HP Open Source Security for OpenVMS Volume 3: Kerberos > Chapter 5 GSSAPI (Generic Security Services Application Programming Interface)

gss_accept_sec_context — Establish a security context

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C Prototype

OM_uint32 gss_accept_sec_context(
OM_uint32 * minor_status,
gss_ctx_id_t * context_handle,
gss_cred_id_t acceptor_cred_handle,
gss_buffer_t input_token_buffer,
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

minor_status (output) 

Mechanism-specific status code.

context_handle (input/output) 

The context handle for the new context. Supply GSS_C_NO_CONTEXT for the first call; use the value returned in subsequent calls. Once gss_accept_sec_context has returned a value via this argument, 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.

acceptor_cred_handle (input) 

The credential handle claimed by the context acceptor. Specify GSS_C_NO_CREDENTIAL to accept the context as a default principal. If GSS_S_NO_CREDENTIAL is specified, but no default acceptor principal is defined, GSS_S_NO_CRED will be returned.

input_token_buffer (input) 

The token obtained from the remote application.

input_chan_bindings (input) 

Application-specified bindings. Allows the application to securely bind channel identification information to the security context. If channel bindings are not used, specify GSS_C_NO_CHANNEL_BINDINGS.

src_name (output) 

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

mech_type (output) 

The 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 (output) 

The token to be passed to the peer application. If the length field of the returned token buffer is zero, then no token need be passed to the peer application. If a nonzero length field is returned, the associated storage must be freed after use by the application with a call to gss_release_buffer.

ret_flags (output) 

A bit mask which contains various independent flags, each of which indicates that the context supports a specific service option. 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 delegated_cred_handle argument.

FALSE — No credentials were delegated.

GSS_C_MUTUAL_FLAG

TRUE — The remote peer asked for mutual authentication.

FALSE — The 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) is available. The gss_wrap routine will provide message encapsulation, data-origination authentication and integrity services only.

GSS_C_INTEG_FLAG

TRUE — Integrity service may be invoked by calling either the gss_get_mic or gss_wrap routine.

FALSE — Per-message integrity service is unavailable.

GSS_C_ANON_FLAG

TRUE — The initiator does not wish to be authenticated; the src_name argument (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 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 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 zero.

time_rec (output) 

The number of seconds for which the context will remain valid. Specify NULL if not required.

delegated_cred_handle (output)
  

The credential handle for credentials received from the context initiator. Only valid if deleg_flag in ret_flags is TRUE, in which case an explicit credential handle (that is, not GSS_C_NO_CREDENTIAL) will be returned; if deleg_flag is false, gss_accept_context will set this argument 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

This routine allows a remotely initiated security context between the application and a remote peer to be established. The routine may return an output_token that 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 arguments.

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. A typical portable caller should always invoke gss_accept_sec_context within a loop. For example:

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 status that includes the value GSS_S_CONTINUE_NEEDED, the context is not fully established and the following restrictions apply to the output arguments:

  • The value returned via the time_rec argument is undefined unless the accompanying ret_flags argument 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 argument may be undefined until the routine returns a status of GSS_S_COMPLETE.

  • The value 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 argument 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 indicate the actual state at the time gss_accept_sec_context returns, whether or not the context is fully established.

    Although this requires that GSSAPI implementations set the GSS_C_PROT_READY_FLAG in the final ret_flags returned to a caller (that is, when accompanied by a GSS_S_COMPLETE status code), applications should not reply on this behavior as the flag was not defined in Version 1 of the GSSAPI. 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 will 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.

  • During context establishment, the information status bits GSS_S_OLD_TOKEN and GSS_S_DUPLICATE_TOKEN indicate fatal errors, and GSSAPI mechanisms return them in association with a routine error of GSS_S_FAILURE. This requirement for pairing did not exist in Version 1 of the GSSAPI specification, so applications that wish to run over Version 1 implementations must special-case these codes.

Return Values

This routine returns one of the following GSS status codes:

GSS_S_COMPLETE

Successful completion.
GSS_S_CONTINUE_NEEDEDThe service completed successfully and synchronously (returned only if the DDTM$M_SYNCH flag is set).
GSS_S_DEFECTIVE_TOKENIndicates that consistency checks performed on the input_token failed.
GSS_S_DEFECTIVE_CREDENTIALThe options flags were invalid or the TID argument was omitted and the bid argument was not 0.

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 argument.

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.