RFC 2078
Generic Security Service Application Program Interface, Version 2
2.4: Support calls This group of calls provides support functions useful to GSS-API callers, independent of the state of established contexts. Their characterization with regard to blocking or non-blocking status in terms of network interactions is unspecified.
2.4.1: GSS_Display_status call Inputs: o status_value INTEGER,-GSS-API major_status or minor_status return value o status_type INTEGER,-1 if major_status, 2 if minor_status o mech_type OBJECT IDENTIFIER-mech_type to be used for minor_ status translation Outputs: o major_status INTEGER, o minor_status INTEGER, o status_string_set SET OF OCTET STRING Return major_status codes: o GSS_S_COMPLETE indicates that a valid printable status representation (possibly representing more than one status event encoded within the status_value) is available in the returned status_string_set. o GSS_S_BAD_MECH indicates that translation in accordance with an unsupported mech_type was requested, so translation could not be performed. o GSS_S_BAD_STATUS indicates that the input status_value was invalid, or that the input status_type carried a value other than 1 or 2, so translation could not be performed. o GSS_S_FAILURE indicates that the requested operation could not be performed for reasons unspecified at the GSS-API level. Provides a means for callers to translate GSS-API-returned major and minor status codes into printable string representations. 2.4.2: GSS_Indicate_mechs call Input: o (none)
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o mech_set SET OF OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates that a set of available mechanisms has
been returned in mech_set.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to determine the set of mechanism types available on
the local system. This call is intended for support of specialized
callers who need to request non-default mech_type sets from
GSS_Acquire_cred(), and should not be needed by other callers.
2.4.3: GSS_Compare_name call
Inputs:
o name1 INTERNAL NAME,
o name2 INTERNAL NAME
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o name_equal BOOLEAN
Return major_status codes:
o GSS_S_COMPLETE indicates that name1 and name2 were comparable,
and that the name_equal result indicates whether name1 and
name2 represent the same entity.
o GSS_S_BAD_NAMETYPE indicates that one or both of name1 and
name2 contained internal type specifiers uninterpretable
by the applicable underlying GSS-API mechanism(s), or that
the two names' types are different and incomparable, so that
the comparison operation could not be completed.
o GSS_S_BAD_NAME indicates that one or both of the input names
was ill-formed in terms of its internal type specifier, so
the comparison operation could not be completed.
o GSS_S_FAILURE indicates that the call's operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to compare two internal name representations to
determine whether they refer to the same entity. If either name
presented to GSS_Compare_name() denotes an anonymous principal,
GSS_Compare_name() shall indicate FALSE. It is not required that
either or both inputs name1 and name2 be MNs; for some
implementations and cases, GSS_S_BAD_NAMETYPE may be returned,
indicating name incomparability, for the case where neither input
name is an MN.
2.4.4: GSS_Display_name call
Inputs:
o name INTERNAL NAME
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o name_string OCTET STRING,
o name_type OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates that a valid printable name
representation is available in the returned name_string.
o GSS_S_BAD_NAMETYPE indicates that the provided name was of a
type uninterpretable by the applicable underlying GSS-API
mechanism(s), so no printable representation could be generated.
o GSS_S_BAD_NAME indicates that the contents of the provided name
were inconsistent with the internally-indicated name type, so
no printable representation could be generated.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to translate an internal name representation into a printable form with associated namespace type descriptor. The syntax of the printable form is a local matter. If the input name represents an anonymous identity, a reserved value (GSS_C_NT_ANONYMOUS) shall be returned for name_type. 2.4.5: GSS_Import_name call Inputs: o input_name_string OCTET STRING, o input_name_type OBJECT IDENTIFIER Outputs: o major_status INTEGER, o minor_status INTEGER, o output_name INTERNAL NAME Return major_status codes: o GSS_S_COMPLETE indicates that a valid name representation is output in output_name and described by the type value in output_name_type. o GSS_S_BAD_NAMETYPE indicates that the input_name_type is unsupported by the applicable underlying GSS-API mechanism(s), so the import operation could not be completed. o GSS_S_BAD_NAME indicates that the provided input_name_string is ill-formed in terms of the input_name_type, so the import operation could not be completed. o GSS_S_FAILURE indicates that the requested operation could not be performed for reasons unspecified at the GSS-API level. Allows callers to provide a name representation as a contiguous octet string, designate the type of namespace in conjunction with which it should be parsed, and convert that representation to an internal form suitable for input to other GSS-API routines. The syntax of the input_name_string is defined in conjunction with its associated name type; depending on the input_name_type, the associated input_name_string may or may not be a printable string. Note: The input_name_type argument serves to describe and qualify the
interpretation of the associated input_name_string; it does not
specify the data type of the returned output_name.
If a mechanism claims support for a particular name type, its
GSS_Import_name() operation shall be able to accept all possible
values conformant to the external name syntax as defined for that
name type. These imported values may correspond to:
(1) locally registered entities (for which credentials may be
acquired),
(2) non-local entities (for which local credentials cannot be
acquired, but which may be referenced as targets of initiated
security contexts or initiators of accepted security contexts), or
to
(3) neither of the above.
Determination of whether a particular name belongs to class (1), (2),
or (3) as described above is not guaranteed to be performed by the
GSS_Import_name() function.
The internal name generated by a GSS_Import_name() operation may be a
single-mechanism MN, and is likely to be an MN within a single-
mechanism implementation, but portable callers must not depend on
this property (and must not, therefore, assume that the output from
GSS_Import_name() can be passed directly to GSS_Export_name() without
first being processed through GSS_Canonicalize_name()).
2.4.6: GSS_Release_name call
Inputs:
o name INTERNAL NAME
Outputs:
o major_status INTEGER,
o minor_status INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates that the storage associated with the
input name was successfully released.
o GSS_S_BAD_NAME indicates that the input name argument did not
contain a valid name.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to release the storage associated with an internal
name representation. This call's specific behavior depends on the
language and programming environment within which a GSS-API
implementation operates, and is therefore detailed within applicable
bindings specifications; in particular, this call may be superfluous
within bindings where memory management is automatic.
2.4.7: GSS_Release_buffer call
Inputs:
o buffer OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates that the storage associated with the
input buffer was successfully released.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to release the storage associated with an OCTET STRING
buffer allocated by another GSS-API call. This call's specific
behavior depends on the language and programming environment within
which a GSS-API implementation operates, and is therefore detailed
within applicable bindings specifications; in particular, this call
may be superfluous within bindings where memory management is
automatic.
2.4.8: GSS_Release_OID_set call
Inputs:
o buffer SET OF OBJECT IDENTIFIER
Outputs:
o major_status INTEGER,
o minor_status INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates that the storage associated with the
input object identifier set was successfully released.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to release the storage associated with an object
identifier set object allocated by another GSS-API call. This call's
specific behavior depends on the language and programming environment
within which a GSS-API implementation operates, and is therefore
detailed within applicable bindings specifications; in particular,
this call may be superfluous within bindings where memory management
is automatic.
2.4.9: GSS_Create_empty_OID_set call
Inputs:
o (none)
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o oid_set SET OF OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates successful completion
o GSS_S_FAILURE indicates that the operation failed
Creates an object identifier set containing no object identifiers, to
which members may be subsequently added using the
GSS_Add_OID_set_member() routine. These routines are intended to be
used to construct sets of mechanism object identifiers, for input to
GSS_Acquire_cred().
2.4.10: GSS_Add_OID_set_member call Inputs: o member_oid OBJECT IDENTIFIER, o oid_set SET OF OBJECT IDENTIFIER Outputs: o major_status INTEGER, o minor_status INTEGER, Return major_status codes: o GSS_S_COMPLETE indicates successful completion o GSS_S_FAILURE indicates that the operation failed Adds an Object Identifier to an Object Identifier set. This routine is intended for use in conjunction with GSS_Create_empty_OID_set() when constructing a set of mechanism OIDs for input to GSS_Acquire_cred(). 2.4.11: GSS_Test_OID_set_member call Inputs: o member OBJECT IDENTIFIER, o set SET OF OBJECT IDENTIFIER Outputs: o major_status INTEGER, o minor_status INTEGER, o present BOOLEAN Return major_status codes: o GSS_S_COMPLETE indicates successful completion o GSS_S_FAILURE indicates that the operation failed
Interrogates an Object Identifier set to determine whether a specified Object Identifier is a member. This routine is intended to be used with OID sets returned by GSS_Indicate_mechs(), GSS_Acquire_cred(), and GSS_Inquire_cred(). 2.4.12: GSS_Release_OID call Inputs: o oid OBJECT IDENTIFIER Outputs: o major_status INTEGER, o minor_status INTEGER Return major_status codes: o GSS_S_COMPLETE indicates successful completion o GSS_S_FAILURE indicates that the operation failed Allows the caller to release the storage associated with an OBJECT IDENTIFIER buffer allocated by another GSS-API call. This call's specific behavior depends on the language and programming environment within which a GSS-API implementation operates, and is therefore detailed within applicable bindings specifications; in particular, this call may be superfluous within bindings where memory management is automatic. 2.4.13: GSS_OID_to_str call Inputs: o oid OBJECT IDENTIFIER Outputs: o major_status INTEGER, o minor_status INTEGER, o oid_str OCTET STRING Return major_status codes: o GSS_S_COMPLETE indicates successful completion
o GSS_S_FAILURE indicates that the operation failed
The function GSS_OID_to_str() returns a string representing the input
OID in numeric ASN.1 syntax format (curly-brace enclosed, space-
delimited, e.g., "{2 16 840 1 113687 1 2 1}"). The string is
releasable using GSS_Release_buffer(). If the input "oid" does not
represent a syntactically valid object identifier, GSS_S_FAILURE
status is returned and the returned oid_str result is NULL.
2.4.14: GSS_Str_to_OID call
Inputs:
o oid_str OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o oid OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates successful completion
o GSS_S_FAILURE indicates that the operation failed
The function GSS_Str_to_OID() constructs and returns an OID from its
printable form; implementations should be able to accept the numeric
ASN.1 syntax form as described for GSS_OID_to_str(), and this form
should be used for portability, but implementations of this routine
may also accept other formats (e.g., "1.2.3.3"). The OID is suitable
for release using the function GSS_Release_OID(). If the input
oid_str cannot be translated into an OID, GSS_S_FAILURE status is
returned and the "oid" result is NULL.
2.4.15: GSS_Inquire_names_for_mech call
Input:
o input_mech_type OBJECT IDENTIFIER, -- mechanism type
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o name_type_set SET OF OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates that the output name_type_set contains
a list of name types which are supported by the locally available
mechanism identified by input_mech_type.
o GSS_S_BAD_MECH indicates that the mechanism identified by
input_mech_type was unsupported within the local implementation,
causing the query to fail.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
Allows callers to determine the set of name types which are
supportable by a specific locally-available mechanism.
2.4.16: GSS_Inquire_mechs_for_name call
Inputs:
o input_name INTERNAL NAME,
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o mech_types SET OF OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates that a set of object identifiers,
corresponding to the set of mechanisms suitable for processing
the input_name, is available in mech_types.
o GSS_S_BAD_NAME indicates that the input_name could not be
processed.
o GSS_S_BAD_NAMETYPE indicates that the type of the input_name
is unsupported by the GSS-API implementation.
o GSS_S_FAILURE indicates that the requested operation could not
be performed for reasons unspecified at the GSS-API level.
This routine returns the mechanism set with which the input_name may be processed. After use, the mech_types object should be freed by the caller via the GSS_Release_OID_set() call. Note: it is anticipated that implementations of GSS_Inquire_mechs_for_name() will commonly operate based on type information describing the capabilities of available mechanisms; it is not guaranteed that all identified mechanisms will necessarily be able to canonicalize (via GSS_Canonicalize_name()) a particular name. 2.4.17: GSS_Canonicalize_name call Inputs: o input_name INTERNAL NAME, o mech_type OBJECT IDENTIFIER -- must be explicit mechanism, not "default" specifier Outputs: o major_status INTEGER, o minor_status INTEGER, o output_name INTERNAL NAME Return major_status codes: o GSS_S_COMPLETE indicates that a mechanism-specific reduction of the input_name, as processed by the mechanism identified by mech_type, is available in output_name. o GSS_S_BAD_MECH indicates that the identified mechanism is unsupported. o GSS_S_BAD_NAMETYPE indicates that the input name does not contain an element with suitable type for processing by the identified mechanism. o GSS_S_BAD_NAME indicates that the input name contains an element with suitable type for processing by the identified mechanism, but that this element could not be processed successfully. o GSS_S_FAILURE indicates that the requested operation could not be performed for reasons unspecified at the GSS-API level.
This routine reduces a GSS-API internal name, which may in general contain elements corresponding to multiple mechanisms, to a mechanism-specific Mechanism Name (MN) by applying the translations corresponding to the mechanism identified by mech_type. 2.4.18: GSS_Export_name call Inputs: o input_name INTERNAL NAME, -- required to be MN Outputs: o major_status INTEGER, o minor_status INTEGER, o output_name OCTET STRING Return major_status codes: o GSS_S_COMPLETE indicates that a flat representation of the input name is available in output_name. o GSS_S_NAME_NOT_MN indicates that the input name contained elements corresponding to multiple mechanisms, so cannot be exported into a single-mechanism flat form. o GSS_S_BAD_NAME indicates that the input name was an MN, but could not be processed. o GSS_S_BAD_NAMETYPE indicates that the input name was an MN, but that its type is unsupported by the GSS-API implementation. o GSS_S_FAILURE indicates that the requested operation could not be performed for reasons unspecified at the GSS-API level. This routine creates a flat name representation, suitable for bytewise comparison or for input to GSS_Import_name() in conjunction with the reserved GSS-API Exported Name Object OID, from a internal- form Mechanism Name (MN) as emitted, e.g., by GSS_Canonicalize_name() or GSS_Accept_sec_context(). The emitted GSS-API Exported Name Object is self-describing; no associated parameter-level OID need be emitted by this call. This flat representation consists of a mechanism-independent wrapper layer, defined in Section 3.2 of this document, enclosing a mechanism-defined name representation.
In all cases, the flat name output by GSS_Export_name() to correspond to a particular input MN must be invariant over time within a particular installation. The GSS_S_NAME_NOT_MN status code is provided to enable implementations to reject input names which are not MNs. It is not, however, required for purposes of conformance to this specification that all non-MN input names must necessarily be rejected. 2.4.19: GSS_Duplicate_name call Inputs: o src_name INTERNAL NAME Outputs: o major_status INTEGER, o minor_status INTEGER, o dest_name INTERNAL NAME Return major_status codes: o GSS_S_COMPLETE indicates that dest_name references an internal name object containing the same name as passed to src_name. o GSS_S_BAD_NAME indicates that the input name was invalid. o GSS_S_BAD_NAMETYPE indicates that the input name's type is unsupported by the GSS-API implementation. o GSS_S_FAILURE indicates that the requested operation could not be performed for reasons unspecified at the GSS-API level. This routine takes input internal name src_name, and returns another reference (dest_name) to that name which can be used even if src_name is later freed. (Note: This may be implemented by copying or through use of reference counts.) 3: Data Structure Definitions for GSS-V2 Usage Subsections of this section define, for interoperability and portability purposes, certain data structures for use with GSS-V2.
3.1: Mechanism-Independent Token Format This section specifies a mechanism-independent level of encapsulating representation for the initial token of a GSS-API context establishment sequence, incorporating an identifier of the mechanism type to be used on that context and enabling tokens to be interpreted unambiguously at GSS-API peers. Use of this format is required for initial context establishment tokens of Internet standards-track GSS-API mechanisms; use in non-initial tokens is optional. The encoding format for the token tag is derived from ASN.1 and DER (per illustrative ASN.1 syntax included later within this subsection), but its concrete representation is defined directly in terms of octets rather than at the ASN.1 level in order to facilitate interoperable implementation without use of general ASN.1 processing code. The token tag consists of the following elements, in order: 1. 0x60 -- Tag for [APPLICATION 0] SEQUENCE; indicates that constructed form, definite length encoding follows. 2. Token length octets, specifying length of subsequent data (i.e., the summed lengths of elements 3-5 in this list, and of the mechanism-defined token object following the tag). This element comprises a variable number of octets: 2a. If the indicated value is less than 128, it shall be represented in a single octet with bit 8 (high order) set to "0" and the remaining bits representing the value. 2b. If the indicated value is 128 or more, it shall be represented in two or more octets, with bit 8 of the first octet set to "1" and the remaining bits of the first octet specifying the number of additional octets. The subsequent octets carry the value, 8 bits per octet, most significant digit first. The minimum number of octets shall be used to encode the length (i.e., no octets representing leading zeros shall be included within the length encoding). 3. 0x06 -- Tag for OBJECT IDENTIFIER 4. Object identifier length -- length (number of octets) of the encoded object identifier contained in element 5, encoded per rules as described in 2a. and 2b. above. 5. Object identifier octets -- variable number of octets, encoded per ASN.1 BER rules:
5a. The first octet contains the sum of two values: (1) the top-
level object identifier component, multiplied by 40 (decimal), and
(2) the second-level object identifier component. This special
case is the only point within an object identifier encoding where
a single octet represents contents of more than one component.
5b. Subsequent octets, if required, encode successively-lower
components in the represented object identifier. A component's
encoding may span multiple octets, encoding 7 bits per octet (most
significant bits first) and with bit 8 set to "1" on all but the
final octet in the component's encoding. The minimum number of
octets shall be used to encode each component (i.e., no octets
representing leading zeros shall be included within a component's
encoding).
(Note: In many implementations, elements 3-5 may be stored and
referenced as a contiguous string constant.)
The token tag is immediately followed by a mechanism-defined token
object. Note that no independent size specifier intervenes following
the object identifier value to indicate the size of the mechanism-
defined token object. While ASN.1 usage within mechanism-defined
tokens is permitted, there is no requirement that the mechanism-
specific innerContextToken, innerMsgToken, and sealedUserData data
elements must employ ASN.1 BER/DER encoding conventions.
The following ASN.1 syntax is included for descriptive purposes only,
to illustrate structural relationships among token and tag objects.
For interoperability purposes, token and tag encoding shall be
performed using the concrete encoding procedures described earlier in
this subsection.
GSS-API DEFINITIONS ::=
BEGIN
MechType ::= OBJECT IDENTIFIER
-- data structure definitions
-- callers must be able to distinguish among
-- InitialContextToken, SubsequentContextToken,
-- PerMsgToken, and SealedMessage data elements
-- based on the usage in which they occur
InitialContextToken ::=
-- option indication (delegation, etc.) indicated within
-- mechanism-specific token
[APPLICATION 0] IMPLICIT SEQUENCE {
thisMech MechType,
innerContextToken ANY DEFINED BY thisMech
-- contents mechanism-specific
-- ASN.1 structure not required
}
SubsequentContextToken ::= innerContextToken ANY
-- interpretation based on predecessor InitialContextToken
-- ASN.1 structure not required
PerMsgToken ::=
-- as emitted by GSS_GetMIC and processed by GSS_VerifyMIC
-- ASN.1 structure not required
innerMsgToken ANY
SealedMessage ::=
-- as emitted by GSS_Wrap and processed by GSS_Unwrap
-- includes internal, mechanism-defined indicator
-- of whether or not encrypted
-- ASN.1 structure not required
sealedUserData ANY
END
3.2: Mechanism-Independent Exported Name Object Format This section specifies a mechanism-independent level of encapsulating representation for names exported via the GSS_Export_name() call, including an object identifier representing the exporting mechanism. The format of names encapsulated via this representation shall be defined within individual mechanism drafts. Name objects of this type will be identified with the following Object Identifier: {1(iso), 3(org), 6(dod), 1(internet), 5(security), 6(nametypes), 4(gss-api-exported-name)} No name type OID is included in this mechanism-independent level of format definition, since (depending on individual mechanism specifications) the enclosed name may be implicitly typed or may be explicitly typed using a means other than OID encoding. Length Name Description 2 TOK_ID Token Identifier For exported name objects, this must be hex 04 01. 2 MECH_OID_LEN Length of the Mechanism OID MECH_OID_LEN MECH_OID Mechanism OID, in DER 4 NAME_LEN Length of name NAME_LEN NAME Exported name; format defined in applicable mechanism draft. 4: Name Type Definitions This section includes definitions for name types and associated syntaxes which are defined in a mechanism-independent fashion at the GSS-API level rather than being defined in individual mechanism specifications. 4.1: Host-Based Service Name Form The following Object Identifier value is provided as a means to identify this name form: {1(iso), 3(org), 6(dod), 1(internet), 5(security), 6(nametypes), 2(gss-host-based-services)} The recommended symbolic name for this type is "GSS_C_NT_HOSTBASED_SERVICE".
This name type is used to represent services associated with host
computers. This name form is constructed using two elements,
"service" and "hostname", as follows:
service@hostname
When a reference to a name of this type is resolved, the "hostname"
is canonicalized by attempting a DNS lookup and using the fully-
qualified domain name which is returned, or by using the "hostname"
as provided if the DNS lookup fails. The canonicalization operation
also maps the host's name into lower-case characters.
The "hostname" element may be omitted. If no "@" separator is
included, the entire name is interpreted as the service specifier,
with the "hostname" defaulted to the canonicalized name of the local
host.
Values for the "service" element are registered with the IANA.
4.2: User Name Form
This name form shall be represented by the Object Identifier {iso(1)
member-body(2) United States(840) mit(113554) infosys(1) gssapi(2)
generic(1) user_name(1)}. The recommended mechanism-independent
symbolic name for this type is "GSS_C_NT_USER_NAME". (Note: the same
name form and OID is defined within the Kerberos V5 GSS-API
mechanism, but the symbolic name recommended there begins with a
"GSS_KRB5_NT_" prefix.)
This name type is used to indicate a named user on a local system.
Its interpretation is OS-specific. This name form is constructed as:
username
4.3: Machine UID Form
This name form shall be represented by the Object Identifier {iso(1)
member-body(2) United States(840) mit(113554) infosys(1) gssapi(2)
generic(1) machine_uid_name(2)}. The recommended mechanism-
independent symbolic name for this type is
"GSS_C_NT_MACHINE_UID_NAME". (Note: the same name form and OID is
defined within the Kerberos V5 GSS-API mechanism, but the symbolic
name recommended there begins with a "GSS_KRB5_NT_" prefix.)
This name type is used to indicate a numeric user identifier
corresponding to a user on a local system. Its interpretation is
OS-specific. The gss_buffer_desc representing a name of this type
should contain a locally-significant uid_t, represented in host byte
order. The GSS_Import_name() operation resolves this uid into a username, which is then treated as the User Name Form. 4.4: String UID Form This name form shall be represented by the Object Identifier {iso(1) member-body(2) United States(840) mit(113554) infosys(1) gssapi(2) generic(1) string_uid_name(3)}. The recommended symbolic name for this type is "GSS_C_NT_STRING_UID_NAME". (Note: the same name form and OID is defined within the Kerberos V5 GSS-API mechanism, but the symbolic name recommended there begins with a "GSS_KRB5_NT_" prefix.) This name type is used to indicate a string of digits representing the numeric user identifier of a user on a local system. Its interpretation is OS-specific. This name type is similar to the Machine UID Form, except that the buffer contains a string representing the uid_t. 5: Mechanism-Specific Example Scenarios This section provides illustrative overviews of the use of various candidate mechanism types to support the GSS-API. These discussions are intended primarily for readers familiar with specific security technologies, demonstrating how GSS-API functions can be used and implemented by candidate underlying mechanisms. They should not be regarded as constrictive to implementations or as defining the only means through which GSS-API functions can be realized with a particular underlying technology, and do not demonstrate all GSS-API features with each technology. 5.1: Kerberos V5, single-TGT OS-specific login functions yield a TGT to the local realm Kerberos server; TGT is placed in a credentials structure for the client. Client calls GSS_Acquire_cred() to acquire a cred_handle in order to reference the credentials for use in establishing security contexts. Client calls GSS_Init_sec_context(). If the requested service is located in a different realm, GSS_Init_sec_context() gets the necessary TGT/key pairs needed to traverse the path from local to target realm; these data are placed in the owner's TGT cache. After any needed remote realm resolution, GSS_Init_sec_context() yields a service ticket to the requested service with a corresponding session key; these data are stored in conjunction with the context. GSS-API code sends KRB_TGS_REQ request(s) and receives KRB_TGS_REP response(s) (in the successful case) or KRB_ERROR.
Assuming success, GSS_Init_sec_context() builds a Kerberos-formatted KRB_AP_REQ message, and returns it in output_token. The client sends the output_token to the service. The service passes the received token as the input_token argument to GSS_Accept_sec_context(), which verifies the authenticator, provides the service with the client's authenticated name, and returns an output_context_handle. Both parties now hold the session key associated with the service ticket, and can use this key in subsequent GSS_GetMIC(), GSS_VerifyMIC(), GSS_Wrap(), and GSS_Unwrap() operations. 5.2: Kerberos V5, double-TGT TGT acquisition as above. Note: To avoid unnecessary frequent invocations of error paths when implementing the GSS-API atop Kerberos V5, it seems appropriate to represent "single-TGT K-V5" and "double-TGT K-V5" with separate mech_types, and this discussion makes that assumption. Based on the (specified or defaulted) mech_type, GSS_Init_sec_context() determines that the double-TGT protocol should be employed for the specified target. GSS_Init_sec_context() returns GSS_S_CONTINUE_NEEDED major_status, and its returned output_token contains a request to the service for the service's TGT. (If a service TGT with suitably long remaining lifetime already exists in a cache, it may be usable, obviating the need for this step.) The client passes the output_token to the service. Note: this scenario illustrates a different use for the GSS_S_CONTINUE_NEEDED status return facility than for support of mutual authentication; note that both uses can coexist as successive operations within a single context establishment operation. The service passes the received token as the input_token argument to GSS_Accept_sec_context(), which recognizes it as a request for TGT. (Note that current Kerberos V5 defines no intra-protocol mechanism to represent such a request.) GSS_Accept_sec_context() returns GSS_S_CONTINUE_NEEDED major_status and provides the service's TGT in its output_token. The service sends the output_token to the client. The client passes the received token as the input_token argument to a continuation of GSS_Init_sec_context(). GSS_Init_sec_context() caches the received service TGT and uses it as part of a service ticket request to the Kerberos authentication server, storing the returned service ticket and session key in conjunction with the context. GSS_Init_sec_context() builds a Kerberos-formatted authenticator,
and returns it in output_token along with GSS_S_COMPLETE return major_status. The client sends the output_token to the service. Service passes the received token as the input_token argument to a continuation call to GSS_Accept_sec_context(). GSS_Accept_sec_context() verifies the authenticator, provides the service with the client's authenticated name, and returns major_status GSS_S_COMPLETE. GSS_GetMIC(), GSS_VerifyMIC(), GSS_Wrap(), and GSS_Unwrap() as above. 5.3: X.509 Authentication Framework This example illustrates use of the GSS-API in conjunction with public-key mechanisms, consistent with the X.509 Directory Authentication Framework. The GSS_Acquire_cred() call establishes a credentials structure, making the client's private key accessible for use on behalf of the client. The client calls GSS_Init_sec_context(), which interrogates the Directory to acquire (and validate) a chain of public-key certificates, thereby collecting the public key of the service. The certificate validation operation determines that suitable integrity checks were applied by trusted authorities and that those certificates have not expired. GSS_Init_sec_context() generates a secret key for use in per-message protection operations on the context, and enciphers that secret key under the service's public key. The enciphered secret key, along with an authenticator quantity signed with the client's private key, is included in the output_token from GSS_Init_sec_context(). The output_token also carries a certification path, consisting of a certificate chain leading from the service to the client; a variant approach would defer this path resolution to be performed by the service instead of being asserted by the client. The client application sends the output_token to the service. The service passes the received token as the input_token argument to GSS_Accept_sec_context(). GSS_Accept_sec_context() validates the certification path, and as a result determines a certified binding between the client's distinguished name and the client's public key. Given that public key, GSS_Accept_sec_context() can process the input_token's authenticator quantity and verify that the client's private key was used to sign the input_token. At this point, the
client is authenticated to the service. The service uses its private key to decipher the enciphered secret key provided to it for per- message protection operations on the context. The client calls GSS_GetMIC() or GSS_Wrap() on a data message, which causes per-message authentication, integrity, and (optional) confidentiality facilities to be applied to that message. The service uses the context's shared secret key to perform corresponding GSS_VerifyMIC() and GSS_Unwrap() calls. 6: Security Considerations Security issues are discussed throughout this memo. 7: Related Activities In order to implement the GSS-API atop existing, emerging, and future security mechanisms: object identifiers must be assigned to candidate GSS-API mechanisms and the name types which they support concrete data element formats and processing procedures must be defined for candidate mechanisms Calling applications must implement formatting conventions which will enable them to distinguish GSS-API tokens from other data carried in their application protocols. Concrete language bindings are required for the programming environments in which the GSS-API is to be employed, as RFC-1509 defines for the C programming language and GSS-V1.
APPENDIX A MECHANISM DESIGN CONSTRAINTS The following constraints on GSS-API mechanism designs are adopted in response to observed caller protocol requirements, and adherence thereto is anticipated in subsequent descriptions of GSS-API mechanisms to be documented in standards-track Internet specifications. It is strongly recommended that mechanisms offering per-message protection services also offer at least one of the replay detection and sequencing services, as mechanisms offering neither of the latter will fail to satisfy recognized requirements of certain candidate caller protocols. APPENDIX B COMPATIBILITY WITH GSS-V1 It is the intent of this document to define an interface and procedures which preserve compatibility between GSS-V1 (RFC-1508) callers and GSS- V2 providers. All calls defined in GSS-V1 are preserved, and it has been a goal that GSS-V1 callers should be able to operate atop GSS-V2 provider implementations. Certain detailed changes, summarized in this section, have been made in order to resolve omissions identified in GSS-V1. The following GSS-V1 constructs, while supported within GSS-V2, are deprecated: Names for per-message processing routines: GSS_Seal() deprecated in favor of GSS_Wrap(); GSS_Sign() deprecated in favor of GSS_GetMIC(); GSS_Unseal() deprecated in favor of GSS_Unwrap(); GSS_Verify() deprecated in favor of GSS_VerifyMIC(). GSS_Delete_sec_context() facility for context_token usage, allowing mechanisms to signal context deletion, is retained for compatibility with GSS-V1. For current usage, it is recommended that both peers to a context invoke GSS_Delete_sec_context() independently, passing a null output_context_token buffer to indicate that no context_token is required. Implementations of GSS_Delete_sec_context() should delete relevant locally-stored context information.
This GSS-V2 specification adds the following calls which are not
present in GSS-V1:
Credential management calls: GSS_Add_cred(),
GSS_Inquire_cred_by_mech().
Context-level calls: GSS_Inquire_context(), GSS_Wrap_size_limit(),
GSS_Export_sec_context(), GSS_Import_sec_context().
Per-message calls: No new calls. Existing calls have been renamed.
Support calls: GSS_Create_empty_OID_set(),
GSS_Add_OID_set_member(), GSS_Test_OID_set_member(),
GSS_Release_OID(), GSS_OID_to_str(), GSS_Str_to_OID(),
GSS_Inquire_names_for_mech(), GSS_Inquire_mechs_for_name(),
GSS_Canonicalize_name(), GSS_Export_name(), GSS_Duplicate_name().
This GSS-V2 specification introduces three new facilities applicable
to security contexts, indicated using the following context state
values which are not present in GSS-V1:
anon_state, set TRUE to indicate that a context's initiator is
anonymous from the viewpoint of the target; Section 1.2.5 of this
specification provides a summary description of the GSS-V2
anonymity support facility, support and use of which is optional.
prot_ready_state, set TRUE to indicate that a context may be used
for per-message protection before final completion of context
establishment; Section 1.2.7 of this specification provides a
summary description of the GSS-V2 facility enabling mechanisms to
selectively permit per-message protection during context
establishment, support and use of which is optional.
trans_state, set TRUE to indicate that a context is transferable to
another process using the GSS-V2 GSS_Export_sec_context() facility.
These state values are represented (at the C bindings level) in
positions within a bit vector which are unused in GSS-V1, and may be
safely ignored by GSS-V1 callers.
Relative to GSS-V1, GSS-V2 provides additional guidance to GSS-API
implementors in the following areas: implementation robustness,
credential management, behavior in multi-mechanism configurations,
naming support, and inclusion of optional sequencing services. The
token tagging facility as defined in GSS-V2, Section 3.1, is now
described directly in terms of octets to facilitate interoperable
implementation without general ASN.1 processing code; the
corresponding ASN.1 syntax, included for descriptive purposes, is
unchanged from that in GSS-V1. For use in conjunction with added
naming support facilities, a new Exported Name Object construct is
added. Additional name types are introduced in Section 4.
This GSS-V2 specification adds the following major_status values
which are not defined in GSS-V1:
GSS_S_BAD_QOP unsupported QOP value
GSS_S_UNAUTHORIZED operation unauthorized
GSS_S_UNAVAILABLE operation unavailable
GSS_S_DUPLICATE_ELEMENT duplicate credential element requested
GSS_S_NAME_NOT_MN name contains multi-mechanism elements
GSS_S_GAP_TOKEN skipped predecessor token(s)
detected
Of these added status codes, only two values are defined to be
returnable by calls existing in GSS-V1: GSS_S_BAD_QOP (returnable by
GSS_GetMIC() and GSS_Wrap()), and GSS_S_GAP_TOKEN (returnable by
GSS_VerifyMIC() and GSS_Unwrap()).
Additionally, GSS-V2 descriptions of certain calls present in GSS-V1
have been updated to allow return of additional major_status values
from the set as defined in GSS-V1: GSS_Inquire_cred() has
GSS_S_DEFECTIVE_CREDENTIAL and GSS_S_CREDENTIALS_EXPIRED defined as
returnable, GSS_Init_sec_context() has GSS_S_OLD_TOKEN,
GSS_S_DUPLICATE_TOKEN, and GSS_S_BAD_MECH defined as returnable, and
GSS_Accept_sec_context() has GSS_S_BAD_MECH defined as returnable.
Author's Address
John Linn
OpenVision Technologies
One Main St.
Cambridge, MA 02142 USA
Phone: +1 617.374.2245
EMail: John.Linn@ov.com