GSS_ACCEPT_SEC_CONTEXT(3) Programmer's Manual GSS_ACCEPT_SEC_CONTEXT(3)NAMEgss_accept_sec_context — Accept a security context initiated by a peer
application
SYNOPSIS
#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_buffer,
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);
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(3). 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 con‐
text 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 fol‐
lowing 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 suc‐
cessful 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 ser‐
vices 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 per‐
mitted 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_han‐
dle parameter) 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
context_handle
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 correspond‐
ing context, and must be freed by the application after use
with a call to gss_delete_sec_context(3).
acceptor_cred_handle
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.
input_token_buffer
Token obtained from remote application.
input_chan_bindings
Application-specified bindings. Allows application to
securely bind channel identification information to the
security context. If channel bindings are not used, spec‐
ify GSS_C_NO_CHANNEL_BINDINGS.
src_name Authenticated name of context initiator. After use, this
name should be deallocated by passing it to
gss_release_name(3). If not required, specify NULL.
mech_type 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.
output_token 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(3).
ret_flags 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. The flags are:
GSS_C_DELEG_FLAG
True Delegated credentials are available via the del‐
egated_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 authentica‐
tion
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 call‐
ing the 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 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 trans‐
ferred to other processes via a call to
gss_export_sec_context(3).
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.
Specify NULL if not required.
delegated_cred_handle
Credential handle for credentials received from context
initiator. Only valid if GSS_C_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 false,
gss_accept_context() will set this parameter to
GSS_C_NO_CREDENTIAL. If a credential handle is returned,
the associated resources must be released by the applica‐
tion after use with a call to gss_release_cred(3). Specify
NULL if not required.
minor_status Mechanism specific status code.
RETURN VALUES
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 creden‐
tial failed.
GSS_S_NO_CRED
The supplied credentials were not valid for context accep‐
tance, or the credential handle did not reference any cre‐
dentials.
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 sup‐
ported by the implementation or the provided credential.
SEE ALSOgss_delete_sec_context(3), gss_export_sec_context(3), gss_get_mic(3),
gss_init_sec_context(3), gss_release_buffer(3), gss_release_cred(3),
gss_release_name(3), gss_wrap(3)STANDARDS
RFC 2743 Generic Security Service Application Program Interface Ver‐
sion 2, Update 1
RFC 2744 Generic Security Service API Version 2 : C-bindings
HISTORY
The gss_accept_sec_context function first appeared in FreeBSD 7.0.
AUTHORS
John Wray, Iris Associates
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