Internet DRAFT - draft-ietf-cat-spkmgss

draft-ietf-cat-spkmgss



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Internet Draft                          C. Adams, Bell-Northern Research
draft-ietf-cat-spkmgss-06.txt                              Jan. 19, 1996


              The Simple Public-Key GSS-API Mechanism (SPKM)



STATUS OF THIS MEMO

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six 
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   "work in progress."

   To learn the current status of any Internet Draft, please check the 
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   Rim).

   Comments on this document should be sent to "cat-ietf@mit.edu", the 
   IETF Common Authentication Technology WG discussion list.


ABSTRACT

   This specification defines protocols, procedures, and conventions to 
   be employed by peers implementing the Generic Security Service 
   Application Program Interface (as specified in RFCs 1508 and 1509) 
   when using the Simple Public-Key Mechanism.


BACKGROUND

   Although the Kerberos Version 5 GSS-API mechanism [KRB5] is becoming 
   well-established in many environments, it is important in some 
   applications to have a GSS-API mechanism which is based on a public-
   key, rather than a symmetric-key, infrastructure.  The mechanism 
   described in this document has been proposed to meet this need and to 
   provide the following features.

      1)  The SPKM allows both unilateral and mutual authentication 
          to be accomplished without the use of secure timestamps.  This 
          enables environments which do not have access to secure time 
          to nevertheless have access to secure authentication. 




Adams                Document Expiration:  19 July 1996                1



      2)  The SPKM uses Algorithm Identifiers to specify various 
          algorithms to be used by the communicating peers.  This allows 
          maximum flexibility for a variety of environments, for future 
          enhancements, and for alternative algorithms.

      3)  The SPKM allows the option of a true, asymmetric algorithm-
          based, digital signature in the gss_sign() and gss_seal() 
          operations (now called gss_getMIC() and gss_wrap() in 
          [GSSv2]), rather than an integrity checksum based on a MAC 
          computed with a symmetric algorithm (e.g., DES).  For some 
          environments, the availability of true digital signatures 
          supporting non-repudiation is a necessity.

      4)  SPKM data formats and procedures are designed to be as similar 
          to those of the Kerberos mechanism as is practical.  This is 
          done for ease of implementation in those environments where 
          Kerberos has already been implemented.

   For the above reasons, it is felt that the SPKM will offer 
   flexibility and functionality, without undue complexity or overhead.



KEY MANAGEMENT

   The key management employed in SPKM is intended to be as compatible 
   as possible with both X.509 [X.509] and PEM [RFC-1422], since these 
   represent large communities of interest and show relative maturity in 
   standards.



ACKNOWLEDGMENTS

   Much of the material in this document is based on the Kerberos 
   Version 5 GSS-API mechanism [KRB5], and is intended to be as 
   compatible with it as possible.  This document also owes a great debt 
   to Warwick Ford and Paul Van Oorschot of Bell-Northern Research for 
   many fruitful discussions, to Kelvin Desplanque for implementation-
   related clarifications, to John Linn of OpenVision Technologies for 
   helpful comments, and to Bancroft Scott of OSS for ASN.1 assistance.














Adams                Document Expiration:  19 July 1996                2

1. OVERVIEW

   The goal of the Generic Security Service Application Program 
   Interface (GSS-API) is stated in the abstract of [RFC-1508] as 
   follows:

     "This Generic Security Service Application Program Interface (GSS-
      API) definition 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."

   The SPKM is an instance of the latter type of document and is 
   therefore termed a "GSS-API Mechanism".  This mechanism provides 
   authentication, key establishment, data integrity, and data 
   confidentiality in an on-line distributed application environment 
   using a public-key infrastructure.  Because it conforms to the 
   interface defined by [RFC-1508], SPKM can be used as a drop-in 
   replacement by any application which makes use of security services 
   through GSS-API calls (for example, any application which already 
   uses the Kerberos GSS-API for security).  The use of a public-key 
   infrastructure allows digital signatures supporting non-repudiation 
   to be employed for message exchanges, and provides other benefits 
   such as scalability to large user populations.

   The tokens defined in SPKM are intended to be used by application 
   programs according to the GSS API "operational paradigm" (see 
   [RFC-1508] for further details):

      The operational paradigm in which GSS-API operates is as follows.
      A typical GSS-API caller is itself a communications protocol [or 
      is an application program which uses 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 [i.e., its GSS-API mechanism] 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.

   This document defines two separate GSS-API mechanisms, SPKM-1 and 
   SPKM-2, whose primary difference is that SPKM-2 requires the presence 
   of secure timestamps for the purpose of replay detection during 
   context establishment and SPKM-1 does not.  This allows greater 
   flexibility for applications since secure timestamps cannot always 
   be guaranteed to be available in a given environment.

Adams                Document Expiration:  19 July 1996                3

2. ALGORITHMS

   A number of algorithm types are employed in SPKM.  Each type, along
   with its purpose and a set of specific examples, is described in this
   section.  In order to ensure at least a minimum level of interoper-
   ability among various implementations of SPKM, one of the integrity 
   algorithms is specified as MANDATORY; all remaining examples (and 
   any other algorithms) may optionally be supported by a given SPKM 
   implementation (note that a GSS-conformant mechanism need not support 
   confidentiality).  Making a confidentiality algorithm mandatory may 
   preclude exportability of the mechanism implementation; this document 
   therefore specifies certain algorithms as RECOMMENDED (that is, 
   interoperability will be enhanced if these algorithms are included in 
   all SPKM implementations for which exportability is not a concern).

2.1 Integrity Algorithm (I-ALG):

       Purpose:
      
         This algorithm is used to ensure that a message has not been 
         altered in any way after being constructed by the legitimate 
         sender.  Depending on the algorithm used, the application of
         this algorithm may also provide authenticity and support non-
         repudiation for the message.

       Examples:

         md5WithRSAEncryption OBJECT IDENTIFIER ::= {
           iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
           pkcs-1(1) 4        -- imported from [PKCS1]
         }

            This algorithm (MANDATORY) provides data integrity and 
            authenticity and supports non-repudiation by computing an 
            RSA signature on the MD5 hash of that data.  This is 
            essentially equivalent to md5WithRSA {1 3 14 3 2 3},
            which is defined by OIW (the Open Systems Environment 
            Implementors' Workshop).

            Note that since this is the only integrity/authenticity 
            algorithm specified to be mandatory at this time, for 
            interoperability reasons it is also stipulated that 
            md5WithRSA be the algorithm used to sign all context 
            establishment tokens which are signed rather than MACed -- 
            see Section 3.1.1 for details.  In future versions of this 
            document, alternate or additional algorithms may be 
            specified to be mandatory and so this stipulation on the 
            context establishment tokens may be removed.









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         DES-MAC OBJECT IDENTIFIER ::= {
            iso(1) identified-organization(3) oiw(14) secsig(3) 
            algorithm(2) 10  -- carries length in bits of the MAC as 
         }                   -- an INTEGER parameter, constrained to 
                             -- multiples of eight from 16 to 64

            This algorithm (RECOMMENDED) provides integrity by computing 
            a DES MAC (as specified by [FIPS-113]) on that data.


         md5-DES-CBC OBJECT IDENTIFIER ::= {
            iso(1) identified-organization(3) dod(6) internet(1) 
            security(5) integrity(3) md5-DES-CBC(1)
         }

            This algorithm provides data integrity by encrypting, using
            DES CBC, the "confounded" MD5 hash of that data (see Section 
            3.2.2.1 for the definition and purpose of confounding).  
            This will typically be faster in practice than computing a 
            DES MAC unless the input data is extremely short (e.g., a 
            few bytes).  Note that without the confounder the strength 
            of this integrity mechanism is (at most) equal to the 
            strength of DES under a known-plaintext attack. 


         sum64-DES-CBC OBJECT IDENTIFIER ::= {
            iso(1) identified-organization(3) dod(6) internet(1) 
            security(5) integrity(3) sum64-DES-CBC(2)
         }

            This algorithm provides data integrity by encrypting, using
            DES CBC, the concatenation of the confounded data and the 
            sum of all the input data blocks (the sum computed using 
            addition modulo 2**64 - 1).  Thus, in this algorithm, 
            encryption is a requirement for the integrity to be secure.

            For comments regarding the security of this integrity 
            algorithm, see [Juen84, Davi89].


2.2 Confidentiality Algorithm (C-ALG):

       Purpose:

         This symmetric algorithm is used to generate the encrypted 
         data for gss_seal() / gss_wrap().

       Example:

         DES-CBC OBJECT IDENTIFIER ::= {
            iso(1) identified-organization(3) oiw(14) secsig(3) 
            algorithm(2) 7 -- carries IV (OCTET STRING) as a parameter; 
         }                 -- this (optional) parameter is unused in 
                           -- SPKM due to the use of confounding 

            This algorithm is RECOMMENDED.

Adams                Document Expiration:  19 July 1996                5


2.3 Key Establishment Algorithm (K-ALG):

       Purpose:

         This algorithm is used to establish a symmetric key for use 
         by both the initiator and the target over the established 
         context.  The keys used for C-ALG and any keyed I-ALGs (for 
         example, DES-MAC) are derived from this context key.  As will 
         be seen in Section 3.1, key establishment is done within the 
         X.509 authentication exchange and so the resulting shared
         symmetric key is authenticated.

       Examples:

         RSAEncryption OBJECT IDENTIFIER ::= {
           iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
           pkcs-1(1) 1        -- imported from [PKCS1] and [RFC-1423]
         }

            In this algorithm (MANDATORY), the context key is generated 
            by the initiator, encrypted with the RSA public key of the 
            target, and sent to the target.  The target need not respond 
            to the initiator for the key to be established.

         id-rsa-key-transport OBJECT IDENTIFIER ::= {
            iso(1) identified-organization(3) oiw(14) secsig(3) 
            algorithm(2) 22   -- imported from [X9.44]
         }

            Similar to RSAEncryption, but source authenticating info.
            is also encrypted with the target's RSA public key.

        dhKeyAgreement OBJECT IDENTIFIER ::= {
           iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
           pkcs-3(3) 1
        }

            In this algorithm, the context key is generated jointly by 
            the initiator and the target using the Diffie-Hellman key 
            establishment algorithm.  The target must therefore respond 
            to the initiator for the key to be established (so this 
            K-ALG cannot be used with unilateral authentication in 
            SPKM-2 (see Section 3.1)).













Adams                Document Expiration:  19 July 1996                6


2.4 One-Way Function (O-ALG) for Subkey Derivation Algorithm:

       Purpose:

         Having established a context key using the negotiated K-ALG, 
         both initiator and target must be able to derive a set of 
         subkeys for the various C-ALGs and keyed I-ALGs supported over 
         the context.  Let the (ordered) list of agreed C-ALGs be 
         numbered consecutively, so that the first algorithm (the 
         "default") is numbered "0", the next is numbered "1", and so 
         on.  Let the numbering for the (ordered) list of agreed I-ALGs 
         be identical.  Finally, let the context key be a binary string 
         of arbitrary length "M", subject to the following constraint:  
         L <= M <= U  (where the lower limit "L" is the bit length of 
         the longest key needed by any agreed C-ALG or keyed I-ALG, and 
         the upper limit "U" is the largest bit size which will fit 
         within the K-ALG parameters).

         For example, if DES and two-key-triple-DES are the negotiated 
         confidentiality algorithms and DES-MAC is the negotiated keyed 
         integrity algorithm (note that digital signatures do not use a 
         context key), then the context key must be at least 112 bits 
         long.  If 512-bit RSAEncryption is the K-ALG in use then the 
         originator can randomly generate a context key of any greater 
         length up to 424 bits (the longest allowable RSA input 
         specified in [PKCS-1]) -- the target can determine the length 
         which was chosen by removing the padding bytes during the RSA 
         decryption operation.  On the other hand, if dhKeyAgreement is 
         the K-ALG in use then the context key is the result of the 
         Diffie-Hellman computation (with the exception of the high-
         order byte, which is discarded for security reasons), so that 
         its length is that of the Diffie-Hellman modulus, p, minus 8 
         bits.

         The derivation algorithm for a k-bit subkey is specified as 
         follows:  

      rightmost_k_bits (OWF(context_key || x || n || s || context_key)) 

         where 

          - "x" is the ASCII character "C" (0x43) if the subkey is 
            for a confidentiality algorithm or the ASCII character "I" 
            (0x49) if the subkey is for a keyed integrity algorithm;
          - "n" is the number of the algorithm in the appropriate agreed 
            list for the context (the ASCII character "0" (0x30), "1" 
            (0x31), and so on);
          - "s" is the "stage" of processing -- always the ASCII 
            character "0" (0x30), unless "k" is greater than the output 
            size of OWF, in which case the OWF is computed repeatedly 
            with increasing ASCII values of "stage" (each OWF output 
            being concatenated to the end of previous OWF outputs), 
            until "k" bits have been generated; 
          - "||" is the concatenation operation; and 
          - "OWF" is any appropriate One-Way Function.

Adams                Document Expiration:  19 July 1996                7


       Examples:

         MD5 OBJECT IDENTIFIER ::= {
           iso(1) member-body(2) US(840) rsadsi(113549) 
           digestAlgorithm(2) 5 
         }

           This algorithm is MANDATORY.

         SHA OBJECT IDENTIFIER ::= {
            iso(1) identified-organization(3) oiw(14) secsig(3) 
            algorithm(2) 18 
         }

         It is recognized that existing hash functions may not satisfy 
         all required properties of OWFs.  This is the reason for 
         allowing negotiation of the O-ALG OWF during the context 
         establishment process (see Section 2.5), since in this way 
         future improvements in OWF design can easily be accommodated.  
         For example, in some environments a preferred OWF technique 
         might be an encryption algorithm which encrypts the input 
         specified above using the context_key as the encryption key.  

2.5 Negotiation:

   During context establishment in SPKM, the initiator offers a set of 
   possible confidentiality algorithms and a set of possible integrity 
   algorithms to the target (note that the term "integrity algorithms" 
   includes digital signature algorithms).  The confidentiality 
   algorithms selected by the target become ones that may be used for 
   C-ALG over the established context, and the integrity algorithms 
   selected by the target become ones that may be used for I-ALG over 
   the established context (the target "selects" algorithms by 
   returning, in the same relative order, the subset of each offered 
   list that it supports).  Note that any C-ALG and I-ALG may be used 
   for any message over the context and that the first confidentiality 
   algorithm and the first integrity algorithm in the agreed sets become 
   the default algorithms for that context.

   The agreed confidentiality and integrity algorithms for a specific 
   context define the valid values of the Quality of Protection (QOP) 
   parameter used in the gss_getMIC() and gss_wrap() calls -- see 
   Section 5.2 for further details.  If no response is expected from the 
   target (unilateral authentication in SPKM-2) then the algorithms 
   offered by the initiator are the ones that may be used over the 
   context (if this is unacceptable to the target then a delete token 
   must be sent to the initiator so that the context is never 
   established).








Adams                Document Expiration:  19 July 1996                8


   Furthermore, in the first context establishment token the initiator 
   offers a set of possible K-ALGs, along with the key (or key half) 
   corresponding to the first algorithm in the set (its preferred 
   algorithm).  If this K-ALG is unacceptable to the target then the 
   target must choose one of the other K-ALGs in the set and send this 
   choice along with the key (or key half) corresponding to this choice 
   in its response (otherwise a delete token must be sent so that the 
   context is never established).  If necessary (that is, if the target 
   chooses a 2-pass K-ALG such as dhKeyAgreement), the initiator will 
   send its key half in a response to the target.

   Finally, in the first context establishment token the initiator 
   offers a set of possible O-ALGs (only a single O-ALG if no response 
   is expected).  The (single) O-ALG chosen by the target becomes the 
   subkey derivation algorithm OWF to be used over the context.



   In future versions of SPKM, other algorithms may be specified for any 
   or all of I-ALG, C-ALG, K-ALG, and O-ALG.



3. TOKEN FORMATS

   This section discusses protocol-visible characteristics of the SPKM; 
   it defines elements of protocol for interoperability and is 
   independent of language bindings per [RFC-1509].

   The SPKM GSS-API mechanism will be identified by an Object Identifier 
   representing "SPKM-1" or "SPKM-2", having the value {spkm spkm-1(1)} 
   or {spkm spkm-2(2)}, where spkm has the value
   {iso(1) identified-organization(3) dod(6) internet(1) security(5) 
   mechanisms(5) spkm(1)}.  SPKM-1 uses random numbers for replay 
   detection during context establishment and SPKM-2 uses timestamps 
   (note that for both mechanisms, sequence numbers are used to provide 
   replay and out-of-sequence detection during the context, if this has 
   been requested by the application).

   Tokens transferred between GSS-API peers (for security context 
   management and per-message protection purposes) are defined.  

3.1. Context Establishment Tokens

   Three classes of tokens are defined in this section:  "Initiator" 
   tokens, emitted by calls to gss_init_sec_context() and consumed by 
   calls to gss_accept_sec_context(); "Target" tokens, emitted by calls 
   to gss_accept_sec_context() and consumed by calls to 
   gss_init_sec_context(); and "Error" tokens, potentially emitted by 
   calls to gss_init_sec_context() or gss_accept_sec_context(), and 
   potentially consumed by calls to gss_init_sec_context() or 
   gss_accept_sec_context().

   Per RFC-1508, Appendix B, the initial context establishment token 
   will be enclosed within framing as follows:

Adams                Document Expiration:  19 July 1996                9


   InitialContextToken ::= [APPLICATION 0] IMPLICIT SEQUENCE {
           thisMech           MechType,
                   -- MechType is OBJECT IDENTIFIER
                   -- representing "SPKM-1" or "SPKM-2"
           innerContextToken  ANY DEFINED BY thisMech
   }               -- contents mechanism-specific

   When thisMech is SPKM-1 or SPKM-2, innerContextToken is defined as 
   follows:

      SPKMInnerContextToken ::= CHOICE { 
         req    [0] SPKM-REQ, 
         rep-ti [1] SPKM-REP-TI, 
         rep-it [2] SPKM-REP-IT, 
         error  [3] SPKM-ERROR, 
         mic    [4] SPKM-MIC, 
         wrap   [5] SPKM-WRAP, 
         del    [6] SPKM-DEL 
      }

   The above GSS-API framing shall be applied to all tokens emitted by 
   the SPKM GSS-API mechanism, including SPKM-REP-TI (the response from 
   the Target to the Initiator), SPKM-REP-IT (the response from the 
   Initiator to the Target), SPKM-ERROR, context-deletion, and 
   per-message tokens, not just to the initial token in a context 
   establishment exchange.  While not required by RFC-1508, this enables 
   implementations to perform enhanced error-checking.  The tag values 
   provided in SPKMInnerContextToken ("[0]" through "[6]") specify a 
   token-id for each token; similar information is contained in each 
   token's tok-id field.  While seemingly redundant, the tag value and 
   tok-id actually perform different tasks:  the tag ensures that 
   InitialContextToken can be properly decoded; tok-id ensures, among 
   other things, that data associated with the per-message tokens is 
   cryptographically linked to the intended token type.  Every 
   innerContextToken also includes a context-id field; see Section 6 for 
   a discussion of both token-id and context-id information and their 
   use in an SPKM support function).

   The innerContextToken field of context establishment tokens for the 
   SPKM GSS-API mechanism will contain one of the following messages: 
   SPKM-REQ; SPKM-REP-TI; SPKM-REP-IT; and SPKM-ERROR.  Furthermore, all 
   innerContextTokens are encoded using ASN.1 BER (constrained, in the 
   interests of parsing simplicity, to the DER subset defined in 
   [X.509], clause 8.7).

   The SPKM context establishment tokens are defined according to 
   [X.509] Section 10 and are compatible with [9798].  SPKM-1 (random 
   numbers) uses Section 10.3, "Two-way Authentication", when 
   performing unilateral authentication of the target to the initiator 
   and uses Section 10.4, "Three-way Authentication", when mutual 
   authentication is requested by the initiator.  SPKM-2 (timestamps) 
   uses Section 10.2, "One-way Authentication", when performing 
   unilateral authentication of the initiator to the target and uses 
   Section 10.3, "Two-way Authentication", when mutual authentication is 
   requested by the initiator.

Adams                Document Expiration:  19 July 1996               10


   The implication of the previous paragraph is that for SPKM-2 
   unilateral authentication no negotiation of K-ALG can be done (the 
   target either accepts the K-ALG and context key given by the 
   initiator or disallows the context).  For SPKM-2 mutual or SPKM-1 
   unilateral authentication some negotiation is possible, but the 
   target can only choose among the one-pass K-ALGs offered by the 
   initiator (or disallow the context).  Alternatively, the initiator 
   can request that the target generate and transmit the context key.  
   For SPKM-1 mutual authentication the target can choose any one- or 
   two-pass K-ALG offered by the initiator and, again, can be requested 
   to generate and transmit the context key.

   It is envisioned that typical use of SPKM-1 or SPKM-2 will involve 
   mutual authentication.  Although unilateral authentication is avail- 
   able for both mechanisms, its use is not generally recommended.


3.1.1. Context Establishment Tokens - Initiator (first token)

   In order to accomplish context establishment, it may be necessary 
   that both the initiator and the target have access to the other 
   partys public-key certificate(s).  In some environments the 
   initiator may choose to acquire all certificates and send the 
   relevant ones to the target in the first token.  In other environ-
   ments the initiator may request that the target send certificate data 
   in its response token, or each side may individually obtain the 
   certificate data it needs.  In any case, however, the SPKM 
   implementation must have the ability to obtain certificates which 
   correspond to a supplied Name.  The actual mechanism to be used to 
   achieve this is a local implementation matter and is therefore 
   outside the scope of this specification.


   Relevant SPKM-REQ syntax is as follows (note that imports from other 
   documents are given in Appendix A):


   SPKM-REQ ::= SEQUENCE {
           requestToken      REQ-TOKEN,
           certif-data [0]   CertificationData OPTIONAL,
           auth-data [1]     AuthorizationData OPTIONAL
              -- see [RFC-1510] for a discussion of auth-data
   }

   CertificationData ::= SEQUENCE {
           certificationPath [0]          CertificationPath OPTIONAL,
           certificateRevocationList [1]  CertificateList OPTIONAL
   }  -- at least one of the above shall be present








Adams                Document Expiration:  19 July 1996               11


   CertificationPath ::= SEQUENCE {
           userKeyId [0]         OCTET STRING OPTIONAL,
              -- identifier for user's public key
           userCertif [1]        Certificate OPTIONAL,
              -- certificate containing user's public key
           verifKeyId [2]        OCTET STRING OPTIONAL,
              -- identifier for user's public verification key
           userVerifCertif [3]   Certificate OPTIONAL,
              -- certificate containing user's public verification key
           theCACertificates [4] SEQUENCE OF CertificatePair OPTIONAL
   }          -- certification path from target to source

   Having separate verification fields allows different key pairs 
   (possibly corresponding to different algorithms) to be used for 
   encryption/decryption and signing/verification.  Presence of [0] or 
   [1] and absence of [2] and [3] implies that the same key pair is to 
   be used for enc/dec and verif/signing (note that this practice is not 
   typically recommended).  Presence of [2] or [3] implies that a 
   separate key pair is to be used for verif/signing, and so [0] or [1] 
   must also be present.  Presence of [4] implies that at least one of 
   [0], [1], [2], and [3] must also be present.


   REQ-TOKEN ::= SEQUENCE {
           req-contents     Req-contents,
           algId            AlgorithmIdentifier,
           req-integrity    Integrity  -- "token" is Req-contents
   }

   Integrity ::= BIT STRING
     -- If corresponding algId specifies a signing algorithm, 
     -- "Integrity" holds the result of applying the signing procedure 
     -- specified in algId to the BER-encoded octet string which results 
     -- from applying the hashing procedure (also specified in algId) to 
     -- the DER-encoded octets of "token".
     -- Alternatively, if corresponding algId specifies a MACing 
     -- algorithm, "Integrity" holds the result of applying the MACing 
     -- procedure specified in algId to the DER-encoded octets of 
     -- "token" (note that for MAC, algId must be one of the integrity 
     -- algorithms offered by the initiator with the appropriate subkey 
     -- derived from the context key (see Section 2.4) used as the key 
     -- input)

   It is envisioned that typical use of the Integrity field for each of 
   REQ-TOKEN, REP-TI-TOKEN, and REP-IT-TOKEN will be a true digital 
   signature, providing unilateral or mutual authentication along with 
   replay protection, as required.  However, there are situations in 
   which the MAC choice will be appropriate.  One example is the case in 
   which the initiator wishes to remain anonymous (so that the first, or 
   first and third, token(s) will be MACed and the second token will be 
   signed).  Another example is the case in which a previously authenti-
   cated, established, and cached context is being re-established at 
   some later time (here all exchanged tokens will be MACed). 



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   The primary advantage of the MAC choice is that it reduces processing 
   overhead for cases in which either authentication is not required 
   (e.g., anonymity) or authentication is established by some other 
   means (e.g., ability to form the correct MAC on a "fresh" token in 
   context re-establishment).

   Req-contents ::= SEQUENCE {
           tok-id           INTEGER (256),    -- shall contain 0100(hex)
           context-id       Random-Integer,   -- see Section 6.3
           pvno             BIT STRING,       -- protocol version number
           timestamp        UTCTime OPTIONAL, -- mandatory for SPKM-2
           randSrc          Random-Integer,
           targ-name        Name,
           src-name [0]     Name OPTIONAL, 
              -- must be supplied unless originator is "anonymous"
           req-data         Context-Data,
           validity [1]     Validity OPTIONAL,
              -- validity interval for key (may be used in the
              -- computation of security context lifetime)
           key-estb-set     Key-Estb-Algs,
              -- specifies set of key establishment algorithms
           key-estb-req      BIT STRING OPTIONAL,
              -- key estb. parameter corresponding to first K-ALG in set
              -- (not used if initiator is unable or unwilling to 
              -- generate and securely transmit key material to target).
              -- Established key must satisfy the key length constraints 
              -- specified in Section 2.4.
           key-src-bind      OCTET STRING OPTIONAL
              -- Used to bind the source name to the symmetric key.  
              -- This field must be present for the case of SPKM-2 
              -- unilateral authen. if the K-ALG in use does not provide 
              -- such a binding (but is optional for all other cases).
              -- The octet string holds the result of applying the 
              -- mandatory hashing procedure MD5 (in MANDATORY I-ALG; 
              -- see Section 2.1) as follows:  MD5(src || context_key),
              -- where "src" is the DER-encoded octets of src-name, 
              -- "context-key" is the symmetric key (i.e., the 
              -- unprotected version of what is transmitted in 
              -- key-estb-req), and "||" is the concatenation operation.
           }

   -- The protocol version number (pvno) parameter is a BIT STRING which 
   -- uses as many bits as necessary to specify all the SPKM protocol 
   -- versions supported by the initiator (one bit per protocol 
   -- version).  The protocol specified by this document is version 0.  
   -- Bit 0 of pvno is therefore set if this version is supported; 
   -- similarly, bit 1 is set if version 1 (if defined in the future) is 
   -- supported, and so on.  Note that for unilateral authentication 
   -- using SPKM-2, no response token is expected during context 
   -- establishment, so no protocol negotiation can take place; in this 
   -- case, the initiator must set exactly one bit of pvno.  The version 
   -- of REQ-TOKEN must correspond to the highest bit set in pvno.




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   -- The "validity" parameter above is the only way within SPKM for 
   -- the initiator to transmit desired context lifetime to the target.  
   -- Since it cannot be guaranteed that the initiator and target have 
   -- synchronized time, the span of time specified by "validity" is to 
   -- be taken as definitive (rather than the actual times given in this 
   -- parameter).

   Random-Integer ::= BIT STRING

   -- Each SPKM implementation is responsible for generating a "fresh" 
   -- random number for the purpose of context establishment; that is, 
   -- one which (with high probability) has not been used previously.  
   -- There are no cryptographic requirements on this random number 
   -- (i.e., it need not be unpredictable, it simply needs to be fresh).

   Context-Data ::= SEQUENCE {
           channelId       ChannelId OPTIONAL, -- channel bindings
           seq-number      INTEGER OPTIONAL,   -- sequence number
           options         Options,
           conf-alg        Conf-Algs,          -- confidentiality. algs.
           intg-alg        Intg-Algs,          -- integrity algorithm
           owf-alg         OWF-Algs            -- for subkey derivation
   }

   ChannelId ::= OCTET STRING

   Options ::= BIT STRING {
           delegation-state (0),
           mutual-state (1),
           replay-det-state (2), -- used for replay det. during context
           sequence-state (3),   -- used for sequencing during context
           conf-avail (4),
           integ-avail (5),
           target-certif-data-required (6)
                                 -- used to request targ's certif. data
   }

   Conf-Algs ::= CHOICE {
           algs [0]        SEQUENCE OF AlgorithmIdentifier,
           null [1]        NULL 
            -- used when conf. is not available over context
   } -- for C-ALG (see Section 5.2 for discussion of QOP)

   Intg-Algs ::= SEQUENCE OF AlgorithmIdentifier 
       -- for I-ALG (see Section 5.2 for discussion of QOP)

   OWF-Algs ::= SEQUENCE OF AlgorithmIdentifier 
       -- Contains exactly one algorithm in REQ-TOKEN for SPKM-2 
       -- unilateral, and contains at least one algorithm otherwise. 
       -- Always contains exactly one algorithm in REP-TOKEN.

   Key-Estb-Algs ::= SEQUENCE OF AlgorithmIdentifier
       -- to allow negotiation of K-ALG



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   A context establishment sequence based on the SPKM will perform 
   unilateral authentication if the mutual-req bit is not set in the 
   application's call to gss_init_sec_context().  SPKM-2 accomplishes 
   this using only SPKM-REQ (thereby authenticating the initiator to the 
   target), while SPKM-1 accomplishes this using both SPKM-REQ and 
   SPKM-REP-TI (thereby authenticating the target to the initiator).

   Applications requiring authentication of both peers (initiator as 
   well as target) must request mutual authentication, resulting in 
   "mutual-state" being set within SPKM-REQ Options.  In response to 
   such a request, the context target will reply to the initiator with 
   an SPKM-REP-TI token.  If mechanism SPKM-2 has been chosen, this 
   completes the (timestamp-based) mutual authentication context 
   establishment exchange.  If mechanism SPKM-1 has been chosen and 
   SPKM-REP-TI is sent, the initiator will then reply to the target with 
   an SPKM-REP-IT token, completing the (random-number-based) mutual 
   authentication context establishment exchange.

   Other bits in the Options field of Context-Data are explained in 
   RFC-1508, with the exception of target-certif-data-required, which 
   the initiator sets to TRUE to request that the target return its 
   certification data in the SPKM-REP-TI token.  For unilateral authen-
   tication in SPKM-2 (in which no SPKM-REP-TI token is constructed),
   this option bit is ignored by both initiator and target.


3.1.2. Context Establishment Tokens - Target


   SPKM-REP-TI ::= SEQUENCE {
           responseToken    REP-TI-TOKEN,
           certif-data      CertificationData OPTIONAL
             -- included if target-certif-data-required option was 
             -- set to TRUE in SPKM-REQ
   }


   REP-TI-TOKEN ::= SEQUENCE {
           rep-ti-contents Rep-ti-contents,
           algId           AlgorithmIdentifier,
           rep-ti-integ    Integrity  -- "token" is Rep-ti-contents
   } 














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   Rep-ti-contents ::= SEQUENCE {
           tok-id           INTEGER (512),   -- shall contain 0200 (hex)
           context-id       Random-Integer,  -- see Section 6.3
           pvno [0]         BIT STRING OPTIONAL, -- prot. version number
           timestamp        UTCTime OPTIONAL, -- mandatory for SPKM-2
           randTarg         Random-Integer,
           src-name [1]     Name OPTIONAL, 
             -- must contain whatever value was supplied in REQ-TOKEN
           targ-name        Name,
           randSrc          Random-Integer,
           rep-data         Context-Data,
           validity [2]     Validity  OPTIONAL,
             -- validity interval for key (used if the target can only 
             -- support a shorter context lifetime than was offered in 
             -- REQ-TOKEN)
           key-estb-id      AlgorithmIdentifier OPTIONAL,
             -- used if target is changing key estb. algorithm (must be 
             -- a member of initiators key-estb-set)
           key-estb-str      BIT STRING OPTIONAL
             -- contains (1) the response to the initiators 
             -- key-estb-req (if init. used a 2-pass K-ALG), or (2) the 
             -- key-estb-req corresponding to the K-ALG supplied in 
             -- above key-estb-id, or (3) the key-estb-req corresponding 
             -- to the first K-ALG supplied in initiator's key-estb-id, 
             -- if initiator's (OPTIONAL) key-estb-req was not used 
             -- (target's key-estb-str must be present in this case).
             -- Established key must satisfy the key length constraints 
             -- specified in Section 2.4.
           }

   The protocol version number (pvno) parameter is a BIT STRING which 
   uses as many bits as necessary to specify a single SPKM protocol 
   version offered by the initiator which is supported by the target 
   (one bit per protocol version); that is, the target sets exactly one 
   bit of pvno.  If none of the versions offered by the initiator are 
   supported by the target, a delete token must be returned so that the 
   context is never established.  If the initiator's pvno has only one 
   bit set and the target happens to support this protocol version, 
   then this version is used over the context and the pvno parameter of 
   REP-TOKEN can be omitted.  Finally, if the initiator and target do 
   have one or more versions in common but the version of the REQ-TOKEN 
   received is not supported by the target, a REP-TOKEN must be sent 
   with a desired version bit set in pvno (and dummy values used for 
   all subsequent token fields).  The initiator can then respond with a 
   new REQ-TOKEN of the proper version (essentially starting context 
   establishment anew). 










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3.1.3. Context Establishment Tokens - Initiator (second token)

   Relevant SPKM-REP-IT syntax is as follows:

   SPKM-REP-IT ::= SEQUENCE {
           responseToken    REP-IT-TOKEN,
           algId            AlgorithmIdentifier,
           rep-it-integ     Integrity  -- "token" is REP-IT-TOKEN
   }

   REP-IT-TOKEN ::= SEQUENCE {
           tok-id           INTEGER (768), -- shall contain 0300 (hex)
           context-id       Random-Integer,
           randSrc          Random-Integer,
           randTarg         Random-Integer,
           targ-name        Name,  -- the targ-name specified in REP-TI
           src-name         Name OPTIONAL, 
             -- must contain whatever value was supplied in REQ-TOKEN
           key-estb-rep     BIT STRING OPTIONAL
                 -- contains the response to targets key-estb-str
                 -- (if target selected a 2-pass K-ALG)
           }

3.1.4. Error Token

   The syntax of SPKM-ERROR is as follows:

   SPKM-ERROR ::= SEQUENCE {
           error-token      ERROR-TOKEN,
           algId            AlgorithmIdentifier,
           integrity        Integrity  -- "token" is ERROR-TOKEN
   }

   ERROR-TOKRN ::=   SEQUENCE {
           tok-id           INTEGER (1024), -- shall contain 0400 (hex)
           context-id       Random-Integer
           }

   The SPKM-ERROR token is used only during the context establishment 
   process.  If an SPKM-REQ or SPKM-REP-TI token is received in error, 
   the receiving function (either gss_init_sec_context() or 
   gss_accept_sec_context()) will generate an SPKM-ERROR token to be 
   sent to the peer (if the peer is still in the context establishment 
   process) and will return GSS_S_CONTINUE_NEEDED.  If, on the other 
   hand, no context establishment response is expected from the peer 
   (i.e., the peer has completed context establishment), the function 
   will return the appropriate major status code (e.g., GSS_S_BAD_SIG)
   along with a minor status of GSS_SPKM_S_SG_CONTEXT_ESTB_ABORT and all 
   context-relevant information will be deleted.  The output token will 
   not be an SPKM-ERROR token but will instead be an SPKM-DEL token 
   which will be processed by the peer's gss_process_context_token().





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   If gss_init_sec_context() receives an error token (whether valid or 
   invalid), it will regenerate SPKM-REQ as its output token and return 
   a major status code of GSS_S_CONTINUE_NEEDED.  (Note that if the 
   peer's gss_accept_sec_context() receives SPKM-REQ token when it is 
   expecting a SPKM-REP-IT token, it will ignore SPKM-REQ and return a 
   zero-length output token with a major status of 
   GSS_S_CONTINUE_NEEDED.)

   Similarly, if gss_accept_sec_context() receives an error token 
   (whether valid or invalid), it will regenerate SPKM-REP-TI as its 
   output token and return a major status code of GSS_S_CONTINUE_NEEDED.



   md5WithRsa is currently stipulated for the signing of context 
   establishment tokens.  Discrepancies involving modulus bitlength can 
   be resolved through judicious use of the SPKM-ERROR token.  The 
   context initiator signs REQ-TOKEN using the strongest RSA it supports 
   (e.g., 1024 bits).  If the target is unable to verify signatures of 
   this length, it sends SPKM-ERROR signed with the strongest RSA that 
   it supports (e.g. 512).

   At the completion of this exchange, both sides know what RSA 
   bitlength the other supports, since the size of the signature is 
   equal to the size of the modulus.  Further exchanges can be made 
   (using successively smaller supported bitlengths) until either an 
   agreement is reached or context establishment is aborted because no 
   agreement is possible.





3.2. Per-Message and Context Deletion Tokens

   Three classes of tokens are defined in this section: "MIC" tokens, 
   emitted by calls to gss_getMIC() and consumed by calls to 
   gss_verifyMIC(); "Wrap" tokens, emitted by calls to gss_wrap() and 
   consumed by calls to gss_unwrap(); and context deletion tokens, 
   emitted by calls to gss_init_sec_context(), gss_accept_sec_context(), 
   or gss_delete_sec_context() and consumed by calls to 
   gss_process_context_token().


3.2.1. Per-message Tokens - Sign / MIC

   Use of the gss_sign() / gss_getMIC() call yields a token, separate 
   from the user data being protected, which can be used to verify the 
   integrity of that data as received.  The token and the data may be 
   sent separately by the sending application and it is the receiving 
   application's responsibility to associate the received data with the 
   received token.




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   The SPKM-MIC token has the following format:

   SPKM-MIC ::= SEQUENCE {
           mic-header       Mic-Header,
           int-cksum        BIT STRING
                                -- Checksum over header and data,
                                -- calculated according to algorithm
                                -- specified in int-alg field.
   }

   Mic-Header ::= SEQUENCE {
           tok-id           INTEGER (257),
                                -- shall contain 0101 (hex)
           context-id       Random-Integer,
           int-alg [0]      AlgorithmIdentifier OPTIONAL,
                                -- Integrity algorithm indicator (must
                                -- be one of the agreed integrity
                                -- algorithms for this context).
                                -- field not present = default id.
           snd-seq [1]      SeqNum OPTIONAL  -- sequence number field.
   }

   SeqNum ::= SEQUENCE {
           num      INTEGER, -- the sequence number itself
           dir-ind  BOOLEAN  -- a direction indicator
   }

3.2.1.1. Checksum

   Checksum calculation procedure (common to all algorithms -- note that 
   for SPKM the term "checksum" includes digital signatures as well as 
   hashes and MACs): Checksums are calculated over the data field, 
   logically prepended by the bytes of the plaintext token header 
   (mic-header).  The result binds the data to the entire plaintext 
   header, so as to minimize the possibility of malicious splicing.

   For example, if the int-alg specifies the md5WithRSA algorithm, then 
   the checksum is formed by computing an MD5 [RFC-1321] hash over the 
   plaintext data (prepended by the header), and then computing an RSA 
   signature [PKCS1] on the 16-byte MD5 result.  The signature is 
   computed using the RSA private key retrieved from the credentials 
   structure and the result (whose length is implied by the "modulus" 
   parameter in the private key) is stored in the int-cksum field.

   If the int-alg specifies a keyed hashing algorithm (for example, 
   DES-MAC or md5-DES-CBC), then the key to be used is the appropriate 
   subkey derived from the context key (see Section 2.4).  Again, the 
   result (whose length is implied by int-alg) is stored in the 
   int-cksum field.







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3.2.1.2. Sequence Number

   It is assumed that the underlying transport layers (of whatever pro-
   tocol stack is being used by the application) will provide adequate 
   communications reliability (that is, non-malicious loss, re-ordering,
   etc., of data packets will be handled correctly).  Therefore, 
   sequence numbers are used in SPKM purely for security, as opposed to 
   reliability, reasons (that is, to avoid malicious loss, replay, or 
   re-ordering of SPKM tokens) -- it is therefore recommended that
   applications request sequencing and replay detection over all 
   contexts.  Note that sequence numbers are used so that there is no 
   requirement for secure timestamps in the message tokens.  The 
   initiator's initial sequence number for the current context may be 
   explicitly given in the Context-Data field of SPKM-REQ and the 
   target's initial sequence number may be explicitly given in the 
   Context-Data field of SPKM-REP-TI; if either of these is not given 
   then the default value of 00 is to be used.

   Sequence number field: The sequence number field is formed from the 
   sender's four-byte sequence number and a Boolean direction-indicator 
   (FALSE - sender is the context initiator, TRUE - sender is the 
   context acceptor).  After constructing a gss_sign/getMIC() or 
   gss_seal/wrap() token, the sender's seq. number is incremented by 1.

3.2.1.3. Sequence Number Processing

   The receiver of the token will verify the sequence number field by 
   comparing the sequence number with the expected sequence number and 
   the direction indicator with the expected direction indicator.  If 
   the sequence number in the token is higher than the expected number, 
   then the expected sequence number is adjusted and GSS_S_GAP_TOKEN is 
   returned.  If the token sequence number is lower than the expected 
   number, then the expected sequence number is not adjusted and 
   GSS_S_DUPLICATE_TOKEN, GSS_S_UNSEQ_TOKEN, or GSS_S_OLD_TOKEN is 
   returned, whichever is appropriate.  If the direction indicator is 
   wrong, then the expected sequence number is not adjusted and 
   GSS_S_UNSEQ_TOKEN is returned.

   Since the sequence number is used as part of the input to the 
   integrity checksum, sequence numbers need not be encrypted, and 
   attempts to splice a checksum and sequence number from different 
   messages will be detected.  The direction indicator will detect 
   tokens which have been maliciously reflected.

3.2.2. Per-message Tokens - Seal / Wrap

   Use of the gss_seal() / gss_wrap() call yields a token which 
   encapsulates the input user data (optionally encrypted) along with 
   associated integrity check quantities. The token emitted by 
   gss_seal() / gss_wrap() consists of an integrity header followed by a 
   body portion that contains either the plaintext data (if conf-alg = 
   NULL) or encrypted data (using the appropriate subkey specified in 
   Section 2.4 for one of the agreed C-ALGs for this context).



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   The SPKM-WRAP token has the following format:

   SPKM-WRAP ::= SEQUENCE {
           wrap-header       Wrap-Header,
           wrap-body         Wrap-Body
   }

   Wrap-Header ::= SEQUENCE {
           tok-id           INTEGER (513),
                                -- shall contain 0201 (hex)
           context-id       Random-Integer,
           int-alg [0]      AlgorithmIdentifier OPTIONAL,
                                -- Integrity algorithm indicator (must
                                -- be one of the agreed integrity
                                -- algorithms for this context).
                                -- field not present = default id.
           conf-alg [1]     Conf-Alg OPTIONAL,
                                -- Confidentiality algorithm indicator
                                -- (must be NULL or one of the agreed
                                -- confidentiality algorithms for this
                                -- context).
                                -- field not present = default id.
                                -- NULL = none (no conf. applied).
           snd-seq [2]      SeqNum OPTIONAL
                                -- sequence number field.
   }



   Wrap-Body ::= SEQUENCE {
           int-cksum        BIT STRING,
                                -- Checksum of header and data,
                                -- calculated according to algorithm
                                -- specified in int-alg field.
           data             BIT STRING
                                -- encrypted or plaintext data.
   }

   Conf-Alg ::= CHOICE {
           algId [0]        AlgorithmIdentifier,
           null [1]         NULL
   }




3.2.2.1: Confounding

   As in [KRB5], an 8-byte random confounder is prepended to the data to 
   compensate for the fact that an IV of zero is used for encryption.  
   The result is referred to as the "confounded" data field.





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3.2.2.2. Checksum

   Checksum calculation procedure (common to all algorithms): Checksums 
   are calculated over the plaintext data field, logically prepended by 
   the bytes of the plaintext token header (wrap-header).  As with 
   gss_sign() / gss_getMIC(), the result binds the data to the entire 
   plaintext header, so as to minimize the possibility of malicious 
   splicing.

   The examples for md5WithRSA and DES-MAC are exactly as specified in 
   3.2.1.1.

   If int-alg specifies md5-DES-CBC and conf-alg specifies anything 
   other than DES-CBC, then the checksum is computed according to 
   3.2.1.1 and the result is stored in int-cksum.  However, if conf-alg 
   specifies DES-CBC then the encryption and the integrity are done 
   as follows.  An MD5 [RFC-1321] hash is computed over the plaintext 
   data (prepended by the header).  This 16-byte value is appended to 
   the concatenation of the "confounded" data and 1-8 padding bytes (the 
   padding is as specified in [KRB5] for DES-CBC).  The result is 
   then CBC encrypted using the DES-CBC subkey (see Section 2.4) and 
   placed in the "data" field of Wrap-Body.  The final two blocks of 
   ciphertext (i.e., the encrypted MD5 hash) are also placed in the 
   int-cksum field of Wrap-Body as the integrity checksum.

   If int-alg specifies sum64-DES-CBC then conf-alg must specify DES-CBC 
   (i.e., confidentiality must be requested by the calling application 
   or SPKM will return an error).  Encryption and integrity are done in 
   a single pass using the DES-CBC subkey as follows.  The sum 
   (modulo 2**64 - 1) of all plaintext data blocks (prepended by the 
   header) is computed.  This 8-byte value is appended to the 
   concatenation of the "confounded" data and 1-8 padding bytes (the 
   padding is as specified in [KRB5] for DES-CBC).  As above, the result 
   is then CBC encrypted and placed in the "data" field of Wrap-Body.  
   The final block of ciphertext (i.e., the encrypted sum) is also 
   placed in the int-cksum field of Wrap-Body as the integrity checksum.


3.2.2.3 Sequence Number

   Sequence numbers are computed and processed for gss_wrap() exactly 
   as specified in 3.2.1.2 and 3.2.1.3.














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3.2.2.4: Data Encryption

   The following procedure is followed unless (a) conf-alg is NULL (no 
   encryption), or (b) conf-alg is DES-CBC and int-alg is md5-DES-CBC 
   (encryption as specified in 3.2.2.2), or (c) int-alg is sum64-DES-CBC 
   (encryption as specified in 3.2.2.2):

   The "confounded" data is padded and encrypted according to the 
   algorithm specified in the conf-alg field.  The data is encrypted 
   using CBC with an IV of zero.  The key used is the appropriate subkey 
   derived from the established context key using the subkey derivation 
   algorithm described in Section 2.4 (this ensures that the subkey used 
   for encryption and the subkey used for a separate, keyed integrity 
   algorithm -- for example DES-MAC, but not sum64-DES-CBC -- are 
   different).



3.2.3. Context deletion token

   The token emitted by gss_delete_sec_context() is based on the format 
   for tokens emitted by gss_sign() / gss_getMIC().

   The SPKM-DEL token has the following format:


   SPKM-DEL ::= SEQUENCE {
           del-header       Del-Header,
           int-cksum        BIT STRING
                                -- Checksum of header, calculated
                                -- according to algorithm specified
                                -- in int-alg field.
   }

   Del-Header ::= SEQUENCE {
           tok-id           INTEGER (769),
                                -- shall contain 0301 (hex)
           context-id       Random-Integer,
           int-alg [0]      AlgorithmIdentifier OPTIONAL,
                                -- Integrity algorithm indicator (must
                                -- be one of the agreed integrity
                                -- algorithms for this context).
                                -- field not present = default id.
           snd-seq [1]      SeqNum OPTIONAL
                                -- sequence number field.
   }


   The field snd-seq will be calculated as for tokens emitted by 
   gss_sign() / gss_getMIC().  The field int-cksum will be calculated as 
   for tokens emitted by gss_sign() / gss_getMIC(), except that the 
   user-data component of the checksum data will be a zero-length 
   string.



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   If a valid delete token is received, then the SPKM implementation 
   will delete the context and gss_process_context_token() will return a 
   major status of GSS_S_COMPLETE and a minor status of 
   GSS_SPKM_S_SG_CONTEXT_DELETED.  If, on the other hand, the delete 
   token is invalid, the context will not be deleted and 
   gss_process_context_token() will return the appropriate major status 
   (GSS_S_BAD_SIG, for example) and a minor status of 
   GSS_SPKM_S_SG_BAD_DELETE_TOKEN_RECD.  The application may wish to 
   take some action at this point to check the context status (such as 
   sending a sealed/wrapped test message to its peer and waiting for a 
   sealed/wrapped response).


4. NAME TYPES AND OBJECT IDENTIFIERS

   No mandatory name forms have yet been defined for SPKM.  This section 
   is for further study.

4.1. Optional Name Forms

   This section discusses name forms which may optionally be supported 
   by implementations of the SPKM GSS-API mechanism.  It is recognized 
   that OS-specific functions outside GSS-API are likely to exist in 
   order to perform translations among these forms, and that GSS-API 
   implementations supporting these forms may themselves be layered atop 
   such OS-specific functions.  Inclusion of this support within GSS-API 
   implementations is intended as a convenience to applications.

4.1.1. User Name Form

   This name form shall be represented by the Object Identifier {iso(1)
   member-body(2) United States(840) mit(113554) infosys(1) gssapi(2)
   generic(1) user_name(1)}.  The recommended symbolic name for this
   type is "GSS_SPKM_NT_USER_NAME".

   This name type is used to indicate a named user on a local system.
   Its interpretation is OS-specific.  This name form is constructed as:

   username


4.1.2. Machine UID Form

   This name form shall be represented by the Object Identifier {iso(1)
   member-body(2) United States(840) mit(113554) infosys(1) gssapi(2)
   generic(1) machine_uid_name(2)}.  The recommended symbolic name for
   this type is "GSS_SPKM_NT_MACHINE_UID_NAME".

   This name type is used to indicate a numeric user identifier
   corresponding to a user on a local system.  Its interpretation is
   OS-specific.  The gss_buffer_desc representing a name of this type
   should contain a locally-significant uid_t, represented in host byte
   order.  The gss_import_name() operation resolves this uid into a
   username, which is then treated as the User Name Form.


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4.1.3. String UID Form

   This name form shall be represented by the Object Identifier {iso(1)
   member-body(2) United States(840) mit(113554) infosys(1) gssapi(2)
   generic(1) string_uid_name(3)}.  The recommended symbolic name for
   this type is "GSS_SPKM_NT_STRING_UID_NAME".

   This name type is used to indicate a string of digits representing
   the numeric user identifier of a user on a local system.  Its
   interpretation is OS-specific. This name type is similar to the
   Machine UID Form, except that the buffer contains a string
   representing the uid_t.


5. PARAMETER DEFINITIONS

   This section defines parameter values used by the SPKM GSS-API 
   mechanism.  It defines interface elements in support of portability.

5.1. Minor Status Codes

   This section recommends common symbolic names for minor_status values 
   to be returned by the SPKM GSS-API mechanism.  Use of these 
   definitions will enable independent implementors to enhance 
   application portability across different implementations of the 
   mechanism defined in this specification.  (In all cases, 
   implementations of gss_display_status() will enable callers to 
   convert minor_status indicators to text representations.) Each 
   implementation must make available, through include files or other 
   means, a facility to translate these symbolic names into the concrete 
   values which a particular GSS-API implementation uses to represent 
   the minor_status values specified in this section.  It is recognized 
   that this list may grow over time, and that the need for additional 
   minor_status codes specific to particular implementations may arise.

5.1.1. Non-SPKM-specific codes (Minor Status Code MSB, bit 31, SET)

5.1.1.1. GSS-Related codes (Minor Status Code bit 30 SET)

   GSS_S_G_VALIDATE_FAILED
       /* "Validation error" */
   GSS_S_G_BUFFER_ALLOC
       /* "Couldn't allocate gss_buffer_t data" */
   GSS_S_G_BAD_MSG_CTX
       /* "Message context invalid" */
   GSS_S_G_WRONG_SIZE
       /* "Buffer is the wrong size" */
   GSS_S_G_BAD_USAGE
       /* "Credential usage type is unknown" */
   GSS_S_G_UNAVAIL_QOP
       /* "Unavailable quality of protection specified" */

5.1.1.2. Implementation-Related codes (Minor Status Code bit 30 OFF)

   GSS_S_G_MEMORY_ALLOC
       /* "Couldn't perform requested memory allocation" */

Adams                Document Expiration:  19 July 1996               25

5.1.2. SPKM-specific-codes (Minor Status Code MSB, bit 31, OFF)

   GSS_SPKM_S_SG_CONTEXT_ESTABLISHED
       /* "Context is already fully established" */
   GSS_SPKM_S_SG_BAD_INT_ALG_TYPE
       /* "Unknown integrity algorithm type in token" */
   GSS_SPKM_S_SG_BAD_CONF_ALG_TYPE
       /* "Unknown confidentiality algorithm type in token" */
   GSS_SPKM_S_SG_BAD_KEY_ESTB_ALG_TYPE
       /* "Unknown key establishment algorithm type in token" */
   GSS_SPKM_S_SG_CTX_INCOMPLETE
       /* "Attempt to use incomplete security context" */
   GSS_SPKM_S_SG_BAD_INT_ALG_SET
       /* "No integrity algorithm in common from offered set" */
   GSS_SPKM_S_SG_BAD_CONF_ALG_SET
       /* "No confidentiality algorithm in common from offered set" */
   GSS_SPKM_S_SG_BAD_KEY_ESTB_ALG_SET
       /* "No key establishment algorithm in common from offered set" */
   GSS_SPKM_S_SG_NO_PVNO_IN_COMMON
       /* "No protocol version number in common from offered set" */
   GSS_SPKM_S_SG_INVALID_TOKEN_DATA
       /* "Data is improperly formatted:  cannot encode into token" */
   GSS_SPKM_S_SG_INVALID_TOKEN_FORMAT
       /* "Received token is improperly formatted:  cannot decode" */
   GSS_SPKM_S_SG_CONTEXT_DELETED
       /* "Context deleted at peer's request" */
   GSS_SPKM_S_SG_BAD_DELETE_TOKEN_RECD
       /* "Invalid delete token received -- context not deleted" */
   GSS_SPKM_S_SG_CONTEXT_ESTB_ABORT
      /* "Unrecoverable context establishment error. Context deleted" */

5.2. Quality of Protection Values

   The Quality of Protection (QOP) parameter is used in the SPKM GSS-API 
   mechanism as input to gss_sign() and gss_seal() (gss_getMIC() and 
   gss_wrap()) to select among alternate confidentiality and 
   integrity-checking algorithms.  Once these sets of algorithms have 
   been agreed upon by the context initiator and target, the QOP 
   parameter simply selects from these ordered sets.

   More specifically, the SPKM-REQ token sends an ordered sequence of 
   Alg. IDs specifying integrity-checking algorithms supported by the 
   initiator and an ordered sequence of Alg. IDs specifying 
   confidentiality algorithms supported by the initiator.  The target 
   returns the subset of the offered integrity-checking Alg. IDs which 
   it supports and the subset of the offered confidentiality Alg. IDs 
   which it supports in the SPKM-REP-TI token (in the same relative 
   orders as those given by the initiator).  Thus, the initiator and 
   target each know the algorithms which they themselves support and the 
   algorithms which both sides support (the latter are defined to be 
   those supported over the established context).  The QOP parameter has 
   meaning and validity with reference to this knowledge.  For example, 
   an application may request integrity algorithm number 3 as defined by 
   the mechanism specification.  If this algorithm is supported over 
   this context then it is used; otherwise, GSS_S_FAILURE and an 
   appropriate minor status code are returned.

Adams                Document Expiration:  19 July 1996               26

   If the SPKM-REP-TI token is not used (unilateral authentication using 
   SPKM-2), then the "agreed" sets of Alg. IDs are simply taken to be 
   the initiator's sets (if this is unacceptable to the target then it 
   must return an error token so that the context is never established).  
   Note that, in the interest of interoperability, the initiator is not 
   required to offer every algorithm it supports; rather, it may offer 
   only the mandated/recommended SPKM algorithms since these are likely 
   to be supported by the target.


   The QOP parameter for SPKM is defined to be a 32-bit unsigned integer 
   (an OM_uint32) with the following bit-field assignments:

 Confidentiality                     Integrity
 31 (MSB)                         16 15                         (LSB) 0
------------------------------------|-----------------------------------
|  TS (5)  | U(3) | IA (4) | MA (4) |  TS (5)  | U(3) | IA (4) | MA(4) |
------------------------------------|-----------------------------------

   where 

      TS is a 5-bit Type Specifier (a semantic qualifier whose value 
      specifies the type of algorithm which may be used to protect the 
      corresponding token -- see below for details);

      U is a 3-bit Unspecified field (available for future 
      use/expansion);

      IA is a 4-bit field enumerating Implementation-specific 
      Algorithms; and

      MA is a 4-bit field enumerating Mechanism-defined Algorithms.

   The interpretation of the QOP parameter is as follows (note that the 
   same procedure is used for both the confidentiality and the integrity 
   halves of the parameter).  The MA field is examined first.  If it is 
   non-zero then the algorithm used to protect the token is the 
   mechanism-specified algorithm corresponding to that integer value.

   If MA is zero then IA is examined.  If this field value is non-zero 
   then the algorithm used to protect the token is the implementation-
   specified algorithm corresponding to that integer value (if this 
   algorithm is available over the established context).  Note that use 
   of this field may hinder portability since a particular value may 
   specify one algorithm in one implementation of the mechanism and may 
   not be supported or may specify a completely different algorithm in 
   another implementation of the mechanism.

   Finally, if both MA and IA are zero then TS is examined.  A value of 
   zero for TS specifies the default algorithm for the established 
   context, which is defined to be the first algorithm on the 
   initiator's list of offered algorithms (confidentiality or integrity, 
   depending on which half of QOP is being examined) which is supported 
   over the context.  A non-zero value for TS corresponds to a 
   particular algorithm qualifier and selects the first algorithm 
   supported over the context which satisfies that qualifier.

Adams                Document Expiration:  19 July 1996               27


   The following TS values (i.e., algorithm qualifiers) are specified; 
   other values may be added in the future.

   For the Confidentiality TS field:

      00001 (1) = SPKM_SYM_ALG_STRENGTH_STRONG
      00010 (2) = SPKM_SYM_ALG_STRENGTH_MEDIUM
      00011 (3) = SPKM_SYM_ALG_STRENGTH_WEAK

   For the Integrity TS field:

      00001 (1) = SPKM_INT_ALG_NON_REP_SUPPORT
      00010 (2) = SPKM_INT_ALG_REPUDIABLE

   Clearly, qualifiers such as strong, medium, and weak are debatable 
   and likely to change with time, but for the purposes of this version 
   of the specification we define these terms as follows.  A 
   confidentiality algorithm is "weak" if the effective key length of 
   the cipher is 40 bits or less; it is "medium-strength" if the 
   effective key length is strictly between 40 and 80 bits; and it is 
   "strong" if the effective key length is 80 bits or greater.  (Note 
   that "effective key length" describes the computational effort 
   required to break a cipher using the best-known cryptanalytic attack 
   against that cipher.)

   A five-bit TS field allows up to 31 qualifiers for each of 
   confidentiality and integrity (since "0" is reserved for "default").  
   This document specifies three for confidentiality and two for 
   integrity, leaving a lot of room for future specification.  
   Suggestions of qualifiers such as "fast", "medium-speed", and "slow" 
   have been made, but such terms are difficult to quantify (and in any 
   case are platform- and processor-dependent), and so have been left 
   out of this initial specification.  The intention is that the TS 
   terms be quantitative, environment-independent qualifiers of 
   algorithms, as much as this is possible.


   Use of the QOP structure as defined above is ultimately meant to be 
   as follows.

    - TS values are specified at the GSS-API level and are therefore 
      portable across mechanisms.  Applications which know nothing about 
      algorithms are still able to choose "quality" of protection for 
      their message tokens.

    - MA values are specified at the mechanism level and are therefore 
      portable across implementations of a mechanism.  For example, all 
      implementations of the Kerberos V5 GSS mechanism must support 

         GSS_KRB5_INTEG_C_QOP_MD5     (value: 1) 
         GSS_KRB5_INTEG_C_QOP_DES_MD5 (value: 2) 
         GSS_KRB5_INTEG_C_QOP_DES_MAC (value: 3).

      (Note that these Kerberos-specified integrity QOP values do not 
      conflict with the QOP structure defined above.)

Adams                Document Expiration:  19 July 1996               28

    - IA values are specified at the implementation level (in user 
      documentation, for example) and are therefore typically non-
      portable.  An application which is aware of its own mechanism 
      implementation and the mechanism implementation of its peer, 
      however, is free to use these values since they will be perfectly 
      valid and meaningful over that context and between those peers.

   The receiver of a token must pass back to its calling application a 
   QOP parameter with all relevant fields set.  For example, if 
   triple-DES has been specified by a mechanism as algorithm 8, then 
   a receiver of a triple-DES-protected token must pass to its 
   application (QOP Confidentiality TS=1, IA=0, MA=8).  In this way, 
   the application is free to read whatever part of the QOP it 
   understands (TS or IA/MA).

   To aid in implementation and interoperability, the following 
   stipulation is made.  The set of integrity Alg. IDs sent by the 
   initiator must contain at least one specifying an algorithm which 
   computes a digital signature supporting non-repudiation, and must 
   contain at least one specifying any other (repudiable) integrity 
   algorithm.  The subset of integrity Alg. IDs returned by the target 
   must also contain at least one specifying an algorithm which computes 
   a digital signature supporting non-repudiation, and at least one 
   specifying a repudiable integrity algorithm.

   The reason for this stipulation is to ensure that every SPKM 
   implementation will provide an integrity service which supports non-
   repudiation and one which does not support non-repudiation.  An 
   application with no knowledge of underlying algorithms can choose one 
   or the other by passing (QOP Integrity TS=1, IA=MA=0) or (QOP 
   Integrity TS=2, IA=MA=0).  Although an initiator who wishes to remain 
   anonymous will never actually use the non-repudiable digital 
   signature, this integrity service must be available over the context 
   so that the target can use it if desired.

   Finally, in accordance with the MANDATORY and RECOMMENDED algorithms 
   given in Section 2, the following QOP values are specified for SPKM.

   For the Confidentiality MA field:

      0001 (1) = DES-CBC

   For the Integrity MA field:

      0001 (1) = md5WithRSA
      0010 (2) = DES-MAC


6. SUPPORT FUNCTIONS

   This section describes a mandatory support function for SPKM-
   conformant implementations which may, in fact, be of value in all 
   GSS-API mechanisms.  It makes use of the token-id and context-id 
   information which is included in SPKM context-establishment, error, 
   context-deletion, and per-message tokens.  The function is defined 
   in the following section.

Adams                Document Expiration:  19 July 1996               29


6.1. SPKM_Parse_token call

   Inputs:

   o  input_token OCTET STRING

   Outputs:

   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  mech_type OBJECT IDENTIFIER,

   o  token_type INTEGER,

   o  context_handle CONTEXT HANDLE,


   Return major_status codes:

   o  GSS_S_COMPLETE indicates that the input_token could be parsed for 
      all relevant fields.  The resulting values are stored in 
      mech_type, token_type and context_handle, respectively (with NULLs 
      in any parameters which are not relevant).

   o  GSS_S_DEFECTIVE_TOKEN indicates that either the token-id or the 
      context-id (if it was expected) information could not be parsed.  
      A non-NULL return value in token_type indicates that the latter 
      situation occurred.

   o  GSS_S_NO_TYPE indicates that the token-id information could be 
      parsed, but it did not correspond to any valid token_type.

      (Note that this major status code has not been defined for GSS in 
      RFC-1508.  Until such a definition is made (if ever), SPKM 
      implementations should instead return GSS_S_DEFECTIVE_TOKEN with 
      both token_type and context_handle set to NULL.  This essentially 
      implies that unrecognized token-id information is considered to be 
      equivalent to token-id information which could not be parsed.)

   o  GSS_S_NO_CONTEXT indicates that the context-id could be parsed, 
      but it did not correspond to any valid context_handle.

   o  GSS_S_FAILURE indicates that the mechanism type could not be 
      parsed (for example, the token may be corrupted).

   SPKM_Parse_token() is used to return to an application the mechanism 
   type, token type, and context handle which correspond to a given 
   input token.  Since GSS-API tokens are meant to be opaque to the 
   calling application, this function allows the application to 
   determine information about the token without having to violate the 
   opaqueness intention of GSS.  Of primary importance is the token 
   type, which the application can then use to decide which GSS function 
   to call in order to have the token processed.

Adams                Document Expiration:  19 July 1996               30


   If all tokens are framed as suggested in RFC-1508, Appendix B 
   (specified both in the Kerberos V5 GSS mechanism [KRB5] and in this 
   document), then any mechanism implementation should be able to return 
   at least the mech_type parameter (the other parameters being NULL) 
   for any uncorrupted input token.  If the mechanism implementation 
   whose SPKM_Parse_token() function is being called does recognize the 
   token, it can return token_type so that the application can 
   subsequently call the correct GSS function.  Finally, if the 
   mechanism provides a context-id field in its tokens (as SPKM does), 
   then an implementation can map the context-id to a context_handle and 
   return this to the application.  This is necessary for the situation 
   where an application has multiple contexts open simultaneously, all 
   using the same mechanism.  When an incoming token arrives, the 
   application can use this function to determine not only which GSS 
   function to call, but also which context_handle to use for the call.
   Note that this function does no cryptographic processing to determine 
   the validity of tokens; it simply attempts to parse the mech_type,
   token_type, and context-id fields of any token it is given.  Thus, it 
   is conceivable, for example, that an arbitrary buffer of data might 
   start with random values which look like a valid mech_type and that 
   SPKM_Parse_token() would return incorrect information if given this 
   buffer.  While conceivable, however, such a situation is unlikely.

   The SPKM_Parse_token() function is mandatory for SPKM-conformant 
   implementations, but it is optional for applications.  That is, if 
   an application has only one context open and can guess which GSS 
   function to call (or is willing to put up with some error codes), 
   then it need never call SPKM_Parse_token().  Furthermore, if this 
   function ever migrates up to the GSS-API level, then 
   SPKM_Parse_token() will be deprecated at that time in favour of 
   GSS_Parse_token(), or whatever the new name and function 
   specification might be.  Note finally that no minor status return 
   codes have been defined for this function at this time.



6.2. The token_type Output Parameter

   The following token types are defined:

      GSS_INIT_TOKEN   = 1
      GSS_ACCEPT_TOKEN = 2
      GSS_ERROR_TOKEN  = 3
      GSS_SIGN_TOKEN   = GSS_GETMIC_TOKEN = 4
      GSS_SEAL_TOKEN   = GSS_WRAP_TOKEN   = 5
      GSS_DELETE_TOKEN = 6

   All SPKM mechanisms shall be able to perform the mapping from the 
   token-id information which is included in every token (through the 
   tag values in SPKMInnerContextToken or through the tok-id field) to 
   one of the above token types.  Applications should be able to decide, 
   on the basis of token_type, which GSS function to call (for example, 
   if the token is a GSS_INIT_TOKEN then the application will call 
   gss_accept_sec_context(), and if the token is a GSS_WRAP_TOKEN then 
   the application will call gss_unwrap()).

Adams                Document Expiration:  19 July 1996               31


6.3. The context_handle Output Parameter

   The SPKM mechanism implementation is responsible for maintaining a 
   mapping between the context-id value which is included in every token 
   and a context_handle, thus associating an individual token with its 
   proper context.  Clearly the value of context_handle may be locally 
   determined and may, in fact, be associated with memory containing 
   sensitive data on the local system, and so having the context-id 
   actually be set equal to a computed context_handle will not work in 
   general.  Conversely, having the context_handle actually be set equal 
   to a computed context-id will not work in general either, because 
   context_handle must be returned to the application by the first call 
   to gss_init_sec_context() or gss_accept_sec_context(), whereas 
   uniqueness of the context-id (over all contexts at both ends) 
   may require that both initiator and target be involved in the 
   computation.  Consequently, context_handle and context-id must be 
   computed separately and the mechanism implementation must be able to 
   map from one to the other by the completion of context establishment 
   at the latest.

   Computation of context-id during context establishment is 
   accomplished as follows.  Each SPKM implementation is responsible for 
   generating a "fresh" random number; that is, one which (with high 
   probability) has not been used previously.  Note that there are no 
   cryptographic requirements on this random number (i.e., it need not 
   be unpredictable, it simply needs to be fresh).  The initiator passes 
   its random number to the target in the context-id field of the 
   SPKM-REQ token.  If no further context establishment tokens are 
   expected (as for unilateral authentication in SPKM-2), then this 
   value is taken to be the context-id (if this is unacceptable to the 
   target then an error token must be generated).  Otherwise, the target 
   generates its random number and concatenates it to the end of the 
   initiator's random number.  This concatenated value is then taken to 
   be the context-id and is used in SPKM-REP-TI and in all subsequent 
   tokens over that context.

   Having both peers contribute to the context-id assures each peer of 
   freshness and therefore precludes replay attacks between contexts 
   (where a token from an old context between two peers is maliciously 
   injected into a new context between the same or different peers).  
   Such assurance is not available to the target in the case of 
   unilateral authentication using SPKM-2, simply because it has not 
   contributed to the freshness of the computed context-id (instead, it 
   must trust the freshness of the initiator's random number, or reject 
   the context).  The key-src-bind field in SPKM-REQ is required to be 
   present for the case of SPKM-2 unilateral authentication precisely to 
   assist the target in trusting the freshness of this token (and its 
   proposed context key).



7. SECURITY CONSIDERATIONS

   Security issues are discussed throughout this memo.


Adams                Document Expiration:  19 July 1996               32


8. REFERENCES

   [Davi89]:    D. W. Davies and W. L. Price, "Security for Computer 
   Networks", Second Edition, John Wiley and Sons, New York, 1989.

   [FIPS-113]:  National Bureau of Standards, Federal Information 
   Processing Standard 113, "Computer Data Authentication", May 1985.

   [GSSv2]:     J. Linn, "Generic Security Service Application Program 
   Interface Version 2", Internat Draft:  draft-ietf-cat-gssv2-xx.txt
   (work in progress).

   [Juen84]:    R. R. Jueneman, C. H. Meyer and S. M. Matyas, Message 
   Authentication with Manipulation Detection Codes, in Proceedings of 
   the 1983 IEEE Symposium on Security and Privacy, IEEE Computer 
   Society Press, 1984, pp.33-54.

   [KRB5]:      J. Linn, "The Kerberos Version 5 GSS-API Mechanism",  
   Internet Draft draft-ietf-cat-kerb5gss-xx.txt
   (work in progress).

   [PKCS1]:     RSA Encryption Standard, Version 1.5, RSA Data Security, 
   Inc., Nov. 1993.

   [PKCS3]:     Diffie-Hellman Key-Agreement Standard, Version 1.4, RSA 
   Data Security, Inc., Nov. 1993.

   [RFC-1321]:  R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321.

   [RFC-1422]:  S. Kent, "Privacy Enhancement for Internet Electronic 
   Mail:  Part II: Certificate-Based Key Management", RFC 1422.

   [RFC-1423]:  D. Balenson, "Privacy Enhancement for Internet Elec-
   tronic Mail: Part III: Algorithms, Modes, and Identifiers", RFC 1423.

   [RFC-1508]:  J. Linn, "Generic Security Service Application Program 
   Interface", RFC 1508.

   [RFC-1509]:  J. Wray, "Generic Security Service Application Program 
   Interface: C-bindings", RFC 1509.

   [RFC-1510]:  J. Kohl and C. Neuman, "The Kerberos Network 
   Authentication Service (V5)", RFC 1510.

   [9798]:      ISO/IEC 9798-3, "Information technology - Security 
   Techniques - Entity authentication mechanisms - Part 3:  Entitiy 
   authentication using a public key algorithm", ISO/IEC, 1993.

   [X.501]:     ISO/IEC 9594-2, "Information Technology - Open Systems 
   Interconnection - The Directory:  Models", CCITT/ITU Recommendation 
   X.501, 1993.





Adams                Document Expiration:  19 July 1996               33


   [X.509]:     ISO/IEC 9594-8, "Information Technology - Open Systems 
   Interconnection - The Directory:  Authentication Framework", 
   CCITT/ITU Recommendation X.509, 1993.

   [X9.44]:     ANSI, "Public Key Cryptography Using Reversible 
   Algorithms for the Financial Services Industry:  Transport of 
   Symmetric Algorithm Keys Using RSA", X9.44-1993.









9. AUTHOR'S ADDRESS

   Carlisle Adams
   Bell-Northern Research
   P.O.Box 3511, Station C
   Ottawa, Ontario, CANADA  K1Y 4H7

   Phone: +1 613.763.9008
   E-mail: cadams@bnr.ca































Adams                Document Expiration:  19 July 1996               34


Appendix A:  ASN.1 Module Definition


SpkmGssTokens {iso(1) identified-organization(3) dod(6) internet(1) 
               security(5) mechanisms(5) spkm(1) spkmGssTokens(10)}


DEFINITIONS IMPLICIT TAGS ::=
BEGIN


-- EXPORTS ALL --


IMPORTS

   Name
      FROM InformationFramework {joint-iso-ccitt(2) ds(5) module(1) 
                                informationFramework(1) 2}

   Certificate, CertificateList, CertificatePair, AlgorithmIdentifier, 
   Validity 
      FROM AuthenticationFramework {joint-iso-ccitt(2) ds(5) module(1) 
                                   authenticationFramework(7) 2}  ;



-- types --

   SPKM-REQ ::= SEQUENCE {
           requestToken      REQ-TOKEN,
           certif-data [0]   CertificationData OPTIONAL,
           auth-data [1]     AuthorizationData OPTIONAL
   }


   CertificationData ::= SEQUENCE {
           certificationPath [0]          CertificationPath OPTIONAL,
           certificateRevocationList [1]  CertificateList OPTIONAL
   } -- at least one of the above shall be present


   CertificationPath ::= SEQUENCE {
           userKeyId [0]         OCTET STRING OPTIONAL,
           userCertif [1]        Certificate OPTIONAL,
           verifKeyId [2]        OCTET STRING OPTIONAL,
           userVerifCertif [3]   Certificate OPTIONAL,
           theCACertificates [4] SEQUENCE OF CertificatePair OPTIONAL
   } -- Presence of [2] or [3] implies that [0] or [1] must also be 
     -- present.  Presence of [4] implies that at least one of [0], [1], 
     -- [2], and [3] must also be present.





Adams                Document Expiration:  19 July 1996               35


   REQ-TOKEN ::= SEQUENCE {
           req-contents     Req-contents,
           algId            AlgorithmIdentifier,
           req-integrity    Integrity  -- "token" is Req-contents
   }

  Integrity ::= BIT STRING
     -- If corresponding algId specifies a signing algorithm, 
     -- "Integrity" holds the result of applying the signing procedure 
     -- specified in algId to the BER-encoded octet string which results 
     -- from applying the hashing procedure (also specified in algId) to 
     -- the DER-encoded octets of "token".
     -- Alternatively, if corresponding algId specifies a MACing 
     -- algorithm, "Integrity" holds the result of applying the MACing 
     -- procedure specified in algId to the DER-encoded octets of 
     -- "token" 

   Req-contents ::= SEQUENCE {
           tok-id           INTEGER (256),  -- shall contain 0100 (hex)
           context-id       Random-Integer,
           pvno             BIT STRING,
           timestamp        UTCTime OPTIONAL, -- mandatory for SPKM-2
           randSrc          Random-Integer,
           targ-name        Name,
           src-name [0]     Name OPTIONAL, 
           req-data         Context-Data,
           validity [1]     Validity OPTIONAL,
           key-estb-set     Key-Estb-Algs,
           key-estb-req     BIT STRING OPTIONAL,
           key-src-bind     OCTET STRING OPTIONAL
              -- This field must be present for the case of SPKM-2 
              -- unilateral authen. if the K-ALG in use does not provide 
              -- such a binding (but is optional for all other cases).
              -- The octet string holds the result of applying the 
              -- mandatory hashing procedure (in MANDATORY I-ALG; 
              -- see Section 2.1) as follows:  MD5(src || context_key),
              -- where "src" is the DER-encoded octets of src-name, 
              -- "context-key" is the symmetric key (i.e., the 
              -- unprotected version of what is transmitted in 
              -- key-estb-req), and "||" is the concatenation operation.
   }

   Random-Integer ::= BIT STRING

   Context-Data ::= SEQUENCE {
           channelId       ChannelId OPTIONAL,
           seq-number      INTEGER OPTIONAL,
           options         Options,
           conf-alg        Conf-Algs,
           intg-alg        Intg-Algs,
           owf-alg         OWF-Algs 
   }

   ChannelId ::= OCTET STRING


Adams                Document Expiration:  19 July 1996               36


   Options ::= BIT STRING {
           delegation-state (0),
           mutual-state (1),
           replay-det-state (2),
           sequence-state (3),
           conf-avail (4),
           integ-avail (5),
           target-certif-data-required (6)
   }

   Conf-Algs ::= CHOICE {
           algs [0]         SEQUENCE OF AlgorithmIdentifier,
           null [1]         NULL
   }

   Intg-Algs ::= SEQUENCE OF AlgorithmIdentifier 

   OWF-Algs ::= SEQUENCE OF AlgorithmIdentifier 

   Key-Estb-Algs ::= SEQUENCE OF AlgorithmIdentifier


   SPKM-REP-TI ::= SEQUENCE {
           responseToken    REP-TI-TOKEN,
           certif-data      CertificationData OPTIONAL
             -- present if target-certif-data-required option was 
   }         -- set to TRUE in SPKM-REQ

   REP-TI-TOKEN ::= SEQUENCE {
           rep-ti-contents  Rep-ti-contents,
           algId            AlgorithmIdentifier,
           rep-ti-integ     Integrity  -- "token" is Rep-ti-contents
   }

   Rep-ti-contents ::= SEQUENCE {
           tok-id           INTEGER (512),   -- shall contain 0200 (hex)
           context-id       Random-Integer,
           pvno [0]         BIT STRING OPTIONAL,
           timestamp        UTCTime OPTIONAL, -- mandatory for SPKM-2
           randTarg         Random-Integer,
           src-name [1]     Name OPTIONAL,
           targ-name        Name,
           randSrc          Random-Integer,
           rep-data         Context-Data,
           validity [2]     Validity  OPTIONAL,
           key-estb-id      AlgorithmIdentifier OPTIONAL,
           key-estb-str     BIT STRING OPTIONAL
   }


   SPKM-REP-IT ::= SEQUENCE {
           responseToken    REP-IT-TOKEN,
           algId            AlgorithmIdentifier,
           rep-it-integ     Integrity  -- "token" is REP-IT-TOKEN
   } 

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   REP-IT-TOKEN ::= SEQUENCE {
           tok-id           INTEGER (768),  -- shall contain 0300 (hex)
           context-id       Random-Integer,
           randSrc          Random-Integer,
           randTarg         Random-Integer,
           targ-name        Name,
           src-name         Name OPTIONAL,
           key-estb-rep     BIT STRING OPTIONAL
   }

   SPKM-ERROR ::= SEQUENCE {
           errorToken       ERROR-TOKEN,
           algId            AlgorithmIdentifier,
           integrity        Integrity  -- "token" is ERROR-TOKEN
   } 

   ERROR-TOKEN ::=   SEQUENCE {
           tok-id           INTEGER (1024), -- shall contain 0400 (hex)
           context-id       Random-Integer
   }

   SPKM-MIC ::= SEQUENCE {
           mic-header       Mic-Header,
           int-cksum        BIT STRING
   }

   Mic-Header ::= SEQUENCE {
           tok-id           INTEGER (257), -- shall contain 0101 (hex)
           context-id       Random-Integer,
           int-alg [0]      AlgorithmIdentifier OPTIONAL,
           snd-seq [1]      SeqNum OPTIONAL
   }

   SeqNum ::= SEQUENCE {
           num              INTEGER,
           dir-ind          BOOLEAN
   }

   SPKM-WRAP ::= SEQUENCE {
           wrap-header       Wrap-Header,
           wrap-body         Wrap-Body
   }

   Wrap-Header ::= SEQUENCE {
           tok-id           INTEGER (513), -- shall contain 0201 (hex)
           context-id       Random-Integer,
           int-alg [0]      AlgorithmIdentifier OPTIONAL,
           conf-alg [1]     Conf-Alg OPTIONAL,
           snd-seq [2]      SeqNum OPTIONAL
   }

   Wrap-Body ::= SEQUENCE {
           int-cksum        BIT STRING,
           data             BIT STRING
   }

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   Conf-Alg ::= CHOICE {
           algId [0]        AlgorithmIdentifier,
           null [1]         NULL
   }


   SPKM-DEL ::= SEQUENCE {
           del-header       Del-Header,
           int-cksum        BIT STRING
   }

   Del-Header ::= SEQUENCE {
           tok-id           INTEGER (769), -- shall contain 0301 (hex)
           context-id       Random-Integer,
           int-alg [0]      AlgorithmIdentifier OPTIONAL,
           snd-seq [1]      SeqNum OPTIONAL
   }



-- other types --

   -- from [RFC-1508] -- 

   MechType ::= OBJECT IDENTIFIER

   InitialContextToken ::= [APPLICATION 0] IMPLICIT SEQUENCE {
      thisMech              MechType,
      innerContextToken     SPKMInnerContextToken
   }     -- when thisMech is SPKM-1 or SPKM-2 

   SPKMInnerContextToken ::= CHOICE {   
      req    [0] SPKM-REQ, 
      rep-ti [1] SPKM-REP-TI, 
      rep-it [2] SPKM-REP-IT, 
      error  [3] SPKM-ERROR, 
      mic    [4] SPKM-MIC, 
      wrap   [5] SPKM-WRAP, 
      del    [6] SPKM-DEL 
   }


   -- from [RFC-1510] --

   AuthorizationData ::= SEQUENCE OF SEQUENCE {
     ad-type  INTEGER,
     ad-data  OCTET STRING
   }


-- object identifier assignments --

   md5-DES-CBC OBJECT IDENTIFIER ::= 
      {iso(1) identified-organization(3) dod(6) internet(1) security(5) 
       integrity(3) md5-DES-CBC(1)}

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   sum64-DES-CBC OBJECT IDENTIFIER ::= 
      {iso(1) identified-organization(3) dod(6) internet(1) security(5) 
       integrity(3) sum64-DES-CBC(2)}

   spkm-1 OBJECT IDENTIFIER ::= 
      {iso(1) identified-organization(3) dod(6) internet(1) security(5) 
       mechanisms(5) spkm(1) spkm-1(1)}

   spkm-2 OBJECT IDENTIFIER ::= 
      {iso(1) identified-organization(3) dod(6) internet(1) security(5) 
       mechanisms(5) spkm(1) spkm-2(2)}


END



Appendix B:  Imported Types

This appendix contains, for completeness, the relevant ASN.1 types 
imported from InformationFramework (1993), AuthenticationFramework 
(1993), and [PKCS3].

   AttributeType ::= OBJECT IDENTIFIER
   AttributeValue ::= ANY
   AttributeValueAssertion ::= SEQUENCE {AttributeType,AttributeValue}
   RelativeDistinguishedName ::= SET OF AttributeValueAssertion
      -- note that the 1993 InformationFramework module uses 
      -- different syntax for the above constructs 
   RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
   DistinguishedName ::= RDNSequence
   Name ::= CHOICE {  -- only one for now
           rdnSequence       RDNSequence 
   }

   Certificate ::= SEQUENCE {
           certContents      CertContents,
           algID             AlgorithmIdentifier,
           sig               BIT STRING
   }  -- sig holds the result of applying the signing procedure 
      -- specified in algId to the BER-encoded octet string which 
      -- results from applying the hashing procedure (also specified in 
      -- algId) to the DER-encoded octets of CertContents

   CertContents ::= SEQUENCE {
           version [0]        Version DEFAULT v1,
           serialNumber       CertificateSerialNumber,
           signature          AlgorithmIdentifier,
           issuer             Name,
           validity           Validity,
           subject            Name,
           subjectPublicKeyInfo     SubjectPublicKeyInfo,
           issuerUID [1]      IMPLICIT UID OPTIONAL,  -- used in v2 only
           subjectUID [2]     IMPLICIT UID OPTIONAL   -- used in v2 only
   }

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   Version ::= INTEGER {v1(0), v2(1)}
   CertificateSerialNumber ::= INTEGER
   UID ::= BIT STRING

   Validity ::= SEQUENCE {
           notBefore         UTCTime,
           notAfter          UTCTime
   }

   SubjectPublicKeyInfo ::= SEQUENCE {
           algorithm         AlgorithmIdentifier,
           subjectPublicKey  BIT STRING
   }

   CertificatePair ::= SEQUENCE {
           forward [0]      Certificate OPTIONAL,
           reverse [1]      Certificate OPTIONAL
   }         -- at least one of the pair shall be present

   CertificateList ::= SEQUENCE {
           certListContents        CertListContents,
           algId                   AlgorithmIdentifier,
           sig                     BIT STRING
   }  -- sig holds the result of applying the signing procedure 
      -- specified in algId to the BER-encoded octet string which 
      -- results from applying the hashing procedure (also specified in 
      -- algId) to the DER-encoded octets of CertListContents

   CertListContents ::= SEQUENCE {
           signature               AlgorithmIdentifier,
           issuer                  Name,
           thisUpdate              UTCTime,
           nextUpdate              UTCTime OPTIONAL,
           revokedCertificates     SEQUENCE OF SEQUENCE {
                userCertificate       CertificateSerialNumber,
                revocationDate        UTCTime           } OPTIONAL
   }

   AlgorithmIdentifier ::= SEQUENCE {
           algorithm         OBJECT IDENTIFIER,
           parameter         ANY DEFINED BY algorithm OPTIONAL
   }  -- note that the 1993 AuthenticationFramework module uses 
      -- different syntax for this construct



   --from [PKCS3] (the parameter to be used with dhKeyAgreement) --

   DHParameter ::= SEQUENCE {
     prime              INTEGER,  -- p
     base               INTEGER,  -- g
     privateValueLength INTEGER OPTIONAL
   }



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