Network Working Group                                          M. Eisler
Internet-Draft                                   Network Appliance, Inc.
                                                             N. Williams
                                                  Sun Microsystems, Inc.
                                                            October 2003
                                                               July 2004

               The Channel Conjunction Mechanism (CCM) for GSS
			draft-ietf-nfsv4-ccm-03

Status of this Memo

   This document is an Internet-Draft

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   patent or other IPR claims of which I am aware have been disclosed,
   or will be disclosed, and is any of which I become aware will be
   disclosed, in full conformance accordance with all provisions of Section 10 of RFC2026. RFC 3668.

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ABSTRACT

   This document describes a suite of new mechanisms under the GSS
   [RFC2743].  Some protocols, such as RPCSEC_GSS [RFC2203], use GSS to
   authenticate every message transfer, thereby incurring significant
   overhead due to the costs of cryptographic computation.  While
   hardware-based cryptographic accelerators can mitigate such overhead,
   it is more likely that acceleration will be available for lower layer
   protocols, such as IPsec [RFC2401] than for upper layer protocols
   like RPCSEC_GSS.  CCM can be used as a way to allow GSS mechanism-
   independent upper layer protocols to leverage the data stream
   protections of lower layer protocols, without the inconvenience of
   modifying the upper layer protocol to do so.

TABLE OF CONTENTS

   1.  Conventions Used in this Document . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3
   3.1.  Example Application of CCM  . . . . . . . . . . . . . . . . . 4
   3.2.  A Suite of CCM Mechanisms . . . . . . . . . . . . . . . . . . 5 4
   3.3.  QOPs  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Token Formats . . . . . . . . . . . . . . . . . . . . . . . . . 6 5
   4.1.  Mechanism Object Identifier . . . . . . . . . . . . . . . . . 6 5
   4.2.  Tokens for the CCM-BIND mechanisms  . . . . . . . . . . . . . 6
   4.3.
   4.2.1.  Context Establishment Tokens for CCM-BIND Mechanisms  . . . . 6
   4.3.1.
   4.2.1.1.  Initial Context Token for CCM-BIND  . . . . . . . . . . . . 7
   4.3.2. 6
   4.2.1.2.  Subsequent Context Tokens for CCM-BIND  . . . . . . . . . . 7
   4.3.2.1.  Subsequent Initiator 6
   4.2.2.  Post Context Initialization Token for
             CCM-BIND  . . . . . . . . . . . . . . . . . . . . . . . . 7
   4.3.2.2.  Response Establishment Token for CCM-BIND . . . . . . Formats  . . . . . . . . . 7
   4.4. 8
   4.2.2.1.  MIC Token for CCM-BIND  . . . . . . . . . . . . . . . . . . . 7
   4.5. 9
   4.2.2.2.  Wrap Token for CCM-BIND . . . . . . . . . . . . . . . . . . . 7
   4.6. 9
   4.2.3.  Other Tokens for CCM-BIND . . . . . . . . . . . . . . . . . . 8
   4.7. 9
   4.3.  Tokens for CCM-MIC  . . . . . . . . . . . . . . . . . . . . . 8
   4.8. 9
   4.3.1.  Context Establishment Tokens for CCM-MIC  . . . . . . . . . . 8
   4.8.1. 9
   4.3.1.1.  Initial Context Token for CCM-MIC . . . . . . . . . . . . . 8
   4.8.2. 9
   4.3.1.2.  Subsequent Context Tokens for CCM-MIC . . . . . . . . . . . 9
   4.8.2.1.  11
   4.3.1.2.1.  Subsequent Initiator Context Initialization Token for CCM-MIC  . . . . . . . . . . . . . . . . . . . . . . . . . 9
   4.8.2.2.  11
   4.3.1.2.2.  Response Token for CCM-MIC  . . . . . . . . . . . . . .  10
   4.9.  11
   4.3.2.  MIC Token for CCM-MIC . . . . . . . . . . . . . . . . . . .  12
   4.10.  13
   4.3.3.  Wrap Token for CCM-MIC  . . . . . . . . . . . . . . . . . .  12
   4.11.  13
   4.3.4.  Context Deletion Token  . . . . . . . . . . . . . . . . . .  12
   4.12.  13
   4.3.5.  Exported Context Token  . . . . . . . . . . . . . . . . . .  12
   4.13.  13
   4.3.6.  Other Tokens for CCM-MIC  . . . . . . . . . . . . . . . . .  12  13
   5.  GSS Channel Bindings for Common Secure Channel Protocols  .  Implementation Issues .  12
   5.1.  GSS Channel Bindings for IKEv1 . . . . . . . . . . . . . .  13
   5.2.  GSS Channel Bindings for IKEv2 . . . . .  13
   5.1.  Management of ccmMicCcmBindCtxHandle  . . . . . . . . .  13
   5.3.  GSS Channel Bindings for SSHv2 . .  14
   5.2.  CCM-BIND Versus CCM-MIC . . . . . . . . . . . .  13
   5.4.  GSS Channel Bindings for TLS . . . . . .  14
   5.3.  Initiating CCM-MIC Contexts . . . . . . . . .  13
   6.  Use of Channel Bindings with CCM-BIND and SPKM . . . . . . .  14
   7.  CCM-KEY and Anonymous IPsec . .
   5.4.  Accepting CCM-MIC Contexts  . . . . . . . . . . . . . . .  14
   8.  Other Protocol Issues for CCM .  16
   5.5.  Non-Token Generating GSS-API Routines . . . . . . . . . . .  16
   5.6.  CCM-MIC and GSS_Delete_sec_context()  . . . .  14
   9.  Implementation Issues . . . . . . .  16
   5.7.  GSS Status Codes  . . . . . . . . . . . . .  15
   9.1.  Management of gss_targ_ctx . . . . . . . .  16
   5.7.1.  Status Codes for CCM-BIND . . . . . . . .  15
   9.2.  CCM-BIND Versus CCM-MIC . . . . . . . .  16
   5.7.2.  Status Codes for CCM-MIC  . . . . . . . . . .  15
   9.3.  Initiating CCM-MIC Contexts . . . . . . . . . . . . . . . .  16
   9.4.  Accepting CCM-MIC Contexts  . . . . . . . . . . . . . . . .  17
   9.5.  Non-Token Generating GSS-API Routines . . . . . . . . . . .  17
   9.6.  CCM-MIC and GSS_Delete_sec_context()  . . . . . . .  17
   5.7.2.1.  CCM-MIC: GSS_Accept_sec_context() status codes  . . . .  17
   9.7.  GSS Status Codes  . . . . . . . . . . . . . . . . . . . . .  18
   9.7.1.  Status Codes for CCM-BIND . . . . . . . . . . . . . . . .  18
   9.7.2.  Status Codes for CCM-MIC  . . . . . . . . . . . . . . . .  18
   9.7.2.1.  CCM-MIC: GSS_Accept_sec_context() status codes  . . . .  18
   9.7.2.2.
   5.7.2.2.  CCM-MIC: GSS_Init_sec_context() status codes  . . . . .  19
   9.8.  Channel Bindings on the Target  18
   6.  Advice for NFSv4 Implementors . . . . . . . . . . . . . .  20
   10.  Advice for NFSv4 Implementors . .  19
   7.  Security Considerations . . . . . . . . . . . . .  21
   11.  Man in the Middle Attacks without CCM-KEY . . . . . .  19
   8.  CCM XDR Description . . .  21
   12.  Security Considerations . . . . . . . . . . . . . . . . . .  22
   13.
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . .  25
   14. .  24
   10.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  26
   15.  25
   11.  Normative References . . . . . . . . . . . . . . . . . . . .  27
   16.  25
   12.  Informative References . . . . . . . . . . . . . . . . . . .  28
   17.  26
   13.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  29
   18.  27
   14.  IPR Notices  . . . . . . . . . . . . . . . . . . . . . . . .  29
   19.  27
   15.  Copyright Notice . . . . . . . . . . . . . . . . . . . . . .  29  28

1.  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   The GSS framework provides a general means for authenticating clients
   and servers, as well as providing a general means for encrypting and
   integrity protecting data exchanged during a session.  GSS specifies
   formats for a set of tokens for authentication, integrity, and
   privacy.  The formats consist of a mechanism independent form, and a
   mechanism dependent form.  An example of a set of mechanism dependent
   forms is the Kerberos V5 mechanism definition [RFC1964].

   It is possible for a protocol to use GSS for one time authentication,
   or for per message authentication.  An example of the former is DAFS
   [DAFS].  An example of the latter is RPCSEC_GSS.  Obviously, it is
   more secure to authenticate each message.  On the other hand, it is
   also more expensive.  However, suppose the data stream of the upper
   layer protocol (the layer using GSS) is protected at a lower layer
   protocol from tampering, such as via a cryptographic checksum.  If
   so, it may not be necessary to additionally authenticate each message
   of the upper layer protocol.  Instead, it may suffice to use GSS to
   authenticate at the beginning of the upper layer protocol's session.

   To take advantage of one time authentication, existing consumers of
   GSS that authenticate exclusively on each message have to change.
   One way to change is to modify the protocol that is using GSS.  This
   has disadvantages including, introducing a protocol incompatibility,
   and effectively introducing another authentication paradigm.  Another
   way to change, is the basis of the proposal in this document:  the
   Channel Conjunction Mechanism (CCM).  CCM allows a GSS initiator and
   target to conjunct (bind) a secure session (or channel) at one
   protocol layer with (e.g.  IPsec) a security context of a non-CCM GSS
   mechanism.  Since CCM is yet another mechanism under the GSS, the
   effect is that there are no modifications to the protocol the GSS
   consumer is using.

3.  Overview

   CCM is a "wrapper" mechanism over the set of all other GSS
   mechanisms.  When CCM creates a context, it invokes an underlying
   mechanism to create a child context.  CCM determines the underlying
   mechanism by examining the mechanism object identifier (OID) that it
   is called with.  The prefix will always be the OID of CCM, and the
   suffix will be the OID of the underlying mechanism.  The context
   initiation and acceptance entry points of CCM wrap the resulting the
   context tokens with a CCM header.

   XXX - Note, as currently defined CCM-BIND has a problem with replay
   attacks. Let's suppose the target does not implement a cache

3.1.  Example Application of
   previously accepted context tokens.  An attacker can replay the CCM-
   BIND initial context token, CCM

   Let us use RPCSEC_GSS and NFSv4 [RFC3530] as our example.  Basic
   understanding of the target will accept it. What is
   needed RPCSEC_GSS protocol is proof that assumed.  If an NFSv4
   client uses the initiator actually knows the context session
   key. A future version of this i-d will specify a round trip for CCM-
   BIND (and CCM-MIC) that will force the initiator to sign a nonce from
   the target. See [Kasslin] for more information on the attack.

3.1.  Example Application of CCM

   Let us use RPCSEC_GSS and NFSv4 [RFC3530] as our example.  Basic
   understanding of the RPCSEC_GSS protocol is assumed.  If an NFSv4
   client uses the wrong security mechanism, wrong security mechanism, the server returns the
   NFS4ERR_WRONGSEC error.  The client can then use NFSv4's SECINFO
   operation to ask the server which GSS mechanism to use.

   Let us say the client and server are using Kerberos V5 [RFC1964] to
   secure the traffic.  Suppose the TCP connection NFSv4 uses is secured
   and encrypted with IPsec.  It is therefore not necessary for
   NFSv4/RPCSEC_GSS to use integrity or privacy.  Fortunately,
   RPCSEC_GSS has an authentication mode, whereby only the header of
   each remote procedure call and response is integrity protected.  So,
   this minimizes the overhead somewhat, but there is still the cost of
   the headers being checksummed.  Since IPsec is protecting the
   connection, incurring even that minimal per remote procedure call
   overhead may not be necessary.

   Enter CCM.  The server detects that the connection is protected with
   IPsec.  Via SECINFO, the client is informed that it should use
   CCM/Kerberos V5.  Via the RPCSEC_GSS protocol, the server
   authenticates the end-user on the client with Kerberos V5.  The
   context tokens exchanged over RPCSEC_GSS are wrapped inside CCM
   tokens.

3.2.  A Suite of CCM Mechanisms

   CCM consists of a suite of GSS mechanisms.  CCM-NULL, CCM-ADDR, and
   CCM-KEY bind  GSS can support a concept
   call channel bindings, where a GSS mechanism context is bound to a
   secure channel via GSS
   channel bindings (see section 1.1.6 of RFC2743).  As noted in RFC2743,
   the purpose of channel bindings are is to limit the scope within which an
   intercepted GSS context token can be used by an attacker.  CCM-KEY requires the use of  Non-null
   channel bindings that are can be derived from the secure channel's encryption keys.  CCM-ADDR requires
   the use of channel bindings that are
   keys or derived from the network addresses associated with the secure
   channel. For environments where it is not feasible to use key-based
   channel bindings (e.g., the programming interfaces to get them are
   not available) or address-based channel bindings (e.g., the secure
   channel may be constructed over a path that requires the use of
   Network Address Translation), CCM-NULL is
   also defined.  CCM-NULL requires
   the use of null channel bindings.

   Non-null channel bindings are highly dependent on the underlying
   channel's characteristics. For example with IPsec, the channel
   bindings for manual keys, IKEv1, and IKEv2 would be different from
   each other.  Non-null channel bindings are also underspecified in the
   current GSS specifications.  Thus this document does not define a
   key-based or address-based form for CCM.

   As discussed later in this document CCM-MIC exists for the purpose of
   optimizing the use of CCM.

   Implementations that claim compliance with this document are REQUIRED
   to implement CCM-KEY and CCM-MIC. CCM-NULL and CCM-ADDR
   implementation are OPTIONAL. CCM-MIC. Specifications that make normative
   references to CCM are free to mandate any subset of the suite CCM
   mechanisms.

   Because the GSS channel bindings to IPsec [RFC2401, RFC2409, IKEv2]
   have not been previously defined, and to ensure the usefulness of
   CCM, they are defined in this document.

   Also, the SPKM (1, 2 and 3) [RFC2025, RFC2847] mechanism is not clear
   on how channel bindings work with SPKM; a simple clarification is
   provided.

   CCM-MIC is intended to reduce the instances of full GSS context
   establishment to a per- {initiator principal, target} tuple.  CCM-MIC
   is used to establish a new context by proving that the initiator and
   target both have a previously established, unexpired GSS context; the
   proof is accomplished by exchanging MICs made with the previously
   established GSS context.  The CCM-MIC context creation entry points
   utilize the CCM_REAL_QOP (discussed later Overview in the next section) in the value
   to generate and verify the MICs.  The type of channel bindings
   used when initiating CCM-MIC contexts MUST match that used when
   creating the previously established context.

3.3.  QOPs

   The CCM mechanisms provide two QOPs: the default QOP (0) that amounts
   to no protection, and a QOP (CCM_REAL_QOP, defined as value 1) that
   maps to the default QOP of the underlying GSS mechanism.  When
   qop_req is 0:

   *    The MIC
   tokens token for CCM are is always a string single octet, of 4 octets, each zero filled.  When
   qop_req is 0, the value zero.

   *    The wrap output token for CCM is equal to the concatenation of
        the input token and a single octet (which is equal to zero).

4.  Token Formats

   This section discusses the protocol visible tokens that GSS consumers
   exchange when using CCM.

4.1.  Mechanism Object Identifier

   There are two classes of Mechanism object identifiers Object Identifiers (OIDs) for CCM.
   The first class consists of the channel binding specific OIDs, and
   will be referred to as the CCM-BIND mechanisms:

        {iso(1)identified-organization(3)dod(6)internet(1)security(5)
        mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-null(1)}

        {iso(1)identified-organization(3)dod(6)internet(1)security(5)
        mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-addr(2)}

        {iso(1)identified-organization(3)dod(6)internet(1)security(5)
        mechanisms(5)ccm-family(TBD1)ccm-bind(1)ccm-key(3)} mechanisms. This document defines
   one such mechanism:

        { iso(1) identified-organization(3) dod(6) internet(1)
        security(5) mechanisms(5) ccm-family(TBD1) ccm-bind(1) ccm-
        null(1) }

   The above three object identifiers are identifier is not a complete mechanism OIDs.
   Complete CCM OID.  A
   complete mechanism OIDs MUST OID would consist of one of the above OIDs OID as prefix,
   followed by a real mechanism OID, such as that of Kerberos V5 as
   defined in [RFC1964].  The

   Future extensions to CCM may add non-null channel binding mechanisms
   under the ccm-bind(1) node in the OID space.

   The second class consists of a single OID for the CCM-MIC mechanism.

        {iso(1)identified-organization(3)dod(6)internet(1)security(5)
        mechanisms(5)ccm-family(TBD1)ccm-mic(2)}

        { iso(1) identified-organization(3) dod(6) internet(1)
        security(5) mechanisms(5) ccm-family(TBD1) ccm-mic(2) }

   The CCM-MIC OID is a complete mechanism OIDs, and is not a prefix.

   GSS defines the generic part of a token in ASN.1 encoding.  GSS does
   not require ASN.1 for the mechanism specific part of a token.

4.2.  Tokens for the CCM-BIND mechanisms

4.3.

4.2.1.  Context Establishment Tokens for CCM-BIND Mechanisms

   The CCM-BIND context establishment tokens are simple wrappers around
   a real GSS mechanism's tokens.  The CCM-BIND mechanisms can use the same
   number one
   more context token exchanges as required by they exchange than the underlying real mechanism.

4.3.1.  This
   is so that that target can be protected from a replay attack in the
   event the real mechanism is does not have replay protection. See
   [Kasslin] for more information on the attack.

4.2.1.1.  Initial Context Token for CCM-BIND

   GSS requires that the initial context token from the initiator to the
   target use the format as described in section 3.1 of RFC2743.  The
   format consists of a mechanism independent prefix, and a mechanism
   dependent suffix.  The mechanism independent token includes the
   MechType field.  The MechType MUST be equal to the OID of CCM-NULL,
   CCM-ADDR, or CCM-KEY. CCM-NULL.
   The mechanism dependent portion of the Initial Context Token is
   always equal to the full InitialContextToken as returned by the
   underlying real mechanism.  This will include yet another MechType,
   which will have the underlying mechanism's OID.

4.3.2.

4.2.1.2.  Subsequent Context Tokens for CCM-BIND

   A subsequent context token can be any subsequent context token from
   the initiator context initialization entry point, or any response
   context from the target's context acceptance entry point.  The GSS
   specification [RFC2743] does not prescribe any format.

4.3.2.1.  Subsequent Initiator Context Initialization Token for CCM-BIND

   A

   The form of a SubsequentContextToken for a CCM-BIND mechanism mechanism, is equal to that
   returned by
   always encoded in XDR [RFC1832]. There is a form for the initiator's context initialization routine of the
   underlying real mechanism.

4.3.2.2.  Response Token for CCM-BIND

   The response token
   target produces for the initiator, and a CCM-BIND mechanism is equal to that returned
   by form for the target's context acceptance routine of the underlying real
   mechanism.

4.4.  MIC Token
   initiator produces for CCM-BIND

   This token corresponds to the PerMsgToken type as defined in section
   3.1 target. These forms are:

      enum ccmVerifyState {
              CCM_UNVERIFIED = 0,
              CCM_VERIFY_FAILED = 1,
              CCM_VERIFIED = 2
      };

      struct ccmBindSubCtxTknTargToInit {
              ccmVerifyState ccmBindStatus;
              opaque ccmBindRealToken<>;
              opaque ccmBindNonce<>;
      };

      struct ccmBindSubCtxTknInitToTarg {
              opaque ccmBindRealToken<>;
              opaque ccmBindMic<>;
      };

   If of RFC2743.  When the qop_req is the default QOP (0), then non-zero length, the
   PerMsgToken is a quantity zero bits ccmBindRealToken<> field in length.  A programming API
   that calls GSS_GetMIC() with the default QOP will thus produce an
   octet string each of zero length.

   When the qop_req is CCM_REAL_QOP (1), then PerMsgToken
   above two data types is whatever always that generated by the underlying real mechanism returns from GSS_GetMIC() when passed
   the default QOP value (0).

4.5.  Wrap Token for
   that CCM-BIND

   This token corresponds to the SealedMessage is operating over.

   The ccmBindSubCtxTknTargToInit type as defined in
   section 3.1 of RFC2743.  When the qop_req is the default QOP (0),
   then the SealedMessage token is equal the target returns
   to the unmodified input to
   GSS_Wrap().

   When the qop_req initiator. The ccmBindStatus is CCM_REAL_QOP (1), then SealedMessage usually set to CCM_UNVERIFIED,
   except as described otherwise.  The ccmBindRealToken field is whatever always
   equal to the output of the underlying real mechanism returns from GSS_Wrap(), when passed mechanism's GSS_Accept_sec_context()
   entry point. The ccmBindNonce field will always be a zero length
   until the default QOP value (0).

4.6.  Other Tokens for real mechanism's GSS_Accept_sec_context() routine returns
   GSS_S_COMPLETE. If CCM-BIND

   All other tokens are what knows that the real underlying mechanism returns as a
   token.

4.7.  Tokens for CCM-MIC

4.8.  Context Establishment Tokens for CCM-MIC

4.8.1.  Initial Context Token for CCM-MIC

   The initial has
   replay protection during context token from the initiator establishment, then it MAY set
   ccmBindStatus to CCM_VERIFIED, and set ccmBindNonce to a zero length
   value. In this case, CCM-BIND returns GSS_S_COMPLETE to the target uses the
   format as described in section 3.1 of RFC2743.  The format consists caller of a
   its GSS_Accept_sec_context() entry point.

   If CCM-BIND does not know if the underlying mechanism independent prefix, has replay
   protection, or it knows it does not have replay protection, then
   ccmBindStatus MUST be CCM_UNVERIFIED, and a mechanism dependent suffix.
   The mechanism independent token includes the MechType field.  The
   MechType ccmBindNonce MUST be equal a
   non-zero length randomly generated string, or a pseudo-random string
   generated such that it is unlikely the target will generate a
   duplicate in the future. While the underlying real mechanism returned
   GSS_S_COMPLETE, CCM-BIND returns GSS_S_CONTINUE_NEEDED to the OID caller
   of CCM-MIC.  RFC2743 refers its GSS_Accept_sec_context() entry point.

   When the initiator receives a ccmBindSubCtxTknTargToInit token, it
   will call the real mechanism's GSS_Init_sec_context() entry point to
   process the ccmBindRealToken<> value. If the GSS_Init_sec_context()
   entry point of the real mechanism dependent token as returns GSS_S_CONTINUED needed,
   then the innerContextToken.  This is CCM-BIND initiator will set the
   CCM-MIC specific token and is XDR [RFC1832] encoded as follows, using
   XDR description language:

      typedef struct {
              unsigned int ctx_sh_number;
              unsigned int rand;
      } CCM_nonce_t;

      typedef struct {
              CCM_nonce_t nonce;
              opaque gss_targ_ctx[20];
              opaque chan_bindings<>;
      } CCM_MIC_unwrapped_init_token_t;

      /*
       * The result of CCM_MIC_unwrapped_init_token_t after
       * Invoking GSS_GetMIC() on it.  qop_req is CCM_REAL_QOP, and
       * conf_flag is FALSE.
       */
      typedef opaque CCM_MIC_wrapped_init_token_t<>;

   Once an initiator has established an initial CCM context with a
   target via ccmBindMic field to a CCM-BIND mechanism, zero
   length string.  If GSS_S_COMPLETE was returned, then normally the additional contexts can
   ccmBindStatus will be
   established via CCM_UNVERIFIED. If so, then the CCM-MIC mechanism.  The disadvantage expectation of re-
   establishing additional contexts via
   the CCM-BIND route initiator is that the
   underlying mechanism context set up must ccmBindNonce field from the target
   MUST be repeated, which can non-zero length. The initiator will set the ccmBindMic field
   to the output of GSS_GetMIC() of the ccmBindNonce field, and
   GSS_S_CONTINUED will be
   expensive.  Whereas, returned to the CCM-MIC mechanism route merely requires that caller of CCM-BIND's
   GSS_Init_sec_context() entry point.  If  GSS_GetMIC(), fails, then
   the first CCM context's underlying mechanism context error should be available returned to
   produce an integrity checksum.  The initial context token for CCM-MIC the caller of CCM-BIND's
   GSS_Init_sec_context() entry point, and null output token. If the
   error from GSS_GetMIC() is computed not among the set permitted to be returned
   from GSS_Init_sec_context(), then the error should be mapped as
   follows.

   *    The gss_targ_ctx is computed as GSS_S_CONTEXT_EXPIRED and GSS_S_BAD_QOP should be mapped to
   GSS_S_FAILURE.

   If the SHA-1 checksum of initiator finds that the
        concatenation of SHA-1 [FIPS] checksums of value the context tokens
        exchanged by target returned for
   ccmBindStatus is CCM_VERIFIED, then the CCM-BIND mechanism in context is
   established, and GSS_S_COMPLETE is returned to the order in which they
        were processed. For example, caller of
   CCM_BIND's GSS_Init_sec_context() entry point.

   When the context handle identifier for target receives a
        CCM-KEY context exchange over ccmBindSubCtxTknInitToTarg with a Kerberos V5 context exchange
        would be:  SHA-1( { SHA-1(CCM-KEY's initiator's token), SHA-
        1(CCM-KEY's target's token)) }.  Since the SHA-1 standard
        mandates a 160 bit output, (20 octets), gss_targ_ctx
   ccmBindMic<> value that is a fixed non-zero in length, 20 octet string.

   *    The subfield nonce.rand is set a random or pseudo random value.
        It is provided so as to ensure more variability of the the mic
        that GSS it will calculate when CCM_MIC_unwrapped_init_token_t is
        GSS_Wrap()ed into CCM_MIC_wrapped_init_token_t.

   * call
   GSS_VerifyMIC(). The subfield nonce.ctx_sh_number is message value will be the identifier of ccmBindNonce value the CCM-
        MIC context relative to
   target generated in the CCM-BIND previous context (as identified by
        gss_targ_ctx) that the initiator is assigning. exchange. The value for
        ctx_sh_number is selected by per_msg_token
   argument will be the initiator such ccmBindMic value. The context_handle argument
   will be that it is
        larger than any previous ctx_sh_number for the given
        gss_targ_ctx.  This way, the target need only keep track of the
        largest ctx_sh_number received.  Once ctx_sh_number has reached established context of the maximum underlying real
   mechanism.  If GSS_VerifyMIC() returns GSS_S_COMPLETE, then
   ccmBindStatus will be set to CCM_VERIFIED. Otherwise, ccmBindStatus
   will be set to CCM_VERIFY_FAILED. The return value for an unsigned 32 bit integer, the given
        gss_targ_ctx can no longer of GSS_VerifyMIC()
   will be used.

   *    Once returned to the above fields caller of CCM-BIND's GSS_Accept_sec_context()
   entry point, except for those errors are calculated, GSS_Wrap() is performed on not in the CCM_MIC_unwrapped_init_token_t value, set permitted by
   GSS_Accept_sec_context.  GSS_S_UNSEQ_TOKEN and GSS_S_GAP_TOKEN should
   be mapped to produce GSS_S_OLD_TOKEN.  GSS_S_CONTEXT_EXPIRED should be mapped
   to GSS_S_FAILURE.

   When the initiator receives a
        CCM_MIC_wrapped_init_token_t value that becomes token with ccmBindStatus set to
   CCM_VERIFIED, it marks the initial CCM-BIND context token as established, and
   returns GSS_S_COMPLETE to send the caller of its GSS_Init_sec_context()
   entry point. If ccmBindStatus was set to CCM_DENIED, it returns
   GSS_S_FAILURE to the target.

4.8.2.  Subsequent caller of its  GSS_Init_sec_context() entry
   point.

4.2.2.  Post Context Tokens Establishment Token Formats

4.2.2.1.  MIC Token for CCM-MIC

   A subsequent context CCM-BIND

   This token can be any subsequent context token from
   the initiator context initialization entry point, or any response
   context from the target's context acceptance entry point.  The GSS
   specification [RFC2743] does not prescribe any format.

4.8.2.1.  Subsequent Initiator Context Initialization Token for CCM-MIC

   As CCM-MIC has only one round trip for context token exchange, there
   are no subsequent initiator context tokens.

4.8.2.2.  Response Token for CCM-MIC

   The CCM response token, in XDR encoding is:

      typedef enum {
              CCM_OK = 0,

              /*
               * gss_targ_ctx was malformed.
               */
              CCM_ERR_HANDLE_MALFORMED = 1,

              /*
               * GSS context corresponding to gss_targ_ctx expired.
               */

              CCM_ERR_HANDLE_EXPIRED = 2,

              /*
               * gss_targ_ctx was not found.
               */
              CCM_ERR_HANDLE_NOT_FOUND = 3,

              /*
               * The ctx_sh_number has already been received
               * by the target.  Or the maximum ctx_sh_number has
               * been previously received.
               */
              CCM_ERR_TKN_REPLAY = 4,

              /*
               * Channel binding type mismatch between CCM-BIND context
               * and the CCM-MIC initial context.
               */
              CCM_ERR_CHAN_MISMATCH = 5,

              /*
               * The GSS_Unwrap() failed on initial context token
               */
              CCM_ERR_TKN_UNWRAP = 6,

              /*
               * The GSS_GetMIC() called failed on the target().
               */

              CCM_ERR_TKN_GET_MIC = 7,
              /*
               * The GSS_Wrap() failed on the initiator.  Not reported
               * by target.
               */

              CCM_ERR_TKN_WRAP = 8,

              /*
               * The GSS_VerifyMIC() failed on the initiator.  Not
               * reported by target.
               */

              CCM_ERR_TKN_VER_MIC = 9

      } CCM_MIC_status_t;

      /*
       * GSS errors returned by the underlying mechanism
       */
      typedef struct {
              unsigned int gss_major;
              unsigned int gss_minor;
      } CCM_MIC_real_gss_err_t;

      /*
       * The response context token for CCM-MIC.
       */
      typedef union switch (CCM_MIC_status status) {
              case CCM_OK:
                      opaque mic_init_tkn<>;
              case CCM_ERR_TKN_UNWRAP:
              case CCM_ERR_TKN_GET_MIC:
                      CCM_real_gss_err_t gss_err;
              default:
                      void;
      } CCM_MIC_resp_t;

   If a value of the status field is CCM_OK, then the CCM-MIC context
   has been established on the target.  The field mic_init_tkn is equal
   to the output of GSS_GetMIC() (qop_req is CCM_REAL_QOP (1)) on the
   entire and original token that came from the initiator.  In other
   words, the input_token value to GSS_Accept_sec_context().  This is
   necessary because the inner token from the initiator is wrapped with
   GSS_Wrap(), and thus contains a MIC.  If we performed GSS_GetMIC() on
   the unwrapped inner token, then for some underlying mechanisms, we
   would end up with a mic_init_tkn in the response token equal to what
   was embedded in the request token.

   If the status field is CCM_ERR_TKN_UNWRAP or CCM_ERR_TKN_GET_MIC,
   then gss_err.gss_major and gss_err.minor are set to the major and
   minor GSS statuses as returned by GSS_Unwrap() or GSS_GetMIC().  The
   values for the gss_major field are as defined in [RFC2744].  The
   values for the gss_minor field are both mechanism dependent and
   mechanism implemented dependent.  They are nonetheless potentially
   useful as debugging aids.

4.9.  MIC Token for CCM-MIC

   The MIC token for CCM-MIC is the same as the MIC token for CCM-BIND.

4.10.  Wrap Token for CCM-MIC

   The wrap token for CCM-MIC is the same as the wrap token for CCM-
   BIND.

4.11.  Context Deletion Token

   The context deletion token for CCM-MIC is a zero length token.

4.12.  Exported Context Token

   The Exported context token for CCM-MIC is implementation defined.

4.13.  Other Tokens for CCM-MIC

   All other tokens are the same as corresponding tokens for CCM-BIND.

5.  GSS Channel Bindings for Common Secure Channel Protocols

   For CCM-KEY to be useful and secure, CCM-KEY MUST be used in
   conjunction with channel bindings to bind GSS authentication at the
   application layer to a lower layer in the network that provides
   cryptographic session protection.

   To date only network address type channel bindings have been defined
   for GSS [RFC2743].  But the GSS also allows for channel bindings of
   "transformations of encryption keys" [RFC2743].  The actual generic
   representation of channel bindings is defined in the C-Bindings of
   the GSS-API [RFC2744].

   Modern secure transports generally define some quantity or quantities
   which are either derived from the session keys (or from key exchange
   material) or which are securely exchanged in such a way that both
   peers of any one connection or association can arrive at the same
   derived quantities, while a man-in-the-middle cannot make these
   quantities match for both peers.  Signatures of these quantities can
   be exchanged to prove that there is no man-in-the-middle (because a
   man-in-the-middle cannot cause them to be the same for both peers).
   These quantities correspond to what the GSS terms "transformations of
   encryption keys" that are referred to in [RFC2743].

   Where a secure transport clearly defines a session identifier
   securely derived from session keys or key exchange material, that
   identifier MUST be used as the GSS channel bindings data when CCM-
   BIND is used to bind GSS to that transport.

   This section defines four forms of "transformations of encryption
   keys," one for IKEv1, one for IKEv2, one for SSHv2 and one for TLS.
   All four forms are corresponds to be used as the value of the "application_data"
   field of the gss_channel_bindings_struct PerMsgToken type as defined in [RFC2744].

5.1.  GSS Channel Bindings for IKEv1

   IKEv1 does not define a single value which can be used -- by both the
   IPsec initiator and responder of an IPsec SA -- to identify a given
   SA.  IKEv1 does, however, define public values derived from the IKEv1
   key exchange: 'HASH_I' and 'HASH_R'.

   For IKEv1, the GSS channel bindings data to use with CCM-KEY consists
   of the concatenation of HASH_I and HASH_R octet string values, in
   that order, from the underlying IPsec session being bound to [IKEv1].

5.2.  GSS Channel Bindings for IKEv2

   IKEv2 peers assign and exchange 8-octet "Security Parameters Index"
   (SPI) values, such that a pair in section
   3.1 of SPIs suffices to uniquely identify
   a given IPsec security association.

   For IKEv2 RFC2743.  When the GSS channel bindings data to use with CCM-KEY qop_req is simply the concatenation of default QOP (0), then the SPIi and SPIr values,
   PerMsgToken is one octet in that order, which
   identify the IPsec SA being bound to.

5.3.  GSS Channel Bindings for SSHv2

   SSHv2 defines length with a session ID derived from the initial key exchange of
   an SSHv2 connection; this value of zero.  When the
   qop_req is not secret and CCM_REAL_QOP (1), then PerMsgToken is whatever the same for
   both the client and
   underlying real mechanism returns from GSS_GetMIC() when passed the server
   default QOP value (0).

4.2.2.2.  Wrap Token for any given connection.

   For SSHv2 CCM-BIND

   This token corresponds to the GSS channel bindings data for use with CCM-KEY consists SealedMessage type as defined in
   section 3.1 of RFC2743.  When the SSHv2 session ID.

5.4.  GSS Channel Bindings for TLS

   XXX - This section qop_req is To Be Defined.

6.  Use of Channel Bindings with CCM-BIND and SPKM

   Whereas the Kerberos V5 mechanism specification [RFC1964] default QOP (0),
   then the SealedMessage token is quite
   detailed with respect equal to the use unmodified input to
   GSS_Wrap() concatenated with a single octet with a value of GSS channel bindings, zero.

   When the same qop_req is
   not true CCM_REAL_QOP (1), then SealedMessage is whatever
   the underlying real mechanism returns from GSS_Wrap(), when passed
   the default QOP value (0).

4.2.3.  Other Tokens for SPKM, which merely provides CCM-BIND

   All other tokens are what the real underlying mechanism returns as a field named "channelId"
   token.

4.3.  Tokens for passing channel bindings data, as octet strings, CCM-MIC

4.3.1.  Context Establishment Tokens for CCM-MIC

4.3.1.1.  Initial Context Token for CCM-MIC

   The initial context token from initiators the initiator to acceptors.  No interpretation is given in RFC2025 for the value target uses the
   format as described in section 3.1 of RFC2743.  The format consists
   of a mechanism independent prefix, and a mechanism dependent suffix.
   The mechanism independent token includes the channelId MechType field.  Therefore SPKM requires some clarification to
   be usable with channel bindings and CCM-KEY:  The channelId field of
   SPKM Context-Data ASN.1 structure
   MechType MUST be set equal to the checksum OID of CCM-MIC.  RFC2743 refers to the
   channel bindings data that is defined for the Kerberos V5
   mechanism
   [RFC1964], using SHA-1 instead of MD5 dependent token as the hash algorithm.

   [Note: innerContextToken.  This checksum can be computed independently of the GSS
   language bindings used by the application, even though RFC1964
   references the C-Bindings of the GSS-API [RFC2744] in the
   construction of this checksum (read the RFC1964 text carefully).]

7.  CCM-KEY and Anonymous IPsec

   For sites that do not use IPsec, but use Kerberos V5, SPKM, or
   LIPKEY, deploying IPsec, a PKI infrastructure and certificates for
   use with IKE may prove quite difficult to deploy just for secure
   application (e.g., NFS) performance improvements.  Such sites could
   avoid the need to deploy a PKI and certificates to all clients and
   server by using "anonymous IPsec" for is the application (e.g., NFS
   with/ RPCSEC_GSS)
   CCM-MIC specific token and CCM-KEY.

   Though there is no such thing XDR [RFC1832] encoded as "anonymous IPsec," the effect can be
   achieved by using self-signed certificates.

   By follows, using anonymous IPsec with the application and CCM-KEY, the full
   benefit
   XDR description language:

      struct ccmMicUnWrappedInitToken {
              unsigned int ctxMicIndex;
              opaque ccmMicCcmBindCtxHandle[20];
              opaque ccmMicNonce<>;
      };

      /*
       * The result of offloading session cryptography from upper layer protocol
   layer to the IP layer can be had without having to deploy an
   authentication infrastructure for IPsec.

8.  Other Protocol Issues for CCM

   CCM-BIND ccmMicUnWrappedInitToken after
       * Invoking GSS_GetMIC() on it.  qop_req is a trivial mechanism, CCM_REAL_QOP, and normally will return the same
   major status code as the underlying real mechanism, including
   GSS_S_COMPLETE as returned by GSS_Init_sec_context().  However, the
   first time GSS_Init_sec_context
       * conf_flag is called on FALSE.
       */
      typedef opaque ccmBindMicWrappedInitToken<>;

   Once an initiator has established an initial CCM context with a
   target via a CCM-BIND mechanism, if
   the underlying real mechanism returns GSS_S_COMPLETE, CCM-BIND's
   GSS_Init_sec_context() entry point MUST return GSS_S_CONTINUE_NEEDED
   to the caller.  This way, the initiator will receive another context
   token from additional contexts can be
   established via the target, even if CCM-MIC mechanism.  The disadvantage of
   establishing additional contexts via the CCM-BIND route is that the
   underlying real mechanism context set up is done.  The CCM-BIND initiator will need to record state
   that indicates must be repeated, which can be
   expensive.  Whereas, the CCM-MIC mechanism route merely requires that
   the first CCM context's underlying mechanism has reached a completely
   established state (and so context be available to
   produce an integrity checksum.  The initial context token for CCM-MIC
   is computed as follows.

   *    The ccmMicCcmBindCtxHandle is uninterested computed as the SHA-1 checksum of
        the concatenation of SHA-1 [FIPS] checksums of the context
        tokens exchanged by the CCM-BIND mechanism in any token the target
   returns).  This way, order in which
        they were processed. For example, the context handle identifier
        for a CCM-NULL context exchange over a Kerberos V5 context
        exchange would be:
           SHA-1( {
                SHA-1(CCM-NULL's first initiator can process every token produced
   by token),
                SHA-1(CCM-NULL's first initial target token),
                SHA-1(CCM-NULL's final initiator token),
                SHA-1(CCM-NULL's final target token)
           } )
        Since the target's GSS_Accept_sec_context() routine and so calculate
   gss_targ_ctx  value that matches SHA-1 standard mandates a 160 bit output, (20 octets),
        ccmMicCcmBindCtxHandle is a fixed length, 20 octet string.

   *    The field ccmMicNonce is set a random or pseudo random value. It
        MUST have length greater than or equal to that of ccmBindNonce
        value the target.

9.  Implementation Issues

   The "over target gave the wire" aspects of CCM have been completely specified.
   However, GSS server when the CCM-BIND context was
        established It is usually implemented as an Application Programming
   Interface (the GSS-API), and security mechanisms are often
   implemented provided so as modules that are plugged into to ensure more variability of
        the GSS-API.  It the mic that GSS will calculate when
        ccmMicUnWrappedInitToken is
   useful to discuss implementation issues and workable resolutions. GSS_Wrap()ed into
        ccmBindMicWrappedInitToken.

   *    The reader field ctxMicIndex is cautioned the identifier of the CCM-MIC context
        relative to the CCM-BIND context (as identified by
        ccmMicCcmBindCtxHandle) that the authors have not implemented CCM, so
   what follows initiator is at best a series of educated guesses.

9.1.  Management of gss_targ_ctx assigning.  The gss_targ_ctx
        value for ctxMicIndex is computed selected by the initiator and target based
   on SHA-1 computations of the CCM-BIND context tokens.  There such that it
        is a
   space/time trade off between larger than any previous ctxMicIndex for the initiator and target storing given
        ccmMicCcmBindCtxHandle.  This way, the
   sequence target need only keep
        track of context tokens until needed by CCM-BIND, versus computing the SHA-1 checksums and then disposing of largest ctxMicIndex received.  Once ctxMicIndex has
        reached the context tokens when
   CCM-BIND maximum value for an unsigned 32 bit integer, the
        given ccmMicCcmBindCtxHandle can no longer needs them.  If it is likely there will be CCM-MIC
   contexts created for used.

   *    Once the CCM-BIND context, and if above fields are calculated, GSS_Wrap() is performed on
        the sequence of
   context tokens requires more space than a 20 octet SHA-1 ccmMicUnWrappedInitToken value, then to produce a
        ccmBindMicWrappedInitToken value that becomes the tradeoff is obvious.

   Since initial
        context token to send to the bit space of all possible sequences of CCM-BIND target.

4.3.1.2.  Subsequent Context Tokens for CCM-MIC

   A subsequent context
   tokens is larger than token can be any subsequent context token from
   the 160 bit space of possible SHA-1 checksums,
   in theory two initiator context initialization entry point, or more different CCM-BIND contexts will produce
   produce any response
   context from the same SHA-1 context, and thus target's context acceptance entry point.  The GSS
   specification [RFC2743] does not prescribe any format.

4.3.1.2.1.  Subsequent Initiator Context Token for CCM-MIC

   As CCM-MIC has only one round trip for context
   initiation, token exchange, there will be ambiguity as to which CCM-BIND context the
   are no subsequent initiator is binding to. context tokens.

4.3.1.2.2.  Response Token for CCM-MIC

   The target can resolve this ambiguity by
   attempting CCM response token, in XDR encoding is:

      enum ccmMicStatus {
              CCM_OK = 0,

              /*
               * ccmMicCcmBindCtxHandle was malformed.
               */
              CCM_ERR_HANDLE_MALFORMED = 1,

              /*
               * The GSS context corresponding to unwrap
               * ccmMicCcmBindCtxHandle has expired.
               */

              CCM_ERR_HANDLE_EXPIRED = 2,

              /*
               * ccmMicCcmBindCtxHandle was not found.
               */
              CCM_ERR_HANDLE_NOT_FOUND = 3,

              /*
               * The ctxMicIndex has already been received
               * by the inner target.  Or the maximum ctxMicIndex has
               * been previously received.
               */
              CCM_ERR_TKN_REPLAY = 4,

              /*
               * Channel binding type mismatch between CCM-BIND context token from
               * and the CCM-MIC
   initiator for each matching CCM-BIND initial context.  In theory no more than
   one
               */
              CCM_ERR_CHAN_MISMATCH = 5,

              /*
               * The GSS_Unwrap() attempt for each matching CCM-BIND failed on initial context will
   succeed.  If multiple succeed, then clearly token
               */
              CCM_ERR_TKN_UNWRAP = 6,

              /*
               * The GSS_GetMIC() called failed on the target().
               */

              CCM_ERR_TKN_GET_MIC = 7,

              /*
               * The GSS_Wrap() failed on the initiator.  Not reported
               * by target.
               */

              CCM_ERR_TKN_WRAP = 8,

              /*
               * The GSS_VerifyMIC() failed on the initiator.  Not
               * reported by target.
               */

              CCM_ERR_TKN_VER_MIC = 9

      };

      /*
       * GSS errors returned by the underlying mechanism
   is doing poor job at generating "unique" session keys.  CCM
   implementations that detect this SHOULD log it so that
       */
      struct ccmMicRealGssErr {
              unsigned int ccmMicGssMajor;
              unsigned int ccmMicGssMinor;
      };

      /*
       * The response context token for CCM-MIC.
       */
      union ccmMicResp switch (ccmMicStatus status) {
              case CCM_OK:
                      opaque ccmMicRespInitTkn<>;
              case CCM_ERR_TKN_UNWRAP:
              case CCM_ERR_TKN_GET_MIC:
                      ccmMicRealGssErr ccmMicGssErr;
              default:
                      void;
      };

   If a value of the problem in status field is CCM_OK, then the underlying mechanism can be discovered and fixed.

9.2.  CCM-BIND Versus CCM-MIC

   The first time a CCM context is needed between an principal
   has been established on the
   initiator and a principal on target.  The field ccmMicRespInitTkn is
   equal to the target, output of GSS_GetMIC() (qop_req is CCM_REAL_QOP (1)) on
   the initiator has no choice
   but to create an underlying mechanism context via a CCM-BIND context entire and first token exchange.  Once that is done, subsequent CCM contexts between came from the initiator and target can be created via CCM-MIC.  CCM-MIC context
   establishment is better because no more than one round trip initiator.  In other
   words, the first input_token value to GSS_Accept_sec_context().  This
   is necessary to establish a CCM context, and because the overhead of inner token from the
   establishing a real, underlying mechanism context is avoided.

9.3.  Initiating CCM-MIC Contexts

   The key issue initiator is how to associate an CCM-BIND established security
   context wrapped
   with GSS_Wrap(), and thus contains a new CCM-MIC context, There no existing interfaces
   defined in MIC.  If we performed
   GSS_GetMIC() on the GSS-API unwrapped inner token, then for associating one GSS context some underlying
   mechanisms, we would end up with another.
   This then is a ccmMicRespInitTkn in the key issue for implementations of CCM-MIC.

   We will assume that GSS-API implementation is response
   token equal to what was embedded in the C programming
   language and therefore request token.

   If the GSS-API C bindings [RFC2744] are being
   used.  The CCM mechanism implementation will have a table that maps
   gss_targ_ctx values to gss_ctx_id_t values (see section 5.19 of
   [RFC2744]).  The latter status field is CCM_ERR_TKN_UNWRAP or CCM_ERR_TKN_GET_MIC,
   then ccmMicGssErr.ccmMicGssMajor and ccmMicGssErr.ccmMicGssMinor are GSS-API context handles
   set to the major and minor GSS statuses as returned by
   gss_init_sec_context(). GSS_Unwrap()
   or GSS_GetMIC().  The former are values for the context handles ccmMicGssMajor field are as
   returned
   defined in a response token from [RFC2744].  The values for the CCM target.  In addition, each
   CCM context has a reference to its underlying ccmMicGssMinor field are
   both mechanism context.

   Let us suppose the application decides it will use CCM-MIC.  CCM-MIC
   has a well known dependent and mechanism OID which implementation dependent.
   They are nonetheless potentially useful as debugging aids.

4.3.2.  MIC Token for CCM-MIC

   The MIC token for CCM-MIC is the application can check for. same as the MIC token for CCM-BIND.

4.3.3.  Wrap Token for CCM-MIC

   The point where wrap token for CCM-MIC is the initiator calls GSS_Init_sec_context(), same as the wrap token for CCM-
   BIND.

4.3.4.  Context Deletion Token

   The context deletion token for CCM-MIC is a
   logical place to associate an existing CCM-BIND zero length token.

4.3.5.  Exported Context Token

   The Exported context with a new token for CCM-MIC context.  Here is where special implementation defined.

4.3.6.  Other Tokens for CCM-MIC

   All other tokens are the same as corresponding tokens for CCM-BIND.

5.  Implementation Issues

   The "over the wire" aspects of CCM handling have been completely specified.
   However, GSS is necessary in
   order to associate a usually implemented as an Application Programming
   Interface (the GSS-API), and security context with a CCM context.  We mechanisms are often
   implemented as modules that are plugged into the GSS-API.  It is
   useful to discuss
   several approaches.

   1. implementation issues and workable resolutions.
   The reader is cautioned that the authors have not implemented CCM, so
   what follows is at best a series of educated guesses.

5.1.  Management of ccmMicCcmBindCtxHandle

   The first approach ccmMicCcmBindCtxHandle value is for computed by the CCM-MIC's GSS_Init_sec_context()
        entry point to pass as initiator and
   target based on SHA-1 computations of the claimant_cred_handle CCM-BIND context tokens.
   There is a space/time trade off between the
        output_context_handle as returned initiator and target
   storing the sequence of context tokens until needed by GSS_Init_sec_context() for
        a previously created CCM-BIND,
   versus computing the SHA-1 checksums and then disposing of the
   context tokens when CCM-BIND context.  Such an approach may
        work well with applications that normally pass
        GSS_C_NO_CREDENTIAL as no longer needs them.  If it is likely
   there will be CCM-MIC contexts created for the claimant_cred_handle.

   2.   The second approach derives from CCM-BIND context, and
   if the observation that normally, sequence of context tokens requires more space than a 20 octet
   SHA-1 value, then the first time GSS_Init_sec_context() tradeoff is called, obvious.

   Since the input_token
        field bit space of all possible sequences of CCM-BIND context
   tokens is NULL larger than the 160 bit space of possible SHA-1 checksums,
   in theory two or more different CCM-BIND contexts will produce
   produce the same SHA-1 context, and thus for CCM-MIC context
   initiation, there will be ambiguity as to which CCM-BIND context the initial context_handle (type gss_ctx_id_t)
   initiator is also NULL. binding to.  The input_token is supposed target can resolve this ambiguity by
   attempting to be unwrap the inner context token
        received from the target's CCM-MIC
   initiator for each matching CCM-BIND context.  In theory no more than
   one GSS_Unwrap() attempt for each matching CCM-BIND context acceptance routine, which has will
   succeed.  If multiple succeed, then clearly the XDR type CCM_MIC_resp_t.  Overloading underlying mechanism
   is doing poor job at generating "unique" session keys.  CCM
   implementations that detect this SHOULD log it so that the input_token is one
        way.  By passing problem in a non-null input_token,
   the underlying mechanism can be discovered and fixed.

5.2.  CCM-BIND Versus CCM-MIC

   The first time a NULL pointer
        to CCM context is needed between an principal on the context_handle (using
   initiator and a principal on the C bindings calling conventions
        for gss_init_sec_context()), this will tell target, the CCM-MIC initiator that input_token containing information to has no choice
   but to
        associate a new CCM-MIC context with create an existing underlying mechanism context via a CCM-BIND
        context.  In the C programming language, we could thus have have
        input_token containing:

           typedef struct {
                gss_ctx_id_t context_ptr;
           } CCM_MIC_initiator_bootstrap_t;

        The context
   token exchange.  Once that is done, subsequent CCM entry point for creating contexts on between
   the initiator side
        would, if being called for the first time (*context_handle and target can be created via CCM-MIC.  CCM-MIC context
   establishment is
        NULL), interpret better because no more than one round trip is
   necessary to establish a CCM context, and because the presence overhead of the input token with an invalid
        status as the CCM_MIC_initiator_bootstrap_t.  It would use
        context_ptr
   establishing a real, underlying mechanism context is avoided.

5.3.  Initiating CCM-MIC Contexts

   The issue is how to lookup the  corresponding gss_targ_ctx associate an CCM-BIND established security
   context with a new CCM-MIC context, There are no existing interfaces
   defined in the
        aforementioned gss_ctx_id_t to gss_targ_ctx mapping table.  It
        would GSS-API for associating one GSS context with another.
   This then proceed to generate an output token encoded as XDR
        type CCM_MIC_init_t, described in is the section entitled "Initial
        Context Token key issue for CCM-MIC".

   Regardless implementations of CCM-MIC.

   We will assume that GSS-API implementation is in the approach taken, C programming
   language and therefore the first time GSS_Init_sec_context
   is called, assuming success, it will return GSS_S_CONTINUE_NEEDED,
   because it GSS-API C bindings [RFC2744] are being
   used.  The CCM mechanism implementation will need have a table that maps
   ccmMicCcmBindCtxHandle values to process the token gss_ctx_id_t values (see section
   5.19 of [RFC2744]).  The latter are GSS-API context handles as
   returned by gss_init_sec_context(). In addition, each CCM context has
   a reference to its underlying mechanism context.

   Let us suppose the target.
   The second time it is called, assuming success, application decides it will return
   GSS_S_COMPLETE.

9.4.  Accepting CCM-MIC Contexts

   The use CCM-MIC.  CCM-MIC target receives an opaque gss_targ_ctx value as part of
   the
   has a well known mechanism dependent part of OID which the initial context token.
   Originally, this opaque handle came from application can check for.
   The point where the target as a result of
   previously creating initiator calls GSS_Init_sec_context(), is a
   logical place to associate an existing CCM-BIND context via with a CCM-BIND new
   CCM-MIC context.  Here is where special CCM handling is necessary in
   order to associate a security context exchange.  If
   the opaque handle with a CCM context.  We discuss
   several approaches.

   1.   The first approach is still valid, then for the target can easily
   determine CCM-MIC's GSS_Init_sec_context()
        entry point to pass as the original CCM-BIND context, and from that, claimant_cred_handle the
        output_context_handle as returned by GSS_Init_sec_context() for
        a previously established CCM-BIND
   mechanism's context.  With  Such an approach may
        work well with applications that normally pass
        GSS_C_NO_CREDENTIAL as the underlying context, GSS_VerifyMIC()
   can be invoked (with a qop_req of CCM_REAL_QOP (1)) to verify claimant_cred_handle.

   2.   The second approach derives from the
   mic_nonce of observation that normally,
        the input token, and GSS_GetMIC() can be used to
   generate first time GSS_Init_sec_context() is called, the mic_init_tkn input_token
        field of the output token.  By comparing is NULL and the ctx_sh_number in initial context_handle (type gss_ctx_id_t)
        is also NULL.  The input_token is supposed to be the initiator's token with highest value
   recorded by the target,
        received from the target takes care to ensure that
   initiator target's context acceptance routine, which has not replayed a short token.

9.5.  Non-Token Generating GSS-API Routines

   Since
        the CCM module will record XDR type ccmMicResp.  Overloading the underlying mechanism's context
   pointer input_token is one
        way.  By passing in its internal data structures, this provides a simple
   answer to what to do when GSS-API is invoked on non-null input_token, and a CCM context that
   does not generate any tokens for the GSS peer.  When CCM is called
   for such an operation, it simply re-invokes NULL pointer
        to the GSS-API call, but on context_handle (using the recorded underlying context.

9.6.  CCM-MIC and GSS_Delete_sec_context()

   The CCM-MIC entry point C bindings calling conventions
        for GSS_Delete_sec_context() should not call
   the underlying mechanism's GSS_Delete_sec_context() routine.  If it
   did, gss_init_sec_context()), this would effectively delete all CCM-MIC context's associating
   with the same underlying mechanism.

9.7.  GSS Status Codes

9.7.1.  Status Codes for CCM-BIND

   CCM-BIND mechanisms define no minor status codes.  If will tell the underlying
   mechanism is not available, then CCM-MIC
        initiator that input_token containing information to to
        associate a new CCM-MIC context with an existing CCM-BIND mechanism will return
   GSS_S_BAD_MECH and minor status of zero.  Otherwise, it will return
   whatever major and minor status codes
        context.  In the underlying mechanism
   returns.

9.7.2.  Status Codes for CCM-MIC

   Generally, major and minor status codes C programming language, we could thus have have
        input_token containing:

           typedef struct {
                gss_ctx_id_t ccmMicCcmBindCtxPtr;
           } ccmMicCcmBindBootStrap;

        The CCM entry point for will be whatever major
   and minor status codes creating contexts on the underlying CCM-BIND mechanism returns.
   However, initiator side
        would, if being called for GSS_Init_sec_context() and GSS_Accept_sec_context(),
   this is not the case because first time (*context_handle is
        NULL), interpret the those operations are invoking
   routines (GSS_Wrap() and GSS_Unwrap()) that have major statuses that
   are not subsets presence of the legal input token with an invalid
        status returns from
   GSS_Init_sec_context() and GSS_Accept_sec_context().  Moreover, in
   some cases for GSS_Init_sec_context(), as the minor and major status are
   driven from ccmMicCcmBindBootStrap.  It would use
        ccmMicCcmBindCtxPtr to lookup the target, and  corresponding
        ccmMicCcmBindCtxHandle in the target's codes will not always be
   among aforementioned gss_ctx_id_t to
        ccmMicCcmBindCtxHandle mapping table.  It would then proceed to
        generate an output token encoded as XDR type CCM_MIC_init_t,
        described in the legal set for GSS_Init_sec_context().

9.7.2.1.  CCM-MIC: GSS_Accept_sec_context() status codes

   The minor status code section entitled "Initial Context Token for GSS_Accept_sec_context is always from the
   set defined in
        CCM-MIC".

   Regardless of the CCM_MIC_status_t type.  If GSS_Unwrap() reports a
   major status failure, then approach taken, the minor status first time GSS_Init_sec_context
   is called, assuming success, it will be
   CCM_ERR_TKN_UNWRAP, and return GSS_S_CONTINUE_NEEDED,
   because it will need to process the reported major status token returned by the target.
   The second time it is called, assuming success, it will what
   GSS_Unwrap() reports, with exceptions return
   GSS_S_COMPLETE.

5.4.  Accepting CCM-MIC Contexts

   The CCM-MIC target receives an opaque ccmMicCcmBindCtxHandle value as according to
   part of the following
   table:
      major status code mechanism dependent part of the initial context token.
   Originally, this opaque handle came from GSS_Unwrap      major status code reported
                                             by GSS_Accept_sec_context
                                             to caller.
      -----------------------------------------------------------------
      GSS_S_BAD_SIG                          GSS_S_BAD_SIG
      GSS_S_CONTEXT_EXPIRED                  GSS_S_DEFECTIVE_TOKEN
      GSS_S_GAP_TOKEN                        GSS_S_DEFECTIVE_TOKEN
      GSS_S_UNSEQ_TOKEN                      GSS_S_DUPLICATE_TOKEN

   If GSS_GetMIC() reports the target as a major status failure, result of
   previously creating a context via a CCM-BIND context exchange.  If
   the opaque handle is still valid, then the minor status
   will be CCM_ERR_TKN_GET_MIC, target can easily
   determine the original CCM-BIND context, and from that, the reported major status will CCM-BIND
   mechanism's context.  With the underlying context, GSS_VerifyMIC()
   can be
   what GSS_GetMIC() reports, with exceptions as according invoked (with a qop_req of CCM_REAL_QOP (1)) to verify the
   following table:
      major status code from GSS_GetMIC      major status code reported
                                             by GSS_Accept_sec_context()
                                             to caller.

      ------------------------------------------------------------------
      GSS_S_BAD_QOP                          GSS_S_FAILURE
      GSS_S_CONTEXT_EXPIRED                  GSS_S_DEFECTIVE_TOKEN

   The target will always report
   mic_nonce of the actual GSS major input token, and minor codes GSS_GetMIC() can be used to
   generate the initiator.  The initiator will map the GSS major code as
   described in ccmMicRespInitTkn field of the next subsection.

9.7.2.2.  CCM-MIC: GSS_Init_sec_context() status codes

   The minor status code for GSS_Init_sec_context is always from output token.  By
   comparing the set
   defined ctxMicIndex in the CCM_MIC_status_t type.

   If the minor status code came from initiator's token with highest value
   recorded by the target, then that will always
   be what GSS_Init_sec_context() reports.  The most of the minor codes
   from the target are to be mapped takes care to ensure that
   initiator has not replayed an initial CCM-MIC context token.

5.5.  Non-Token Generating GSS-API Routines

   Since the major status code as follows:
      minor status code          major status code
      from target                reported CCM module will record the underlying mechanism's context
   pointer in its internal data structures, this provides a simple
   answer to caller of
                                 GSS_Init_sec_context()
      ----------------------------------------------------
      CCM_OK                     GSS_S_COMPLETE
      CCM_ERR_HANDLE_MALFORMED   GSS_S_DEFECTIVE_TOKEN
      CCM_ERR_HANDLE_EXPIRED     GSS_S_CREDENTIALS_EXPIRED
      CCM_ERR_HANDLE_NOT_FOUND   GSS_S_CREDENTIALS_EXPIRED
      CCM_ERR_TKN_REPLAY         GSS_S_DUPLICATE_TOKEN
      CCM_ERR_CHAN_MISMATCH      GSS_S_BAD_BINDINGS
      CCM_ERR_TKN_WRAP           GSS_S_FAILURE
      CCM_ERR_TKN_VER_MIC        GSS_S_FAILURE

   Note what to do when GSS-API is invoked on a CCM context that in
   does not generate any tokens for the above table CCM_ERR_TKN_WRAP GSS peer.  When CCM is called
   for such an operation, it simply re-invokes the GSS-API call, but on
   the recorded underlying context.

5.6.  CCM-MIC and CCM_ERR_TKN_VER_MIC
   MUST GSS_Delete_sec_context()

   The CCM-MIC entry point for GSS_Delete_sec_context() should not be returned by the target.  But if they are, then call
   the
   initiator reports GSS_S_FAILURE. underlying mechanism's GSS_Delete_sec_context() routine.  If it
   did, this would effectively delete all CCM-MIC context's associating
   with the same underlying mechanism.

5.7.  GSS Status Codes

5.7.1.  Status Codes for CCM-BIND

   CCM-BIND mechanisms define no minor status code from codes.  If the target underlying
   mechanism is CCM_ERR_TKN_UNWRAP or
   CCM_ERR_TKN_GET_MIC, not available, then the target a CCM-BIND mechanism will also report the major return
   GSS_S_BAD_MECH and minor status code of zero.  Otherwise, it got from GSS_Unwrap() or GSS_GetMIC().  The will return
   whatever major and minor status from codes the target underlying mechanism
   returns.

5.7.2.  Status Codes for CCM-MIC

   Generally, major and minor status codes for will be be reported by whatever major
   and minor status codes the underlying CCM-BIND mechanism returns.
   However, for GSS_Init_sec_context()
   to its caller with exceptions as according to and GSS_Accept_sec_context(),
   this is not the following table: case because the those operations are invoking
   routines (GSS_Wrap() and GSS_Unwrap()) that have major statuses that
   are not subsets of the legal status code returns from target          major status code reported
                                             by
   GSS_Init_sec_context()
                                             to caller
      -----------------------------------------------------------------
      GSS_S_BAD_QOP                          GSS_S_FAILURE
      GSS_S_BAD_SIG                          GSS_S_BAD_SIG
      GSS_S_CONTEXT_EXPIRED                  GSS_S_DEFECTIVE_TOKEN
      GSS_S_GAP_TOKEN                        GSS_S_DEFECTIVE_TOKEN
      GSS_S_UNSEQ_TOKEN                      GSS_S_DUPLICATE_TOKEN
   If GSS_Wrap() fails on the initiator, then and GSS_Accept_sec_context().  Moreover, in
   some cases for GSS_Init_sec_context(), the minor status will be
   CCM_ERR_TKN_WRAP, and the major status are
   driven from the target, and the target's codes will what GSS_Wrap() reports,
   with exceptions as according to not always be
   among the following table:
      major legal set for GSS_Init_sec_context().

5.7.2.1.  CCM-MIC: GSS_Accept_sec_context() status codes

   The minor status code for GSS_Accept_sec_context is always from GSS_Wrap the
   set defined in the ccmMicStatus type.  If GSS_Unwrap() reports a
   major status code reported
                                           by GSS_Init_sec_context()
                                           to caller
      ---------------------------------------------------------------
      GSS_S_CONTEXT_EXPIRED                GSS_S_DEFECTIVE_TOKEN
                                              or
                                           GSS_S_DEFECTIVE_CREDENTIAL

      GSS_S_BAD_QOP                        GSS_S_FAILURE

   If GSS_VerifyMIC() fails on the initiator, failure, then the minor status will be CCM_ERR_TKN_VER_MIC,
   CCM_ERR_TKN_UNWRAP, and the reported major status will what
   GSS_VerifyMIC()
   GSS_Unwrap() reports, with exceptions as according to the following
   table:
      major status code from GSS_VerifyMIC GSS_Unwrap      major status code reported
                                             by GSS_Init_sec_context()
                                            to caller
      ---------------------------------------------------------------
      GSS_S_CONTEXT_EXPIRED                 GSS_S_DEFECTIVE_TOKEN
      GSS_S_GAP_TOKEN                       GSS_S_DEFECTIVE_TOKEN
      GSS_S_UNSEQ_TOKEN                     GSS_S_DUPLICATE_TOKEN

9.8.  Channel Bindings on the Target

   When an application invokes GSS_Accept_sec_context() on a CCM token,
   it won't know if channel bindings are required or not.  Of course, it
   could inspect the OID of the input_token and determine the channel
   bindings directly if it is a CCM-BIND token, but normally
   applications will not parse the mechanism OID in an input token.  And
   in any case, such inspection for a CCM-MIC token provides no
   information about channel bindings to the target application.

   The application on the target will have to try
   GSS_Accept_sec_context() without channel bindings.  If the target CCM
   mechanism requires channel bindings (as indicated by the
   GSS_S_BAD_BINDINGS), then the application will have to re-invoke
   GSS_Accept_sec_context() with the right channel bindings.  If the
   channel bindings are the wrong type, then the CCM mechanism will
   indicate GSS_S_BAD_BINDINGS again.  The application will have to
   iterate through all the valid types of bindings.  The application can
   avoid this iteration if the bindings includes both, address and key
   bindings if at all possible.  The CCM mechanisms should use only
   those parts of the application-provided bindings that they care for.

10.  Advice for NFSv4 Implementors

   The NFSv4.0 specification does not mandate CCM, so clients and
   servers should not insist on its use.  When a server wants a client
   to try GSS_Accept_sec_context
                                             to use CCM, it can return caller.
      -----------------------------------------------------------------
      GSS_S_BAD_SIG                          GSS_S_BAD_SIG
      GSS_S_CONTEXT_EXPIRED                  GSS_S_DEFECTIVE_TOKEN
      GSS_S_GAP_TOKEN                        GSS_S_DEFECTIVE_TOKEN
      GSS_S_UNSEQ_TOKEN                      GSS_S_DUPLICATE_TOKEN

   If GSS_GetMIC() reports a NFS4ERR_WRONGSEC error to major status failure, then the
   client.  The client minor status
   will then follow up be CCM_ERR_TKN_GET_MIC, and the reported major status will be
   what GSS_GetMIC() reports, with a SECINFO request.  The
   response exceptions as according to the SECINFO request should list first the CCM-BIND
   mechanisms it supports, second
   following table:
      major status code from GSS_GetMIC      major status code reported
                                             by GSS_Accept_sec_context()
                                             to caller.
      ------------------------------------------------------------------
      GSS_S_BAD_QOP                          GSS_S_FAILURE
      GSS_S_CONTEXT_EXPIRED                  GSS_S_DEFECTIVE_TOKEN

   The target will always report the CCM-MIC mechanism (if supported), actual GSS major and finally, the conventional security flavors minor codes to
   the server initiator.  The initiator will accept map the GSS major code as
   described in the next subsection.

5.7.2.2.  CCM-MIC: GSS_Init_sec_context() status codes

   The minor status code for access to file object. GSS_Init_sec_context is always from the set
   defined in the ccmMicStatus type.

   If the client supports CCM, it will use
   it.  Otherwise, it minor status code came from the target, then that will have to stick with a conventional flavor.

   Since always
   be what GSS_Init_sec_context() reports.  The most of the CCM-MIC OID is general, rather than a separate CCM-MIC OID
   for every real mechanism, minor codes
   from the NFS server will have target are to be careful mapped to make
   sure that a CCM-MIC context is authorized access an object.  For
   example suppose /export is exported such the major status code as follows:
      minor status code          major status code
      from target                reported to caller of
                                 GSS_Init_sec_context()
      ----------------------------------------------------
      CCM_OK                     GSS_S_COMPLETE
      CCM_ERR_HANDLE_MALFORMED   GSS_S_DEFECTIVE_TOKEN
      CCM_ERR_HANDLE_EXPIRED     GSS_S_CREDENTIALS_EXPIRED
      CCM_ERR_HANDLE_NOT_FOUND   GSS_S_CREDENTIALS_EXPIRED
      CCM_ERR_TKN_REPLAY         GSS_S_DUPLICATE_TOKEN
      CCM_ERR_CHAN_MISMATCH      GSS_S_BAD_BINDINGS
      CCM_ERR_TKN_WRAP           GSS_S_FAILURE
      CCM_ERR_TKN_VER_MIC        GSS_S_FAILURE

   Note that SPKM-3 is in the
   authorized underlying mechanism, and CCM-NULL + SPKM-3 and CCM-MIC
   are similarly authorized to access /export.  Suppose CCM-NULL is
   created over a Kerberos V5 context, above table CCM_ERR_TKN_WRAP and CCM_ERR_TKN_VER_MIC
   MUST not be returned by the target.  But if they are, then CCM-MIC is used to
   derived a context from the CCM-NULL context.
   initiator reports GSS_S_FAILURE.

   If the NFS server
   simply records that minor status code from the OID of CCM-MIC target is authorized to access
   /export, CCM_ERR_TKN_UNWRAP or
   CCM_ERR_TKN_GET_MIC, then Kerberos V5 authenticated users will be mistakenly
   allowed access.  Instead, the server needs to examine what context the CCM-MIC context is associated with, and check that context's OID
   against target will also report the authorized list of OIDs for /export.

11.  Man in major
   status code it got from GSS_Unwrap() or GSS_GetMIC().  The major
   status from the Middle Attacks without CCM-KEY

   In this example, NFS with/ RPCSEC_GSS target will be be reported by GSS_Init_sec_context()
   to its caller with exceptions as according to the application, and
   IPsec the secure channel.

   Man in the middle (MITM) avoidance means making sure that following table:
      major status code from target          major status code reported
                                             by GSS_Init_sec_context()
                                             to caller
      -----------------------------------------------------------------
      GSS_S_BAD_QOP                          GSS_S_FAILURE
      GSS_S_BAD_SIG                          GSS_S_BAD_SIG
      GSS_S_CONTEXT_EXPIRED                  GSS_S_DEFECTIVE_TOKEN
      GSS_S_GAP_TOKEN                        GSS_S_DEFECTIVE_TOKEN
      GSS_S_UNSEQ_TOKEN                      GSS_S_DUPLICATE_TOKEN

   If GSS_Wrap() fails on the client
   and server are initiator, then the same at both layers, NFS minor status will be
   CCM_ERR_TKN_WRAP, and IPsec, but since the
   principal names at the one layer major status will be radically different from what GSS_Wrap() reports,
   with exceptions as according to the
   names at following table:
      major status code from GSS_Wrap      major status code reported
                                           by GSS_Init_sec_context()
                                           to caller
      ---------------------------------------------------------------
      GSS_S_CONTEXT_EXPIRED                GSS_S_DEFECTIVE_TOKEN
                                              or
                                           GSS_S_DEFECTIVE_CREDENTIAL

      GSS_S_BAD_QOP                        GSS_S_FAILURE

   If GSS_VerifyMIC() fails on the other, how can one initiator, then the minor status will
   be certain that there is no MITM at CCM_ERR_TKN_VER_MIC, and the IPsec layer before leaving it to IPsec to provide session
   protection major status will what
   GSS_VerifyMIC() reports, with exceptions as according to the NFS layer?
   following table:
      major status code from GSS_VerifyMIC  major status code reported
                                            by GSS_Init_sec_context()
                                            to caller
      ---------------------------------------------------------------
      GSS_S_CONTEXT_EXPIRED                 GSS_S_DEFECTIVE_TOKEN
      GSS_S_GAP_TOKEN                       GSS_S_DEFECTIVE_TOKEN
      GSS_S_UNSEQ_TOKEN                     GSS_S_DUPLICATE_TOKEN

6.  Advice for NFSv4 Implementors

   The answer is NFSv4.0 specification does not mandate CCM, so client and server
   implementations should not insist on its use.  When a server wants a
   client to try to use channel bindings,
   which, conceptually, are an exchange, at the NFS/GSS layer, of
   signatures of the principal names or session ID/keys involved at the
   IPsec layer.

   Consider an attacker who CCM, it can cause return a client's IPsec stack NFS4ERR_WRONGSEC error to
   establish an SA with the attacker, instead of the server intended by
   the NFS layer (this is accomplished by spoofing
   the DNS server).
   Suppose further that client.  The client will then follow up with a SECINFO request.
   The response to the attacker can fool SECINFO request should list first the client's IPsec layer
   without also fooling its NFS/RPCSEC_GSS layer (for example, if
   Kerberos V5 is being used as CCM-BIND
   mechanisms it supports, second the real mechanism, CCM-MIC mechanism (if supported),
   and avoids finally, the use
   of DNS to canonicalize conventional security flavors the server principal name -- admittedly, this
   avoidance is unlikely -- a DNS spoof attack will be detected by the
   NFS client, because accept
   for access to file object.  If the Kerberos Key Distribution Center (KDC)
   generates tickets associated client supports CCM, it will use
   it.  Otherwise, it will have to stick with pairs of principals, not host
   names).  Suppose that a conventional flavor.

   Since the attacker's host CCM-MIC OID is in part of the site's
   IPsec infrastructure (perhaps the attacker broke into that host).
   Then general, rather than a separate CCM-MIC OID
   for every real mechanism, the attacker might NFS server will have be able careful to act as make
   sure that a MITM between CCM-MIC context is authorized access an object.  For
   example suppose /export is exported such that SPKM-3 is the client
   authorized underlying mechanism, and the server who gets all the plain text CCM-NULL + SPKM-3 and even gets CCM-MIC
   are similarly authorized to modify
   it, if access /export.  Suppose CCM-NULL is wrapping
   created over a Kerberos V5 at the RPCSEC_GSS level.
   Both, the client context, and then CCM-MIC is used to
   derived a context from the CCM-NULL context.  If the NFS server would see
   simply records that IPsec the OID of CCM-MIC is in use
   between them, but they would each see a different ID for its IPsec
   peer.  Channel bindings are used authorized to prove that access
   /export, then Kerberos V5 authenticated users will be mistakenly
   allowed access.  Instead, the client and server
   each see the same two peer names at needs to examine what context
   the lower (in this case, IPsec)
   layer, and therefore with CCM-KEY there CCM-MIC context is no MITM.

   DNSSEC would of course defeat the attack, but DNSSEC was not, at associated with, and check that context's OID
   against the
   time this document was written, in widespread use.

12. authorized list of OIDs for /export.

7.  Security Considerations

   There are many considerations for the use CCM, since it is reducing
   security at one protocol layer in trade for equivalent security at
   another layer.  In this discussion, we will assume that cryptography
   is being used in the application and lower protocol layers.

   *    CCM should not be used whenever the combined key
        strength/algorithm strength of the lower protocol layer securing
        the connection is weaker than what the underlying GSS context
        can provide.

   *    CCM should not be used if the lower level protocol does not
        offer comparable or superior security services to that the
        application would achieve with GSS.  For example, if the lower
        level protocol offers integrity, but the application wants
        privacy, then CCM is inappropriate.

   *    The use of CCM contexts over secured connections can be
        characterized nearly secure instead of as secure as using the
        underlying GSS context for protecting each application message
        procedure call.  The reason is that applications can multiplex
        the traffic of multiple principals over a single connection and
        so the ciphertext in the traffic is encrypted with multiple
        session keys.  Whereas, a secure connection method such as IPsec
        is protected with per host session keys.  Therefore, an attacker
        has more cipher text per session key to perform cryptanalysis
        via connections protected with IPsec, versus connections
        protected with GSS.

   *    Related to the previous bullet, the management of private keys
        for a secure channel is often outside the control of the user of
        CCM.  If the secure channel's private keys are compromised, then
        all users of the secure channel are compromised.

   *    CCM contexts created during one session or transport connection
        SHOULD not be used for subsequent sessions or transport
        connections.  In other words, full initiator to target
        authentication SHOULD occur each time a session or transport
        connection is established.  Otherwise, there is nothing
        preventing an attacker from using a CCM context from one
        authenticated session or connection to trivially establish
        another, unauthenticated session or connection.  For efficiency,
        a CCM-BIND context from a previous session or connection MAY be
        used to establish a CCM-MIC context.

        If the application protocol using CCM has no concept of a
        session and does not use a connection oriented transport, then
        there is no sequence of state transitions that tie the CCM
        context creation steps with the subsequent message traffic of
        the application protocol.  Thus it can be hard to assert that
        the subsequent message traffic is truly originated by the CCM
        initiator's principal.  For this reason, CCM SHOULD NOT be used
        with applications that do not have sessions or do not use
        connection oriented transports.

   *    The underlying secure channel SHOULD be end to end, from
        initiator to the target.  It is permissible for the user to
        configure the underlying secure channel to not be end to end,
        but this should only be done if user has confidence in the
        intermediate end points.  For example, suppose the application
        is being used behind a firewall that performs network address
        translation.  It is possible to have an IPsec secure channel
        from the initiator to the firewall, and a second secure channel
        from the firewall to the target, but not from the initiator to
        the target.  So, if the firewall is compromised by an attacker
        in the middle, the use of CCM to avoid per message
        authentication is useless.  Furthermore, without channel
        bindings mandated by CCM-KEY, it is not possible for the
        initiator and target to enforce end to end channel security.  Of course, if the initiator's node
        created a IP-layer tunnel between it and the target, end to end
        channel security would be
        achieved, but without the use of CCM-KEY, the initiator and
        target applications would have no way of knowing that. achieved.

   *    It has been stated that it is not uncommon to find IPsec
        deployments where multiple nodes share common private keys
        [Black].  The use of CCM is discouraged in such environments,
        since the compromise of one node compromises all the other nodes
        sharing the same private key.

   *    Applications using CCM MUST ensure that the binding between the
        CCM context and the secure channel is legitimate for each
        message that references the CCM context.  In other words, the
        referenced CCM context in a message MUST be established in the
        same secure channel as the message.  The use of CCM-KEY enforces
        this binding.

   *    When the same secure channel is multiplexing traffic for
        multiple users, the initiator has to ensure the CCM context is
        only accessible to the initiator principal that has established
        it in the first place.  One possible way to ensure that is by
        placing CCM contexts in the privileged address space offering
        only controlled indexed access.

   *    CCM does not unnecessarily inflate the scope of the trust
        domain, as does for example AUTH_SYS [RFC1831] over IPSec.  By
        requiring the authentication in the CCM context initialization
        (using a previously established context), the trust domain does
        not extend to the client.

   *    Both the traditional mechanisms and CCM rely on the security of
        the client to protect locally logged on users.  Compromise of
        the client impacts all users on the same client.  CCM does not
        make the problem worse.

   *    The CCM context MUST be established over the same secure channel
        that the subsequent message traffic will be using.  This way,
        the binding between the initial authentication and the
        subsequent traffic is ensured.  Again, the use of CCM-KEY is one
        way to assert this binding.

   *    The section entitled "CCM-KEY and Anonymous IPsec", suggests a
        method for simulating anonymous IPsec via self-signed
        certificates.  If one is careless, this is will neuter all IPsec
        authentication, a real problem for those applications not using
        CCM-KEY.  The use of the self-signed certificates in IPsec
        should be restricted by port in binding between the IPsec Security Policy
        Database (SPD) only to those application using CCM-KEY.  Note
        however, that port selector support initial authentication and the
        subsequent traffic is OPTIONAL in IPsec. ensured.

   *    If an application is using IPsec and is not using CCM-KEY, CCM-NULL then then the site
        where the application is deployed should configure the IPsec SPD
        to carefully limit the ports and nodes that are allowed create
        security  associations to application targets.

   *    CCM-KEY's IPsec bindings use public SA information, and CCM-
        ADDR's bindings are simply public network addresses.  If the
        secure channel is IPsec, and non-anonymous certificates are used
        with IKE, then a MITM cannot spoof the target's and initiator's
        IP addresses, because the attacker will presumably be unable to
        spoof the Certificate Authority that signed the certificates.
        Thus, when IPsec is used as the secure channel, and non-
        anonymous certificates are used with IKE, CCM-ADDR is as secure
        as CCM-KEY.

   *    CCM contexts should not be used forever without re-
        authenticating periodically via the underlying mechanism.  One
        rational approach is for the CCM context to persist no longer
        than the underlying mechanism context.  Implementing this via
        the GSS-API is simple.  Applications can periodically invoke
        gss_context_time() to find out how long the context will be
        valid.  Moreover, CCM can enforce this by invoking
        gss_context_time() and the system time of day API to get an
        expiration date when the CCM mechanism is established.  Each
        subsequent call can check the time of day against the
        expiration, and if expired, return GSS_S_CONTEXT_EXPIRED.

13.

8.  CCM XDR Description

   Here is the XDR description for CCM-BIND and CCM-MIC:

      enum ccmVerifyState {
              CCM_UNVERIFIED = 0,
              CCM_VERIFY_FAILED = 1,
              CCM_VERIFIED = 2
      };

      struct ccmBindSubCtxTknTargToInit {
              ccmVerifyState ccmBindStatus;
              opaque ccmBindRealToken<>;
              opaque ccmBindNonce<>;
      };

      struct ccmBindSubCtxTknInitToTarg {
              opaque ccmBindRealToken<>;
              opaque ccmBindMic<>;
      };

      enum ccmMicStatus {
              CCM_OK = 0,

              /*
               * ccmMicCcmBindCtxHandle was malformed.
               */
              CCM_ERR_HANDLE_MALFORMED = 1,

              /*
               * The GSS context corresponding to
               * ccmMicCcmBindCtxHandle has expired.
               */
              CCM_ERR_HANDLE_EXPIRED = 2,

              /*
               * ccmMicCcmBindCtxHandle was not found.
               */
              CCM_ERR_HANDLE_NOT_FOUND = 3,

              /*
               * The ctxMicIndex has already been received
               * by the target.  Or the maximum ctxMicIndex has
               * been previously received.
               */
              CCM_ERR_TKN_REPLAY = 4,

              /*
               * Channel binding type mismatch between CCM-BIND context
               * and the CCM-MIC initial context.
               */
              CCM_ERR_CHAN_MISMATCH = 5,

              /*
               * The GSS_Unwrap() failed on initial context token
               */
              CCM_ERR_TKN_UNWRAP = 6,

              /*
               * The GSS_GetMIC() called failed on the target().
               */

              CCM_ERR_TKN_GET_MIC = 7,

              /*
               * The GSS_Wrap() failed on the initiator.  Not reported
               * by target.
               */

              CCM_ERR_TKN_WRAP = 8,

              /*
               * The GSS_VerifyMIC() failed on the initiator.  Not
               * reported by target.
               */

              CCM_ERR_TKN_VER_MIC = 9

      };
      /*
       * GSS errors returned by the underlying mechanism
       */
      struct ccmMicRealGssErr {
              unsigned int ccmMicGssMajor;
              unsigned int ccmMicGssMinor;
      };

      /*
       * The response context token for CCM-MIC.
       */
      union ccmMicResp switch (ccmMicStatus status) {
              case CCM_OK:
                      opaque ccmMicRespInitTkn<>;
              case CCM_ERR_TKN_UNWRAP:
              case CCM_ERR_TKN_GET_MIC:
                      ccmMicRealGssErr ccmMicGssErr;
              default:
                      void;
      };

9.  IANA Considerations

   XXX Note 1 to IANA: The CCM-BIND mechanism OID prefixes and the CCM-
   MIC mechanism OID must be assigned and registered by IANA.  Please
   look for TBD1 in this document and notify the RFC Editor what value
   you have assigned.

   XXX Note 1 to RFC Editor: When IANA has made the OID assignments,
   please do the following:

   *    Delete the "XXX Note 1 to RFC Editor: ..." paragraph.

   *    Replace occurrences of TBD1 with the value assigned by IANA.

   *    Replace the "XXX Note 1 to IANA: ..." paragraph with:
             OIDs for the CCM-BIND mechanism prefix, and for the CCM-MIC
             mechanism have been assigned by, and registered with IANA,
             with this document as the reference.

   XXX Note 2 to IANA: Please assign RPC flavor numbers for values
   currently place held in this document as TBD2 through TBD10. TBD5.  Also
   please establish the registry that RFC2623 mandates.

   XXX Note 2 to RFC Editor: When IANA has made the RPC flavor number
   assignments, please do the following:

   *    Delete the "XXX Note 2 to RFC Editor: ..." paragraph.

   *    Replace occurrences of TBD2 through and including TBD10 TBD5 withe
        flavor number assignments from IANA.

   Section 6, "IANA Considerations" of [RFC2623] established a registry
   for mapping GSS mechanism OIDs to RPC pseudo flavor numbers.  This
   registry was augmented in the NFSv4 specification [RFC3530] with
   several more entries.  This document adds the following entries to
   the registry:

    1 == number of pseudo flavor
    2 == name of pseudo flavor
    3 == mechanism's OID
    4 == quality of protection
    5 == RPCSEC_GSS service

   1          2               3                4 5
   --------------------------------------------------------------
   TBD2  ccm-mic         1.3.6.1.5.5.TBD1.2    0 rpc_gss_svc_none

   TBD3  ccm-null-krb5   1.3.6.1.5.5.TBD1.1.1. 0 rpc_gss_svc_none
                         1.2.840.113554.1.2.2

   TBD4  ccm-addr-krb5   1.3.6.1.5.5.TBD1.1.2. 0 rpc_gss_svc_none
                         1.2.840.113554.1.2.2

   TBD5  ccm-key-krb5    1.3.6.1.5.5.TBD1.1.3. 0 rpc_gss_svc_none
                         1.2.840.113554.1.2.2

   TBD6  ccm-null-spkm3  1.3.6.1.5.5.TBD1.1.1. 0 rpc_gss_svc_none
                         1.3.6.1.5.5.1.3

   TBD6  ccm-addr-spkm3  1.3.6.1.5.5.TBD1.1.2. 0 rpc_gss_svc_none
                         1.3.6.1.5.5.1.3

   TBD7  ccm-key-spkm3   1.3.6.1.5.5.TBD1.1.3. 0 rpc_gss_svc_none
                         1.3.6.1.5.5.1.3

   TBD8

   TBD5  ccm-null-lipkey 1.3.6.1.5.5.TBD1.1.1. 0 rpc_gss_svc_none
                         1.3.6.1.5.5.1.3

   TBD9  ccm-addr-lipkey 1.3.6.1.5.5.TBD1.1.2. 0 rpc_gss_svc_none
                         1.3.6.1.5.5.1.3

   TBD10 ccm-addr-lipkey 1.3.6.1.5.5.TBD1.1.3. 0 rpc_gss_svc_none
                         1.3.6.1.5.5.1.3

14.

10.  Acknowledgements

   Dave Noveck, for the observation that NFS version 4 servers could
   downgrade from integrity service to plain authentication service if
   IPsec was enabled.  David Black, Peng Dai, Sam Hartman, Martin Rex,
   and Julian Satran, for their critical comments.  Much of the text for
   the "Security Considerations" section comes directly from David and
   Peng.

15.

11.  Normative References

   [RFC1832]
        R. Srinivasan, RFC1832, "XDR: External Data Representation
        Standard", August, 1995.

   [RFC2025]
        C. Adams, RFC2025: "The Simple Public-Key GSS-API Mechanism
        (SPKM)," October 1996, Status: Standards Track.

   [RFC2119]
        S. Bradner, RFC2119, "Key words for use in RFCs to Indicate
        Requirement Levels," March 1997.

   [RFC2401]
        S. Kent, R. Atkinson, RFC2401, "Security Architecture for the
        Internet Protocol ", November, 1998.

   [RFC2409]
        D. Harkins and D. Carrel, RFC2119: "The Internet Key Exchange
        (IKE)," November 1998.

   [RFC2743]
        J. Linn, RFC2743, "Generic Security Service Application Program
        Interface Version 2, Update 1", January, 2000.

   [RFC2744]
        J. Wray, RFC2744, "Generic Security Service API Version 2 : C-
        bindings", January, 2000.

   [RFC2847]
        M. Eisler, RFC2847: "LIPKEY - A Low Infrastructure Public Key
        Mechanism Using SPKM," June 2000, Status: Standards Track.

   [FIPS]U.S. Department of Commerce / National Institute of Standards
        and Technology, FIPS PUB 180-1, "Secure Hash Standard", May 11,
        1993.

   [IKEv2]
        C. Kaufman, draft-ietf-ipsec-ikev2-07.txt: "Internet Key
        Exchange (IKEv2) Protocol," A work in progress, April 2003.

        XXX - Note 3 to RFC Editor: In the event this work in progress
        is not approved for publication when the CCM document is, then
        the sections of the CCM document that refer to IKEv2 in a
        normative manner are to be removed for submission as a separate
        document.

   [SSHv2]
        T. Ylonen et. al., draft-ietf-secsh-transport-15.txt: "SSH
        Transport Layer Protocol," A work in progress, September 2002.

        XXX - Note 4 to RFC Editor: In the event this work in progress
        is not approved for publication when the CCM document is, then
        the sections of the CCM document that refer to SSHv2 in a
        normative manner are to be removed for submission as a separate
        document.

16.

12.  Informative References

   [RFC1831]
        R. Srinivasan, RFC1831, "RPC: Remote Procedure Call Protocol
        Specification Version 2", August, 1995.

   [RFC1964]
        J. Linn, RFC1964, "The Kerberos Version 5 GSS-API Mechanism",
        June 1996.

   [RFC2203]
        M. Eisler, A. Chiu, L. Ling, RFC2203, "RPCSEC_GSS Protocol
        Specification", September, 1997.

   [RFC2623]
        M. Eisler, RFC2623, "NFS Version 2 and Version 3 Security Issues
        and the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5", June
        1999.

   [RFC3530]
        S. Shepler, B. Callaghan, D. Robinson, R. Thurlow, C.  Beame, M.
        Eisler, D. Noveck, RFC3530, "Network File System (NFS) version 4
        Protocol", April 2003.

   [Black]
        D. Black, EMail message on the NFSv4 working group alias,
        February 28, 2003.

   [DAFS]
        Mark Wittle (Editor), "DAFS Direct Access File System Protocol,
        Version: 1.00", September 1, 2001.

   [Kasslin]
        Kasslin, K. "Attacks on Kerberos V in a Windows 2000
        Environment", 2003.
        http://www.hut.fi/~autikkan/hakkeri/docs/phase1/pdf/
        LATEST_final_report.pdf

17.

13.  Authors' Addresses

   Mike Eisler
   5765 Chase Point Circle
   Colorado Springs, CO 80919
   USA

   Phone: 719-599-9026
   EMail: mike@eisler.com

   Nicolas Williams
   Sun Microsystems, Inc.
   5300 Riata Trace CT
   Austin, TX 78727
   USA

   EMail: nicolas.williams@sun.com

18.

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19.

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