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Kerberos Working Group                              L. Hornquist Astrand
Internet-Draft                                                Apple, Inc
Updates: 4556 (if approved)                                       L. Zhu
Intended status: Standards Track                   Microsoft Corporation
Expires: April 25, 2013                                     M. Wasserman
                                                       Painless Security
                                                        October 22, 2012


                        PKINIT Algorithm Agility
              draft-ietf-krb-wg-pkinit-alg-agility-07.txt

Abstract

   This document updates PKINIT, as defined in RFC 4556, to remove
   protocol structures tied to specific cryptographic algorithms.  The
   PKINIT key derivation function is made negotiable, the digest
   algorithms for signing the pre-authentication data and the client's
   X.509 certificates are made discoverable.

   These changes provide preemptive protection against vulnerabilities
   discovered in the future against any specific cryptographic
   algorithm, and allow incremental deployment of newer algorithms.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 25, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   This document may contain material from IETF Documents or IETF
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   it for publication as an RFC or to translate it into languages other
   than English.
































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  5
   3.  paChecksum Agility . . . . . . . . . . . . . . . . . . . . . .  5
   4.  CMS Digest Algorithm Agility . . . . . . . . . . . . . . . . .  5
   5.  X.509 Certificate Signer Algorithm Agility . . . . . . . . . .  6
   6.  KDF agility  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Test vectors . . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Common Inputs  . . . . . . . . . . . . . . . . . . . . . . 12
     7.2.  Test Vector for SHA-1, enctype 18  . . . . . . . . . . . . 12
       7.2.1.  Specific Inputs  . . . . . . . . . . . . . . . . . . . 12
       7.2.2.  Outputs  . . . . . . . . . . . . . . . . . . . . . . . 12
     7.3.  Test Vector for SHA-256, enctype . . . . . . . . . . . . . 13
       7.3.1.  Specific Inputs  . . . . . . . . . . . . . . . . . . . 13
       7.3.2.  Outputs  . . . . . . . . . . . . . . . . . . . . . . . 13
     7.4.  Test Vector for SHA-512, enctype . . . . . . . . . . . . . 13
       7.4.1.  Specific Inputs  . . . . . . . . . . . . . . . . . . . 13
       7.4.2.  Outputs  . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     11.2. Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  PKINIT ASN.1 Module . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
























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1.  Introduction

   This document updates PKINIT [RFC4556] to remove protocol structures
   tied to specific cryptographic algorithms.  The PKINIT key derivation
   function is made negotiable, the digest algorithms for signing the
   pre-authentication data and the client's X.509 certificates are made
   discoverable.

   These changes provide preemptive protection against vulnerabilities
   discovered in the future against any specific cryptographic
   algorithm, and allow incremental deployment of newer algorithms.

   In August 2004, Xiaoyun Wang's research group reported MD4 [RFC6150]
   collisions generated using hand calculation [WANG04], alongside
   attacks on later hash function designs in the MD4, MD5 [RFC1321] and
   SHA [RFC6234] family.  These attacks and their consequences are
   discussed in [RFC6194].  These discoveries challenged the security of
   protocols relying on the collision resistance properties of these
   hashes.

   The Internet Engineering Task Force (IETF) called for actions to
   update existing protocols to provide crypto algorithm agility so that
   protocols support multiple cryptographic algorithms (including hash
   functions) and provide clean, tested transition strategies between
   algorithms.

   This document updates PKINIT to provide crypto algorithm agility.
   Several protocol structures used in the [RFC4556] protocol are either
   tied to SHA-1, or do not support negotiation or discovery, but are
   instead based on local policy.  The following concerns have been
   addressed in this update:

   o  The checksum algorithm in the authentication request is hardwired
      to use SHA-1 [RFC6234].

   o  The acceptable digest algorithms for signing the authentication
      data are not discoverable.

   o  The key derivation function in Section 3.2.3 of [RFC4556] is
      hardwired to use SHA-1.

   o  The acceptable digest algorithms for signing the client X.509
      certificates are not discoverable.

   To address these concerns, new key derivation functions (KDFs),
   identified by object identifiers, are defined.  The PKINIT client
   provides a list of KDFs in the request and the Key Distribution
   Center (KDC) picks one in the response, thus a mutually-supported KDF



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   is negotiated.

   Furthermore, structures are defined to allow the client to discover
   the Cryptographic Message Syntax (CMS) [RFC5652] digest algorithms
   supported by the KDC for signing the pre-authentication data and
   signing the client X.509 certificate.


2.  Requirements Notation

   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].


3.  paChecksum Agility

   The paChecksum defined in Section 3.2.1 of [RFC4556] provides a
   cryptographic binding between the client's pre-authentication data
   and the corresponding Kerberos request body.  This also prevents the
   KDC body from being tampered with.  SHA-1 is the only allowed
   checksum algorithm defined in [RFC4556].  This facility relies on the
   collision resistance properties of the SHA-1 checksum [RFC6234].

   When the reply key delivery mechanism is based on public key
   encryption as described in Section 3.2.3. of [RFC4556], the
   asChecksum in the KDC reply provides the binding between the pre-
   authentication and the ticket request and response messages, and
   integrity protection for the unauthenticated clear text in these
   messages.  However, if the reply key delivery mechanism is based on
   the Diffie-Hellman key agreement as described in Section 3.2.3.1 of
   [RFC4556], the security provided by using SHA-1 in the paChecksum is
   weak.  In this case, the new KDF selected by the KDC as described in
   Section 6 provides the cryptographic binding and integrity
   protection.


4.  CMS Digest Algorithm Agility

   When the KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error is returned
   as described In section 3.2.2 of [RFC4556], implementations
   comforming to this specification can OPTIONALLY send back a list of
   supported CMS types signifying the digest algorithms supported by the
   KDC, in the decreasing preference order.  This is accomplished by
   including a TD_CMS_DATA_DIGEST_ALGORITHMS typed data element in the
   error data.





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   td-cms-digest-algorithms INTEGER ::= 111


   The corresponding data for the TD_CMS_DATA_DIGEST_ALGORITHMS contains
   the ASN.1 Distinguished Encoding Rules (DER) [X680] [X690] encoded
   TD-CMS-DIGEST-ALGORITHMS-DATA structure defined as follows:


   TD-CMS-DIGEST-ALGORITHMS-DATA ::= SEQUENCE OF
       AlgorithmIdentifier
           -- Contains the list of CMS algorithm [RFC5652]
           -- identifiers that identify the digest algorithms
           -- acceptable by the KDC for signing CMS data in
           -- the order of decreasing preference.


   The algorithm identifiers in the TD-CMS-DIGEST-ALGORITHMS identifiy
   digest algorithms supported by the KDC.

   This information sent by the KDC via TD_CMS_DATA_DIGEST_ALGORITHMS
   can facilitate trouble-shooting when none of the digest algorithms
   supported by the client is supported by the KDC.


5.  X.509 Certificate Signer Algorithm Agility

   When the client's X.509 certificate is rejected and the
   KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error is returned as
   described in section 3.2.2 of [RFC4556], conforming implementations
   can OPTIONALLY send a list of digest algorithms acceptable by the KDC
   for use by the Certificate Authority (CA) in signing the client's
   X.509 certificate, in the decreasing preference order.  This is
   accomplished by including a TD_CERT_DIGEST_ALGORITHMS typed data
   element in the error data.  The corresponding data contains the ASN.1
   DER encoding of the structure TD-CERT-DIGEST-ALGORITHMS-DATA defined
   as follows:















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   td-cert-digest-algorithms INTEGER ::= 112

   TD-CERT-DIGEST-ALGORITHMS-DATA ::= SEQUENCE {
           allowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier,
                      -- Contains the list of CMS algorithm [RFC5652]
                      -- identifiers that identify the digest algorithms
                      -- that are used by the CA to sign the client's
                      -- X.509 certificate and acceptable by the KDC in
                      -- the process of validating the client's X.509
                      -- certificate, in the order of decreasing
                      -- preference.
           rejectedAlgorithm [1] AlgorithmIdentifier OPTIONAL,
                      -- This identifies the digest algorithm that was
                      -- used to sign the client's X.509 certificate and
                      -- has been rejected by the KDC in the process of
                      -- validating the client's X.509 certificate
                      -- [RFC5280].
           ...
   }


   The KDC fills in allowedAlgorithm field with the list of algorithm
   [RFC5652] identifiers that identify digest algorithms that are used
   by the CA to sign the client's X.509 certificate and acceptable by
   the KDC in the process of validating the client's X.509 certificate,
   in the order of decreasing preference.  The rejectedAlgorithm field
   identifies the signing algorithm for use in signing the client's
   X.509 certificate that has been rejected by the KDC in the process of
   validating the client's certificate [RFC5280].


6.  KDF agility

   Based on [RFC3766] and [X9.42], Section 3.2.3.1 of [RFC4556] defines
   a Key Derivation Function (KDF) that derives a Kerberos protocol key
   based on the secret value generated by the Diffie-Hellman key
   exchange.  This KDF requires the use of SHA-1 [RFC6234].

   New KDFs defined in this document based on [SP80056A] can be used in
   conjunction with any hash functions.

   A new KDF is identified by an object identifier.  The following KDF
   object identifiers are defined:








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   id-pkinit-kdf OBJECT IDENTIFIER           ::= { id-pkinit 6 }
       -- PKINIT KDFs
   id-pkinit-kdf-ah-sha1 OBJECT IDENTIFIER   ::= { id-pkinit-kdf 1 }
       -- SP800 56A ASN.1 structured hash based KDF using SHA-1
   id-pkinit-kdf-ah-sha256 OBJECT IDENTIFIER ::= { id-pkinit-kdf 2 }
       -- SP800 56A ASN.1 structured hash based KDF using SHA-256
   id-pkinit-kdf-ah-sha512 OBJECT IDENTIFIER ::= { id-pkinit-kdf 3 }
       -- SP800 56A ASN.1 structured hash based KDF using SHA-512
   id-pkinit-kdf-ah-sha384 OBJECT IDENTIFIER ::= { id-pkinit-kdf 4 }
       -- SP800 56A ASN.1 structured hash based KDF using SHA-384


   Where id-pkinit is defined in [RFC4556].  The id-pkinit-kdf-ah-sha1
   KDF is the ASN.1 structured hash based KDF (HKDF) [SP80056A] that
   uses SHA-1 [RFC6234] as the hash function.  Similarly id-pkinit-kdf-
   ah-sha256 and id-pkinit-kdf-ah-sha512 are the ASN.1 structured HKDF
   using SHA-256 [RFC6234] and SHA-512 [RFC6234] respectively.

   To name the input parameters, an abbreviated version of the ASN.1
   version of the KDF from [SP80056A] is described below, use [SP80056A]
   for the full reference.

   1.  reps = ceiling (keydatalen/hash length (H))

   2.  Initialize a 32-bit, big-endian bit string counter as 1.

   3.  For i = 1 to reps by 1, do the following:

       1.  Compute Hashi = H(counter || Z || OtherInfo).

       2.  Increment counter (modulo 2^32)

   4.  Set key_material = Hash1 || Hash2 || ... so that length of key is
       K bits.

   5.  The above ASN.1 structured [SP80056A] HKDF produces a bit string
       of length K in bits as the keying material, and then the AS reply
       key is the output of random-to-key() [RFC3961] using that
       returned keying material as the input.

   The input parameters for these KDFs are provided as follows:

   o  The key data length (K) is the key-generation seed length in bits
      [RFC3961] for the Authentication Service (AS) reply key.  The
      enctype of the AS reply key is selected according to [RFC4120].

   o  The hash length (H) is 160 bits for id-pkinit-kdf-ah-sha1, 256
      bits for id-pkinit-kdf-ah-sha256, 384 bits for id-pkinit-kdf-ah-



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      sha384 and 512 bits for id-pkinit-kdf-ah-sha512.

   o  The secret value (Z) is the shared secret value generated by the
      Diffie-Hellman exchange.  The Diffie-Hellman shared value is first
      padded with leading zeros such that the size of the secret value
      in octets is the same as that of the modulus, then represented as
      a string of octets in big-endian order.

   o  The algorithm identifier (algorithmID) input parameter is the
      identifier of the respective KDF.  For example, this is id-pkinit-
      kdf-ah-sha1 if the KDF is the [SP80056A] ASN.1 structured HKDF
      using SHA-1 as the hash.

   o  The initiator identifier (partyUInfo) contains the ASN.1 DER
      encoding of the KRB5PrincipalName [RFC4556] that identifies the
      client as specified in the AS-REQ [RFC4120] in the request.

   o  The recipient identifier (partyVInfo) contains the ASN.1 DER
      encoding of the KRB5PrincipalName [RFC4556] that identifies the
      TGS as specified in the AS-REQ [RFC4120] in the request.

   o  The supplemental public information (suppPubInfo) is the ASN.1 DER
      encoding of the structure PkinitSuppPubInfo as defined later in
      this section.

   o  The supplemental private information (suppPrivInfo) is absent.

   o  The maximum hash input length is 2^64 in bits.

   The structure for OtherInfo is defined as follows:

   OtherInfo ::= SEQUENCE {
           algorithmID   AlgorithmIdentifier,
           partyUInfo     [0] OCTET STRING,
           partyVInfo     [1] OCTET STRING,
           suppPubInfo    [2] OCTET STRING OPTIONAL,
           suppPrivInfo   [3] OCTET STRING OPTIONAL
   }


   The structure PkinitSuppPubInfo is defined as follows:










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   PkinitSuppPubInfo ::= SEQUENCE {
          enctype           [0] Int32,
                 -- The enctype of the AS reply key
          as-REQ            [1] OCTET STRING,
              -- This contains the AS-REQ in the request.
          pk-as-rep         [2] OCTET STRING,
              -- Contains the DER encoding of the type
              -- PA-PK-AS-REP [RFC4556] in the KDC reply.
          ...
   }


   The PkinitSuppPubInfo structure contains mutually-known public
   information specific to the authentication exchange.  The enctype
   field is the enctype of the AS reply key as selected according to
   [RFC4120].  The as-REQ field contains the DER encoding of the type
   AS-REQ [RFC4120] in the request sent from the client to the KDC.
   Note that the as-REQ field does not include the wrapping 4 octet
   length field when TCP is used.  The pk-as-rep field contains the DER
   encoding of the type PA-PK-AS-REP [RFC4556] in the KDC reply.  The
   PkinitSuppPubInfo provides a cryptographic bindings between the pre-
   authentication data and the corresponding ticket request and
   response, thus addressing the concerns described in Section 3.

   The KDF is negotiated between the client and the KDC.  The client
   sends an unordered set of supported KDFs in the request, and the KDC
   picks one from the set in the reply.

   To acomplish this, the AuthPack structure in [RFC4556] is extended as
   follows:

   AuthPack ::= SEQUENCE {
          pkAuthenticator   [0] PKAuthenticator,
          clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL,
          supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier
                   OPTIONAL,
          clientDHNonce     [3] DHNonce OPTIONAL,
          ...,
          supportedKDFs     [4] SEQUENCE OF KDFAlgorithmId OPTIONAL,
              -- Contains an unordered set of KDFs supported by the
              -- client.
          ...
   }

   KDFAlgorithmId ::= SEQUENCE {
          kdf-id            [0] OBJECT IDENTIFIER,
              -- The object identifier of the KDF
          ...



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   }


   The new field supportedKDFs contains an unordered set of KDFs
   supported by the client.

   The KDFAlgorithmId structure contains an object identifier that
   identifies a KDF.  The algorithm of the KDF and its parameters are
   defined by the corresponding specification of that KDF.

   The DHRepInfo structure in [RFC4556] is extended as follows:

   DHRepInfo ::= SEQUENCE {
           dhSignedData         [0] IMPLICIT OCTET STRING,
           serverDHNonce        [1] DHNonce OPTIONAL,
           ...,
           kdf                  [2] KDFAlgorithmId OPTIONAL,
               -- The KDF picked by the KDC.
           ...
   }


   The new field kdf in the extended DHRepInfo structure identifies the
   KDF picked by the KDC.  This kdf field MUST be filled by the
   comforming KDC if the supportedKDFs field is present in the request,
   and it MUST be one of the KDFs supported by the client as indicated
   in the request.  Which KDF is chosen is a matter of the local policy
   on the KDC.

   If the supportedKDFs field is not present in the request, the kdf
   field in the reply MUST be absent.

   If the client fills the supportedKDFs field in the request, but the
   kdf field in the reply is not present, the client can deduce that the
   KDC is not updated to conform with this specification.  In that case,
   it is a matter of local policy on the client whether to reject the
   reply when the kdf field is absent in the reply.

   Implementations comforming to this specification MUST support id-
   pkinit-kdf-ah-sha256.

   This document introduces the following new PKINIT error code:

   o  KDC_ERR_NO_ACCEPTABLE_KDF 82

   If no acceptable KDF is found, the error KDC_ERR_NO_ACCEPTABLE_KDF
   (82) will be returned..




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7.  Test vectors

   This section contains test vectors for the KDF defined above.

7.1.  Common Inputs

Z: Length = 256 bytes, Hex Representation = (All Zeros)
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 000000000 00000000 00000000 00000000

client: Length = 9 bytes, ASCII Representation = lha@SU.SE

server: Length = 18 bytes, ASCII Representation = krbtgt/SU.SE@SU.SE

as-req: Length = 10 bytes, Hex Representation =
AAAAAAAA AAAAAAAA AAAA

pk-as-rep:  Length = 9 bytes, Hex Representation =
BBBBBBBB BBBBBBBB BB

ticket: Length =  55 bytes, Hex Representation =
61353033 A0030201 05A1071B 0553552E 5345A210 300EA003 020101A1 0730051B
036C6861 A311300F A0030201 12A20804 0668656A 68656A


7.2.  Test Vector for SHA-1, enctype 18

7.2.1.  Specific Inputs

   algorithm-id: (id-pkinit-kdf-ah-sha1) Length = 8 bytes, Hex
   Representation = 2B060105 02030601

   enctype: (aes256-cts-hmac-sha1-96) Length = 1 byte, Decimal
   Representation = 18


7.2.2.  Outputs








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 key-material: Length = 32 bytes, Hex Representation =
 E6AB38C9 413E035B B079201E D0B6B73D 8D49A814 A737C04E E6649614 206F73AD

 key: Length = 32 bytes, Hex Representation =
 E6AB38C9 413E035B B079201E D0B6B73D 8D49A814 A737C04E E6649614 206F73AD


7.3.  Test Vector for SHA-256, enctype

7.3.1.  Specific Inputs

   algorithm-id: (id-pkinit-kdf-ah-sha256) Length = 8 bytes, Hex
   Representation = 2B060105 02030602

   enctype: (aes256-cts-hmac-sha1-96) Length = 1 byte, Decimal
   Representation = 18


7.3.2.  Outputs

 key-material: Length = 32 bytes, Hex Representation =
 77EF4E48 C420AE3F EC75109D 7981697E ED5D295C 90C62564 F7BFD101 FA9bC1D5

 key: Length = 32 bytes, Hex Representation =
 77EF4E48 C420AE3F EC75109D 7981697E ED5D295C 90C62564 F7BFD101 FA9bC1D5


7.4.  Test Vector for SHA-512, enctype

7.4.1.  Specific Inputs

algorithm-id: (id-pkinit-kdf-ah-sha512) Length = 8 bytes, Hex
Representation = 2B060105 02030603

enctype: (des3-cbc-sha1-kd) Length = 1 byte, Decimal Representation = 16


7.4.2.  Outputs

   key-material: Length = 24 bytes, Hex Representation =
   D3C78A79 D65213EF E9A826F7 5DFB01F7 2362FB16 FB01DAD6

   key: Length = 32 bytes, Hex Representation =
   D3C78A79 D65213EF E9A826F7 5DFB01F7 2362FB16 FB01DAD6







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8.  Security Considerations

   This document describes negotiation of checksum types, key derivation
   functions and other cryptographic functions.  If negotiation is done
   unauthenticated, care MUST be taken to accept only acceptable values.


9.  Acknowledgements

   Jeffery Hutzelman, Shawn Emery, Tim Polk and Kelley Burgin reviewed
   the document and provided suggestions for improvements.


10.  IANA Considerations

   IANA is requested to update the following registrations in the
   Kerberos Pre-authentication and Typed Data Registry created by
   section 7.1 of RFC 6113 to refer to this specification.  These values
   were reserved for this specification in the initial registrations.



               TD-CMS-DIGEST-ALGORITHMS   111  [ALG-AGILITY]
               TD-CERT-DIGEST-ALGORITHMS  112  [ALG-AGILITY]



11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3766]  Orman, H. and P. Hoffman, "Determining Strengths For
              Public Keys Used For Exchanging Symmetric Keys", BCP 86,
              RFC 3766, April 2004.

   [RFC3961]  Raeburn, K., "Encryption and Checksum Specifications for
              Kerberos 5", RFC 3961, February 2005.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              July 2005.

   [RFC4556]  Zhu, L. and B. Tung, "Public Key Cryptography for Initial
              Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.




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   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

   [RFC6194]  Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
              Considerations for the SHA-0 and SHA-1 Message-Digest
              Algorithms", RFC 6194, March 2011.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

   [SP80056A]
              Barker, E., Don, D., and M. Smid, "Recommendation for
              Pair-Wise Key Establishment Schemes Using Discrete
              Logarithm Cryptography", March 2006.

   [X680]     ITU, "ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-
              1:2002, Information technology - Abstract Syntax Notation
              One (ASN.1): Specification of basic notation".

   [X690]     ITU, "ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-
              1:2002, Information technology - ASN.1 encoding Rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)".

11.2.  Informative References

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC6150]  Turner, S. and L. Chen, "MD4 to Historic Status",
              RFC 6150, March 2011.

   [WANG04]   Wang, X., Lai, X., Fheg, D., Chen, H., and X. Yu,
              "Cryptanalysis of Hash functions MD4 and RIPEMD",
              August 2004.

   [X9.42]    ANSI, "Public Key Cryptography for the Financial Services
              Industry: Agreement of Symmetric Keys Using Discrete
              Logarithm Cryptography", 2003.






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Appendix A.  PKINIT ASN.1 Module



   KerberosV5-PK-INIT-Agility-SPEC {
          iso(1) identified-organization(3) dod(6) internet(1)
          security(5) kerberosV5(2) modules(4) pkinit(5) agility (1)
   } DEFINITIONS EXPLICIT TAGS ::= BEGIN

   IMPORTS
      AlgorithmIdentifier, SubjectPublicKeyInfo
          FROM PKIX1Explicit88 { iso (1)
            identified-organization (3) dod (6) internet (1)
            security (5) mechanisms (5) pkix (7) id-mod (0)
            id-pkix1-explicit (18) }
            -- As defined in RFC 5280.

      Ticket, Int32, Realm, EncryptionKey, Checksum
          FROM KerberosV5Spec2 { iso(1) identified-organization(3)
            dod(6) internet(1) security(5) kerberosV5(2)
            modules(4) krb5spec2(2) }
            -- as defined in RFC 4120.

      PKAuthenticator, DHNonce
          FROM KerberosV5-PK-INIT-SPEC {
            iso(1) identified-organization(3) dod(6) internet(1)
            security(5) kerberosV5(2) modules(4) pkinit(5) };
            -- as defined in RFC 4556.

   TD-CMS-DIGEST-ALGORITHMS-DATA ::= SEQUENCE OF
       AlgorithmIdentifier
           -- Contains the list of CMS algorithm [RFC5652]
           -- identifiers that identify the digest algorithms
           -- acceptable by the KDC for signing CMS data in
           -- the order of decreasing preference.

   TD-CERT-DIGEST-ALGORITHMS-DATA ::= SEQUENCE {
          allowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier,
              -- Contains the list of CMS algorithm [RFC5652]
              -- identifiers that identify the digest algorithms
              -- that are used by the CA to sign the client's
              -- X.509 certificate and acceptable by the KDC in
              -- the process of validating the client's X.509
              -- certificate, in the order of decreasing
              -- preference.
          rejectedAlgorithm [1] AlgorithmIdentifier OPTIONAL,
              -- This identifies the digest algorithm that was
              -- used to sign the client's X.509 certificate and



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              -- has been rejected by the KDC in the process of
              -- validating the client's X.509 certificate
              -- [RFC5280].
          ...
   }

   OtherInfo ::= SEQUENCE {
           algorithmID   AlgorithmIdentifier,
           partyUInfo     [0] OCTET STRING,
           partyVInfo     [1] OCTET STRING,
           suppPubInfo    [2] OCTET STRING OPTIONAL,
           suppPrivInfo   [3] OCTET STRING OPTIONAL
   }

   PkinitSuppPubInfo ::= SEQUENCE {
          enctype           [0] Int32,
              -- The enctype of the AS reply key.
          as-REQ            [1] OCTET STRING,
              -- This contains the AS-REQ in the request.
          pk-as-rep         [2] OCTET STRING,
              -- Contains the DER encoding of the type
              -- PA-PK-AS-REP [RFC4556] in the KDC reply.
          ...
   }

   AuthPack ::= SEQUENCE {
          pkAuthenticator   [0] PKAuthenticator,
          clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL,
          supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier
                   OPTIONAL,
          clientDHNonce     [3] DHNonce OPTIONAL,
          ...,
          supportedKDFs     [4] SEQUENCE OF KDFAlgorithmId OPTIONAL,
              -- Contains an unordered set of KDFs supported by the
              -- client.
          ...
   }

   KDFAlgorithmId ::= SEQUENCE {
          kdf-id            [0] OBJECT IDENTIFIER,
              -- The object identifier of the KDF
          ...
   }

   DHRepInfo ::= SEQUENCE {
          dhSignedData      [0] IMPLICIT OCTET STRING,
          serverDHNonce     [1] DHNonce OPTIONAL,
          ...,



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          kdf               [2] KDFAlgorithmId OPTIONAL,
              -- The KDF picked by the KDC.
          ...
   }
   END



Authors' Addresses

   Love Hornquist Astrand
   Apple, Inc
   Cupertino, CA
   USA

   Email: lha@apple.com


   Larry Zhu
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   USA

   Email: lzhu@microsoft.com


   Margaret Wasserman
   Painless Security
   356 Abbott Street
   North Andover, MA  01845
   USA

   Phone: +1 781 405-7464
   Email: mrw@painless-security.com
   URI:   http://www.painless-security.com















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