Network Working Group J. Linn
Request for Comments: 2078 OpenVision Technologies
Category: Standards Track January 1997
Obsoletes: 1508
Generic Security Service Application Program Interface, Version 2
Status of this Memo
This document 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" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The Generic Security Service Application Program Interface (GSS-API),
as defined in RFC-1508, provides security services to callers in a
generic fashion, supportable with a range of underlying mechanisms
and technologies and hence allowing source-level portability of
applications to different environments. This specification defines
GSS-API services and primitives at a level independent of underlying
mechanism and programming language environment, and is to be
complemented by other, related specifications:
documents defining specific parameter bindings for particular
language environments
documents defining token formats, protocols, and procedures to be
implemented in order to realize GSS-API services atop particular
security mechanisms
This memo revises RFC-1508, making specific, incremental changes in
response to implementation experience and liaison requests. It is
intended, therefore, that this memo or a successor version thereto
will become the basis for subsequent progression of the GSS-API
specification on the standards track.
Table of Contents
1: GSS-API Characteristics and Concepts.......................... 3
1.1: GSS-API Constructs.......................................... 6
1.1.1: Credentials.............................................. 6
1.1.1.1: Credential Constructs and Concepts...................... 6
1.1.1.2: Credential Management................................... 7
1.1.1.3: Default Credential Resolution........................... 8
Linn Standards Track [Page 1]RFC 2078 GSS-API January 1997
1.1.2: Tokens.................................................... 9
1.1.3: Security Contexts........................................ 10
1.1.4: Mechanism Types.......................................... 11
1.1.5: Naming................................................... 12
1.1.6: Channel Bindings......................................... 14
1.2: GSS-API Features and Issues................................ 15
1.2.1: Status Reporting......................................... 15
1.2.2: Per-Message Security Service Availability................. 17
1.2.3: Per-Message Replay Detection and Sequencing............... 18
1.2.4: Quality of Protection.................................... 20
1.2.5: Anonymity Support......................................... 21
1.2.6: Initialization............................................ 22
1.2.7: Per-Message Protection During Context Establishment....... 22
1.2.8: Implementation Robustness................................. 23
2: Interface Descriptions....................................... 23
2.1: Credential management calls................................ 25
2.1.1: GSS_Acquire_cred call.................................... 26
2.1.2: GSS_Release_cred call.................................... 28
2.1.3: GSS_Inquire_cred call.................................... 29
2.1.4: GSS_Add_cred call........................................ 31
2.1.5: GSS_Inquire_cred_by_mech call............................ 33
2.2: Context-level calls........................................ 34
2.2.1: GSS_Init_sec_context call................................ 34
2.2.2: GSS_Accept_sec_context call.............................. 40
2.2.3: GSS_Delete_sec_context call.............................. 44
2.2.4: GSS_Process_context_token call........................... 46
2.2.5: GSS_Context_time call.................................... 47
2.2.6: GSS_Inquire_context call................................. 47
2.2.7: GSS_Wrap_size_limit call................................. 49
2.2.8: GSS_Export_sec_context call.............................. 50
2.2.9: GSS_Import_sec_context call.............................. 52
2.3: Per-message calls.......................................... 53
2.3.1: GSS_GetMIC call.......................................... 54
2.3.2: GSS_VerifyMIC call....................................... 55
2.3.3: GSS_Wrap call............................................ 56
2.3.4: GSS_Unwrap call.......................................... 58
2.4: Support calls.............................................. 59
2.4.1: GSS_Display_status call.................................. 60
2.4.2: GSS_Indicate_mechs call.................................. 60
2.4.3: GSS_Compare_name call.................................... 61
2.4.4: GSS_Display_name call.................................... 62
2.4.5: GSS_Import_name call..................................... 63
2.4.6: GSS_Release_name call.................................... 64
2.4.7: GSS_Release_buffer call.................................. 65
2.4.8: GSS_Release_OID_set call................................. 65
2.4.9: GSS_Create_empty_OID_set call............................ 66
2.4.10: GSS_Add_OID_set_member call.............................. 67
2.4.11: GSS_Test_OID_set_member call............................. 67
Linn Standards Track [Page 2]
RFC 2078 GSS-API January 1997
2.4.12: GSS_Release_OID call..................................... 68
2.4.13: GSS_OID_to_str call...................................... 68
2.4.14: GSS_Str_to_OID call...................................... 69
2.4.15: GSS_Inquire_names_for_mech call.......................... 69
2.4.16: GSS_Inquire_mechs_for_name call.......................... 70
2.4.17: GSS_Canonicalize_name call............................... 71
2.4.18: GSS_Export_name call..................................... 72
2.4.19: GSS_Duplicate_name call.................................. 73
3: Data Structure Definitions for GSS-V2 Usage................... 73
3.1: Mechanism-Independent Token Format.......................... 74
3.2: Mechanism-Independent Exported Name Object Format........... 77
4: Name Type Definitions......................................... 77
4.1: Host-Based Service Name Form................................ 77
4.2: User Name Form.............................................. 78
4.3: Machine UID Form............................................ 78
4.4: String UID Form............................................. 79
5: Mechanism-Specific Example Scenarios......................... 79
5.1: Kerberos V5, single-TGT..................................... 79
5.2: Kerberos V5, double-TGT..................................... 80
5.3: X.509 Authentication Framework............................. 81
6: Security Considerations...................................... 82
7: Related Activities........................................... 82
Appendix A: Mechanism Design Constraints......................... 83
Appendix B: Compatibility with GSS-V1............................ 83
1: GSS-API Characteristics and Concepts
GSS-API operates in the following paradigm. A typical GSS-API caller
is itself a communications protocol, calling on GSS-API in order to
protect its communications with authentication, integrity, and/or
confidentiality security services. A GSS-API caller accepts tokens
provided to it by its local GSS-API implementation and transfers the
tokens to a peer on a remote system; that peer passes the received
tokens to its local GSS-API implementation for processing. The
security services available through GSS-API in this fashion are
implementable (and have been implemented) over a range of underlying
mechanisms based on secret-key and public-key cryptographic
technologies.
The GSS-API separates the operations of initializing a security
context between peers, achieving peer entity authentication (This
security service definition, and other definitions used in this
document, corresponds to that provided in International Standard ISO
7498-2-1988(E), Security Architecture.) (GSS_Init_sec_context() and
GSS_Accept_sec_context() calls), from the operations of providing
per-message data origin authentication and data integrity protection
(GSS_GetMIC() and GSS_VerifyMIC() calls) for messages subsequently
transferred in conjunction with that context. When establishing a
Linn Standards Track [Page 3]
RFC 2078 GSS-API January 1997
security context, the GSS-API enables a context initiator to
optionally permit its credentials to be delegated, meaning that the
context acceptor may initiate further security contexts on behalf of
the initiating caller. Per-message GSS_Wrap() and GSS_Unwrap() calls
provide the data origin authentication and data integrity services
which GSS_GetMIC() and GSS_VerifyMIC() offer, and also support
selection of confidentiality services as a caller option. Additional
calls provide supportive functions to the GSS-API's users.
The following paragraphs provide an example illustrating the
dataflows involved in use of the GSS-API by a client and server in a
mechanism-independent fashion, establishing a security context and
transferring a protected message. The example assumes that credential
acquisition has already been completed. The example assumes that the
underlying authentication technology is capable of authenticating a
client to a server using elements carried within a single token, and
of authenticating the server to the client (mutual authentication)
with a single returned token; this assumption holds for presently-
documented CAT mechanisms but is not necessarily true for other
cryptographic technologies and associated protocols.
The client calls GSS_Init_sec_context() to establish a security
context to the server identified by targ_name, and elects to set the
mutual_req_flag so that mutual authentication is performed in the
course of context establishment. GSS_Init_sec_context() returns an
output_token to be passed to the server, and indicates
GSS_S_CONTINUE_NEEDED status pending completion of the mutual
authentication sequence. Had mutual_req_flag not been set, the
initial call to GSS_Init_sec_context() would have returned
GSS_S_COMPLETE status. The client sends the output_token to the
server.
The server passes the received token as the input_token parameter to
GSS_Accept_sec_context(). GSS_Accept_sec_context indicates
GSS_S_COMPLETE status, provides the client's authenticated identity
in the src_name result, and provides an output_token to be passed to
the client. The server sends the output_token to the client.
The client passes the received token as the input_token parameter to
a successor call to GSS_Init_sec_context(), which processes data
included in the token in order to achieve mutual authentication from
the client's viewpoint. This call to GSS_Init_sec_context() returns
GSS_S_COMPLETE status, indicating successful mutual authentication
and the completion of context establishment for this example.
The client generates a data message and passes it to GSS_Wrap().
GSS_Wrap() performs data origin authentication, data integrity, and
(optionally) confidentiality processing on the message and
Linn Standards Track [Page 4]
RFC 2078 GSS-API January 1997
encapsulates the result into output_message, indicating
GSS_S_COMPLETE status. The client sends the output_message to the
server.
The server passes the received message to GSS_Unwrap(). GSS_Unwrap()
inverts the encapsulation performed by GSS_Wrap(), deciphers the
message if the optional confidentiality feature was applied, and
validates the data origin authentication and data integrity checking
quantities. GSS_Unwrap() indicates successful validation by
returning GSS_S_COMPLETE status along with the resultant
output_message.
For purposes of this example, we assume that the server knows by
out-of-band means that this context will have no further use after
one protected message is transferred from client to server. Given
this premise, the server now calls GSS_Delete_sec_context() to flush
context-level information. Optionally, the server-side application
may provide a token buffer to GSS_Delete_sec_context(), to receive a
context_token to be transferred to the client in order to request
that client-side context-level information be deleted.
If a context_token is transferred, the client passes the
context_token to GSS_Process_context_token(), which returns
GSS_S_COMPLETE status after deleting context-level information at the
client system.
The GSS-API design assumes and addresses several basic goals,
including:
Mechanism independence: The GSS-API defines an interface to
cryptographically implemented strong authentication and other
security services at a generic level which is independent of
particular underlying mechanisms. For example, GSS-API-provided
services can be implemented by secret-key technologies (e.g.,
Kerberos) or public-key approaches (e.g., X.509).
Protocol environment independence: The GSS-API is independent of
the communications protocol suites with which it is employed,
permitting use in a broad range of protocol environments. In
appropriate environments, an intermediate implementation "veneer"
which is oriented to a particular communication protocol (e.g.,
Remote Procedure Call (RPC)) may be interposed between
applications which call that protocol and the GSS-API, thereby
invoking GSS-API facilities in conjunction with that protocol's
communications invocations.
Protocol association independence: The GSS-API's security context
construct is independent of communications protocol association
Linn Standards Track [Page 5]RFC 2078 GSS-API January 1997
constructs. This characteristic allows a single GSS-API
implementation to be utilized by a variety of invoking protocol
modules on behalf of those modules' calling applications. GSS-API
services can also be invoked directly by applications, wholly
independent of protocol associations.
Suitability to a range of implementation placements: GSS-API
clients are not constrained to reside within any Trusted Computing
Base (TCB) perimeter defined on a system where the GSS-API is
implemented; security services are specified in a manner suitable
to both intra-TCB and extra-TCB callers.
1.1: GSS-API Constructs
This section describes the basic elements comprising the GSS-API.
1.1.1: Credentials
1.1.1.1: Credential Constructs and Concepts
Credentials provide the prerequisites which permit GSS-API peers to
establish security contexts with each other. A caller may designate
that the credential elements which are to be applied for context
initiation or acceptance be selected by default. Alternately, those
GSS-API callers which need to make explicit selection of particular
credentials structures may make references to those credentials
through GSS-API-provided credential handles ("cred_handles"). In all
cases, callers' credential references are indirect, mediated by GSS-
API implementations and not requiring callers to access the selected
credential elements.
A single credential structure may be used to initiate outbound
contexts and to accept inbound contexts. Callers needing to operate
in only one of these modes may designate this fact when credentials
are acquired for use, allowing underlying mechanisms to optimize
their processing and storage requirements. The credential elements
defined by a particular mechanism may contain multiple cryptographic
keys, e.g., to enable authentication and message encryption to be
performed with different algorithms.
A GSS-API credential structure may contain multiple credential
elements, each containing mechanism-specific information for a
particular underlying mechanism (mech_type), but the set of elements
within a given credential structure represent a common entity. A
credential structure's contents will vary depending on the set of
mech_types supported by a particular GSS-API implementation. Each
credential element identifies the data needed by its mechanism in
order to establish contexts on behalf of a particular principal, and
Linn Standards Track [Page 6]RFC 2078 GSS-API January 1997
may contain separate credential references for use in context
initiation and context acceptance. Multiple credential elements
within a given credential having overlapping combinations of
mechanism, usage mode, and validity period are not permitted.
Commonly, a single mech_type will be used for all security contexts
established by a particular initiator to a particular target. A major
motivation for supporting credential sets representing multiple
mech_types is to allow initiators on systems which are equipped to
handle multiple types to initiate contexts to targets on other
systems which can accommodate only a subset of the set supported at
the initiator's system.
1.1.1.2: Credential Management
It is the responsibility of underlying system-specific mechanisms and
OS functions below the GSS-API to ensure that the ability to acquire
and use credentials associated with a given identity is constrained
to appropriate processes within a system. This responsibility should
be taken seriously by implementors, as the ability for an entity to
utilize a principal's credentials is equivalent to the entity's
ability to successfully assert that principal's identity.
Once a set of GSS-API credentials is established, the transferability
of that credentials set to other processes or analogous constructs
within a system is a local matter, not defined by the GSS-API. An
example local policy would be one in which any credentials received
as a result of login to a given user account, or of delegation of
rights to that account, are accessible by, or transferable to,
processes running under that account.
The credential establishment process (particularly when performed on
behalf of users rather than server processes) is likely to require
access to passwords or other quantities which should be protected
locally and exposed for the shortest time possible. As a result, it
will often be appropriate for preliminary credential establishment to
be performed through local means at user login time, with the
result(s) cached for subsequent reference. These preliminary
credentials would be set aside (in a system-specific fashion) for
subsequent use, either:
to be accessed by an invocation of the GSS-API GSS_Acquire_cred()
call, returning an explicit handle to reference that credential
to comprise default credential elements to be installed, and to be
used when default credential behavior is requested on behalf of a
process
Linn Standards Track [Page 7]RFC 2078 GSS-API January 1997
1.1.1.3: Default Credential Resolution
The gss_init_sec_context and gss_accept_sec_context routines allow
the value GSS_C_NO_CREDENTIAL to be specified as their credential
handle parameter. This special credential-handle indicates a desire
by the application to act as a default principal. While individual
GSS-API implementations are free to determine such default behavior
as appropriate to the mechanism, the following default behavior by
these routines is recommended for portability:
GSS_Init_sec_context:
(i) If there is only a single principal capable of initiating
security contexts that the application is authorized to act on
behalf of, then that principal shall be used, otherwise
(ii) If the platform maintains a concept of a default network-
identity, and if the application is authorized to act on behalf of
that identity for the purpose of initiating security contexts,
then the principal corresponding to that identity shall be used,
otherwise
(iii) If the platform maintains a concept of a default local
identity, and provides a means to map local identities into
network-identities, and if the application is authorized to act on
behalf of the network-identity image of the default local identity
for the purpose of initiating security contexts, then the
principal corresponding to that identity shall be used, otherwise
(iv) A user-configurable default identity should be used.
GSS_Accept_sec_context:
(i) If there is only a single authorized principal identity
capable of accepting security contexts, then that principal shall
be used, otherwise
(ii) If the mechanism can determine the identity of the target
principal by examining the context-establishment token, and if the
accepting application is authorized to act as that principal for
the purpose of accepting security contexts, then that principal
identity shall be used, otherwise
(iii) If the mechanism supports context acceptance by any
principal, and mutual authentication was not requested, any
principal that the application is authorized to accept security
contexts under may be used, otherwise
Linn Standards Track [Page 8]RFC 2078 GSS-API January 1997
(iv) A user-configurable default identity shall be used.
The purpose of the above rules is to allow security contexts to be
established by both initiator and acceptor using the default behavior
wherever possible. Applications requesting default behavior are
likely to be more portable across mechanisms and platforms than ones
that use GSS_Acquire_cred to request a specific identity.
1.1.2: Tokens
Tokens are data elements transferred between GSS-API callers, and are
divided into two classes. Context-level tokens are exchanged in order
to establish and manage a security context between peers. Per-message
tokens relate to an established context and are exchanged to provide
protective security services (i.e., data origin authentication,
integrity, and optional confidentiality) for corresponding data
messages.
The first context-level token obtained from GSS_Init_sec_context() is
required to indicate at its very beginning a globally-interpretable
mechanism identifier, i.e., an Object Identifier (OID) of the
security mechanism. The remaining part of this token as well as the
whole content of all other tokens are specific to the particular
underlying mechanism used to support the GSS-API. Section 3 of this
document provides, for designers of GSS-API support mechanisms, the
description of the header of the first context-level token which is
then followed by mechanism-specific information.
Tokens' contents are opaque from the viewpoint of GSS-API callers.
They are generated within the GSS-API implementation at an end
system, provided to a GSS-API caller to be transferred to the peer
GSS-API caller at a remote end system, and processed by the GSS-API
implementation at that remote end system. Tokens may be output by
GSS-API calls (and should be transferred to GSS-API peers) whether or
not the calls' status indicators indicate successful completion.
Token transfer may take place in an in-band manner, integrated into
the same protocol stream used by the GSS-API callers for other data
transfers, or in an out-of-band manner across a logically separate
channel.
Different GSS-API tokens are used for different purposes (e.g.,
context initiation, context acceptance, protected message data on an
established context), and it is the responsibility of a GSS-API
caller receiving tokens to distinguish their types, associate them
with corresponding security contexts, and pass them to appropriate
GSS-API processing routines. Depending on the caller protocol
environment, this distinction may be accomplished in several ways.
Linn Standards Track [Page 9]RFC 2078 GSS-API January 1997
The following examples illustrate means through which tokens' types
may be distinguished:
- implicit tagging based on state information (e.g., all tokens on
a new association are considered to be context establishment
tokens until context establishment is completed, at which point
all tokens are considered to be wrapped data objects for that
context),
- explicit tagging at the caller protocol level,
- a hybrid of these approaches.
Commonly, the encapsulated data within a token includes internal
mechanism-specific tagging information, enabling mechanism-level
processing modules to distinguish tokens used within the mechanism
for different purposes. Such internal mechanism-level tagging is
recommended to mechanism designers, and enables mechanisms to
determine whether a caller has passed a particular token for
processing by an inappropriate GSS-API routine.
Development of GSS-API support primitives based on a particular
underlying cryptographic technique and protocol (i.e., conformant to
a specific GSS-API mechanism definition) does not necessarily imply
that GSS-API callers using that GSS-API mechanism will be able to
interoperate with peers invoking the same technique and protocol
outside the GSS-API paradigm, or with peers implementing a different
GSS-API mechanism based on the same underlying technology. The
format of GSS-API tokens defined in conjunction with a particular
mechanism, and the techniques used to integrate those tokens into
callers' protocols, may not be interoperable with the tokens used by
non-GSS-API callers of the same underlying technique.
1.1.3: Security Contexts
Security contexts are established between peers, using credentials
established locally in conjunction with each peer or received by
peers via delegation. Multiple contexts may exist simultaneously
between a pair of peers, using the same or different sets of
credentials. Coexistence of multiple contexts using different
credentials allows graceful rollover when credentials expire.
Distinction among multiple contexts based on the same credentials
serves applications by distinguishing different message streams in a
security sense.
The GSS-API is independent of underlying protocols and addressing
structure, and depends on its callers to transport GSS-API-provided
data elements. As a result of these factors, it is a caller
Linn Standards Track [Page 10]RFC 2078 GSS-API January 1997
responsibility to parse communicated messages, separating GSS-API-
related data elements from caller-provided data. The GSS-API is
independent of connection vs. connectionless orientation of the
underlying communications service.
No correlation between security context and communications protocol
association is dictated. (The optional channel binding facility,
discussed in Section 1.1.6 of this document, represents an
intentional exception to this rule, supporting additional protection
features within GSS-API supporting mechanisms.) This separation
allows the GSS-API to be used in a wide range of communications
environments, and also simplifies the calling sequences of the
individual calls. In many cases (depending on underlying security
protocol, associated mechanism, and availability of cached
information), the state information required for context setup can be
sent concurrently with initial signed user data, without interposing
additional message exchanges.
1.1.4: Mechanism Types
In order to successfully establish a security context with a target
peer, it is necessary to identify an appropriate underlying mechanism
type (mech_type) which both initiator and target peers support. The
definition of a mechanism embodies not only the use of a particular
cryptographic technology (or a hybrid or choice among alternative
cryptographic technologies), but also definition of the syntax and
semantics of data element exchanges which that mechanism will employ
in order to support security services.
It is recommended that callers initiating contexts specify the
"default" mech_type value, allowing system-specific functions within
or invoked by the GSS-API implementation to select the appropriate
mech_type, but callers may direct that a particular mech_type be
employed when necessary.
The means for identifying a shared mech_type to establish a security
context with a peer will vary in different environments and
circumstances; examples include (but are not limited to):
use of a fixed mech_type, defined by configuration, within an
environment
syntactic convention on a target-specific basis, through
examination of a target's name
lookup of a target's name in a naming service or other database in
order to identify mech_types supported by that target
Linn Standards Track [Page 11]RFC 2078 GSS-API January 1997
explicit negotiation between GSS-API callers in advance of
security context setup
When transferred between GSS-API peers, mech_type specifiers (per
Section 3, represented as Object Identifiers (OIDs)) serve to qualify
the interpretation of associated tokens. (The structure and encoding
of Object Identifiers is defined in ISO/IEC 8824, "Specification of
Abstract Syntax Notation One (ASN.1)" and in ISO/IEC 8825,
"Specification of Basic Encoding Rules for Abstract Syntax Notation
One (ASN.1)".) Use of hierarchically structured OIDs serves to
preclude ambiguous interpretation of mech_type specifiers. The OID
representing the DASS MechType, for example, is 1.3.12.2.1011.7.5,
and that of the Kerberos V5 mechanism, once advanced to the level of
Proposed Standard, will be 1.2.840.113554.1.2.2.
1.1.5: Naming
The GSS-API avoids prescribing naming structures, treating the names
which are transferred across the interface in order to initiate and
accept security contexts as opaque objects. This approach supports
the GSS-API's goal of implementability atop a range of underlying
security mechanisms, recognizing the fact that different mechanisms
process and authenticate names which are presented in different
forms. Generalized services offering translation functions among
arbitrary sets of naming environments are outside the scope of the
GSS-API; availability and use of local conversion functions to
translate among the naming formats supported within a given end
system is anticipated.
Different classes of name representations are used in conjunction
with different GSS-API parameters:
- Internal form (denoted in this document by INTERNAL NAME),
opaque to callers and defined by individual GSS-API
implementations. GSS-API implementations supporting multiple
namespace types must maintain internal tags to disambiguate the
interpretation of particular names. A Mechanism Name (MN) is a
special case of INTERNAL NAME, guaranteed to contain elements
corresponding to one and only one mechanism; calls which are
guaranteed to emit MNs or which require MNs as input are so
identified within this specification.
- Contiguous string ("flat") form (denoted in this document by
OCTET STRING); accompanied by OID tags identifying the namespace
to which they correspond. Depending on tag value, flat names may
or may not be printable strings for direct acceptance from and
presentation to users. Tagging of flat names allows GSS-API
callers and underlying GSS-API mechanisms to disambiguate name
Linn Standards Track [Page 12]RFC 2078 GSS-API January 1997
types and to determine whether an associated name's type is one
which they are capable of processing, avoiding aliasing problems
which could result from misinterpreting a name of one type as a
name of another type.
- The GSS-API Exported Name Object, a special case of flat name
designated by a reserved OID value, carries a canonicalized form
of a name suitable for binary comparisons.
In addition to providing means for names to be tagged with types,
this specification defines primitives to support a level of naming
environment independence for certain calling applications. To provide
basic services oriented towards the requirements of callers which
need not themselves interpret the internal syntax and semantics of
names, GSS-API calls for name comparison (GSS_Compare_name()),
human-readable display (GSS_Display_name()), input conversion
(GSS_Import_name()), internal name deallocation (GSS_Release_name()),
and internal name duplication (GSS_Duplicate_name()) functions are
defined. (It is anticipated that these proposed GSS-API calls will be
implemented in many end systems based on system-specific name
manipulation primitives already extant within those end systems;
inclusion within the GSS-API is intended to offer GSS-API callers a
portable means to perform specific operations, supportive of
authorization and audit requirements, on authenticated names.)
GSS_Import_name() implementations can, where appropriate, support
more than one printable syntax corresponding to a given namespace
(e.g., alternative printable representations for X.500 Distinguished
Names), allowing flexibility for their callers to select among
alternative representations. GSS_Display_name() implementations
output a printable syntax selected as appropriate to their
operational environments; this selection is a local matter. Callers
desiring portability across alternative printable syntaxes should
refrain from implementing comparisons based on printable name forms
and should instead use the GSS_Compare_name() call to determine
whether or not one internal-format name matches another.
The GSS_Canonicalize_name() and GSS_Export_name() calls enable
callers to acquire and process Exported Name Objects, canonicalized
and translated in accordance with the procedures of a particular
GSS-API mechanism. Exported Name Objects can, in turn, be input to
GSS_Import_name(), yielding equivalent MNs. These facilities are
designed specifically to enable efficient storage and comparison of
names (e.g., for use in access control lists).
Linn Standards Track [Page 13]RFC 2078 GSS-API January 1997
The following diagram illustrates the intended dataflow among name-
related GSS-API processing routines.
GSS-API library defaults
|
|
V text, for
text --------------> internal_name (IN) -----------> display only
import_name() / display_name()
/
/
/
accept_sec_context() /
| /
| /
| / canonicalize_name()
| /
| /
| /
| /
| /
| |
V V <---------------------
single mechanism import_name() exported name: flat
internal_name (MN) binary "blob" usable
----------------------> for access control
export_name()
1.1.6: Channel Bindings
The GSS-API accommodates the concept of caller-provided channel
binding ("chan_binding") information. Channel bindings are used to
strengthen the quality with which peer entity authentication is
provided during context establishment, by limiting the scope within
which an intercepted context establishment token can be reused by an
attacker. Specifically, they enable GSS-API callers to bind the
establishment of a security context to relevant characteristics
(e.g., addresses, transformed representations of encryption keys) of
the underlying communications channel, of protection mechanisms
applied to that communications channel, and to application-specific
data.
The caller initiating a security context must determine the
appropriate channel binding values to provide as input to the
GSS_Init_sec_context() call, and consistent values must be provided
to GSS_Accept_sec_context() by the context's target, in order for
both peers' GSS-API mechanisms to validate that received tokens
possess correct channel-related characteristics. Use or non-use of
Linn Standards Track [Page 14]RFC 2078 GSS-API January 1997
the GSS-API channel binding facility is a caller option. GSS-API
mechanisms can operate in an environment where NULL channel bindings
are presented; mechanism implementors are encouraged, but not
required, to make use of caller-provided channel binding data within
their mechanisms. Callers should not assume that underlying
mechanisms provide confidentiality protection for channel binding
information.
When non-NULL channel bindings are provided by callers, certain
mechanisms can offer enhanced security value by interpreting the
bindings' content (rather than simply representing those bindings, or
integrity check values computed on them, within tokens) and will
therefore depend on presentation of specific data in a defined
format. To this end, agreements among mechanism implementors are
defining conventional interpretations for the contents of channel
binding arguments, including address specifiers (with content
dependent on communications protocol environment) for context
initiators and acceptors. (These conventions are being incorporated
in GSS-API mechanism specifications and into the GSS-API C language
bindings specification.) In order for GSS-API callers to be portable
across multiple mechanisms and achieve the full security
functionality which each mechanism can provide, it is strongly
recommended that GSS-API callers provide channel bindings consistent
with these conventions and those of the networking environment in
which they operate.
1.2: GSS-API Features and Issues
This section describes aspects of GSS-API operations, of the security
services which the GSS-API provides, and provides commentary on
design issues.
1.2.1: Status Reporting
Each GSS-API call provides two status return values. Major_status
values provide a mechanism-independent indication of call status
(e.g., GSS_S_COMPLETE, GSS_S_FAILURE, GSS_S_CONTINUE_NEEDED),
sufficient to drive normal control flow within the caller in a
generic fashion. Table 1 summarizes the defined major_status return
codes in tabular fashion.
Linn Standards Track [Page 15]
RFC 2078 GSS-API January 1997
Table 1: GSS-API Major Status Codes
FATAL ERROR CODES
GSS_S_BAD_BINDINGS channel binding mismatch
GSS_S_BAD_MECH unsupported mechanism requested
GSS_S_BAD_NAME invalid name provided
GSS_S_BAD_NAMETYPE name of unsupported type provided
GSS_S_BAD_STATUS invalid input status selector
GSS_S_BAD_SIG token had invalid integrity check
GSS_S_CONTEXT_EXPIRED specified security context expired
GSS_S_CREDENTIALS_EXPIRED expired credentials detected
GSS_S_DEFECTIVE_CREDENTIAL defective credential detected
GSS_S_DEFECTIVE_TOKEN defective token detected
GSS_S_FAILURE failure, unspecified at GSS-API
level
GSS_S_NO_CONTEXT no valid security context specified
GSS_S_NO_CRED no valid credentials provided
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
INFORMATORY STATUS CODES
GSS_S_COMPLETE normal completion
GSS_S_CONTINUE_NEEDED continuation call to routine
required
GSS_S_DUPLICATE_TOKEN duplicate per-message token
detected
GSS_S_OLD_TOKEN timed-out per-message token
detected
GSS_S_UNSEQ_TOKEN reordered (early) per-message token
detected
GSS_S_GAP_TOKEN skipped predecessor token(s)
detected
Minor_status provides more detailed status information which may
include status codes specific to the underlying security mechanism.
Minor_status values are not specified in this document.
GSS_S_CONTINUE_NEEDED major_status returns, and optional message
outputs, are provided in GSS_Init_sec_context() and
GSS_Accept_sec_context() calls so that different mechanisms'
employment of different numbers of messages within their
authentication sequences need not be reflected in separate code paths
within calling applications. Instead, such cases are accommodated
Linn Standards Track [Page 16]RFC 2078 GSS-API January 1997
with sequences of continuation calls to GSS_Init_sec_context() and
GSS_Accept_sec_context(). The same mechanism is used to encapsulate
mutual authentication within the GSS-API's context initiation calls.
For mech_types which require interactions with third-party servers in
order to establish a security context, GSS-API context establishment
calls may block pending completion of such third-party interactions.
On the other hand, no GSS-API calls pend on serialized interactions
with GSS-API peer entities. As a result, local GSS-API status
returns cannot reflect unpredictable or asynchronous exceptions
occurring at remote peers, and reflection of such status information
is a caller responsibility outside the GSS-API.
1.2.2: Per-Message Security Service Availability
When a context is established, two flags are returned to indicate the
set of per-message protection security services which will be
available on the context:
the integ_avail flag indicates whether per-message integrity and
data origin authentication services are available
the conf_avail flag indicates whether per-message confidentiality
services are available, and will never be returned TRUE unless the
integ_avail flag is also returned TRUE
GSS-API callers desiring per-message security services should
check the values of these flags at context establishment time, and
must be aware that a returned FALSE value for integ_avail means
that invocation of GSS_GetMIC() or GSS_Wrap() primitives on the
associated context will apply no cryptographic protection to user
data messages.
The GSS-API per-message integrity and data origin authentication
services provide assurance to a receiving caller that protection was
applied to a message by the caller's peer on the security context,
corresponding to the entity named at context initiation. The GSS-API
per-message confidentiality service provides assurance to a sending
caller that the message's content is protected from access by
entities other than the context's named peer.
Linn Standards Track [Page 17]RFC 2078 GSS-API January 1997
The GSS-API per-message protection service primitives, as the
category name implies, are oriented to operation at the granularity
of protocol data units. They perform cryptographic operations on the
data units, transfer cryptographic control information in tokens,
and, in the case of GSS_Wrap(), encapsulate the protected data unit.
As such, these primitives are not oriented to efficient data
protection for stream-paradigm protocols (e.g., Telnet) if
cryptography must be applied on an octet-by-octet basis.
1.2.3: Per-Message Replay Detection and Sequencing
Certain underlying mech_types offer support for replay detection
and/or sequencing of messages transferred on the contexts they
support. These optionally-selectable protection features are distinct
from replay detection and sequencing features applied to the context
establishment operation itself; the presence or absence of context-
level replay or sequencing features is wholly a function of the
underlying mech_type's capabilities, and is not selected or omitted
as a caller option.
The caller initiating a context provides flags (replay_det_req_flag
and sequence_req_flag) to specify whether the use of per-message
replay detection and sequencing features is desired on the context
being established. The GSS-API implementation at the initiator system
can determine whether these features are supported (and whether they
are optionally selectable) as a function of mech_type, without need
for bilateral negotiation with the target. When enabled, these
features provide recipients with indicators as a result of GSS-API
processing of incoming messages, identifying whether those messages
were detected as duplicates or out-of-sequence. Detection of such
events does not prevent a suspect message from being provided to a
recipient; the appropriate course of action on a suspect message is a
matter of caller policy.
The semantics of the replay detection and sequencing services applied
to received messages, as visible across the interface which the GSS-
API provides to its clients, are as follows:
When replay_det_state is TRUE, the possible major_status returns for
well-formed and correctly signed messages are as follows:
1. GSS_S_COMPLETE indicates that the message was within the window
(of time or sequence space) allowing replay events to be detected,
and that the message was not a replay of a previously-processed
message within that window.
Linn Standards Track [Page 18]RFC 2078 GSS-API January 1997
2. GSS_S_DUPLICATE_TOKEN indicates that the cryptographic
checkvalue on the received message was correct, but that the
message was recognized as a duplicate of a previously-processed
message.
3. GSS_S_OLD_TOKEN indicates that the cryptographic checkvalue on
the received message was correct, but that the message is too old
to be checked for duplication.
When sequence_state is TRUE, the possible major_status returns for
well-formed and correctly signed messages are as follows:
1. GSS_S_COMPLETE indicates that the message was within the window
(of time or sequence space) allowing replay events to be detected,
that the message was not a replay of a previously-processed
message within that window, and that no predecessor sequenced
messages are missing relative to the last received message (if
any) processed on the context with a correct cryptographic
checkvalue.
2. GSS_S_DUPLICATE_TOKEN indicates that the integrity check value
on the received message was correct, but that the message was
recognized as a duplicate of a previously-processed message.
3. GSS_S_OLD_TOKEN indicates that the integrity check value on the
received message was correct, but that the token is too old to be
checked for duplication.
4. GSS_S_UNSEQ_TOKEN indicates that the cryptographic checkvalue
on the received message was correct, but that it is earlier in a
sequenced stream than a message already processed on the context.
[Note: Mechanisms can be architected to provide a stricter form of
sequencing service, delivering particular messages to recipients
only after all predecessor messages in an ordered stream have been
delivered. This type of support is incompatible with the GSS-API
paradigm in which recipients receive all messages, whether in
order or not, and provide them (one at a time, without intra-GSS-
API message buffering) to GSS-API routines for validation. GSS-
API facilities provide supportive functions, aiding clients to
achieve strict message stream integrity in an efficient manner in
conjunction with sequencing provisions in communications
protocols, but the GSS-API does not offer this level of message
stream integrity service by itself.]
Linn Standards Track [Page 19]RFC 2078 GSS-API January 1997
5. GSS_S_GAP_TOKEN indicates that the cryptographic checkvalue on
the received message was correct, but that one or more predecessor
sequenced messages have not been successfully processed relative
to the last received message (if any) processed on the context
with a correct cryptographic checkvalue.
As the message stream integrity features (especially sequencing) may
interfere with certain applications' intended communications
paradigms, and since support for such features is likely to be
resource intensive, it is highly recommended that mech_types
supporting these features allow them to be activated selectively on
initiator request when a context is established. A context initiator
and target are provided with corresponding indicators
(replay_det_state and sequence_state), signifying whether these
features are active on a given context.
An example mech_type supporting per-message replay detection could
(when replay_det_state is TRUE) implement the feature as follows: The
underlying mechanism would insert timestamps in data elements output
by GSS_GetMIC() and GSS_Wrap(), and would maintain (within a time-
limited window) a cache (qualified by originator-recipient pair)
identifying received data elements processed by GSS_VerifyMIC() and
GSS_Unwrap(). When this feature is active, exception status returns
(GSS_S_DUPLICATE_TOKEN, GSS_S_OLD_TOKEN) will be provided when
GSS_VerifyMIC() or GSS_Unwrap() is presented with a message which is
either a detected duplicate of a prior message or which is too old to
validate against a cache of recently received messages.
1.2.4: Quality of Protection
Some mech_types provide their users with fine granularity control
over the means used to provide per-message protection, allowing
callers to trade off security processing overhead dynamically against
the protection requirements of particular messages. A per-message
quality-of-protection parameter (analogous to quality-of-service, or
QOS) selects among different QOP options supported by that mechanism.
On context establishment for a multi-QOP mech_type, context-level
data provides the prerequisite data for a range of protection
qualities.
It is expected that the majority of callers will not wish to exert
explicit mechanism-specific QOP control and will therefore request
selection of a default QOP. Definitions of, and choices among, non-
default QOP values are mechanism-specific, and no ordered sequences
of QOP values can be assumed equivalent across different mechanisms.
Meaningful use of non-default QOP values demands that callers be
familiar with the QOP definitions of an underlying mechanism or
mechanisms, and is therefore a non-portable construct. The
Linn Standards Track [Page 20]RFC 2078 GSS-API January 1997
GSS_S_BAD_QOP major_status value is defined in order to indicate that
a provided QOP value is unsupported for a security context, most
likely because that value is unrecognized by the underlying
mechanism.
1.2.5: Anonymity Support
In certain situations or environments, an application may wish to
authenticate a peer and/or protect communications using GSS-API per-
message services without revealing its own identity. For example,
consider an application which provides read access to a research
database, and which permits queries by arbitrary requestors. A
client of such a service might wish to authenticate the service, to
establish trust in the information received from it, but might not
wish to disclose its identity to the service for privacy reasons.
In ordinary GSS-API usage, a context initiator's identity is made
available to the context acceptor as part of the context
establishment process. To provide for anonymity support, a facility
(input anon_req_flag to GSS_Init_sec_context()) is provided through
which context initiators may request that their identity not be
provided to the context acceptor. Mechanisms are not required to
honor this request, but a caller will be informed (via returned
anon_state indicator from GSS_Init_sec_context()) whether or not the
request is honored. Note that authentication as the anonymous
principal does not necessarily imply that credentials are not
required in order to establish a context.
The following Object Identifier value is provided as a means to
identify anonymous names, and can be compared against in order to
determine, in a mechanism-independent fashion, whether a name refers
to an anonymous principal:
{1(iso), 3(org), 6(dod), 1(internet), 5(security), 6(nametypes),
3(gss-anonymous-name)}
The recommended symbolic name corresponding to this definition is
GSS_C_NT_ANONYMOUS.
Four possible combinations of anon_state and mutual_state are
possible, with the following results:
anon_state == FALSE, mutual_state == FALSE: initiator
authenticated to target.
anon_state == FALSE, mutual_state == TRUE: initiator authenticated
to target, target authenticated to initiator.
Linn Standards Track [Page 21]RFC 2078 GSS-API January 1997
anon_state == TRUE, mutual_state == FALSE: initiator authenticated
as anonymous principal to target.
anon_state == TRUE, mutual_state == TRUE: initiator authenticated
as anonymous principal to target, target authenticated to
initiator.
1.2.6: Initialization
No initialization calls (i.e., calls which must be invoked prior to
invocation of other facilities in the interface) are defined in GSS-
API. As an implication of this fact, GSS-API implementations must
themselves be self-initializing.
1.2.7: Per-Message Protection During Context Establishment
A facility is defined in GSS-V2 to enable protection and buffering of
data messages for later transfer while a security context's
establishment is in GSS_S_CONTINUE_NEEDED status, to be used in cases
where the caller side already possesses the necessary session key to
enable this processing. Specifically, a new state Boolean, called
prot_ready_state, is added to the set of information returned by
GSS_Init_sec_context(), GSS_Accept_sec_context(), and
GSS_Inquire_context().
For context establishment calls, this state Boolean is valid and
interpretable when the associated major_status is either
GSS_S_CONTINUE_NEEDED, or GSS_S_COMPLETE. Callers of GSS-API (both
initiators and acceptors) can assume that per-message protection (via
GSS_Wrap(), GSS_Unwrap(), GSS_GetMIC() and GSS_VerifyMIC()) is
available and ready for use if either: prot_ready_state == TRUE, or
major_status == GSS_S_COMPLETE, though mutual authentication (if
requested) cannot be guaranteed until GSS_S_COMPLETE is returned.
This achieves full, transparent backward compatibility for GSS-API V1
callers, who need not even know of the existence of prot_ready_state,
and who will get the expected behavior from GSS_S_COMPLETE, but who
will not be able to use per-message protection before GSS_S_COMPLETE
is returned.
It is not a requirement that GSS-V2 mechanisms ever return TRUE
prot_ready_state before completion of context establishment (indeed,
some mechanisms will not evolve usable message protection keys,
especially at the context acceptor, before context establishment is
complete). It is expected but not required that GSS-V2 mechanisms
will return TRUE prot_ready_state upon completion of context
establishment if they support per-message protection at all (however
GSS-V2 applications should not assume that TRUE prot_ready_state will
Linn Standards Track [Page 22]RFC 2078 GSS-API January 1997
always be returned together with the GSS_S_COMPLETE major_status,
since GSS-V2 implementations may continue to support GSS-V1 mechanism
code, which will never return TRUE prot_ready_state).
When prot_ready_state is returned TRUE, mechanisms shall also set
those context service indicator flags (deleg_state, mutual_state,
replay_det_state, sequence_state, anon_state, trans_state,
conf_avail, integ_avail) which represent facilities confirmed, at
that time, to be available on the context being established. In
situations where prot_ready_state is returned before GSS_S_COMPLETE,
it is possible that additional facilities may be confirmed and
subsequently indicated when GSS_S_COMPLETE is returned.
1.2.8: Implementation Robustness
This section recommends aspects of GSS-API implementation behavior in
the interests of overall robustness.
If a token is presented for processing on a GSS-API security context
and that token is determined to be invalid for that context, the
context's state should not be disrupted for purposes of processing
subsequent valid tokens.
Certain local conditions at a GSS-API implementation (e.g.,
unavailability of memory) may preclude, temporarily or permanently,
the successful processing of tokens on a GSS-API security context,
typically generating GSS_S_FAILURE major_status returns along with
locally-significant minor_status. For robust operation under such
conditions, the following recommendations are made:
Failing calls should free any memory they allocate, so that
callers may retry without causing further loss of resources.
Failure of an individual call on an established context should not
preclude subsequent calls from succeeding on the same context.
Whenever possible, it should be possible for
GSS_Delete_sec_context() calls to be successfully processed even
if other calls cannot succeed, thereby enabling context-related
resources to be released.
2: Interface Descriptions
This section describes the GSS-API's service interface, dividing the
set of calls offered into four groups. Credential management calls
are related to the acquisition and release of credentials by
principals. Context-level calls are related to the management of
security contexts between principals. Per-message calls are related
Linn Standards Track [Page 23]RFC 2078 GSS-API January 1997
to the protection of individual messages on established security
contexts. Support calls provide ancillary functions useful to GSS-API
callers. Table 2 groups and summarizes the calls in tabular fashion.
Table 2: GSS-API Calls
CREDENTIAL MANAGEMENT
GSS_Acquire_cred acquire credentials for use
GSS_Release_cred release credentials after use
GSS_Inquire_cred display information about
credentials
GSS_Add_cred construct credentials incrementally
GSS_Inquire_cred_by_mech display per-mechanism credential
information
CONTEXT-LEVEL CALLS
GSS_Init_sec_context initiate outbound security context
GSS_Accept_sec_context accept inbound security context
GSS_Delete_sec_context flush context when no longer needed
GSS_Process_context_token process received control token on
context
GSS_Context_time indicate validity time remaining on
context
GSS_Inquire_context display information about context
GSS_Wrap_size_limit determine GSS_Wrap token size limit
GSS_Export_sec_context transfer context to other process
GSS_Import_sec_context import transferred context
PER-MESSAGE CALLS
GSS_GetMIC apply integrity check, receive as
token separate from message
GSS_VerifyMIC validate integrity check token
along with message
GSS_Wrap sign, optionally encrypt,
encapsulate
GSS_Unwrap decapsulate, decrypt if needed,
validate integrity check
Linn Standards Track [Page 24]RFC 2078 GSS-API January 1997
SUPPORT CALLS
GSS_Display_status translate status codes to printable
form
GSS_Indicate_mechs indicate mech_types supported on
local system
GSS_Compare_name compare two names for equality
GSS_Display_name translate name to printable form
GSS_Import_name convert printable name to
normalized form
GSS_Release_name free storage of normalized-form
name
GSS_Release_buffer free storage of printable name
GSS_Release_OID free storage of OID object
GSS_Release_OID_set free storage of OID set object
GSS_Create_empty_OID_set create empty OID set
GSS_Add_OID_set_member add member to OID set
GSS_Test_OID_set_member test if OID is member of OID set
GSS_OID_to_str display OID as string
GSS_Str_to_OID construct OID from string
GSS_Inquire_names_for_mech indicate name types supported by
mechanism
GSS_Inquire_mechs_for_name indicates mechanisms supporting name
type
GSS_Canonicalize_name translate name to per-mechanism form
GSS_Export_name externalize per-mechanism name
GSS_Duplicate_name duplicate name object
2.1: Credential management calls
These GSS-API calls provide functions related to the management of
credentials. Their characterization with regard to whether or not
they may block pending exchanges with other network entities (e.g.,
directories or authentication servers) depends in part on OS-specific
(extra-GSS-API) issues, so is not specified in this document.
The GSS_Acquire_cred() call is defined within the GSS-API in support
of application portability, with a particular orientation towards
support of portable server applications. It is recognized that (for
certain systems and mechanisms) credentials for interactive users may
be managed differently from credentials for server processes; in such
environments, it is the GSS-API implementation's responsibility to
distinguish these cases and the procedures for making this
distinction are a local matter. The GSS_Release_cred() call provides
a means for callers to indicate to the GSS-API that use of a
credentials structure is no longer required. The GSS_Inquire_cred()
call allows callers to determine information about a credentials
structure. The GSS_Add_cred() call enables callers to append
Linn Standards Track [Page 25]RFC 2078 GSS-API January 1997
elements to an existing credential structure, allowing iterative
construction of a multi-mechanism credential. The
GSS_Inquire_cred_by_mech() call enables callers to extract per-
mechanism information describing a credentials structure.
2.1.1: GSS_Acquire_cred call
Inputs:
o desired_name INTERNAL NAME, -NULL requests locally-determined
default
o lifetime_req INTEGER,-in seconds; 0 requests default
o desired_mechs SET OF OBJECT IDENTIFIER,-empty set requests
system-selected default
o cred_usage INTEGER -0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
2=ACCEPT-ONLY
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o output_cred_handle CREDENTIAL HANDLE,
o actual_mechs SET OF OBJECT IDENTIFIER,
o lifetime_rec INTEGER -in seconds, or reserved value for
INDEFINITE
Return major_status codes:
o GSS_S_COMPLETE indicates that requested credentials were
successfully established, for the duration indicated in
lifetime_rec, suitable for the usage requested in cred_usage,
for the set of mech_types indicated in actual_mechs, and that
those credentials can be referenced for subsequent use with
the handle returned in output_cred_handle.
o GSS_S_BAD_MECH indicates that a mech_type unsupported by the
GSS-API implementation type was requested, causing the
credential establishment operation to fail.
Linn Standards Track [Page 26]RFC 2078 GSS-API January 1997
o GSS_S_BAD_NAMETYPE indicates that the provided desired_name is
uninterpretable or of a type unsupported by the applicable
underlying GSS-API mechanism(s), so no credentials could be
established for the accompanying desired_name.
o GSS_S_BAD_NAME indicates that the provided desired_name is
inconsistent in terms of internally-incorporated type specifier
information, so no credentials could be established for the
accompanying desired_name.
o GSS_S_FAILURE indicates that credential establishment failed
for reasons unspecified at the GSS-API level, including lack
of authorization to establish and use credentials associated
with the identity named in the input desired_name argument.
GSS_Acquire_cred() is used to acquire credentials so that a
principal can (as a function of the input cred_usage parameter)
initiate and/or accept security contexts under the identity
represented by the desired_name input argument. On successful
completion, the returned output_cred_handle result provides a handle
for subsequent references to the acquired credentials. Typically,
single-user client processes requesting that default credential
behavior be applied for context establishment purposes will have no
need to invoke this call.
A caller may provide the value NULL for desired_name, signifying a
request for credentials corresponding to a principal identity
selected by default for the caller. The procedures used by GSS-API
implementations to select the appropriate principal identity in
response to such a request are local matters. It is possible that
multiple pre-established credentials may exist for the same principal
identity (for example, as a result of multiple user login sessions)
when GSS_Acquire_cred() is called; the means used in such cases to
select a specific credential are local matters. The input
lifetime_req argument to GSS_Acquire_cred() may provide useful
information for local GSS-API implementations to employ in making
this disambiguation in a manner which will best satisfy a caller's
intent.
The lifetime_rec result indicates the length of time for which the
acquired credentials will be valid, as an offset from the present. A
mechanism may return a reserved value indicating INDEFINITE if no
constraints on credential lifetime are imposed. A caller of
GSS_Acquire_cred() can request a length of time for which acquired
credentials are to be valid (lifetime_req argument), beginning at the
present, or can request credentials with a default validity interval.
(Requests for postdated credentials are not supported within the
GSS-API.) Certain mechanisms and implementations may bind in
Linn Standards Track [Page 27]RFC 2078 GSS-API January 1997
credential validity period specifiers at a point preliminary to
invocation of the GSS_Acquire_cred() call (e.g., in conjunction with
user login procedures). As a result, callers requesting non-default
values for lifetime_req must recognize that such requests cannot
always be honored and must be prepared to accommodate the use of
returned credentials with different lifetimes as indicated in
lifetime_rec.
The caller of GSS_Acquire_cred() can explicitly specify a set of
mech_types which are to be accommodated in the returned credentials
(desired_mechs argument), or can request credentials for a system-
defined default set of mech_types. Selection of the system-specified
default set is recommended in the interests of application
portability. The actual_mechs return value may be interrogated by the
caller to determine the set of mechanisms with which the returned
credentials may be used.
2.1.2: GSS_Release_cred call
Input:
o cred_handle CREDENTIAL HANDLE - NULL specifies that
the credential elements used when default credential behavior
is requested be released.
Outputs:
o major_status INTEGER,
o minor_status INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates that the credentials referenced by the
input cred_handle were released for purposes of subsequent
access by the caller. The effect on other processes which may
be authorized shared access to such credentials is a local
matter.
o GSS_S_NO_CRED indicates that no release operation was
performed, either because the input cred_handle was invalid or
because the caller lacks authorization to access the
referenced credentials.
o GSS_S_FAILURE indicates that the release operation failed for
reasons unspecified at the GSS-API level.
Linn Standards Track [Page 28]RFC 2078 GSS-API January 1997
Provides a means for a caller to explicitly request that credentials
be released when their use is no longer required. Note that system-
specific credential management functions are also likely to exist,
for example to assure that credentials shared among processes are
properly deleted when all affected processes terminate, even if no
explicit release requests are issued by those processes. Given the
fact that multiple callers are not precluded from gaining authorized
access to the same credentials, invocation of GSS_Release_cred()
cannot be assumed to delete a particular set of credentials on a
system-wide basis.
2.1.3: GSS_Inquire_cred call
Input:
o cred_handle CREDENTIAL HANDLE -NULL specifies that the
credential elements used when default credential behavior is
requested are to be queried
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o cred_name INTERNAL NAME,
o lifetime_rec INTEGER -in seconds, or reserved value for
INDEFINITE
o cred_usage INTEGER, -0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
2=ACCEPT-ONLY
o mech_set SET OF OBJECT IDENTIFIER
Return major_status codes:
o GSS_S_COMPLETE indicates that the credentials referenced by the
input cred_handle argument were valid, and that the output
cred_name, lifetime_rec, and cred_usage values represent,
respectively, the credentials' associated principal name,
remaining lifetime, suitable usage modes, and supported
mechanism types.
o GSS_S_NO_CRED indicates that no information could be returned
about the referenced credentials, either because the input
cred_handle was invalid or because the caller lacks
authorization to access the referenced credentials.
Linn Standards Track [Page 29]RFC 2078 GSS-API January 1997
o GSS_S_DEFECTIVE_CREDENTIAL indicates that the referenced
credentials are invalid.
o GSS_S_CREDENTIALS_EXPIRED indicates that the referenced
credentials have expired.
o GSS_S_FAILURE indicates that the operation failed for
reasons unspecified at the GSS-API level.
The GSS_Inquire_cred() call is defined primarily for the use of those
callers which request use of default credential behavior rather than
acquiring credentials explicitly with GSS_Acquire_cred(). It enables
callers to determine a credential structure's associated principal
name, remaining validity period, usability for security context
initiation and/or acceptance, and supported mechanisms.
For a multi-mechanism credential, the returned "lifetime" specifier
indicates the shortest lifetime of any of the mechanisms' elements in
the credential (for either context initiation or acceptance
purposes).
GSS_Inquire_cred() should indicate INITIATE-AND-ACCEPT for
"cred_usage" if both of the following conditions hold:
(1) there exists in the credential an element which allows context
initiation using some mechanism
(2) there exists in the credential an element which allows context
acceptance using some mechanism (allowably, but not necessarily,
one of the same mechanism(s) qualifying for (1)).
If condition (1) holds but not condition (2), GSS_Inquire_cred()
should indicate INITIATE-ONLY for "cred_usage". If condition (2)
holds but not condition (1), GSS_Inquire_cred() should indicate
ACCEPT-ONLY for "cred_usage".
Callers requiring finer disambiguation among available combinations
of lifetimes, usage modes, and mechanisms should call the
GSS_Inquire_cred_by_mech() routine, passing that routine one of the
mech OIDs returned by GSS_Inquire_cred().
Linn Standards Track [Page 30]RFC 2078 GSS-API January 1997
2.1.4: GSS_Add_cred call
Inputs:
o input_cred_handle CREDENTIAL HANDLE - handle to credential
structure created with prior GSS_Acquire_cred() or
GSS_Add_cred() call, or NULL to append elements to the set
which are applied for the caller when default credential
behavior is specified.
o desired_name INTERNAL NAME - NULL requests locally-determined
default
o initiator_time_req INTEGER - in seconds; 0 requests default
o acceptor_time_req INTEGER - in seconds; 0 requests default
o desired_mech OBJECT IDENTIFIER
o cred_usage INTEGER - 0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
2=ACCEPT-ONLY
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o output_cred_handle CREDENTIAL HANDLE, - NULL to request that
credential elements be added "in place" to the credential
structure identified by input_cred_handle, non-NULL pointer
to request that a new credential structure and handle be created.
o actual_mechs SET OF OBJECT IDENTIFIER,
o initiator_time_rec INTEGER - in seconds, or reserved value for
INDEFINITE
o acceptor_time_rec INTEGER - in seconds, or reserved value for
INDEFINITE
o cred_usage INTEGER, -0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
2=ACCEPT-ONLY
o mech_set SET OF OBJECT IDENTIFIER -- full set of mechanisms
supported by resulting credential.
Linn Standards Track [Page 31]RFC 2078 GSS-API January 1997
Return major_status codes:
o GSS_S_COMPLETE indicates that the credentials referenced by
the input_cred_handle argument were valid, and that the
resulting credential from GSS_Add_cred() is valid for the
durations indicated in initiator_time_rec and acceptor_time_rec,
suitable for the usage requested in cred_usage, and for the
mechanisms indicated in actual_mechs.
o GSS_S_DUPLICATE_ELEMENT indicates that the input desired_mech
specified a mechanism for which the referenced credential
already contained a credential element with overlapping
cred_usage and validity time specifiers.
o GSS_S_BAD_MECH indicates that the input desired_mech specified
a mechanism unsupported by the GSS-API implementation, causing
the GSS_Add_cred() operation to fail.
o GSS_S_BAD_NAMETYPE indicates that the provided desired_name
is uninterpretable or of a type unsupported by the applicable
underlying GSS-API mechanism(s), so the GSS_Add_cred() operation
could not be performed for that name.
o GSS_S_BAD_NAME indicates that the provided desired_name is
inconsistent in terms of internally-incorporated type specifier
information, so the GSS_Add_cred() operation could not be
performed for that name.
o GSS_S_NO_CRED indicates that the input_cred_handle referenced
invalid or inaccessible credentials.
o GSS_S_FAILURE indicates that the operation failed for
reasons unspecified at the GSS-API level, including lack of
authorization to establish or use credentials representing
the requested identity.
GSS_Add_cred() enables callers to construct credentials iteratively
by adding credential elements in successive operations, corresponding
to different mechanisms. This offers particular value in multi-
mechanism environments, as the major_status and minor_status values
returned on each iteration are individually visible and can therefore
be interpreted unambiguously on a per-mechanism basis.
The same input desired_name, or default reference, should be used on
all GSS_Acquire_cred() and GSS_Add_cred() calls corresponding to a
particular credential.
Linn Standards Track [Page 32]RFC 2078 GSS-API January 1997
2.1.5: GSS_Inquire_cred_by_mech call
Inputs:
o cred_handle CREDENTIAL HANDLE -- NULL specifies that the
credential elements used when default credential behavior is
requested are to be queried
o mech_type OBJECT IDENTIFIER -- specific mechanism for
which credentials are being queried
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o cred_name INTERNAL NAME, -- guaranteed to be MN
o lifetime_rec_initiate INTEGER -- in seconds, or reserved value for
INDEFINITE
o lifetime_rec_accept INTEGER -- in seconds, or reserved value for
INDEFINITE
o cred_usage INTEGER, -0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
2=ACCEPT-ONLY
Return major_status codes:
o GSS_S_COMPLETE indicates that the credentials referenced by the
input cred_handle argument were valid, that the mechanism
indicated by the input mech_type was represented with elements
within those credentials, and that the output cred_name,
lifetime_rec_initiate, lifetime_rec_accept, and cred_usage values
represent, respectively, the credentials' associated principal
name, remaining lifetimes, and suitable usage modes.
o GSS_S_NO_CRED indicates that no information could be returned
about the referenced credentials, either because the input
cred_handle was invalid or because the caller lacks
authorization to access the referenced credentials.
o GSS_S_DEFECTIVE_CREDENTIAL indicates that the referenced
credentials are invalid.
o GSS_S_CREDENTIALS_EXPIRED indicates that the referenced
credentials have expired.
Linn Standards Track [Page 33]RFC 2078 GSS-API January 1997
o GSS_S_BAD_MECH indicates that the referenced credentials do not
contain elements for the requested mechanism.
o GSS_S_FAILURE indicates that the operation failed for reasons
unspecified at the GSS-API level.
The GSS_Inquire_cred_by_mech() call enables callers in multi-
mechanism environments to acquire specific data about available
combinations of lifetimes, usage modes, and mechanisms within a
credential structure. The lifetime_rec_initiate result indicates the
available lifetime for context initiation purposes; the
lifetime_rec_accept result indicates the available lifetime for
context acceptance purposes.
2.2: Context-level calls
This group of calls is devoted to the establishment and management of
security contexts between peers. A context's initiator calls
GSS_Init_sec_context(), resulting in generation of a token which the
caller passes to the target. At the target, that token is passed to
GSS_Accept_sec_context(). Depending on the underlying mech_type and
specified options, additional token exchanges may be performed in the
course of context establishment; such exchanges are accommodated by
GSS_S_CONTINUE_NEEDED status returns from GSS_Init_sec_context() and
GSS_Accept_sec_context().
Either party to an established context may invoke
GSS_Delete_sec_context() to flush context information when a context
is no longer required. GSS_Process_context_token() is used to
process received tokens carrying context-level control information.
GSS_Context_time() allows a caller to determine the length of time
for which an established context will remain valid.
GSS_Inquire_context() returns status information describing context
characteristics. GSS_Wrap_size_limit() allows a caller to determine
the size of a token which will be generated by a GSS_Wrap()
operation. GSS_Export_sec_context() and GSS_Import_sec_context()
enable transfer of active contexts between processes on an end
system.
2.2.1: GSS_Init_sec_context call
Inputs:
o claimant_cred_handle CREDENTIAL HANDLE, -NULL specifies "use
default"
o input_context_handle CONTEXT HANDLE, -0 specifies "none assigned
yet"
Linn Standards Track [Page 34]RFC 2078 GSS-API January 1997
o targ_name INTERNAL NAME,
o mech_type OBJECT IDENTIFIER, -NULL parameter specifies "use
default"
o deleg_req_flag BOOLEAN,
o mutual_req_flag BOOLEAN,
o replay_det_req_flag BOOLEAN,
o sequence_req_flag BOOLEAN,
o anon_req_flag BOOLEAN,
o lifetime_req INTEGER,-0 specifies default lifetime
o chan_bindings OCTET STRING,
o input_token OCTET STRING-NULL or token received from target
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o output_context_handle CONTEXT HANDLE,
o mech_type OBJECT IDENTIFIER, -actual mechanism always
indicated, never NULL
o output_token OCTET STRING, -NULL or token to pass to context
target
o deleg_state BOOLEAN,
o mutual_state BOOLEAN,
o replay_det_state BOOLEAN,
o sequence_state BOOLEAN,
o anon_state BOOLEAN,
o trans_state BOOLEAN,
o prot_ready_state BOOLEAN, -- see Section 1.2.7
Linn Standards Track [Page 35]RFC 2078 GSS-API January 1997
o conf_avail BOOLEAN,
o integ_avail BOOLEAN,
o lifetime_rec INTEGER - in seconds, or reserved value for
INDEFINITE
This call may block pending network interactions for those mech_types
in which an authentication server or other network entity must be
consulted on behalf of a context initiator in order to generate an
output_token suitable for presentation to a specified target.
Return major_status codes:
o GSS_S_COMPLETE indicates that context-level information was
successfully initialized, and that the returned output_token
will provide sufficient information for the target to perform
per-message processing on the newly-established context.
o GSS_S_CONTINUE_NEEDED indicates that control information in the
returned output_token must be sent to the target, and that a
reply must be received and passed as the input_token argument
to a continuation call to GSS_Init_sec_context(), before
per-message processing can be performed in conjunction with
this context.
o GSS_S_DEFECTIVE_TOKEN indicates that consistency checks
performed on the input_token failed, preventing further
processing from being performed based on that token.
o GSS_S_DEFECTIVE_CREDENTIAL indicates that consistency checks
performed on the credential structure referenced by
claimant_cred_handle failed, preventing further processing from
being performed using that credential structure.
o GSS_S_BAD_SIG indicates that the received input_token
contains an incorrect integrity check, so context setup cannot
be accomplished.
o GSS_S_NO_CRED indicates that no context was established,
either because the input cred_handle was invalid, because the
referenced credentials are valid for context acceptor use
only, or because the caller lacks authorization to access the
referenced credentials.
o GSS_S_CREDENTIALS_EXPIRED indicates that the credentials
provided through the input claimant_cred_handle argument are no
longer valid, so context establishment cannot be completed.
Linn Standards Track [Page 36]RFC 2078 GSS-API January 1997
o GSS_S_BAD_BINDINGS indicates that a mismatch between the
caller-provided chan_bindings and those extracted from the
input_token was detected, signifying a security-relevant
event and preventing context establishment. (This result will
be returned by GSS_Init_sec_context only for contexts where
mutual_state is TRUE.)
o GSS_S_OLD_TOKEN indicates that the input_token is too old to
be checked for integrity. This is a fatal error during context
establishment.
o GSS_S_DUPLICATE_TOKEN indicates that the input token has a
correct integrity check, but is a duplicate of a token already
processed. This is a fatal error during context establishment.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided; this major status will
be returned only for successor calls following GSS_S_CONTINUE_
NEEDED status returns.
o GSS_S_BAD_NAMETYPE indicates that the provided targ_name is
of a type uninterpretable or unsupported by the applicable
underlying GSS-API mechanism(s), so context establishment
cannot be completed.
o GSS_S_BAD_NAME indicates that the provided targ_name is
inconsistent in terms of internally-incorporated type specifier
information, so context establishment cannot be accomplished.
o GSS_S_BAD_MECH indicates receipt of a context establishment token
or of a caller request specifying a mechanism unsupported by
the local system or with the caller's active credentials
o GSS_S_FAILURE indicates that context setup could not be
accomplished for reasons unspecified at the GSS-API level, and
that no interface-defined recovery action is available.
This routine is used by a context initiator, and ordinarily emits one
(or, for the case of a multi-step exchange, more than one)
output_token suitable for use by the target within the selected
mech_type's protocol. Using information in the credentials structure
referenced by claimant_cred_handle, GSS_Init_sec_context()
initializes the data structures required to establish a security
context with target targ_name. The targ_name may be any valid
INTERNAL NAME; it need not be an MN. The claimant_cred_handle must
correspond to the same valid credentials structure on the initial
call to GSS_Init_sec_context() and on any successor calls resulting
from GSS_S_CONTINUE_NEEDED status returns; different protocol
Linn Standards Track [Page 37]RFC 2078 GSS-API January 1997
sequences modeled by the GSS_S_CONTINUE_NEEDED facility will require
access to credentials at different points in the context
establishment sequence.
The input_context_handle argument is 0, specifying "not yet
assigned", on the first GSS_Init_sec_context() call relating to a
given context. If successful (i.e., if accompanied by major_status
GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED), and only if successful, the
initial GSS_Init_sec_context() call returns a non-zero
output_context_handle for use in future references to this context.
Once a non-zero output_context_handle has been returned, GSS-API
callers should call GSS_Delete_sec_context() to release context-
related resources if errors occur in later phases of context
establishment, or when an established context is no longer required.
When continuation attempts to GSS_Init_sec_context() are needed to
perform context establishment, the previously-returned non-zero
handle value is entered into the input_context_handle argument and
will be echoed in the returned output_context_handle argument. On
such continuation attempts (and only on continuation attempts) the
input_token value is used, to provide the token returned from the
context's target.
The chan_bindings argument is used by the caller to provide
information binding the security context to security-related
characteristics (e.g., addresses, cryptographic keys) of the
underlying communications channel. See Section 1.1.6 of this document
for more discussion of this argument's usage.
The input_token argument contains a message received from the target,
and is significant only on a call to GSS_Init_sec_context() which
follows a previous return indicating GSS_S_CONTINUE_NEEDED
major_status.
It is the caller's responsibility to establish a communications path
to the target, and to transmit any returned output_token (independent
of the accompanying returned major_status value) to the target over
that path. The output_token can, however, be transmitted along with
the first application-provided input message to be processed by
GSS_GetMIC() or GSS_Wrap() in conjunction with a successfully-
established context.
The initiator may request various context-level functions through
input flags: the deleg_req_flag requests delegation of access rights,
the mutual_req_flag requests mutual authentication, the
replay_det_req_flag requests that replay detection features be
applied to messages transferred on the established context, and the
sequence_req_flag requests that sequencing be enforced. (See Section
Linn Standards Track [Page 38]
RFC 2078 GSS-API January 1997
1.2.3 for more information on replay detection and sequencing
features.) The anon_req_flag requests that the initiator's identity
not be transferred within tokens to be sent to the acceptor.
Not all of the optionally-requestable features will be available in
all underlying mech_types. The corresponding return state values
deleg_state, mutual_state, replay_det_state, and sequence_state
indicate, as a function of mech_type processing capabilities and
initiator-provided input flags, the set of features which will be
active on the context. The returned trans_state value indicates
whether the context is transferable to other processes through use of
GSS_Export_sec_context(). These state indicators' values are
undefined unless either the routine's major_status indicates
GSS_S_COMPLETE, or TRUE prot_ready_state is returned along with
GSS_S_CONTINUE_NEEDED major_status; for the latter case, it is
possible that additional features, not confirmed or indicated along
with TRUE prot_ready_state, will be confirmed and indicated when
GSS_S_COMPLETE is subsequently returned.
The returned anon_state and prot_ready_state values are significant
for both GSS_S_COMPLETE and GSS_S_CONTINUE_NEEDED major_status
returns from GSS_Init_sec_context(). When anon_state is returned
TRUE, this indicates that neither the current token nor its
predecessors delivers or has delivered the initiator's identity.
Callers wishing to perform context establishment only if anonymity
support is provided should transfer a returned token from
GSS_Init_sec_context() to the peer only if it is accompanied by a
TRUE anon_state indicator. When prot_ready_state is returned TRUE in
conjunction with GSS_S_CONTINUE_NEEDED major_status, this indicates
that per-message protection operations may be applied on the context:
see Section 1.2.7 for further discussion of this facility.
Failure to provide the precise set of features requested by the
caller does not cause context establishment to fail; it is the
caller's prerogative to delete the context if the feature set
provided is unsuitable for the caller's use.
The returned mech_type value indicates the specific mechanism
employed on the context, is valid only along with major_status
GSS_S_COMPLETE, and will never indicate the value for "default".
Note that, for the case of certain mechanisms which themselves
perform negotiation, the returned mech_type result may indicate
selection of a mechanism identified by an OID different than that
passed in the input mech_type argument.
The conf_avail return value indicates whether the context supports
per-message confidentiality services, and so informs the caller
whether or not a request for encryption through the conf_req_flag
Linn Standards Track [Page 39]
RFC 2078 GSS-API January 1997
input to GSS_Wrap() can be honored. In similar fashion, the
integ_avail return value indicates whether per-message integrity
services are available (through either GSS_GetMIC() or GSS_Wrap()) on
the established context. These state indicators' values are undefined
unless either the routine's major_status indicates GSS_S_COMPLETE, or
TRUE prot_ready_state is returned along with GSS_S_CONTINUE_NEEDED
major_status.
The lifetime_req input specifies a desired upper bound for the
lifetime of the context to be established, with a value of 0 used to
request a default lifetime. The lifetime_rec return value indicates
the length of time for which the context will be valid, expressed as
an offset from the present; depending on mechanism capabilities,
credential lifetimes, and local policy, it may not correspond to the
value requested in lifetime_req. If no constraints on context
lifetime are imposed, this may be indicated by returning a reserved
value representing INDEFINITE lifetime_req. The value of lifetime_rec
is undefined unless the routine's major_status indicates
GSS_S_COMPLETE.
If the mutual_state is TRUE, this fact will be reflected within the
output_token. A call to GSS_Accept_sec_context() at the target in
conjunction with such a context will return a token, to be processed
by a continuation call to GSS_Init_sec_context(), in order to
achieve mutual authentication.
2.2.2: GSS_Accept_sec_context call
Inputs:
o acceptor_cred_handle CREDENTIAL HANDLE, -- NULL specifies
"use default"
o input_context_handle CONTEXT HANDLE, -- 0 specifies
"not yet assigned"
o chan_bindings OCTET STRING,
o input_token OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o src_name INTERNAL NAME, -- guaranteed to be MN
Linn Standards Track [Page 40]RFC 2078 GSS-API January 1997
o mech_type OBJECT IDENTIFIER,
o output_context_handle CONTEXT HANDLE,
o deleg_state BOOLEAN,
o mutual_state BOOLEAN,
o replay_det_state BOOLEAN,
o sequence_state BOOLEAN,
o anon_state BOOLEAN,
o trans_state BOOLEAN,
o prot_ready_state BOOLEAN, -- see Section 1.2.7 for discussion
o conf_avail BOOLEAN,
o integ_avail BOOLEAN,
o lifetime_rec INTEGER, - in seconds, or reserved value for
INDEFINITE
o delegated_cred_handle CREDENTIAL HANDLE,
o output_token OCTET STRING -NULL or token to pass to context
initiator
This call may block pending network interactions for those mech_types
in which a directory service or other network entity must be
consulted on behalf of a context acceptor in order to validate a
received input_token.
Return major_status codes:
o GSS_S_COMPLETE indicates that context-level data structures
were successfully initialized, and that per-message processing
can now be performed in conjunction with this context.
o GSS_S_CONTINUE_NEEDED indicates that control information in the
returned output_token must be sent to the initiator, and that
a response must be received and passed as the input_token
argument to a continuation call to GSS_Accept_sec_context(),
before per-message processing can be performed in conjunction
with this context.
Linn Standards Track [Page 41]RFC 2078 GSS-API January 1997
o GSS_S_DEFECTIVE_TOKEN indicates that consistency checks performed
on the input_token failed, preventing further processing from
being performed based on that token.
o GSS_S_DEFECTIVE_CREDENTIAL indicates that consistency checks
performed on the credential structure referenced by
acceptor_cred_handle failed, preventing further processing from
being performed using that credential structure.
o GSS_S_BAD_SIG indicates that the received input_token contains
an incorrect integrity check, so context setup cannot be
accomplished.
o GSS_S_DUPLICATE_TOKEN indicates that the integrity check on the
received input_token was correct, but that the input_token
was recognized as a duplicate of an input_token already
processed. No new context is established.
o GSS_S_OLD_TOKEN indicates that the integrity check on the received
input_token was correct, but that the input_token is too old
to be checked for duplication against previously-processed
input_tokens. No new context is established.
o GSS_S_NO_CRED indicates that no context was established, either
because the input cred_handle was invalid, because the
referenced credentials are valid for context initiator use
only, or because the caller lacks authorization to access the
referenced credentials.
o GSS_S_CREDENTIALS_EXPIRED indicates that the credentials provided
through the input acceptor_cred_handle argument are no
longer valid, so context establishment cannot be completed.
o GSS_S_BAD_BINDINGS indicates that a mismatch between the
caller-provided chan_bindings and those extracted from the
input_token was detected, signifying a security-relevant
event and preventing context establishment.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided; this major status will
be returned only for successor calls following GSS_S_CONTINUE_
NEEDED status returns.
o GSS_S_BAD_MECH indicates receipt of a context establishment token
specifying a mechanism unsupported by the local system or with
the caller's active credentials.
Linn Standards Track [Page 42]RFC 2078 GSS-API January 1997
o GSS_S_FAILURE indicates that context setup could not be
accomplished for reasons unspecified at the GSS-API level, and
that no interface-defined recovery action is available.
The GSS_Accept_sec_context() routine is used by a context target.
Using information in the credentials structure referenced by the
input acceptor_cred_handle, it verifies the incoming input_token and
(following the successful completion of a context establishment
sequence) returns the authenticated src_name and the mech_type used.
The returned src_name is guaranteed to be an MN, processed by the
mechanism under which the context was established. The
acceptor_cred_handle must correspond to the same valid credentials
structure on the initial call to GSS_Accept_sec_context() and on any
successor calls resulting from GSS_S_CONTINUE_NEEDED status returns;
different protocol sequences modeled by the GSS_S_CONTINUE_NEEDED
mechanism will require access to credentials at different points in
the context establishment sequence.
The input_context_handle argument is 0, specifying "not yet
assigned", on the first GSS_Accept_sec_context() call relating to a
given context. If successful (i.e., if accompanied by major_status
GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED), and only if successful, the
initial GSS_Accept_sec_context() call returns a non-zero
output_context_handle for use in future references to this context.
Once a non-zero output_context_handle has been returned, GSS-API
callers should call GSS_Delete_sec_context() to release context-
related resources if errors occur in later phases of context
establishment, or when an established context is no longer required.
The chan_bindings argument is used by the caller to provide
information binding the security context to security-related
characteristics (e.g., addresses, cryptographic keys) of the
underlying communications channel. See Section 1.1.6 of this document
for more discussion of this argument's usage.
The returned state results (deleg_state, mutual_state,
replay_det_state, sequence_state, anon_state, trans_state, and
prot_ready_state) reflect the same information as described for
GSS_Init_sec_context(), and their values are significant under the
same return state conditions.
Linn Standards Track [Page 43]RFC 2078 GSS-API January 1997
The conf_avail return value indicates whether the context supports
per-message confidentiality services, and so informs the caller
whether or not a request for encryption through the conf_req_flag
input to GSS_Wrap() can be honored. In similar fashion, the
integ_avail return value indicates whether per-message integrity
services are available (through either GSS_GetMIC() or GSS_Wrap())
on the established context. These values are significant under the
same return state conditions as described under
GSS_Init_sec_context().
The lifetime_rec return value is significant only in conjunction with
GSS_S_COMPLETE major_status, and indicates the length of time for
which the context will be valid, expressed as an offset from the
present.
The mech_type return value indicates the specific mechanism employed
on the context, is valid only along with major_status GSS_S_COMPLETE,
and will never indicate the value for "default".
The delegated_cred_handle result is significant only when deleg_state
is TRUE, and provides a means for the target to reference the
delegated credentials. The output_token result, when non-NULL,
provides a context-level token to be returned to the context
initiator to continue a multi-step context establishment sequence. As
noted with GSS_Init_sec_context(), any returned token should be
transferred to the context's peer (in this case, the context
initiator), independent of the value of the accompanying returned
major_status.
Note: A target must be able to distinguish a context-level
input_token, which is passed to GSS_Accept_sec_context(), from the
per-message data elements passed to GSS_VerifyMIC() or GSS_Unwrap().
These data elements may arrive in a single application message, and
GSS_Accept_sec_context() must be performed before per-message
processing can be performed successfully.
2.2.3: GSS_Delete_sec_context call
Input:
o context_handle CONTEXT HANDLE
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
Linn Standards Track [Page 44]
RFC 2078 GSS-API January 1997
o output_context_token OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates that the context was recognized, and that
relevant context-specific information was flushed. If the caller
provides a non-null buffer to receive an output_context_token, and
the mechanism returns a non-NULL token into that buffer, the
returned output_context_token is ready for transfer to the
context's peer.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided, so no deletion was
performed.
o GSS_S_FAILURE indicates that the context is recognized, but
that the GSS_Delete_sec_context() operation could not be
performed for reasons unspecified at the GSS-API level.
This call may block pending network interactions for mech_types in
which active notification must be made to a central server when a
security context is to be deleted.
This call can be made by either peer in a security context, to flush
context-specific information. If a non-null output_context_token
parameter is provided by the caller, an output_context_token may be
returned to the caller. If an output_context_token is provided to
the caller, it can be passed to the context's peer to inform the
peer's GSS-API implementation that the peer's corresponding context
information can also be flushed. (Once a context is established, the
peers involved are expected to retain cached credential and context-
related information until the information's expiration time is
reached or until a GSS_Delete_sec_context() call is made.)
The facility for context_token usage to signal context deletion is
retained for compatibility with GSS-API Version 1. 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.
Attempts to perform per-message processing on a deleted context will
result in error returns.
Linn Standards Track [Page 45]RFC 2078 GSS-API January 1997
2.2.4: GSS_Process_context_token call
Inputs:
o context_handle CONTEXT HANDLE,
o input_context_token OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
Return major_status codes:
o GSS_S_COMPLETE indicates that the input_context_token was
successfully processed in conjunction with the context
referenced by context_handle.
o GSS_S_DEFECTIVE_TOKEN indicates that consistency checks
performed on the received context_token failed, preventing
further processing from being performed with that token.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided.
o GSS_S_FAILURE indicates that the context is recognized, but
that the GSS_Process_context_token() operation could not be
performed for reasons unspecified at the GSS-API level.
This call is used to process context_tokens received from a peer once
a context has been established, with corresponding impact on
context-level state information. One use for this facility is
processing of the context_tokens generated by
GSS_Delete_sec_context(); GSS_Process_context_token() will not block
pending network interactions for that purpose. Another use is to
process tokens indicating remote-peer context establishment failures
after the point where the local GSS-API implementation has already
indicated GSS_S_COMPLETE status.
Linn Standards Track [Page 46]RFC 2078 GSS-API January 1997
2.2.5: GSS_Context_time call
Input:
o context_handle CONTEXT HANDLE,
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o lifetime_rec INTEGER - in seconds, or reserved value for
INDEFINITE
Return major_status codes:
o GSS_S_COMPLETE indicates that the referenced context is valid,
and will remain valid for the amount of time indicated in
lifetime_rec.
o GSS_S_CONTEXT_EXPIRED indicates that data items related to the
referenced context have expired.
o GSS_S_CREDENTIALS_EXPIRED indicates that the context is
recognized, but that its associated credentials have expired.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided.
o GSS_S_FAILURE indicates that the requested operation failed for
reasons unspecified at the GSS-API level.
This call is used to determine the amount of time for which a
currently established context will remain valid.
2.2.6: GSS_Inquire_context call
Input:
o context_handle CONTEXT HANDLE,
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
Linn Standards Track [Page 47]RFC 2078 GSS-API January 1997
o src_name INTERNAL NAME, -- name of context initiator,
-- guaranteed to be MN
o targ_name INTERNAL NAME, -- name of context target,
-- guaranteed to be MN
o lifetime_rec INTEGER -- in seconds, or reserved value for
INDEFINITE,
o mech_type OBJECT IDENTIFIER, -- the mechanism supporting this
security context
o deleg_state BOOLEAN,
o mutual_state BOOLEAN,
o replay_det_state BOOLEAN,
o sequence_state BOOLEAN,
o anon_state BOOLEAN,
o trans_state BOOLEAN,
o prot_ready_state BOOLEAN,
o conf_avail BOOLEAN,
o integ_avail BOOLEAN,
o locally_initiated BOOLEAN, -- TRUE if initiator, FALSE if acceptor
Return major_status codes:
o GSS_S_COMPLETE indicates that the referenced context is valid
and that src_name, targ_name, lifetime_rec, mech_type, deleg_state,
mutual_state, replay_det_state, sequence_state, anon_state,
trans_state, prot_ready_state, conf_avail, integ_avail, and
locally_initiated return values describe the corresponding
characteristics of the context.
o GSS_S_CONTEXT_EXPIRED indicates that the provided input
context_handle is recognized, but that the referenced context
has expired. Return values other than major_status and
minor_status are undefined.
Linn Standards Track [Page 48]RFC 2078 GSS-API January 1997
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided. Return values other than
major_status and minor_status are undefined.
o GSS_S_FAILURE indicates that the requested operation failed for
reasons unspecified at the GSS-API level. Return values other than
major_status and minor_status are undefined.
This call is used to extract information describing characteristics
of a security context.
2.2.7: GSS_Wrap_size_limit call
Inputs:
o context_handle CONTEXT HANDLE,
o qop INTEGER,
o output_size INTEGER
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o max_input_size INTEGER
Return major_status codes:
o GSS_S_COMPLETE indicates a successful token size determination:
an input message with a length in octets equal to the
returned max_input_size value will, when passed to GSS_Wrap()
for processing on the context identified by the context_handle
parameter and with the quality of protection specifier provided
in the qop parameter, yield an output token no larger than the
value of the provided output_size parameter.
o GSS_S_CONTEXT_EXPIRED indicates that the provided input
context_handle is recognized, but that the referenced context
has expired. Return values other than major_status and
minor_status are undefined.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided. Return values other than
major_status and minor_status are undefined.
Linn Standards Track [Page 49]RFC 2078 GSS-API January 1997
o GSS_S_BAD_QOP indicates that the provided QOP value is not
recognized or supported for the context.
o GSS_S_FAILURE indicates that the requested operation failed for
reasons unspecified at the GSS-API level. Return values other than
major_status and minor_status are undefined.
This call is used to determine the largest input datum which may be
passed to GSS_Wrap() without yielding an output token larger than a
caller-specified value.
2.2.8: GSS_Export_sec_context call
Inputs:
o context_handle CONTEXT HANDLE
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o interprocess_token OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates that the referenced context has been
successfully exported to a representation in the interprocess_token,
and is no longer available for use by the caller.
o GSS_S_UNAVAILABLE indicates that the context export facility
is not available for use on the referenced context. (This status
should occur only for contexts for which the trans_state value is
FALSE.) Return values other than major_status and minor_status are
undefined.
o GSS_S_CONTEXT_EXPIRED indicates that the provided input
context_handle is recognized, but that the referenced context has
expired. Return values other than major_status and minor_status are
undefined.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided. Return values other than
major_status and minor_status are undefined.
Linn Standards Track [Page 50]
RFC 2078 GSS-API January 1997
o GSS_S_FAILURE indicates that the requested operation failed for
reasons unspecified at the GSS-API level. Return values other than
major_status and minor_status are undefined.
This call generates an interprocess token for transfer to another
process within an end system, in order to transfer control of a
security context to that process. The recipient of the interprocess
token will call GSS_Import_sec_context() to accept the transfer. The
GSS_Export_sec_context() operation is defined for use only with
security contexts which are fully and successfully established (i.e.,
those for which GSS_Init_sec_context() and GSS_Accept_sec_context()
have returned GSS_S_COMPLETE major_status).
To ensure portability, a caller of GSS_Export_sec_context() must not
assume that a context may continue to be used once it has been
exported; following export, the context referenced by the
context_handle cannot be assumed to remain valid. Further, portable
callers must not assume that a given interprocess token can be
imported by GSS_Import_sec_context() more than once, thereby creating
multiple instantiations of a single context. GSS-API implementations
may detect and reject attempted multiple imports, but are not
required to do so.
The internal representation contained within the interprocess token
is an implementation-defined local matter. Interprocess tokens
cannot be assumed to be transferable across different GSS-API
implementations.
It is recommended that GSS-API implementations adopt policies suited
to their operational environments in order to define the set of
processes eligible to import a context, but specific constraints in
this area are local matters. Candidate examples include transfers
between processes operating on behalf of the same user identity, or
processes comprising a common job. However, it may be impossible to
enforce such policies in some implementations.
In support of the above goals, implementations may protect the
transferred context data by using cryptography to protect data within
the interprocess token, or by using interprocess tokens as a means to
reference local interprocess communication facilities (protected by
other means) rather than storing the context data directly within the
tokens.
Transfer of an open context may, for certain mechanisms and
implementations, reveal data about the credential which was used to
establish the context. Callers should, therefore, be cautious about
the trustworthiness of processes to which they transfer contexts.
Although the GSS-API implementation may provide its own set of
Linn Standards Track [Page 51]
RFC 2078 GSS-API January 1997
protections over the exported context, the caller is responsible for
protecting the interprocess token from disclosure, and for taking
care that the context is transferred to an appropriate destination
process.
2.2.9: GSS_Import_sec_context call
Inputs:
o interprocess_token OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o context_handle CONTEXT HANDLE
Return major_status codes:
o GSS_S_COMPLETE indicates that the context represented by the
input interprocess_token has been successfully transferred to
the caller, and is available for future use via the output
context_handle.
o GSS_S_CONTEXT_EXPIRED indicates that the context represented by
the input interprocess_token has expired. Return values other
than major_status and minor_status are undefined.
o GSS_S_NO_CONTEXT indicates that the context represented by the
input interprocess_token was invalid. Return values other than
major_status and minor_status are undefined.
o GSS_S_DEFECTIVE_TOKEN indicates that the input interprocess_token
was defective. Return values other than major_status and
minor_status are undefined.
o GSS_S_UNAVAILABLE indicates that the context import facility
is not available for use on the referenced context. Return values
other than major_status and minor_status are undefined.
o GSS_S_UNAUTHORIZED indicates that the context represented by
the input interprocess_token is unauthorized for transfer to the
caller. Return values other than major_status and minor_status
are undefined.
Linn Standards Track [Page 52]
RFC 2078 GSS-API January 1997
o GSS_S_FAILURE indicates that the requested operation failed for
reasons unspecified at the GSS-API level. Return values other than
major_status and minor_status are undefined.
This call processes an interprocess token generated by
GSS_Export_sec_context(), making the transferred context available
for use by the caller. After a successful GSS_Import_sec_context()
operation, the imported context is available for use by the importing
process.
For further discussion of the security and authorization issues
regarding this call, please see the discussion in Section 2.2.8.
2.3: Per-message calls
This group of calls is used to perform per-message protection
processing on an established security context. None of these calls
block pending network interactions. These calls may be invoked by a
context's initiator or by the context's target. The four members of
this group should be considered as two pairs; the output from
GSS_GetMIC() is properly input to GSS_VerifyMIC(), and the output
from GSS_Wrap() is properly input to GSS_Unwrap().
GSS_GetMIC() and GSS_VerifyMIC() support data origin authentication
and data integrity services. When GSS_GetMIC() is invoked on an
input message, it yields a per-message token containing data items
which allow underlying mechanisms to provide the specified security
services. The original message, along with the generated per-message
token, is passed to the remote peer; these two data elements are
processed by GSS_VerifyMIC(), which validates the message in
conjunction with the separate token.
GSS_Wrap() and GSS_Unwrap() support caller-requested confidentiality
in addition to the data origin authentication and data integrity
services offered by GSS_GetMIC() and GSS_VerifyMIC(). GSS_Wrap()
outputs a single data element, encapsulating optionally enciphered
user data as well as associated token data items. The data element
output from GSS_Wrap() is passed to the remote peer and processed by
GSS_Unwrap() at that system. GSS_Unwrap() combines decipherment (as
required) with validation of data items related to authentication and
integrity.
Linn Standards Track [Page 53]
RFC 2078 GSS-API January 1997
2.3.1: GSS_GetMIC call
Note: This call is functionally equivalent to the GSS_Sign call as
defined in previous versions of this specification. In the interests
of backward compatibility, it is recommended that implementations
support this function under both names for the present; future
references to this function as GSS_Sign are deprecated.
Inputs:
o context_handle CONTEXT HANDLE,
o qop_req INTEGER,-0 specifies default QOP
o message OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o per_msg_token OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates that an integrity check, suitable for an
established security context, was successfully applied and
that the message and corresponding per_msg_token are ready
for transmission.
o GSS_S_CONTEXT_EXPIRED indicates that context-related data
items have expired, so that the requested operation cannot be
performed.
o GSS_S_CREDENTIALS_EXPIRED indicates that the context is recognized,
but that its associated credentials have expired, so
that the requested operation cannot be performed.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided.
o GSS_S_BAD_QOP indicates that the provided QOP value is not
recognized or supported for the context.
o GSS_S_FAILURE indicates that the context is recognized, but
that the requested operation could not be performed for
reasons unspecified at the GSS-API level.
Linn Standards Track [Page 54]RFC 2078 GSS-API January 1997
Using the security context referenced by context_handle, apply an
integrity check to the input message (along with timestamps and/or
other data included in support of mech_type-specific mechanisms) and
return the result in per_msg_token. The qop_req parameter,
interpretation of which is discussed in Section 1.2.4, allows
quality-of-protection control. The caller passes the message and the
per_msg_token to the target.
The GSS_GetMIC() function completes before the message and
per_msg_token is sent to the peer; successful application of
GSS_GetMIC() does not guarantee that a corresponding GSS_VerifyMIC()
has been (or can necessarily be) performed successfully when the
message arrives at the destination.
Mechanisms which do not support per-message protection services
should return GSS_S_FAILURE if this routine is called.
2.3.2: GSS_VerifyMIC call
Note: This call is functionally equivalent to the GSS_Verify call as
defined in previous versions of this specification. In the interests
of backward compatibility, it is recommended that implementations
support this function under both names for the present; future
references to this function as GSS_Verify are deprecated.
Inputs:
o context_handle CONTEXT HANDLE,
o message OCTET STRING,
o per_msg_token OCTET STRING
Outputs:
o qop_state INTEGER,
o major_status INTEGER,
o minor_status INTEGER,
Return major_status codes:
o GSS_S_COMPLETE indicates that the message was successfully
verified.
Linn Standards Track [Page 55]RFC 2078 GSS-API January 1997
o GSS_S_DEFECTIVE_TOKEN indicates that consistency checks performed
on the received per_msg_token failed, preventing
further processing from being performed with that token.
o GSS_S_BAD_SIG indicates that the received per_msg_token contains
an incorrect integrity check for the message.
o GSS_S_DUPLICATE_TOKEN, GSS_S_OLD_TOKEN, GSS_S_UNSEQ_TOKEN,
and GSS_S_GAP_TOKEN values appear in conjunction with the
optional per-message replay detection features described
in Section 1.2.3; their semantics are described in that section.
o GSS_S_CONTEXT_EXPIRED indicates that context-related data
items have expired, so that the requested operation cannot be
performed.
o GSS_S_CREDENTIALS_EXPIRED indicates that the context is
recognized,
but that its associated credentials have expired, so
that the requested operation cannot be performed.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided.
o GSS_S_FAILURE indicates that the context is recognized, but
that the GSS_VerifyMIC() operation could not be performed for
reasons unspecified at the GSS-API level.
Using the security context referenced by context_handle, verify that
the input per_msg_token contains an appropriate integrity check for
the input message, and apply any active replay detection or
sequencing features. Return an indication of the quality-of-
protection applied to the processed message in the qop_state result.
Since the GSS_VerifyMIC() routine never provides a confidentiality
service, its implementations should not return non-zero values in the
confidentiality fields of the output qop_state.
Mechanisms which do not support per-message protection services
should return GSS_S_FAILURE if this routine is called.
2.3.3: GSS_Wrap call
Note: This call is functionally equivalent to the GSS_Seal call as
defined in previous versions of this specification. In the interests
of backward compatibility, it is recommended that implementations
support this function under both names for the present; future
references to this function as GSS_Seal are deprecated.
Linn Standards Track [Page 56]RFC 2078 GSS-API January 1997
Inputs:
o context_handle CONTEXT HANDLE,
o conf_req_flag BOOLEAN,
o qop_req INTEGER,-0 specifies default QOP
o input_message OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o conf_state BOOLEAN,
o output_message OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates that the input_message was successfully
processed and that the output_message is ready for
transmission.
o GSS_S_CONTEXT_EXPIRED indicates that context-related data
items have expired, so that the requested operation cannot be
performed.
o GSS_S_CREDENTIALS_EXPIRED indicates that the context is
recognized,
but that its associated credentials have expired, so
that the requested operation cannot be performed.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided.
o GSS_S_BAD_QOP indicates that the provided QOP value is not
recognized or supported for the context.
o GSS_S_FAILURE indicates that the context is recognized, but
that the GSS_Wrap() operation could not be performed for
reasons unspecified at the GSS-API level.
Performs the data origin authentication and data integrity functions
of GSS_GetMIC(). If the input conf_req_flag is TRUE, requests that
confidentiality be applied to the input_message. Confidentiality may
Linn Standards Track [Page 57]RFC 2078 GSS-API January 1997
not be supported in all mech_types or by all implementations; the
returned conf_state flag indicates whether confidentiality was
provided for the input_message. The qop_req parameter, interpretation
of which is discussed in Section 1.2.4, allows quality-of-protection
control.
In all cases, the GSS_Wrap() call yields a single output_message
data element containing (optionally enciphered) user data as well as
control information.
Mechanisms which do not support per-message protection services
should return GSS_S_FAILURE if this routine is called.
2.3.4: GSS_Unwrap call
Note: This call is functionally equivalent to the GSS_Unseal call as
defined in previous versions of this specification. In the interests
of backward compatibility, it is recommended that implementations
support this function under both names for the present; future
references to this function as GSS_Unseal are deprecated.
Inputs:
o context_handle CONTEXT HANDLE,
o input_message OCTET STRING
Outputs:
o conf_state BOOLEAN,
o qop_state INTEGER,
o major_status INTEGER,
o minor_status INTEGER,
o output_message OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates that the input_message was
successfully processed and that the resulting output_message is
available.
o GSS_S_DEFECTIVE_TOKEN indicates that consistency checks performed
on the per_msg_token extracted from the input_message
failed, preventing further processing from being performed.
Linn Standards Track [Page 58]RFC 2078 GSS-API January 1997
o GSS_S_BAD_SIG indicates that an incorrect integrity check was
detected
for the message.
o GSS_S_DUPLICATE_TOKEN, GSS_S_OLD_TOKEN, GSS_S_UNSEQ_TOKEN,
and GSS_S_GAP_TOKEN values appear in conjunction with the
optional per-message replay detection features described
in Section 1.2.3; their semantics are described in that section.
o GSS_S_CONTEXT_EXPIRED indicates that context-related data
items have expired, so that the requested operation cannot be
performed.
o GSS_S_CREDENTIALS_EXPIRED indicates that the context is
recognized,
but that its associated credentials have expired, so
that the requested operation cannot be performed.
o GSS_S_NO_CONTEXT indicates that no valid context was recognized
for the input context_handle provided.
o GSS_S_FAILURE indicates that the context is recognized, but
that the GSS_Unwrap() operation could not be performed for
reasons unspecified at the GSS-API level.
Processes a data element generated (and optionally enciphered) by
GSS_Wrap(), provided as input_message. The returned conf_state value
indicates whether confidentiality was applied to the input_message.
If conf_state is TRUE, GSS_Unwrap() deciphers the input_message.
Returns an indication of the quality-of-protection applied to the
processed message in the qop_state result. GSS_Wrap() performs the
data integrity and data origin authentication checking functions of
GSS_VerifyMIC() on the plaintext data. Plaintext data is returned in
output_message.
Mechanisms which do not support per-message protection services
should return GSS_S_FAILURE if this routine is called.
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.
Linn Standards Track [Page 59]RFC 2078 GSS-API January 1997
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)
Linn Standards Track [Page 60]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 61]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 62]RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 63]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 64]RFC 2078 GSS-API January 1997
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,
Linn Standards Track [Page 65]RFC 2078 GSS-API January 1997
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().
Linn Standards Track [Page 66]RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 67]
RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 68]
RFC 2078 GSS-API January 1997
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,
Linn Standards Track [Page 69]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 70]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 71]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 72]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 73]RFC 2078 GSS-API January 1997
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:
Linn Standards Track [Page 74]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 75]RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 76]RFC 2078 GSS-API January 1997
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".
Linn Standards Track [Page 77]RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 78]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 79]RFC 2078 GSS-API January 1997
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,
Linn Standards Track [Page 80]
RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 81]
RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 82]RFC 2078 GSS-API January 1997
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.
Linn Standards Track [Page 83]RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 84]RFC 2078 GSS-API January 1997
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
Linn Standards Track [Page 85]
