This document is obsolete. Please
refer to RFC 2744.
Network Working Group J. Wray Request for Comments: 1509 Digital Equipment Corporation September 1993
Generic Security Service API : C-bindings
Status of this Memo
This RFC specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document specifies C language bindings for the Generic Security Service Application Program Interface (GSS-API), which is described at a language-independent conceptual level in other documents.
The Generic Security Service Application Programming Interface (GSS- API) provides security services to its callers, and is intended for implementation atop alternative underlying cryptographic mechanisms. Typically, GSS-API callers will be application protocols into which security enhancements are integrated through invocation of services provided by the GSS-API. The GSS-API allows a caller application to authenticate a principal identity associated with a peer application, to delegate rights to a peer, and to apply security services such as confidentiality and integrity on a per-message basis.
The Generic Security Service Application Programming Interface [1] provides security services to calling applications. It allows a communicating application to authenticate the user associated with another application, to delegate rights to another application, and to apply security services such as confidentiality and integrity on a per-message basis.
There are four stages to using the GSSAPI:
(a) The application acquires a set of credentials with which it may prove its identity to other processes. The application's credentials vouch for its global identity, which may or may not be related to the local username under which it is running.
Wray [Page 1]
RFC 1509 GSSAPI - Overview and C bindings September 1993
(b) A pair of communicating applications establish a joint security context using their credentials. The security context is a pair of GSSAPI data structures that contain shared state information, which is required in order that per-message security services may be provided. As part of the establishment of a security context, the context initiator is authenticated to the responder, and may require that the responder is authenticated in turn. The initiator may optionally give the responder the right to initiate further security contexts. This transfer of rights is termed delegation, and is achieved by creating a set of credentials, similar to those used by the originating application, but which may be used by the responder. To establish and maintain the shared information that makes up the security context, certain GSSAPI calls will return a token data structure, which is a cryptographically protected opaque data type. The caller of such a GSSAPI routine is responsible for transferring the token to the peer application, which should then pass it to a corresponding GSSAPI routine which will decode it and extract the information.
(c) Per-message services are invoked to apply either:
(i) integrity and data origin authentication, or
(ii) confidentiality, integrity and data origin authentication to application data, which are treated by GSSAPI as arbitrary octet-strings. The application transmitting a message that it wishes to protect will call the appropriate GSSAPI routine (sign or seal) to apply protection, specifying the appropriate security context, and send the result to the receiving application. The receiver will pass the received data to the corresponding decoding routine (verify or unseal) to remove the protection and validate the data.
(d) At the completion of a communications session (which may extend across several connections), the peer applications call GSSAPI routines to delete the security context. Multiple contexts may also be used (either successively or simultaneously) within a single communications association.
This section lists the functions performed by each of the GSSAPI routines and discusses their major parameters, describing how they are to be passed to the routines. The routines are listed in figure 4-1.
Wray [Page 2]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Figure 4-1 GSSAPI Routines
Routine Function
gss_acquire_cred Assume a global identity
gss_release_cred Discard credentials
gss_init_sec_context Initiate a security context with a peer application
gss_accept_sec_context Accept a security context initiated by a peer application
gss_process_context_token Process a token on a security context from a peer application
gss_delete_sec_context Discard a security context
gss_context_time Determine for how long a context will remain valid
gss_sign Sign a message; integrity service
gss_verify Check signature on a message
gss_seal Sign (optionally encrypt) a message; confidentiality service
gss_unseal Verify (optionally decrypt) message
gss_display_status Convert an API status code to text
RFC 1509 GSSAPI - Overview and C bindings September 1993
gss_import_name Convert a textual name to internal-form
gss_release_name Discard an internal-form name
gss_release_buffer Discard a buffer
gss_release_oid_set Discard a set of object identifiers
gss_inquire_cred Determine information about a credential
Individual GSSAPI implementations may augment these routines by providing additional mechanism-specific routines if required functionality is not available from the generic forms. Applications are encouraged to use the generic routines wherever possible on portability grounds.
Wherever these GSSAPI C-bindings describe structured data, only fields that must be provided by all GSSAPI implementation are documented. Individual implementations may provide additional fields, either for internal use within GSSAPI routines, or for use by non-portable applications.
Where guaranteed minimum bit-count is important, this portable data type is used by the GSSAPI routine definitions. Individual GSSAPI implementations will include appropriate typedef definitions to map this type onto a built-in data type.
Many of the GSSAPI routines take arguments and return values that describe contiguous multiple-byte data. All such data is passed between the GSSAPI and the caller using the gss_buffer_t data type.
Wray [Page 4]
RFC 1509 GSSAPI - Overview and C bindings September 1993
This data type is a pointer to a buffer descriptor, which consists of a length field that contains the total number of bytes in the datum, and a value field which contains a pointer to the actual datum:
Storage for data passed to the application by a GSSAPI routine using the gss_buffer_t conventions is allocated by the GSSAPI routine. The application may free this storage by invoking the gss_release_buffer routine. Allocation of the gss_buffer_desc object is always the responsibility of the application; Unused gss_buffer_desc objects may be initialized to the value GSS_C_EMPTY_BUFFER.
Certain multiple-word data items are considered opaque data types at the GSSAPI, because their internal structure has no significance either to the GSSAPI or to the caller. Examples of such opaque data types are the input_token parameter to gss_init_sec_context (which is opaque to the caller), and the input_message parameter to gss_seal (which is opaque to the GSSAPI). Opaque data is passed between the GSSAPI and the application using the gss_buffer_t datatype.
Certain multiple-word data items may be regarded as simple ISO Latin-1 character strings. An example of this is the input_name_buffer parameter to gss_import_name. Some GSSAPI routines also return character strings. Character strings are passed between the application and the GSSAPI using the gss_buffer_t datatype, defined earlier.
Certain GSSAPI procedures take parameters of the type gss_OID, or Object identifier. This is a type containing ISO-defined tree- structured values, and is used by the GSSAPI caller to select an underlying security mechanism. A value of type gss_OID has the following structure:
RFC 1509 GSSAPI - Overview and C bindings September 1993
The elements field of this structure points to the first byte of an octet string containing the ASN.1 BER encoding of the value of the gss_OID. The length field contains the number of bytes in this value. For example, the gss_OID value corresponding to {iso(1) identified- oganization(3) icd-ecma(12) member-company(2) dec(1011) cryptoAlgorithms(7) SPX(5)} meaning SPX (Digital's X.509 authentication mechanism) has a length field of 7 and an elements field pointing to seven octets containing the following octal values: 53,14,2,207,163,7,5. GSSAPI implementations should provide constant gss_OID values to allow callers to request any supported mechanism, although applications are encouraged on portability grounds to accept the default mechanism. gss_OID values should also be provided to allow applications to specify particular name types (see section 2.1.10). Applications should treat gss_OID_desc values returned by GSSAPI routines as read-only. In particular, the application should not attempt to deallocate them. The gss_OID_desc datatype is equivalent to the X/Open OM_object_identifier datatype [2].
Certain GSSAPI procedures take parameters of the type gss_OID_set. This type represents one or more object identifiers (section 2.1.4). A gss_OID_set object has the following structure:
The count field contains the number of OIDs within the set. The elements field is a pointer to an array of gss_OID_desc objects, each of which describes a single OID. gss_OID_set values are used to name the available mechanisms supported by the GSSAPI, to request the use of specific mechanisms, and to indicate which mechanisms a given credential supports. Storage associated with gss_OID_set values returned to the application by the GSSAPI may be deallocated by the gss_release_oid_set routine.
A credential handle is a caller-opaque atomic datum that identifies a GSSAPI credential data structure. It is represented by the caller- opaque type gss_cred_id_t, which may be implemented as either an arithmetic or a pointer type. Credentials describe a principal, and they give their holder the ability to act as that principal. The GSSAPI does not make the actual credentials available to applications; instead the credential handle is used to identify a particular credential, held internally by GSSAPI or underlying
Wray [Page 6]
RFC 1509 GSSAPI - Overview and C bindings September 1993
mechanism. Thus the credential handle contains no security-relavent information, and requires no special protection by the application. Depending on the implementation, a given credential handle may refer to different credentials when presented to the GSSAPI by different callers. Individual GSSAPI implementations should define both the scope of a credential handle and the scope of a credential itself (which must be at least as wide as that of a handle). Possibilities for credential handle scope include the process that acquired the handle, the acquiring process and its children, or all processes sharing some local identification information (e.g., UID). If no handles exist by which a given credential may be reached, the GSSAPI may delete the credential.
Certain routines allow credential handle parameters to be omitted to indicate the use of a default credential. The mechanism by which a default credential is established and its scope should be defined by the individual GSSAPI implementation.
The gss_ctx_id_t data type contains a caller-opaque atomic value that identifies one end of a GSSAPI security context. It may be implemented as either an arithmetic or a pointer type. Depending on the implementation, a given gss_ctx_id_t value may refer to different GSSAPI security contexts when presented to the GSSAPI by different callers. The security context holds state information about each end of a peer communication, including cryptographic state information. Individual GSSAPI implementations should define the scope of a context. Since no way is provided by which a new gss_ctx_id_t value may be obtained for an existing context, the scope of a context should be the same as the scope of a gss_ctx_id_t.
A token is a caller-opaque type that GSSAPI uses to maintain synchronization between the context data structures at each end of a GSSAPI security context. The token is a cryptographically protected bit-string, generated by the underlying mechanism at one end of a GSSAPI security context for use by the peer mechanism at the other end. Encapsulation (if required) and transfer of the token are the responsibility of the peer applications. A token is passed between the GSSAPI and the application using the gss_buffer_t conventions.
One or more status codes are returned by each GSSAPI routine. Two distinct sorts of status codes are returned. These are termed GSS status codes and Mechanism status codes.
Wray [Page 7]
RFC 1509 GSSAPI - Overview and C bindings September 1993
GSSAPI routines return GSS status codes as their OM_uint32 function value. These codes indicate errors that are independent of the underlying mechanism used to provide the security service. The errors that can be indicated via a GSS status code are either generic API routine errors (errors that are defined in the GSSAPI specification) or calling errors (errors that are specific to these bindings).
A GSS status code can indicate a single fatal generic API error from the routine and a single calling error. In addition, supplementary status information may be indicated via the setting of bits in the supplementary info field of a GSS status code.
These errors are encoded into the 32-bit GSS status code as follows:
Hence if a GSSAPI routine returns a GSS status code whose upper 16 bits contain a non-zero value, the call failed. If the calling error field is non-zero, the invoking application's call of the routine was erroneous. Calling errors are defined in table 5-1. If the routine error field is non-zero, the routine failed for one of the routine- specific reasons listed below in table 5-2. Whether or not the upper 16 bits indicate a failure or a success, the routine may indicate additional information by setting bits in the supplementary info field of the status code. The meaning of individual bits is listed below in table 5-3.
Table 5-1 Calling Errors
Name Value in Meaning Field GSS_S_CALL_INACCESSIBLE_READ 1 A required input parameter could not be read. GSS_S_CALL_INACCESSIBLE_WRITE 2 A required output parameter could not be written. GSS_S_CALL_BAD_STRUCTURE 3 A parameter was malformed
Wray [Page 8]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Table 5-2 Routine Errors
Name Value in Meaning Field
GSS_S_BAD_MECH 1 An unsupported mechanism was requested GSS_S_BAD_NAME 2 An invalid name was supplied GSS_S_BAD_NAMETYPE 3 A supplied name was of an unsupported type GSS_S_BAD_BINDINGS 4 Incorrect channel bindings were supplied GSS_S_BAD_STATUS 5 An invalid status code was supplied
GSS_S_BAD_SIG 6 A token had an invalid signature GSS_S_NO_CRED 7 No credentials were supplied GSS_S_NO_CONTEXT 8 No context has been established GSS_S_DEFECTIVE_TOKEN 9 A token was invalid GSS_S_DEFECTIVE_CREDENTIAL 10 A credential was invalid GSS_S_CREDENTIALS_EXPIRED 11 The referenced credentials have expired GSS_S_CONTEXT_EXPIRED 12 The context has expired GSS_S_FAILURE 13 Miscellaneous failure (see text)
Table 5-3 Supplementary Status Bits
Name Bit Number Meaning GSS_S_CONTINUE_NEEDED 0 (LSB) The routine must be called again to complete its function. See routine documentation for detailed description. GSS_S_DUPLICATE_TOKEN 1 The token was a duplicate of an earlier token GSS_S_OLD_TOKEN 2 The token's validity period has expired GSS_S_UNSEQ_TOKEN 3 A later token has already been processed
The routine documentation also uses the name GSS_S_COMPLETE, which is a zero value, to indicate an absence of any API errors or supplementary information bits.
Wray [Page 9]
RFC 1509 GSSAPI - Overview and C bindings September 1993
All GSS_S_xxx symbols equate to complete OM_uint32 status codes, rather than to bitfield values. For example, the actual value of the symbol GSS_S_BAD_NAMETYPE (value 3 in the routine error field) is 3 << 16.
The macros GSS_CALLING_ERROR(), GSS_ROUTINE_ERROR() and GSS_SUPPLEMENTARY_INFO() are provided, each of which takes a GSS status code and removes all but the relevant field. For example, the value obtained by applying GSS_ROUTINE_ERROR to a status code removes the calling errors and supplementary info fields, leaving only the routine errors field. The values delivered by these macros may be directly compared with a GSS_S_xxx symbol of the appropriate type. The macro GSS_ERROR() is also provided, which when applied to a GSS status code returns a non-zero value if the status code indicated a calling or routine error, and a zero value otherwise.
A GSSAPI implementation may choose to signal calling errors in a platform-specific manner instead of, or in addition to the routine value; routine errors and supplementary info should be returned via routine status values only.
GSSAPI routines return a minor_status parameter, which is used to indicate specialized errors from the underlying security mechanism. This parameter may contain a single mechanism-specific error, indicated by a OM_uint32 value.
The minor_status parameter will always be set by a GSSAPI routine, even if it returns a calling error or one of the generic API errors indicated above as fatal, although other output parameters may remain unset in such cases. However, output parameters that are expected to return pointers to storage allocated by a routine must always set set by the routine, even in the event of an error, although in such cases the GSSAPI routine may elect to set the returned parameter value to NULL to indicate that no storage was actually allocated. Any length field associated with such pointers (as in a gss_buffer_desc structure) should also be set to zero in such cases.
The GSS status code GSS_S_FAILURE is used to indicate that the underlying mechanism detected an error for which no specific GSS status code is defined. The mechanism status code will provide more details about the error.
A name is used to identify a person or entity. GSSAPI authenticates the relationship between a name and the entity claiming the name.
Wray [Page 10]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Two distinct representations are defined for names:
(a) A printable form, for presentation to a user
(b) An internal form, for presentation at the API
The syntax of a printable name is defined by the GSSAPI implementation, and may be dependent on local system configuration, or on individual user preference. The internal form provides a canonical representation of the name that is independent of configuration.
A given GSSAPI implementation may support names drawn from multiple namespaces. In such an implementation, the internal form of the name must include fields that identify the namespace from which the name is drawn. The namespace from which a printable name is drawn is specified by an accompanying object identifier.
Routines (gss_import_name and gss_display_name) are provided to convert names between their printable representations and the gss_name_t type. gss_import_name may support multiple syntaxes for each supported namespace, allowing users the freedom to choose a preferred name representation. gss_display_name should use an implementation-chosen preferred syntax for each supported name-type.
Comparison of internal-form names is accomplished via the gss_compare_names routine. This removes the need for the application program to understand the syntaxes of the various printable names that a given GSSAPI implementation may support.
Storage is allocated by routines that return gss_name_t values. A procedure, gss_release_name, is provided to free storage associated with a name.
GSSAPI supports the use of user-specified tags to identify a given context to the peer application. These tags are used to identify the particular communications channel that carries the context. Channel bindings are communicated to the GSSAPI using the following structure:
Wray [Page 11]
RFC 1509 GSSAPI - Overview and C bindings September 1993
The initiator_addrtype and acceptor_addrtype fields denote the type of addresses contained in the initiator_address and acceptor_address buffers. The address type should be one of the following:
GSS_C_AF_UNSPEC Unspecified address type GSS_C_AF_LOCAL Host-local address type GSS_C_AF_INET DARPA Internet address type GSS_C_AF_IMPLINK ARPAnet IMP address type (eg IP) GSS_C_AF_PUP pup protocols (eg BSP) address type GSS_C_AF_CHAOS MIT CHAOS protocol address type GSS_C_AF_NS XEROX NS address type GSS_C_AF_NBS nbs address type GSS_C_AF_ECMA ECMA address type GSS_C_AF_DATAKIT datakit protocols address type GSS_C_AF_CCITT CCITT protocols (eg X.25) GSS_C_AF_SNA IBM SNA address type GSS_C_AF_DECnet DECnet address type GSS_C_AF_DLI Direct data link interface address type GSS_C_AF_LAT LAT address type GSS_C_AF_HYLINK NSC Hyperchannel address type GSS_C_AF_APPLETALK AppleTalk address type GSS_C_AF_BSC BISYNC 2780/3780 address type GSS_C_AF_DSS Distributed system services address type GSS_C_AF_OSI OSI TP4 address type GSS_C_AF_X25 X25 GSS_C_AF_NULLADDR No address specified
Note that these name address families rather than specific addressing formats. For address families that contain several alternative address forms, the initiator_address and acceptor_address fields must contain sufficient information to determine which address form is used. When not otherwise specified, addresses should be specified in network byte-order.
Conceptually, the GSSAPI concatenates the initiator_addrtype, initiator_address, acceptor_addrtype, acceptor_address and application_data to form an octet string. The mechanism signs this octet string, and binds the signature to the context establishment token emitted by gss_init_sec_context. The same bindings are presented by the context acceptor to gss_accept_sec_context, and a
Wray [Page 12]
RFC 1509 GSSAPI - Overview and C bindings September 1993
signature is calculated in the same way. The calculated signature is compared with that found in the token, and if the signatures differ, gss_accept_sec_context will return a GSS_S_BAD_BINDINGS error, and the context will not be established. Some mechanisms may include the actual channel binding data in the token (rather than just a signature); applications should therefore not use confidential data as channel-binding components. Individual mechanisms may impose additional constraints on addresses and address types that may appear in channel bindings. For example, a mechanism may verify that the initiator_address field of the channel bindings presented to gss_init_sec_context contains the correct network address of the host system.
Various parameters are described as optional. This means that they follow a convention whereby a default value may be requested. The following conventions are used for omitted parameters. These conventions apply only to those parameters that are explicitly documented as optional.
Specify GSS_C_NO_BUFFER as a value. For an input parameter this signifies that default behavior is requested, while for an output parameter it indicates that the information that would be returned via the parameter is not required by the application.
Allows an application to acquire a handle for a pre-existing credential by name. GSSAPI implementations must impose a local access-control policy on callers of this routine to prevent unauthorized callers from acquiring credentials to which they are not entitled. This routine is not intended to provide a "login to the network" function, as such a function would result in the creation of new credentials rather than merely acquiring a handle to existing credentials. Such functions, if required, should be defined in implementation-specific extensions to the API.
If credential acquisition is time-consuming for a mechanism, the mechanism may chooses to delay the actual acquisition until the credential is required (e.g., by gss_init_sec_context or gss_accept_sec_context). Such mechanism-specific implementation decisions should be invisible to the calling application; thus a call of gss_inquire_cred immediately following the call of gss_acquire_cred must return valid credential data, and may therefore incur the overhead of a deferred credential acquisition.
Parameters:
desired_name gss_name_t, read Name of principal whose credential should be acquired
Wray [Page 14]
RFC 1509 GSSAPI - Overview and C bindings September 1993
time_req integer, read number of seconds that credentials should remain valid
desired_mechs Set of Object IDs, read set of underlying security mechanisms that may be used. GSS_C_NULL_OID_SET may be used to obtain an implementation-specific default.
cred_usage integer, read GSS_C_BOTH - Credentials may be used either to initiate or accept security contexts. GSS_C_INITIATE - Credentials will only be used to initiate security contexts. GSS_C_ACCEPT - Credentials will only be used to accept security contexts.
output_cred_handle gss_cred_id_t, modify The returned credential handle.
actual_mechs Set of Object IDs, modify, optional The set of mechanisms for which the credential is valid. Specify NULL if not required.
time_rec Integer, modify, optional Actual number of seconds for which the returned credentials will remain valid. If the implementation does not support expiration of credentials, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required
minor_status Integer, modify Mechanism specific status code. Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_BAD_MECH Unavailable mechanism requested
GSS_S_BAD_NAMETYPE Type contained within desired_name parameter is not supported
GSS_S_BAD_NAME Value supplied for desired_name parameter is
Wray [Page 15]
RFC 1509 GSSAPI - Overview and C bindings September 1993
ill-formed.
GSS_S_FAILURE Unspecified failure. The minor_status parameter contains more detailed information
Informs GSSAPI that the specified credential handle is no longer required by the process. When all processes have released a credential, it will be deleted.
Parameters:
cred_handle gss_cred_id_t, modify, optional buffer containing opaque credential handle. If GSS_C_NO_CREDENTIAL is supplied, the default credential will be released
minor_status integer, modify Mechanism specific status code.
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_NO_CRED Credentials could not be accessed.
Wray [Page 16]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Initiates the establishment of a security context between the application and a remote peer. Initially, the input_token parameter should be specified as GSS_C_NO_BUFFER. The routine may return a output_token which 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 indicating 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_init_sec_context via the input_token parameters.
The values returned via the ret_flags and time_rec parameters are not defined unless the routine returns GSS_S_COMPLETE.
Parameters:
claimant_cred_handle gss_cred_id_t, read, optional handle for credentials claimed. Supply GSS_C_NO_CREDENTIAL to use default credentials.
context_handle gss_ctx_id_t, read/modify context handle for new context. Supply GSS_C_NO_CONTEXT for first call; use value returned by first call in continuation calls.
Wray [Page 17]
RFC 1509 GSSAPI - Overview and C bindings September 1993
target_name gss_name_t, read Name of target
mech_type OID, read, optional Object ID of desired mechanism. Supply GSS_C_NULL_OID to obtain an implementation specific default
req_flags bit-mask, read Contains four 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:
GSS_C_DELEG_FLAG True - Delegate credentials to remote peer False - Don't delegate GSS_C_MUTUAL_FLAG True - Request that remote peer authenticate itself False - Authenticate self to remote peer only GSS_C_REPLAY_FLAG True - Enable replay detection for signed or sealed messages False - Don't attempt to detect replayed messages GSS_C_SEQUENCE_FLAG True - Enable detection of out-of-sequence signed or sealed messages False - Don't attempt to detect out-of-sequence messages
time_req integer, read Desired number of seconds for which context should remain valid. Supply 0 to request a default validity period.
input_chan_bindings channel bindings, read Application-specified bindings. Allows application to securely bind channel identification information to the security context.
Wray [Page 18]
RFC 1509 GSSAPI - Overview and C bindings September 1993
input_token buffer, opaque, read, optional (see text) Token received from peer application. Supply GSS_C_NO_BUFFER on initial call.
actual_mech_type OID, modify actual mechanism used.
output_token buffer, opaque, modify 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.
ret_flags bit-mask, modify Contains six 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 - Credentials were delegated to the remote peer False - No credentials were delegated GSS_C_MUTUAL_FLAG True - Remote peer has been asked to authenticated itself False - Remote peer has not been asked to authenticate itself GSS_C_REPLAY_FLAG True - replay of signed or sealed messages will be detected False - replayed messages will not be detected GSS_C_SEQUENCE_FLAG True - out-of-sequence signed or sealed 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 seal routine False - No confidentiality service (via seal) available. seal will provide message encapsulation, data-origin
Wray [Page 19]
RFC 1509 GSSAPI - Overview and C bindings September 1993
authentication and integrity services only. GSS_C_INTEG_FLAG True - Integrity service may be invoked by calling either gss_sign or gss_seal routines. False - Per-message integrity service unavailable.
time_rec integer, modify, optional 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.
minor_status integer, modify Mechanism specific status code.
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_CONTINUE_NEEDED Indicates that a token from the peer application is required to complete thecontext, and that gss_init_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 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 parameter
GSS_S_BAD_SIG The input_token contains an invalid signature, or a signature that could not be verified
Wray [Page 20]
RFC 1509 GSSAPI - Overview and C bindings September 1993
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_NAMETYPE The provided target_name parameter contained an invalid or unsupported type of name
GSS_S_BAD_NAME The provided target_name parameter was ill-formed.
GSS_S_FAILURE Failure. See minor_status for more information
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. 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 parameters.
Wray [Page 21]
RFC 1509 GSSAPI - Overview and C bindings September 1993
The values returned via the src_name, ret_flags, time_rec, and delegated_cred_handle parameters are not defined unless the routine returns GSS_S_COMPLETE.
Parameters:
context_handle gss_ctx_id_t, read/modify context handle for new context. Supply GSS_C_NO_CONTEXT for first call; use value returned in subsequent calls.
verifier_cred_handle gss_cred_id_t, read, optional Credential handle claimed by context acceptor. Specify GSS_C_NO_CREDENTIAL to use default credentials. If GSS_C_NO_CREDENTIAL is specified, but the caller has no default credentials established, an implementation-defined default credential may be used.
input_token_buffer buffer, opaque, read token obtained from remote application
input_chan_bindings channel bindings, read Application-specified bindings. Allows application to securely bind channel identification information to the security context.
src_name gss_name_t, modify, optional Authenticated name of context initiator. After use, this name should be deallocated by passing it to gss_release_name. If not required, specify NULL.
mech_type Object ID, modify Security mechanism used. The returned OID value will be a pointer into static storage, and should be treated as read-only by the caller.
output_token buffer, opaque, modify 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.
Wray [Page 22]
RFC 1509 GSSAPI - Overview and C bindings September 1993
ret_flags bit-mask, modify Contains six 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 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 authentication GSS_C_REPLAY_FLAG True - replay of signed or sealed messages will be detected False - replayed messages will not be detected GSS_C_SEQUENCE_FLAG True - out-of-sequence signed or sealed 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 seal routine False - No confidentiality service (via seal) available. seal 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_sign or gss_seal routines. False - Per-message integrity service unavailable.
time_rec integer, modify, optional number of seconds for which the context will remain valid. Specify NULL if not required.
Wray [Page 23]
RFC 1509 GSSAPI - Overview and C bindings September 1993
delegated_cred_handle gss_cred_id_t, modify credential handle for credentials received from context initiator. Only valid if deleg_flag in ret_flags is true.
minor_status integer, modify Mechanism specific status code.
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
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 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 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 signature.
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.
Wray [Page 24]
RFC 1509 GSSAPI - Overview and C bindings September 1993
GSS_S_FAILURE Failure. See minor_status for more information.
Provides a way to pass a token to the security service. Usually, tokens are associated either with context establishment (when they would be passed to gss_init_sec_context or gss_accept_sec_context) or with per-message security service (when they would be passed to gss_verify or gss_unseal). Occasionally, tokens may be received at other times, and gss_process_context_token allows such tokens to be passed to the underlying security service for processing. At present, such additional tokens may only be generated by gss_delete_sec_context. GSSAPI implementation may use this service to implement deletion of the security context.
Parameters:
context_handle gss_ctx_id_t, read context handle of context on which token is to be processed
token_buffer buffer, opaque, read pointer to first byte of token to process
minor_status integer, modify Implementation specific status code.
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_DEFECTIVE_TOKEN Indicates that consistency checks performed on the token failed
GSS_S_FAILURE Failure. See minor_status for more information
GSS_S_NO_CONTEXT The context_handle did not refer to a valid context
Wray [Page 25]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Delete a security context. gss_delete_sec_context will delete the local data structures associated with the specified security context, and generate an output_token, which when passed to the peer gss_process_context_token will instruct it to do likewise. No further security services may be obtained using the context specified by context_handle.
Parameters:
minor_status integer, modify Mechanism specific status code.
context_handle gss_ctx_id_t, modify context handle identifying context to delete.
output_token buffer, opaque, modify token to be sent to remote application to instruct it to also delete the context
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_FAILURE Failure, see minor_status for more information
Determines the number of seconds for which the specified context will remain valid.
Wray [Page 26]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Parameters:
minor_status integer, modify Implementation specific status code.
context_handle gss_ctx_id_t, read Identifies the context to be interrogated.
time_rec integer, modify Number of seconds that the context will remain valid. If the context has already expired, zero will be returned. Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_CONTEXT_EXPIRED The context has already expired
GSS_S_CREDENTIALS_EXPIRED The context is recognized, but associated credentials have expired
GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context
Generates a cryptographic signature for the supplied message, and places the signature in a token for transfer to the peer application. The qop_req parameter allows a choice between several cryptographic algorithms, if supported by the chosen mechanism.
Parameters:
minor_status integer, modify Implementation specific status code.
context_handle gss_ctx_id_t, read identifies the context on which the message
Wray [Page 27]
RFC 1509 GSSAPI - Overview and C bindings September 1993
will be sent
qop_req integer, read, optional Specifies requested quality of protection. Callers are encouraged, on portability grounds, to accept the default quality of protection offered by the chosen mechanism, which may be requested by specifying GSS_C_QOP_DEFAULT for this parameter. If an unsupported protection strength is requested, gss_sign will return a major_status of GSS_S_FAILURE.
message_buffer buffer, opaque, read message to be signed
msg_token buffer, opaque, modify buffer to receive token
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_CONTEXT_EXPIRED The context has already expired
GSS_S_CREDENTIALS_EXPIRED The context is recognized, but associated credentials have expired
GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context
GSS_S_FAILURE Failure. See minor_status for more information.
Verifies that a cryptographic signature, contained in the token parameter, fits the supplied message. The qop_state parameter allows a message recipient to determine the strength of protection that was applied to the message.
Wray [Page 28]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Parameters:
minor_status integer, modify Mechanism specific status code.
context_handle gss_ctx_id_t, read identifies the context on which the message arrived
message_buffer buffer, opaque, read message to be verified
token_buffer buffer, opaque, read token associated with message
qop_state integer, modify quality of protection gained from signature
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_DEFECTIVE_TOKEN The token failed consistency checks
GSS_S_BAD_SIG The signature was incorrect
GSS_S_DUPLICATE_TOKEN The token was valid, and contained a correct signature for the message, but it had already been processed
GSS_S_OLD_TOKEN The token was valid, and contained a correct signature for the message, but it is too old
GSS_S_UNSEQ_TOKEN The token was valid, and contained a correct signature for the message, but has been verified out of sequence; an earlier token has been signed or sealed by the remote application, but not yet been processed locally.
GSS_S_CONTEXT_EXPIRED The context has already expired
GSS_S_CREDENTIALS_EXPIRED The context is recognized, but associated credentials have expired
Wray [Page 29]
RFC 1509 GSSAPI - Overview and C bindings September 1993
GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context
GSS_S_FAILURE Failure. See minor_status for more information.
OM_uint32 gss_seal ( OM_uint32 * minor_status, gss_ctx_id_t context_handle, int conf_req_flag, int qop_req gss_buffer_t input_message_buffer, int * conf_state, gss_buffer_t output_message_buffer)
Purpose:
Cryptographically signs and optionally encrypts the specified input_message. The output_message contains both the signature and the message. The qop_req parameter allows a choice between several cryptographic algorithms, if supported by the chosen mechanism.
Parameters:
minor_status integer, modify Mechanism specific status code.
context_handle gss_ctx_id_t, read identifies the context on which the message will be sent
conf_req_flag boolean, read True - Both confidentiality and integrity services are requested False - Only integrity service is requested
qop_req integer, read, optional Specifies required quality of protection. A mechanism-specific default may be requested by setting qop_req to GSS_C_QOP_DEFAULT. If an unsupported protection strength is requested, gss_seal will return a major_status of GSS_S_FAILURE.
input_message_buffer buffer, opaque, read message to be sealed
Wray [Page 30]
RFC 1509 GSSAPI - Overview and C bindings September 1993
conf_state boolean, modify True - Confidentiality, data origin authentication and integrity services have been applied False - Integrity and data origin services only has been applied.
output_message_buffer buffer, opaque, modify buffer to receive sealed message
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_CONTEXT_EXPIRED The context has already expired
GSS_S_CREDENTIALS_EXPIRED The context is recognized, but associated credentials have expired
GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context
GSS_S_FAILURE Failure. See minor_status for more information.
OM_uint32 gss_unseal ( OM_uint32 * minor_status, gss_ctx_id_t context_handle, gss_buffer_t input_message_buffer, gss_buffer_t output_message_buffer, int * conf_state, int * qop_state)
Purpose:
Converts a previously sealed message back to a usable form, verifying the embedded signature. The conf_state parameter indicates whether the message was encrypted; the qop_state parameter indicates the strength of protection that was used to provide the confidentiality and integrity services.
Parameters:
minor_status integer, modify Mechanism specific status code.
Wray [Page 31]
RFC 1509 GSSAPI - Overview and C bindings September 1993
context_handle gss_ctx_id_t, read identifies the context on which the message arrived
output_message_buffer buffer, opaque, modify buffer to receive unsealed message
conf_state boolean, modify True - Confidentiality and integrity protection were used False - Inteegrity service only was used
qop_state integer, modify quality of protection gained from signature
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_DEFECTIVE_TOKEN The token failed consistency checks
GSS_S_BAD_SIG The signature was incorrect
GSS_S_DUPLICATE_TOKEN The token was valid, and contained a correct signature for the message, but it had already been processed
GSS_S_OLD_TOKEN The token was valid, and contained a correct signature for the message, but it is too old
GSS_S_UNSEQ_TOKEN The token was valid, and contained a correct signature for the message, but has been verified out of sequence; an earlier token has been signed or sealed by the remote application, but not yet been processed locally.
GSS_S_CONTEXT_EXPIRED The context has already expired
GSS_S_CREDENTIALS_EXPIRED The context is recognized, but associated credentials have expired
Wray [Page 32]
RFC 1509 GSSAPI - Overview and C bindings September 1993
GSS_S_NO_CONTEXT The context_handle parameter did not identify a valid context
GSS_S_FAILURE Failure. See minor_status for more information.
OM_uint32 gss_display_status ( OM_uint32 * minor_status, int status_value, int status_type, gss_OID mech_type, int * message_context, gss_buffer_t status_string)
Purpose:
Allows an application to obtain a textual representation of a GSSAPI status code, for display to the user or for logging purposes. Since some status values may indicate multiple errors, applications may need to call gss_display_status multiple times, each call generating a single text string. The message_context parameter is used to indicate which error message should be extracted from a given status_value; message_context should be initialized to 0, and gss_display_status will return a non-zero value if there are further messages to extract.
Parameters:
minor_status integer, modify Mechanism specific status code.
status_value integer, read Status value to be converted
status_type integer, read GSS_C_GSS_CODE - status_value is a GSS status code GSS_C_MECH_CODE - status_value is a mechanism status code
mech_type Object ID, read, optional Underlying mechanism (used to interpret a minor status value) Supply GSS_C_NULL_OID to obtain the system default.
message_context integer, read/modify Should be initialized to zero by caller
Wray [Page 33]
RFC 1509 GSSAPI - Overview and C bindings September 1993
on first call. If further messages are contained in the status_value parameter, message_context will be non-zero on return, and this value should be passed back to subsequent calls, along with the same status_value, status_type and mech_type parameters.
status_string buffer, character string, modify textual interpretation of the status_value
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_BAD_MECH Indicates that translation in accordance with an unsupported mechanism type was requested
GSS_S_BAD_STATUS The status value was not recognized, or the status type was neither GSS_C_GSS_CODE nor GSS_C_MECH_CODE.
Allows an application to determine which underlying security mechanisms are available.
Parameters:
minor_status integer, modify Mechanism specific status code.
mech_set set of Object IDs, modify set of implementation-supported mechanisms. The returned gss_OID_set value will be a pointer into static storage, and should be treated as read-only by the caller.
Wray [Page 34]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Allows an application to compare two internal-form names to determine whether they refer to the same entity.
Parameters:
minor_status integer, modify Mechanism specific status code.
name1 gss_name_t, read internal-form name
name2 gss_name_t, read internal-form name
name_equal boolean, modify True - names refer to same entity False - names refer to different entities (strictly, the names are not known to refer to the same identity). Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_BAD_NAMETYPE The type contained within either name1 or name2 was unrecognized, or the names were of incomparable types.
GSS_S_BAD_NAME One or both of name1 or name2 was ill-formed
Wray [Page 35]
RFC 1509 GSSAPI - Overview and C bindings September 1993
Allows an application to obtain a textual representation of an opaque internal-form name for display purposes. The syntax of a printable name is defined by the GSSAPI implementation.
Parameters:
minor_status integer, modify Mechanism specific status code.
input_name gss_name_t, read name to be displayed
output_name_buffer buffer, character-string, modify buffer to receive textual name string
output_name_type Object ID, modify The type of the returned name. The returned gss_OID will be a pointer into static storage, and should be treated as read-only by the caller
Function value:
GSS status code:
GSS_S_COMPLETE Successful completion
GSS_S_BAD_NAMETYPE The type of input_name was not recognized
RFC 1509 GSSAPI - Overview and C bindings September 1993
Purpose:
Convert a printable name to internal form.
Parameters:
minor_status integer, modify Mechanism specific status code
input_name_buffer buffer, character-string, read buffer containing printable name to convert
input_name_type Object ID, read, optional Object Id specifying type of printable name. Applications may specify either GSS_C_NULL_OID to use a local system-specific printable syntax, or an OID registered by the GSSAPI implementation to name a particular namespace.
output_name gss_name_t, modify returned name in internal form
Function value:
GSS status code
GSS_S_COMPLETE Successful completion
GSS_S_BAD_NAMETYPE The input_name_type was unrecognized
GSS_S_BAD_NAME The input_name parameter could not be interpreted as a name of the specified type
Free storage associated with a buffer format name. The storage must have been allocated by a GSSAPI routine. In addition to freeing the associated storage, the routine will zero the length field in the buffer parameter.
Parameters:
minor_status integer, modify Mechanism specific status code
buffer buffer, modify The storage associated with the buffer will be deleted. The gss_buffer_desc object will not be freed, but its length field will be zeroed.
Obtains information about a credential. The caller must already have obtained a handle that refers to the credential.
Parameters:
minor_status integer, modify Mechanism specific status code
cred_handle gss_cred_id_t, read A handle that refers to the target credential. Specify GSS_C_NO_CREDENTIAL to inquire about the default credential.
name gss_name_t, modify The name whose identity the credential asserts. Specify NULL if not required.
lifetime Integer, modify
Wray [Page 39]
RFC 1509 GSSAPI - Overview and C bindings September 1993
The number of seconds for which the credential will remain valid. If the credential has expired, this parameter will be set to zero. If the implementation does not support credential expiration, the value GSS_C_INDEFINITE will be returned. Specify NULL if not required.
cred_usage Integer, modify How the credential may be used. One of the following: GSS_C_INITIATE GSS_C_ACCEPT GSS_C_BOTH Specify NULL if not required.
mechanisms gss_OID_set, modify Set of mechanisms supported by the credential. Specify NULL if not required.
Function value:
GSS status code
GSS_S_COMPLETE Successful completion
GSS_S_NO_CRED The referenced credentials could not be accessed.
GSS_S_DEFECTIVE_CREDENTIAL The referenced credentials were invalid.
GSS_S_CREDENTIALS_EXPIRED The referenced credentials have expired. If the lifetime parameter was not passed as NULL, it will be set to 0.
RFC 1509 GSSAPI - Overview and C bindings September 1993
/* * Note that a platform supporting the xom.h X/Open header file * may make use of that header for the definitions of OM_uint32 * and the structure to which gss_OID_desc equates. */
/* * Six independent flags each of which indicates that a context * supports a specific service option. */ #define GSS_C_DELEG_FLAG 1 #define GSS_C_MUTUAL_FLAG 2 #define GSS_C_REPLAY_FLAG 4 #define GSS_C_SEQUENCE_FLAG 8 #define GSS_C_CONF_FLAG 16 #define GSS_C_INTEG_FLAG 32
/* * Define the default Quality of Protection for per-message * services. Note that an implementation that offers multiple * levels of QOP may either reserve a value (for example zero, * as assumed here) to mean "default protection", or alternatively * may simply equate GSS_C_QOP_DEFAULT to a specific explicit QOP * value.
Wray [Page 42]
RFC 1509 GSSAPI - Overview and C bindings September 1993
*/ #define GSS_C_QOP_DEFAULT 0
/* * Expiration time of 2^32-1 seconds means infinite lifetime for a * credential or security context */ #define GSS_C_INDEFINITE 0xfffffffful
/* Major status codes */
#define GSS_S_COMPLETE 0
/* * Some "helper" definitions to make the status code macros obvious. */ #define GSS_C_CALLING_ERROR_OFFSET 24 #define GSS_C_ROUTINE_ERROR_OFFSET 16 #define GSS_C_SUPPLEMENTARY_OFFSET 0 #define GSS_C_CALLING_ERROR_MASK 0377ul #define GSS_C_ROUTINE_ERROR_MASK 0377ul #define GSS_C_SUPPLEMENTARY_MASK 0177777ul
/* * The macros that test status codes for error conditions */ #define GSS_CALLING_ERROR(x) \ (x & (GSS_C_CALLING_ERROR_MASK << GSS_C_CALLING_ERROR_OFFSET)) #define GSS_ROUTINE_ERROR(x) \ (x & (GSS_C_ROUTINE_ERROR_MASK << GSS_C_ROUTINE_ERROR_OFFSET)) #define GSS_SUPPLEMENTARY_INFO(x) \ (x & (GSS_C_SUPPLEMENTARY_MASK << GSS_C_SUPPLEMENTARY_OFFSET)) #define GSS_ERROR(x) \ ((GSS_CALLING_ERROR(x) != 0) || (GSS_ROUTINE_ERROR(x) != 0))
[1] Linn, J., "Generic Security Service Application Program Interface", RFC 1508, Geer Zolot Associate, September 1993.
[2] "OSI Object Management API Specification, Version 2.0 t", X.400 API Association & X/Open Company Limited, August 24, 1990. Specification of datatypes and routines for manipulating information objects.
Security Considerations
Security issues are discussed throughout this memo.
Author's Address
John Wray Digital Equipment Corporation 550 King Street, LKG2-2/AA6 Littleton, MA 01460 USA