTEG_FLAG and
.Dv GSS_C_CONF_FLAG values.
.It
All other bits within the
.Fa ret_flags
argument should be set to
zero.
.El
.Pp
If the initial call of
.Fn gss_init_sec_context
fails, the
implementation should not create a context object, and should leave
the value of the
.Fa context_handle
parameter set to
.Dv 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
.Fa context_handle
parameter to
.Dv GSS_C_NO_CONTEXT ), but the preferred behavior is to leave the
security context untouched for the application to delete (using
.Xr gss_delete_sec_context 3 ).
.Pp
During context establishment, the informational status bits
.Dv GSS_S_OLD_TOKEN and
.Dv GSS_S_DUPLICATE_TOKEN indicate fatal errors, and
GSS-API mechanisms should always return them in association with a
routine error of
.Dv 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.
.Sh PARAMETERS
.Bl -tag -width ".It initiator_cred_handle"
.It minor_status
Mechanism specific status code.
.It initiator_cred_handle
handle for credentials claimed. Supply
.Dv GSS_C_NO_CREDENTIAL to act as a default
initiator principal.  If no default
initiator is defined, the function will
return
.Dv GSS_S_NO_CRED.
.It context_handle
context handle for new context.  Supply
.Dv 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
.Fn gss_delete_sec_context .
.It target_name
Name of target
.It mech_type
Object ID of desired mechanism. Supply
.Dv GSS_C_NO_OID to obtain an implementation
specific default
.It 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:
.Bl -tag -width "WW"
.It GSS_C_DELEG_FLAG
.Bl -tag -width "False"
.It True
Delegate credentials to remote peer
.It False
Don't delegate
.El
.It GSS_C_MUTUAL_FLAG
.Bl -tag -width "False"
.It True
Request that remote peer authenticate itself
.It False
Authenticate self to remote peer only
.El
.It GSS_C_REPLAY_FLAG
.Bl -tag -width "False"
.It True
Enable replay detection for messages protected with
.Xr gss_wrap 3
or
.Xr gss_get_mic 3
.It False
Don't attempt to detect replayed messages
.El
.It GSS_C_SEQUENCE_FLAG
.Bl -tag -width "False"
.It True
Enable detection of out-of-sequence protected messages
.It False
Don't attempt to detect out-of-sequence messages
.El
.It GSS_C_CONF_FLAG
.Bl -tag -width "False"
.It True
Request that confidentiality service be made available (via
.Xr gss_wrap 3 )
.It False
No per-message confidentiality service is required.
.El
.It GSS_C_INTEG_FLAG
.Bl -tag -width "False"
.It True
Request that integrity service be made available (via
.Xr gss_wrap 3
or
.Xr gss_get_mic 3 )
.It False
No per-message integrity service is required.
.El
.It GSS_C_ANON_FLAG
.Bl -tag -width "False"
.It True
Do not reveal the initiator's identity to the acceptor.
.It False
Authenticate normally.
.El
.El
.It time_req
Desired number of seconds for which context
should remain valid.  Supply 0 to request a
default validity period.
.It input_chan_bindings
Application-specified bindings.  Allows
application to securely bind channel
identification information to the security
context.  Specify
.Dv GSS_C_NO_CHANNEL_BINDINGS
if channel bindings are not used.
.It input_token
Token received from peer application.
Supply
.Dv GSS_C_NO_BUFFER, or a pointer to
a buffer containing the value
.Dv GSS_C_EMPTY_BUFFER
on initial call.
.It 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
.Dv NULL if not required.
.It 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
.Xr gss_release_buffer 3 .
.It ret_flags
Contains various independent flags, each of which
indicates that the context supports a specific
service option.  Specify
.Dv 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
.Fa ret_flags
value to test
whether a given option is supported by the
context.  The flags are:
.Bl -tag -width "WW"
.It GSS_C_DELEG_FLAG
.Bl -tag -width "False"
.It True
Credentials were delegated to the remote peer
.It False
No credentials were delegated
.El
.It GSS_C_MUTUAL_FLAG
.Bl -tag -width "False"
.It True
The remote peer has authenticated itself.
.It False
Remote peer has not authenticated itself.
.El
.It GSS_C_REPLAY_FLAG
.Bl -tag -width "False"
.It True
Replay of protected messages will be detected
.It False
Replayed messages will not be detected
.El
.It GSS_C_SEQUENCE_FLAG
.Bl -tag -width "False"
.It True
Out-of-sequence protected messages will be detected
.It False
Out-of-sequence messages will not be detected
.El
.It GSS_C_CONF_FLAG
.Bl -tag -width "False"
.It True
Confidentiality service may be invoked by calling
.Xr gss_wrap 3
routine
.It False
No confidentiality service (via
.Xr gss_wrap 3 ) available.
.Xr gss_wrap 3 will
provide message encapsulation,
data-origin authentication and
integrity services only.
.El
.It GSS_C_INTEG_FLAG
.Bl -tag -width "False"
.It True
Integrity service may be invoked by calling either
.Xr gss_get_mic 3
or
.Xr gss_wrap 3
routines.
.It False
Per-message integrity service unavailable.
.El
.It GSS_C_ANON_FLAG
.Bl -tag -width "False"
.It True
The initiator's identity has not been
revealed, and will not be revealed if
any emitted token is passed to the
acceptor.
.It False
The initiator's identity has been or will be authenticated normally.
.El
.It GSS_C_PROT_READY_FLAG
.Bl -tag -width "False"
.It True
Protection services (as specified by the states of the
.Dv GSS_C_CONF_FLAG
and
.Dv GSS_C_INTEG_FLAG ) are available for
use if the accompanying major status
return value is either
.Dv GSS_S_COMPLETE
or
.Dv GSS_S_CONTINUE_NEEDED.
.It False
Protection services (as specified by the states of the
.Dv GSS_C_CONF_FLAG
and
.Dv GSS_C_INTEG_FLAG ) are available
only if the accompanying major status
return value is
.Dv GSS_S_COMPLETE.
.El
.It GSS_C_TRANS_FLAG
.Bl -tag -width "False"
.It True
The resultant security context may be transferred to other processes via
a call to
.Fn gss_export_sec_context .
.It False
The security context is not transferable.
.El
.El
.Pp
All other bits should be set to zero.
.It time_rec
Number of seconds for which the context
will remain valid. If the implementation does
not support context expiration, the value
.Dv GSS_C_INDEFINITE will be returned.  Specify
.Dv NULL if not required.
.El
.Sh RETURN VALUES
.Bl -tag -width ".It GSS_S_CREDENTIALS_EXPIRED"
.It GSS_S_COMPLETE
Successful completion
.It 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.
.It GSS_S_DEFECTIVE_TOKEN
Indicates that consistency checks performed
on the input_token failed
.It GSS_S_DEFECTIVE_CREDENTIAL
Indicates that consistency checks
performed on the credential failed.
.It GSS_S_NO_CRED
The supplied credentials were not valid for
context initiation, or the credential handle
did not reference any credentials.
.It GSS_S_CREDENTIALS_EXPIRED
The referenced credentials have expired
.It GSS_S_BAD_BINDINGS
The input_token contains different channel
bindings to those specified via the
input_chan_bindings parameter
.It GSS_S_BAD_SIG
The input_token contains an invalid MIC, or a MIC
that could not be verified
.It GSS_S_OLD_TOKEN
The input_token was too old.  This is a fatal
error during context establishment
.It 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.
.It GSS_S_NO_CONTEXT
Indicates that the supplied context handle did
not refer to a valid context
.It GSS_S_BAD_NAMETYPE
The provided target_name parameter contained an
invalid or unsupported type of name
.It GSS_S_BAD_NAME
The provided target_name parameter was ill-formed.
.It GSS_S_BAD_MECH
The specified mechanism is not supported by the
provided credential, or is unrecognized by the
implementation.
.El
.Sh SEE ALSO
.Xr gss_accept_sec_context 3 ,
.Xr gss_delete_sec_context 3 ,
.Xr gss_get_mic 3 ,
.Xr gss_release_buffer 3 ,
.Xr gss_wrap 3
.Sh STANDARDS
.Bl -tag -width ".It RFC 2743"
.It RFC 2743
Generic Security Service Application Program Interface Version 2, Update 1
.It RFC 2744
Generic Security Service API Version 2 : C-bindings
.El
.Sh HISTORY
The
.Nm
function first appeared in
.Fx 7.0 .
.Sh AUTHORS
John Wray, Iris Associates
.Sh COPYRIGHT
Copyright (C) The Internet Society (2000).  All Rights Reserved.
.Pp
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