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

gss_init_sec_context — Establish a security context

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C Prototype

OM_uint32 gss_init_sec_context(
OM_uint32 * minor_status,
gss_cred_id_t claimant_cred_handle,
gss_ctx_id_t * context_handle,
gss_name_t target_name,
gss_OID mech_type,
OM_uint32 req_flags,
OM_uint32 time_req,
gss_channel_bindings_t input_chan_bindings,
gss_buffer_t input_token,
gss_OID * actual_mech_type,
gss_buffer_t output_token,
OM_uint32 * ret_flags,
OM_uint32 * time_rec );

Arguments

minor_status (output) 

An implementation-specific status code.

claimant_cred_handle (input) 

A handle for credentials claimed. Supply GSS_C_NO_CREDENTIAL to act as a default initiator principal. If no default initiator is defined, the routine will return GSS_S_NO_CRED.

context_handle (input/output) 

The context handle for the new context. Supply GSS_C_NO_CONTEXT for the first call; use the value returned by the first call in continuation calls. Resources associated with this context handle must be released by the application after use with a call to gss_delete_sec_context.

target_name (input) 

The name of the target.

mech_type (input) 

The object ID of the desired mechanism. Supply GSS_C_NOOID to obtain A mechanism-specific default.

req_flags (input) 

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. Valid values are:

GSS_C_DELEG_FLAG

TRUE — Delegate credentials to the remote peer.

FALSE — Do not delegate.

GSS_C_MUTUAL_FLAG

TRUE — Request that the remote peer authenticate itself.FALSE — Authenticate self to the remote peer only.

GSS_C_REPLAY_FLAG

TRUE — Enable replay detection for messages protected with gss_wrap or gss_get_mic.FALSE — Do not attempt to detect replayed messages.

GSS_C_SEQUENCE_FLAG

TRUE — Enable detection of out-of-sequence protected messages.FALSE — Do not attempt to detect out-of-sequence messages.

GSS_C_CONF_FLAG

TRUE — Request that confidentiality service be made available (by calling gss_wrap).FALSE — No per-message confidentiality service is required.

GSS_C_INTEG_FLAG

TRUE — Request that integrity service be made available (by calling either gss_get_mic or gss_wrap).FALSE — No per-message integrity service is required.

GSS_C_ANON_FLAG

TRUE — Do not reveal the initiator's identity to the acceptor.FALSE — Authenticate normally.

time_req (input) 

The desired number of seconds for which the context should remain valid. Supply zero to request a default validity period.

input_chan_bindings (input) 

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

input_token (input) 

The token received from the peer application. Supply GSS_C_NO_BUFFER, or a pointer to a buffer containing the value GSS_C_EMPTY_BUFFER on the initial call.

actual_mech_type (output) 

The actual mechanism used. The OID returned via this argument 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 NULL if not required.

output_token (output) 

The token to be sent to the 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 gss_release_buffer.

ret_flags (output) 

Contains various independent flags, each of which indicates that the context supports a specific service option. Specify 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 ret_flags value to test whether a given option is supported by the context. The flags are:

GSS_C_DELEG_FLAG

TRUE — Credentials were delegated to the remote peer.FALSE — No credentials were delegated.

GSS_C_MUTUAL_FLAG

TRUE — The remote peer has authenticated itself.FALSE — The remote peer has not authenticated itself.

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-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 is unavailable.

GSS_C_ANON_FLAG

TRUE — The initiator's identity has not been revealed, and will not be revealed if any emitted token is passed to the acceptor.FALSE — The initiator's identity has been or will be 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 for use 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 major status return value is GSS_S_COMPLETE.

GSS_S_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.

time_rec (output) 

The number of seconds for which the context will remain valid. If the implementation does not support credential expiration, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required.

Description

This routine indicates the establishment of a security context between the application and a remote peer. Initially, the input_token argument should be specified either as 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 an output_token that should be transferred to the peer application, where the peer application will present it to gss_accept_sec_context. If no token need be sent, gss_init_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_init_sec_context will return a status containing the supplementary information bit GSS_S_CONTINUE_NEEDED. In this case, gss_init_sec_context should be called again when the reply token is received from the peer application, passing the token to gss_init_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. Thus a typical portable caller should always invoke gss_init_sec_context within a loop:

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;
};
};

Whenever the routine returns a status that indicates 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 actual_mech_type argument is undefined until the routine returns a 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_GLAG, 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. In particular, if the application has requested a service such as delegation or anonymous authentication via the req_flags argument, and such a service is unavailable from the underlying mechanism, gss_init_sec_context generates a token that will not provide the service, and indicates via the ret_flags argument that the service will not be supported. The application may choose to abort the context establishment by calling gss_delete_sec_context (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).

  • 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_init_sec_context returns, whether or not the context is fully established.

  • GSSAPI implementations that support per-message protection are encouraged to 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). However, applications should not rely on this behavior, as the flag was not defined in Version 1 of the GSSAPI. Instead, applications should determine what per-message services are available after a successful context establishment according to the GSS_C_INTEG_FLAG and GSS_C_CONF_FLAG values.

If the initial call of gss_init_sec_context fails, a context object is not created, and the value of the context_handle argument is set to GSS_C_NO_CONTEXT to indicate this.

During context establishment, the informational status bits GSS_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_NEEDEDIndicates 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.
GSS_S_DEFECTIVE_TOKENIndicates that consistency checks performed on the input_token failed.
GSS_S_DEFECTIVE_CREDENTIALIndicates that consistency checks performed on the credential failed.
GSS_S_NO_CRED

The supplied credentials were not valid for context initiation, 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_BAD_SIG

The input_token contains an invalid MIC, or a MIC that could not be verified.

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_NO_CONTEXT

Indicates that the supplied context handle did not refer to a valid context.

GSS_S_BAD_NAMETYPEThe provided target_name argument contained an invalid or unsupported type of name.

GSS_S_BAD_NAME

The provided target_name argument was ill formed.

GSS_S_BAD_MECH

The specified mechanism is not supported by the provided credential, or is unrecognized by the implementation.