Tribblix: manual page: gss_accept_sec

GSS_ACCEPT_SEC_CONTEXT(3GSS) Generic Security Services API Library Functions

NAME

gss_accept_sec_context - accept a security context initiated by a
peer application

SYNOPSIS

cc [ flag... ] file... -lgss [ library... ]
#include <gssapi/gssapi.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,
const gss_channel_bindings_t input_chan_bindings,
const 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);

PARAMETERS

The parameter descriptions for gss_accept_sec_context() follow:

minor_status

The status code returned by the underlying mechanism.

context_handle

The context handle to return to the initiator. This should be set
to GSS_C_NO_CONTEXT before the loop begins.

acceptor_cred_handle

The handle for the credentials acquired by the acceptor,
typically through gss_acquire_cred(). It may be initialized to
GSS_C_NO_CREDENTIAL to indicate a default credential to use. If
no default credential is defined, the function returns
GSS_C_NO_CRED.

input_token_buffer

Token received from the context initiative.

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.

src_name

The authenticated name of the context initiator. After use, this
name should be deallocated by passing it to gss_release_name().
See gss_release_name(3GSS). If not required, specify NULL.

mech_type

The security mechanism used. Set to NULL if it does not matter
which mechanism is used.

output_token

The token to send to the acceptor. Initialize it to
GSS_C_NO_BUFFER before the function is called (or its length
field set to zero). If the length is zero, no token need be sent.

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, delegated credentials are available by means of the
delegated_cred_handle parameter. If false, no credentials
were delegated.

GSS_C_MUTUAL_FLAG

If true, a remote peer asked for mutual authentication. If
false, no remote peer asked for mutual authentication.

GSS_C_REPLAY_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, confidentiality service may be invoked by calling
the gss_wrap() routine. If false, no confidentiality service
is available by means of gss_wrap(). 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_get_mic(3GSS) or the gss_wrap(3GSS) routine. If
false, per-message integrity service is not available.

GSS_C_ANON_FLAG

If true, the initiator does not wish to be authenticated. The
src_name parameter, if requested, contains an anonymous
internal name. If false, the initiator has been 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 sections for which the context will remain value
Specify NULL if not required.

delegated_cred_handle

The credential value for credentials received from the context's
initiator. It is valid only if the initiator has requested that
the acceptor act as a proxy: that is, if the ret_flag argument
resolves to GSS_C_DELEG_FLAG.

DESCRIPTION

The gss_accept_sec_context() function allows a remotely initiated
security context between the application and a remote peer to be
established. The routine may return an output_token, which should be
transferred to the peer application, where the peer application will
present it to gss_init_sec_context(). See gss_init_sec_context(3GSS).
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() by means
of the input_token parameters.

Portable applications should be constructed to use the token length
and return status to determine whether to send or to wait for a
token.

Whenever gss_accept_sec_context() 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:

o The value returned by means of the time_rec parameter is
undefined.

o 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 the mech_type
parameter may be undefined until gss_accept_sec_context()
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 means of the
ret_flags parameter are values that 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 indicate the actual state at the time
gss_accept_sec_context() returns, whether or not the context is fully
established. However, applications should not rely on this behavior,
as GSS_C_PROT_READY_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, based upon the
GSS_C_INTEG_FLAG and GSS_C_CONF_FLAG values.

All other bits within the ret_flags argument are set to zero.

While gss_accept_sec_context() returns GSS_S_CONTINUE_NEEDED, the
values returned by means of the ret_flags argument indicate the
services available from the established context. If the initial call
of gss_accept_sec_context() fails, no context object is created, and
the value of the context_handle parameter is set to GSS_C_NO_CONTEXT.
In the event of a failure on a subsequent call, the security context
and the context_handle parameter are left 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; GSS-API mechanisms
always return them in association with a routine error of
GSS_S_FAILURE. This pairing requirement 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.

ERRORS

gss_accept_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
that gss_accept_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 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 than those specified
by means of the input_chan_bindings
parameter.

GSS_S_NO_CONTEXT
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 while establishing context.

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

GSS_S_BAD_MECH
The token received specified 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.

EXAMPLES

Example 1: Invoking gss_accept_sec_context() Within a Loop

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);

/* Check client_name authorization */
...

(void) gss_release_name(&min_stat, &client_name);

/* Use and/or store delegated credential */
...

(void) gss_release_cred(&min_stat, &deleg_cred);

ATTRIBUTES