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RFC 2743

Generic Security Service Application Program Interface Version 2, Update 1

Pages: 101
Group: CAT
Proposed STD
Obsoletes:  2078
Updated by:  5554
Part 1 of 4 – Pages 1 to 29
None   None   Next

Top   ToC   RFC2743 - Page 1
Network Working Group                                            J. Linn
Request for Comments: 2743                              RSA Laboratories
Obsoletes: 2078                                             January 2000
Category: Standards Track

         Generic Security Service Application Program Interface
                          Version 2, Update 1

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.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.


   The Generic Security Service Application Program Interface (GSS-API),
   Version 2, as defined in [RFC-2078], 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

      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 obsoletes [RFC-2078], 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.
Top   ToC   RFC2743 - Page 2

   1: GSS-API Characteristics and Concepts . . . . . . . . . . . .  4
   1.1: GSS-API Constructs . . . . . . . . . . . . . . . . . . . .  6
   1.1.1:  Credentials . . . . . . . . . . . . . . . . . . . . . .  6 Credential Constructs and Concepts . . . . . . . . . .  6 Credential Management  . . . . . . . . . . . . . . . .  7 Default Credential Resolution  . . . . . . . . . . . .  8
   1.1.2: Tokens . . . . . . . . . . . . . . . . . . . . . . . . .  9
   1.1.3:  Security Contexts . . . . . . . . . . . . . . . . . . . 11
   1.1.4:  Mechanism Types . . . . . . . . . . . . . . . . . . . . 12
   1.1.5:  Naming  . . . . . . . . . . . . . . . . . . . . . . . . 13
   1.1.6:  Channel Bindings  . . . . . . . . . . . . . . . . . . . 16
   1.2:  GSS-API Features and Issues . . . . . . . . . . . . . . . 17
   1.2.1:  Status Reporting  and Optional Service Support  . . . . 17 Status Reporting . . . . . . . . . . . . . . . . . . . 17 Optional Service Support . . . . . . . . . . . . . . . 19
   1.2.2: Per-Message Security Service Availability  . . . . . . . 20
   1.2.3: Per-Message Replay Detection and Sequencing  . . . . . . 21
   1.2.4:  Quality of Protection . . . . . . . . . . . . . . . . . 24
   1.2.5: Anonymity Support  . . . . . . . . . . . . . . . . . . . 25
   1.2.6: Initialization . . . . . . . . . . . . . . . . . . . . . 25
   1.2.7: Per-Message Protection During Context Establishment  . . 26
   1.2.8: Implementation Robustness  . . . . . . . . . . . . . . . 27
   1.2.9: Delegation . . . . . . . . . . . . . . . . . . . . . . . 28
   1.2.10: Interprocess Context Transfer . . . . . . . . . . . . . 28
   2:  Interface Descriptions  . . . . . . . . . . . . . . . . . . 29
   2.1:  Credential management calls . . . . . . . . . . . . . . . 31
   2.1.1:  GSS_Acquire_cred call . . . . . . . . . . . . . . . . . 31
   2.1.2:  GSS_Release_cred call . . . . . . . . . . . . . . . . . 34
   2.1.3:  GSS_Inquire_cred call . . . . . . . . . . . . . . . . . 35
   2.1.4:  GSS_Add_cred call . . . . . . . . . . . . . . . . . . . 37
   2.1.5:  GSS_Inquire_cred_by_mech call . . . . . . . . . . . . . 40
   2.2:  Context-level calls . . . . . . . . . . . . . . . . . . . 41
   2.2.1:  GSS_Init_sec_context call . . . . . . . . . . . . . . . 42
   2.2.2:  GSS_Accept_sec_context call . . . . . . . . . . . . . . 49
   2.2.3:  GSS_Delete_sec_context call . . . . . . . . . . . . . . 53
   2.2.4:  GSS_Process_context_token call  . . . . . . . . . . . . 54
   2.2.5:  GSS_Context_time call . . . . . . . . . . . . . . . . . 55
   2.2.6:  GSS_Inquire_context call  . . . . . . . . . . . . . . . 56
   2.2.7:  GSS_Wrap_size_limit call  . . . . . . . . . . . . . . . 57
   2.2.8:  GSS_Export_sec_context call . . . . . . . . . . . . . . 59
   2.2.9:  GSS_Import_sec_context call . . . . . . . . . . . . . . 61
   2.3:  Per-message calls . . . . . . . . . . . . . . . . . . . . 62
   2.3.1:  GSS_GetMIC call . . . . . . . . . . . . . . . . . . . . 63
   2.3.2:  GSS_VerifyMIC call  . . . . . . . . . . . . . . . . . . 64
   2.3.3:  GSS_Wrap call . . . . . . . . . . . . . . . . . . . . . 65
   2.3.4:  GSS_Unwrap call . . . . . . . . . . . . . . . . . . . . 66
Top   ToC   RFC2743 - Page 3
   2.4:  Support calls . . . . . . . . . . . . . . . . . . . . . . 68
   2.4.1:  GSS_Display_status call . . . . . . . . . . . . . . . . 68
   2.4.2:  GSS_Indicate_mechs call . . . . . . . . . . . . . . . . 69
   2.4.3:  GSS_Compare_name call . . . . . . . . . . . . . . . . . 70
   2.4.4:  GSS_Display_name call . . . . . . . . . . . . . . . . . 71
   2.4.5:  GSS_Import_name call  . . . . . . . . . . . . . . . . . 72
   2.4.6:  GSS_Release_name call . . . . . . . . . . . . . . . . . 73
   2.4.7:  GSS_Release_buffer call . . . . . . . . . . . . . . . . 74
   2.4.8:  GSS_Release_OID_set call  . . . . . . . . . . . . . . . 74
   2.4.9:  GSS_Create_empty_OID_set call . . . . . . . . . . . . . 75
   2.4.10: GSS_Add_OID_set_member call . . . . . . . . . . . . . . 76
   2.4.11: GSS_Test_OID_set_member call  . . . . . . . . . . . . . 76
   2.4.12: GSS_Inquire_names_for_mech call . . . . . . . . . . . . 77
   2.4.13: GSS_Inquire_mechs_for_name call . . . . . . . . . . . . 77
   2.4.14: GSS_Canonicalize_name call  . . . . . . . . . . . . . . 78
   2.4.15: GSS_Export_name call  . . . . . . . . . . . . . . . . . 79
   2.4.16: GSS_Duplicate_name call . . . . . . . . . . . . . . . . 80
   3: Data Structure Definitions for GSS-V2 Usage  . . . . . . . . 81
   3.1: Mechanism-Independent Token Format . . . . . . . . . . . . 81
   3.2: Mechanism-Independent Exported Name Object Format  . . . . 84
   4: Name Type Definitions  . . . . . . . . . . . . . . . . . . . 85
   4.1: Host-Based Service Name Form . . . . . . . . . . . . . . . 85
   4.2: User Name Form . . . . . . . . . . . . . . . . . . . . . . 86
   4.3: Machine UID Form . . . . . . . . . . . . . . . . . . . . . 87
   4.4: String UID Form  . . . . . . . . . . . . . . . . . . . . . 87
   4.5: Anonymous Nametype . . . . . . . . . . . . . . . . . . . . 87
   4.6: GSS_C_NO_OID . . . . . . . . . . . . . . . . . . . . . . . 88
   4.7: Exported Name Object . . . . . . . . . . . . . . . . . . . 88
   4.8: GSS_C_NO_NAME  . . . . . . . . . . . . . . . . . . . . . . 88
   5:  Mechanism-Specific Example Scenarios  . . . . . . . . . . . 88
   5.1: Kerberos V5, single-TGT  . . . . . . . . . . . . . . . . . 89
   5.2: Kerberos V5, double-TGT  . . . . . . . . . . . . . . . . . 89
   5.3:  X.509 Authentication Framework  . . . . . . . . . . . . . 90
   6:  Security Considerations . . . . . . . . . . . . . . . . . . 91
   7:  Related Activities  . . . . . . . . . . . . . . . . . . . . 92
   8:  Referenced Documents  . . . . . . . . . . . . . . . . . . . 93
   Appendix A: Mechanism Design Constraints  . . . . . . . . . . . 94
   Appendix B: Compatibility with GSS-V1 . . . . . . . . . . . . . 94
   Appendix C: Changes Relative to RFC-2078  . . . . . . . . . . . 96
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . .100
   Full Copyright Statement  . . . . . . . . . . . . . . . . . . .101
Top   ToC   RFC2743 - Page 4
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

   The GSS-API separates the operations of initializing a security
   context between peers, achieving peer entity authentication
   (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.  (The definition for the peer entity authentication service,
   and other definitions used in this document, corresponds to that
   provided in [ISO-7498-2].) When establishing a 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 also 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 some 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
Top   ToC   RFC2743 - Page 5
   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

   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
   encapsulates the result into output_message, indicating
   GSS_S_COMPLETE status. The client sends the output_message to the

   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.
Top   ToC   RFC2743 - Page 6
   The GSS-API design assumes and addresses several basic goals,

      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 have been implemented using secret-key technologies
      (e.g., Kerberos, per [RFC-1964]) and with public-key approaches
      (e.g., SPKM, per [RFC-2025]).

      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 may be
      interposed between applications which call that protocol and the
      GSS-API (e.g., as defined in [RFC-2203] for Open Network Computing
      Remote Procedure Call (RPC)), 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
      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 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
Top   ToC   RFC2743 - Page 7
   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
   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. 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.
Top   ToC   RFC2743 - Page 8
   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 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.
   In support of application portability, support for the default
   resolution behavior described below for initiator credentials
   (GSS_Init_sec_context() usage) is mandated; support for the default
   resolution behavior described below for acceptor credentials
   (GSS_Accept_sec_context() usage) is recommended. If default
   credential resolution fails, GSS_S_NO_CRED status is to be returned.


         (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
Top   ToC   RFC2743 - Page 9
         (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,

         (iv) A user-configurable default identity should be used.


         (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

         (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 those
   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
Top   ToC   RFC2743 - Page 10
   protective security services (i.e., data origin authentication,
   integrity, and optional confidentiality) for corresponding data

   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 3.1 of this
   document provides, for designers of GSS-API 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.

   Context-level 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.  Per-message tokens, in
   contrast, are to be returned only upon successful completion of per-
   message calls. Zero-length tokens are never returned by GSS routines
   for transfer to a peer. 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.

   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
Top   ToC   RFC2743 - Page 11
      - 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 mechanisms 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
   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
Top   ToC   RFC2743 - Page 12
   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.  Messages may be protected and
   transferred in both directions on an established GSS-API security
   context concurrently; protection of messages in one direction does
   not interfere with protection of messages in the reverse direction.

   GSS-API implementations are expected to retain inquirable context
   data on a context until the context is released by a caller, even
   after the context has expired, although underlying cryptographic data
   elements may be deleted after expiration in order to limit their

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.

   For GSS-API purposes, the phrase "negotiating mechanism" refers to a
   mechanism which itself performs negotiation in order to select a
   concrete mechanism which is shared between peers and is then used for
   context establishment.  Only those mechanisms which are defined in
   their specifications as negotiating mechanisms are to yield selected
   mechanisms with different identifier values than the value which is
   input by a GSS-API caller, except for the case of a caller requesting
   the "default" mech_type.

   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):
Top   ToC   RFC2743 - Page 13
      use of a fixed mech_type, defined by configuration, within an

      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

      explicit negotiation between GSS-API callers in advance of
      security context setup

      use of a negotiating mechanism

   When transferred between GSS-API peers, mech_type specifiers (per
   Section 3 of this document, represented as Object Identifiers (OIDs))
   serve to qualify the interpretation of associated tokens. (The
   structure and encoding of Object Identifiers is defined in [ISOIEC-
   8824] and [ISOIEC-8825].) Use of hierarchically structured OIDs
   serves to preclude ambiguous interpretation of mech_type specifiers.
   The OID representing the DASS ([RFC-1507]) MechType, for example, is, and that of the Kerberos V5 mechanism ([RFC-
   1964]), having been advanced to the level of Proposed Standard, is

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
Top   ToC   RFC2743 - Page 14
      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
      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.
Top   ToC   RFC2743 - Page 15
   When used in large access control lists, the overhead of invoking
   GSS_Import_name() and GSS_Compare_name() on each name from the ACL
   may be prohibitive.  As an alternative way of supporting this case,
   GSS-API defines a special form of the contiguous string name which
   may be compared directly (e.g., with memcmp()).  Contiguous names
   suitable for comparison are generated by the GSS_Export_name()
   routine, which requires an MN as input.  Exported names may be re-
   imported by the GSS_Import_name() routine, and the resulting internal
   name will also be an MN.  The symbolic constant GSS_C_NT_EXPORT_NAME
   identifies the "export name" type. Structurally, an exported name
   object consists of a header containing an OID identifying the
   mechanism that authenticated the name, and a trailer containing the
   name itself, where the syntax of the trailer is defined by the
   individual mechanism specification.  The precise format of an
   exported name is defined in Section 3.2 of this specification.

   Note that the results obtained by using GSS_Compare_name() will in
   general be different from those obtained by invoking
   GSS_Canonicalize_name() and GSS_Export_name(), and then comparing the
   exported names.  The first series of operations determines whether
   two (unauthenticated) names identify the same principal; the second
   whether a particular mechanism would authenticate them as the same
   principal.  These two operations will in general give the same
   results only for MNs.

   The following diagram illustrates the intended dataflow among name-
   related GSS-API processing routines.
Top   ToC   RFC2743 - Page 16
                        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

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

   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
   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
Top   ToC   RFC2743 - Page 17
   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

   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 and Optional Service Support Status Reporting

   Each GSS-API call provides two status return values. Major_status
   values provide a mechanism-independent indication of call status
   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.

   Sequencing-related informatory major_status codes
   GSS_S_GAP_TOKEN) can be indicated in conjunction with either
   GSS_S_COMPLETE or GSS_S_FAILURE status for GSS-API per-message calls.
   For context establishment calls, these sequencing-related codes will
   be indicated only in conjunction with GSS_S_FAILURE status (never in
Top   ToC   RFC2743 - Page 18
   conjunction with GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED), and,
   therefore, always correspond to fatal failures if encountered during
   the context establishment phase.

   Table 1: GSS-API Major Status 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_BAD_MIC                   preferred alias for GSS_S_BAD_SIG
   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
   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


   GSS_S_COMPLETE                normal completion
   GSS_S_CONTINUE_NEEDED         continuation call to routine
   GSS_S_DUPLICATE_TOKEN         duplicate per-message token
   GSS_S_OLD_TOKEN               timed-out per-message token
   GSS_S_UNSEQ_TOKEN             reordered (early) per-message token
   GSS_S_GAP_TOKEN               skipped predecessor token(s)

   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.
Top   ToC   RFC2743 - Page 19
   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
   with sequences of continuation calls to GSS_Init_sec_context()  and
   GSS_Accept_sec_context().  The same facility 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. Optional Service Support

   A context initiator may request various optional services at context
   establishment time. Each of these services is requested by setting a
   flag in the req_flags input parameter to GSS_Init_sec_context().

   The optional services currently defined are:

      - Delegation - The (usually temporary) transfer of rights from
      initiator to acceptor, enabling the acceptor to authenticate
      itself as an agent of the initiator.

      - Mutual Authentication - In addition to the initiator
      authenticating its identity to the context acceptor, the context
      acceptor should also authenticate itself to the initiator.

      - Replay detection - In addition to providing message integrity
      services, GSS_GetMIC() and GSS_Wrap() should include message
      numbering information to enable GSS_VerifyMIC() and GSS_Unwrap()
      to detect if a message has been duplicated.

      - Out-of-sequence detection - In addition to providing message
      integrity services, GSS_GetMIC() and GSS_Wrap() should include
      message sequencing information to enable GSS_VerifyMIC() and
      GSS_Unwrap() to detect if a message has been received out of
Top   ToC   RFC2743 - Page 20
      - Anonymous authentication - The establishment of the security
      context should not reveal the initiator's identity to the context

      - Available per-message confidentiality - requests that per-
      message confidentiality services be available on the context.

      - Available per-message integrity - requests that per-message
      integrity services be available on the context.

   Any currently undefined bits within such flag arguments should be
   ignored by GSS-API implementations when presented by an application,
   and should be set to zero when returned to the application by the
   GSS-API implementation.

   Some mechanisms may not support all optional services, and some
   mechanisms may only support some services in conjunction with others.
   Both GSS_Init_sec_context() and GSS_Accept_sec_context() inform the
   applications which services will be available from the context when
   the establishment phase is complete, via the ret_flags output
   parameter.  In general, if the security mechanism is capable of
   providing a requested service, it should do so, even if additional
   services must be enabled in order to provide the requested service.
   If the mechanism is incapable of providing a requested service, it
   should proceed without the service, leaving the application to abort
   the context establishment process if it considers the requested
   service to be mandatory.

   Some mechanisms may specify that support for some services is
   optional, and that implementors of the mechanism need not provide it.
   This is most commonly true of the confidentiality service, often
   because of legal restrictions on the use of data-encryption, but may
   apply to any of the services.  Such mechanisms are required to send
   at least one token from acceptor to initiator during context
   establishment when the initiator indicates a desire to use such a
   service, so that the initiating GSS-API can correctly indicate
   whether the service is supported by the acceptor's 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
Top   ToC   RFC2743 - Page 21
      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.

   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 the selected mechanism,
   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
Top   ToC   RFC2743 - Page 22
   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, without concurrent indication of
      GSS_S_DUPLICATE_TOKEN or GSS_S_OLD_TOKEN, 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.

      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.  In addition to identifying duplicated tokens originated
      by a context's peer, this status may also be used to identify
      reflected copies of locally-generated tokens; it is recommended
      that mechanism designers include within their protocols facilities
      to detect and report such tokens.

      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, without concurrent indication of
      GSS_S_GAP_TOKEN, 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

      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.  In
      addition to identifying duplicated tokens originated by a
      context's peer, this status may also be used to identify reflected
Top   ToC   RFC2743 - Page 23
      copies of locally-generated tokens; it is recommended that
      mechanism designers include within their protocols facilities to
      detect and report such tokens.

      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.]

      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
Top   ToC   RFC2743 - Page 24
   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

   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
   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

   In the interests of interoperability, mechanisms which allow optional
   support of particular QOP values shall satisfy one of the following
   conditions.  Either:

      (i) All implementations of the mechanism are required to be
      capable of processing messages protected using any QOP value,
      regardless of whether they can apply protection corresponding to
      that QOP, or

      (ii) The set of mutually-supported receiver QOP values must be
      determined during context establishment, and messages may be
      protected by either peer using only QOP values from this
      mutually-supported set.

   NOTE: (i) is just a special-case of (ii), where implementations are
   required to support all QOP values on receipt.
Top   ToC   RFC2743 - Page 25
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.

   Section 4.5 of this document defines the Object Identifier value used
   to identify an anonymous principal.

   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.

      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

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.
Top   ToC   RFC2743 - Page 26
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

   For context establishment calls, this state Boolean is valid and
   interpretable when the associated major_status is either
   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.
   Callers making use of per-message protection services in advance of
   GSS_S_COMPLETE status should be aware of the possibility that a
   subsequent context establishment step may fail, and that certain
   context data (e.g., mech_type) as returned for subsequent calls may

   This approach 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
   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
Top   ToC   RFC2743 - Page 27
   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.

   Invocation of GSS-API calls is to incur no undocumented side effects
   visible at the GSS-API level.

   If a token is presented for processing on a GSS-API security context
   and that token generates a fatal error in processing or is otherwise
   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.

   A failure of GSS_GetMIC() or GSS_Wrap() due to an attempt to use an
   unsupported QOP will not interfere with context validity, nor shall
   such a failure impact the ability of the application to subsequently
   invoke GSS_GetMIC() or GSS_Wrap() using a supported QOP. Any state
   information concerning sequencing of outgoing messages shall be
   unchanged by an unsuccessful call of GSS_GetMIC() or GSS_Wrap().
Top   ToC   RFC2743 - Page 28
1.2.9: Delegation

   The GSS-API allows delegation to be controlled by the initiating
   application via a Boolean parameter to GSS_Init_sec_context(), the
   routine that establishes a security context.  Some mechanisms do not
   support delegation, and for such mechanisms attempts by an
   application to enable delegation are ignored.

   The acceptor of a security context for which the initiator enabled
   delegation will receive (via the delegated_cred_handle parameter of
   GSS_Accept_sec_context()) a credential handle that contains the
   delegated identity, and this credential handle may be used to
   initiate subsequent GSS-API security contexts as an agent or delegate
   of the initiator.  If the original initiator's identity is "A" and
   the delegate's identity is "B", then, depending on the underlying
   mechanism, the identity embodied by the delegated credential may be
   either "A" or "B acting for A".

   For many mechanisms that support delegation, a simple Boolean does
   not provide enough control.  Examples of additional aspects of
   delegation control that a mechanism might provide to an application
   are duration of delegation, network addresses from which delegation
   is valid, and constraints on the tasks that may be performed by a
   delegate.  Such controls are presently outside the scope of the GSS-
   API.  GSS-API implementations supporting mechanisms offering
   additional controls should provide extension routines that allow
   these controls to be exercised (perhaps by modifying the initiator's
   GSS-API credential prior to its use in establishing a context).
   However, the simple delegation control provided by GSS-API should
   always be able to over-ride other mechanism-specific delegation
   controls; if the application instructs GSS_Init_sec_context() that
   delegation is not desired, then the implementation must not permit
   delegation to occur.  This is an exception to the general rule that a
   mechanism may enable services even if they are not requested;
   delegation may only be provided at the explicit request of the

1.2.10: Interprocess Context Transfer

   GSS-API V2 provides routines (GSS_Export_sec_context() and
   GSS_Import_sec_context()) which allow a security context to be
   transferred between processes on a single machine.  The most common
   use for such a feature is a client-server design where the server is
   implemented as a single process that accepts incoming security
   contexts, which then launches child processes to deal with the data
   on these contexts.  In such a design, the child processes must have
   access to the security context data structure created within the
Top   ToC   RFC2743 - Page 29
   parent by its call to GSS_Accept_sec_context() so that they can use
   per-message protection services and delete the security context when
   the communication session ends.

   Since the security context data structure is expected to contain
   sequencing information, it is impractical in general to share a
   context between processes.  Thus GSS-API provides a call
   (GSS_Export_sec_context()) that the process which currently owns the
   context can call to declare that it has no intention to use the
   context subsequently, and to create an inter-process token containing
   information needed by the adopting process to successfully import the
   context.  After successful completion of this call, the original
   security context is made inaccessible to the calling process by GSS-
   API, and any context handles referring to this context are no longer
   valid.  The originating process transfers the inter-process token to
   the adopting process, which passes it to GSS_Import_sec_context(),
   and a fresh context handle is created such that it is functionally
   identical to the original context.

   The inter-process token may contain sensitive data from the original
   security context (including cryptographic keys).  Applications using
   inter-process tokens to transfer security contexts must take
   appropriate steps to protect these tokens in transit.
   Implementations are not required to support the inter-process
   transfer of security contexts.  The ability to transfer a security
   context is indicated when the context is created, by
   GSS_Init_sec_context() or GSS_Accept_sec_context() indicating a TRUE
   trans_state return value.

(page 29 continued on part 2)

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