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RFC 2078

Generic Security Service Application Program Interface, Version 2

Pages: 85
Obsoletes:  1508
Obsoleted by:  2743
Part 1 of 3 – Pages 1 to 23
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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
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   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
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   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
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   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
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   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
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      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
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   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
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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
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      (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.
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   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
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   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
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      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
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      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).
ToP   noToC   RFC2078 - Page 14
   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
ToP   noToC   RFC2078 - Page 15
   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.
ToP   noToC   RFC2078 - Page 16
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
ToP   noToC   RFC2078 - Page 17
   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.
ToP   noToC   RFC2078 - Page 18
   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.
ToP   noToC   RFC2078 - Page 19
      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.]
ToP   noToC   RFC2078 - Page 20
      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
ToP   noToC   RFC2078 - Page 21
   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.
ToP   noToC   RFC2078 - Page 22
      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
ToP   noToC   RFC2078 - Page 23
   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.



(page 23 continued on part 2)

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