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doc/standardisation/draft-ietf-krb-wg-pkinit-alg-agility-00.txt

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+Network Working Group                               L. Hornquist Astrand
+Internet-Draft                                      Stockholm University
+Expires: September 2, 2006                                        L. Zhu
+                                                   Microsoft Corporation
+                                                              March 2006
+
+
+                       PK-INIT algorithm agility
+                draft-ietf-krb-wg-pkinit-alg-agility-00
+
+Status of this Memo
+
+   By submitting this Internet-Draft, each author represents that any
+   applicable patent or other IPR claims of which he or she is aware
+   have been or will be disclosed, and any of which he or she becomes
+   aware will be disclosed, in accordance with Section 6 of BCP 79.
+
+   Internet-Drafts are working documents of the Internet Engineering
+   Task Force (IETF), its areas, and its working groups.  Note that
+   other groups may also distribute working documents as Internet-
+   Drafts.
+
+   Internet-Drafts are draft documents valid for a maximum of six 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."
+
+   The list of current Internet-Drafts can be accessed at
+   http://www.ietf.org/ietf/1id-abstracts.txt.
+
+   The list of Internet-Draft Shadow Directories can be accessed at
+   http://www.ietf.org/shadow.html.
+
+   This Internet-Draft will expire on September 2, 2006.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2006).
+
+Abstract
+
+   The PK-INIT protocol have in several places hard coded crypto
+   algorithms.  The protocol specification needs to be updated so it can
+   support negotiation to upgrading to newer versions of crypto
+   algorithms.  This document addresses this issue.
+
+
+
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+
+
+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 1]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+Table of Contents
+
+   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
+   2.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  4
+   3.  paChecksum agility . . . . . . . . . . . . . . . . . . . . . .  5
+   4.  CMS Digest Algorithm agility . . . . . . . . . . . . . . . . .  6
+   5.  Certificate Signer Algorithm Identifier agility  . . . . . . .  7
+   6.  octetstring2key function agility . . . . . . . . . . . . . . .  8
+   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
+   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
+   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
+   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
+   Intellectual Property and Copyright Statements . . . . . . . . . . 12
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 2]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+1.  Introduction
+
+   The Kerberos PK-INIT document contains several hardcoded algorithms
+   that was know designed at design time that they had to be replaced by
+   something else at a later time, this document described how to use
+   other algorithms other then those that are hard-coded.
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 3]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+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].
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 4]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+3.  paChecksum agility
+
+   The paChecksum binds the PK-INIT part of the request to main body of
+   the Kerberos request (KDC-REQ-BODY).  This is to makes sure an
+   attacker can not change the request from the client to the server.
+   The problem is that paChecksum is hardcoded to use SHA1-1, however,
+   there is a mechaism to provide algorithm agility for the paChecksum
+   within the PK-INIT prototcol.  Newer clients can choose not send the
+   paChecksum field, but rather add some new fields after the existing
+   fields, older KDC will send back know failure-code so that newer
+   clients can fall back to the old protocol if local policy allows
+   that.
+
+   If the attacker can preserve the checksum in paChecksum, an attacker
+   can, for example, change the KDC-REQ-BODY is to downgrade the
+   encryption types used, expend the expiration time, etc, and then try
+   to brute-force the request.
+
+   In the Public Key Encryption case of PK-INIT the reply contains a
+   checksum over the whole request in the asChecksum field, in this case
+   the client will detect any modifications to the request.  Since the
+   asChecksum is using the associated checksum of the session key
+   encryption type, asChecksum field is algorithm agile.
+
+   One way to solve this problem is to add the asChecksum to the Diffie-
+   Hellman case reply too, and just ignore the paCheckSum field.  The
+   KDC should still not issue tickets that are too weak, since that
+   exposes the problem.  This is regardless of the using PK-INIT or not.
+
+   Questions for wg: Wait for Kerberos Extensions that will solve this
+   problem (ignore the problem for how), or use add asChecksum to DH
+   case.
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 5]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+4.  CMS Digest Algorithm agility
+
+   The client can tell KDC what the supported CMS types are in the
+   requset packet, but there are no equivalent for KDC to the the client
+   what the digest algorithm are support in an reply.
+
+   Have KDC send the CMS list of supported encryption types in the
+   e-data field of KRB-ERROR when returning the
+   KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error.
+
+   DER encoded TS-SD-PARAMETERS specifies supported digest algorithms.
+   The list is in decreasing preference order.
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+   TD-SD-PARAMETERS ::= SEQUENCE OF AlgorithmIdentifier
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 6]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+5.  Certificate Signer Algorithm Identifier agility
+
+   The KDC can reject a certificate based on the signers hash algorithm
+   with the error KDC_ERR_DIGEST_IN_CERT_NOT_ACCEPTED, but doesn't tell
+   the client what algorithm are supported.
+
+   DER encoded TS-DC-PARAMETERS specifies supported certificate digest
+   algorithms.  The AllowedAlgorithms is in decreasing preference order.
+   RejectedAlgorithm may be include my the KDC to tell what algorithm
+   was rejected in case the rejected certificate was part of a computed
+   chain.
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+   TD-DC-PARAMETERS ::= SEQUENCE {
+       AllowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier,
+       RejectedAlgorithm [1] AlgorithmIdentifier OPTIONAL
+   }
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 7]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+6.  octetstring2key function agility
+
+   The PK-INIT standard uses a home-grown string 2 key function in the
+   DH case.  The function uses SHA-1 to mix and stretch the DH shared
+   key.
+
+   Describe how the client announces that is supports the new String to
+   key function.  Probably by stuffing it into the supportCMSTypes field
+   in the request.
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+   Use NIST SP 800 56B when its published.
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 8]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+7.  Security Considerations
+
+   This document describes negotiation of checksum types and other
+   cryptographic functions.  Most of this negotiation is done
+   unauthenticated with no way to very
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+Hornquist Astrand & Zhu  Expires September 2, 2006              [Page 9]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+8.  IANA Considerations
+
+   No IANA considerations.
+
+9.  Normative References
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119, March 1997.
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+Hornquist Astrand & Zhu  Expires September 2, 2006             [Page 10]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+Authors' Addresses
+
+   Love Hornquist Astrand
+   Stockholm University
+   SE-106 91  STOCKHOLM
+   SWEDEN
+
+   Email: lha@it.su.se
+
+
+   Larry Zhu
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: lzhu@microsoft.com
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+Hornquist Astrand & Zhu  Expires September 2, 2006             [Page 11]
+
+Internet-Draft          PK-INIT algorithm agility             March 2006
+
+
+Intellectual Property Statement
+
+   The IETF takes no position regarding the validity or scope of any
+   Intellectual Property Rights or other rights that might be claimed to
+   pertain to the implementation or use of the technology described in
+   this document or the extent to which any license under such rights
+   might or might not be available; nor does it represent that it has
+   made any independent effort to identify any such rights.  Information
+   on the procedures with respect to rights in RFC documents can be
+   found in BCP 78 and BCP 79.
+
+   Copies of IPR disclosures made to the IETF Secretariat and any
+   assurances of licenses to be made available, or the result of an
+   attempt made to obtain a general license or permission for the use of
+   such proprietary rights by implementers or users of this
+   specification can be obtained from the IETF on-line IPR repository at
+   http://www.ietf.org/ipr.
+
+   The IETF invites any interested party to bring to its attention any
+   copyrights, patents or patent applications, or other proprietary
+   rights that may cover technology that may be required to implement
+   this standard.  Please address the information to the IETF at
+   ietf-ipr@ietf.org.
+
+
+Disclaimer of Validity
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
+   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
+   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
+   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
+   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+
+Copyright Statement
+
+   Copyright (C) The Internet Society (2006).  This document is subject
+   to the rights, licenses and restrictions contained in BCP 78, and
+   except as set forth therein, the authors retain all their rights.
+
+
+Acknowledgment
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
+
+
+
+Hornquist Astrand & Zhu  Expires September 2, 2006             [Page 12]
+

doc/standardisation/draft-ietf-krb-wg-tcp-expansion-00.txt

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+Network Working Group                                       S. Josefsson
+Internet-Draft                                                       SJD
+Updates: 4120 (if approved)                                 May 10, 2006
+Expires: November 11, 2006
+
+
+Extended Kerberos Version 5 Key Distribution Center (KDC) Exchanges Over
+                                  TCP
+                   draft-ietf-krb-wg-tcp-expansion-00
+
+Status of this Memo
+
+   By submitting this Internet-Draft, each author represents that any
+   applicable patent or other IPR claims of which he or she is aware
+   have been or will be disclosed, and any of which he or she becomes
+   aware will be disclosed, in accordance with Section 6 of BCP 79.
+
+   Internet-Drafts are working documents of the Internet Engineering
+   Task Force (IETF), its areas, and its working groups.  Note that
+   other groups may also distribute working documents as Internet-
+   Drafts.
+
+   Internet-Drafts are draft documents valid for a maximum of six 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."
+
+   The list of current Internet-Drafts can be accessed at
+   http://www.ietf.org/ietf/1id-abstracts.txt.
+
+   The list of Internet-Draft Shadow Directories can be accessed at
+   http://www.ietf.org/shadow.html.
+
+   This Internet-Draft will expire on November 11, 2006.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2006).
+
+Abstract
+
+   This document describes an extensibility mechanism for the Kerberos
+   v5 protocol when used over TCP transports.
+
+
+
+
+
+
+
+
+Josefsson               Expires November 11, 2006               [Page 1]
+
+Internet-Draft          Kerberos V5 TCP extension               May 2006
+
+
+Table of Contents
+
+   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
+   2.  Conventions used in this document . . . . . . . . . . . . . . . 3
+   3.  Extension Mechanism for TCP transport . . . . . . . . . . . . . 3
+   4.  Interoperability Consideration  . . . . . . . . . . . . . . . . 4
+   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
+   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
+   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
+   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
+   Appendix A.  Copying conditions . . . . . . . . . . . . . . . . . . 5
+   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
+   Intellectual Property and Copyright Statements  . . . . . . . . . . 7
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+Josefsson               Expires November 11, 2006               [Page 2]
+
+Internet-Draft          Kerberos V5 TCP extension               May 2006
+
+
+1.  Introduction
+
+   The Kerberos 5 [3] specification, in section 7.2.2, reserve the high
+   order bit in the initial length field for TCP transport for future
+   expansion.  This document update [3] to describe the behaviour when
+   that bit is set.  This mechanism is intended for extensions that are
+   specific for the TCP transport.
+
+
+2.  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 RFC 2119 [1].
+
+
+3.  Extension Mechanism for TCP transport
+
+   The reserved high bit of the request length field is used to signal
+   the use of this extension mechanism.  When the reserved high bit is
+   set, the remaining 31 bits of the initial 4 octets are interpreted as
+   a bitmap.  Each bit in the bitmask can be used to request a
+   particular extension.  The 31 bits form the "extension bitmask".  It
+   is expected that other documents will describe the details associated
+   with particular bits.
+
+   A 4-octet value with only the high bit set, and thus the extension
+   bitmask all zeros, is called a PROBE.  A client may send a probe to
+   find out which extensions a KDC support.  A client may also set
+   particular bits in the extension bitmask directly, if it does not
+   need to query the KDC for available extensions before deciding which
+   extension to request.
+
+   If a KDC receive a PROBE, or if a KDC does not support all extensions
+   corresponding to set bits in the extension bitmask, the KDC MUST
+   return 4 octets with the high bit set, and with the remaining bitmask
+   indicate which extensions it supports.  The KDC SHOULD NOT close the
+   connection, and SHOULD wait for the client to then send a second
+   4-octet value, with the high bit set and the remaining bits as the
+   bitmask, to request a particular extension.  If the second 4-octet
+   value is a PROBE or an unsupported extension, the KDC MUST close the
+   connection.  This is used by the client to shutdown a session when
+   the KDC did not support a, by the client, required extension.
+
+   Resource avaibility considerations may influence whether, and for how
+   long, the KDC will wait for the client to send requests.
+
+   The behaviour when more than one non-high bit is set depends on the
+
+
+
+Josefsson               Expires November 11, 2006               [Page 3]
+
+Internet-Draft          Kerberos V5 TCP extension               May 2006
+
+
+   particular extension mechanisms.  If a requested extension (bit X)
+   does not specify how it interact with another requested extensions
+   (bit Y), the KDC MUST treat the request as a PROBE or unsupported
+   extension, and proceed as above.
+
+   Each extension MUST describe the structure of protocol data beyond
+   the length field, and the behaviour of the client and KDC.  If an
+   extension mechanism reserve multiple bits, it MUST describe how they
+   interact.
+
+
+4.  Interoperability Consideration
+
+   Implementations with support for TCP that do not claim to conform to
+   RFC 4120 may not handle the high bit correctly.  Behaviour may
+   include closing the TCP connection without any response, and logging
+   an error message in the KDC log.  When this was written, this problem
+   existed in modern versions of popular implementations.
+   Implementations experiencing trouble getting the expected responses
+   from a server SHOULD assume that it does not support this extension
+   mechanism.  Clients MAY remember this semi-permanently, to avoid
+   excessive logging in the server.  Care should be taken to avoid
+   unexpected behaviour for the user when the KDC is eventually
+   upgraded.  Implementations MAY also provide a way to enable and
+   disable this extension on a per-realm basis.  How to handle these
+   backwards compatibility quirks are in general left unspecified.
+
+
+5.  Security Considerations
+
+   Because the initial length field is not protected, it is possible for
+   an active attacker (i.e., one that is able to modify traffic between
+   the client and the KDC) to make it appear to the client that the
+   server does not support this extension mechanism.  Client and KDC
+   policies can be used to reject connections that does not use any
+   expansion.
+
+
+6.  IANA Considerations
+
+   IANA needs to create a new registry for "Kerberos 5 TCP Extensions".
+   The initial contents of this registry should be:
+
+   [[RFC Editor: Replace xxxx below with the number of this RFC.]]
+
+   Bit #         Meaning                             Reference
+   -----         -------                             ---------
+   0..29         AVAILABLE for registration.
+
+
+
+Josefsson               Expires November 11, 2006               [Page 4]
+
+Internet-Draft          Kerberos V5 TCP extension               May 2006
+
+
+   30            RESERVED.                           RFC XXXX
+
+   IANA will register values 0 to 29 after IESG Approval, as defined in
+   BCP 64 [2].  Assigning value 30 requires a Standards Action that
+   update or obsolete this document.
+
+
+7.  Acknowledgements
+
+   Thanks to Andrew Bartlett who pointed out that some implementations
+   (MIT Kerberos and Heimdal) did not follow RFC 4120 properly with
+   regards to the high bit, which resulted in an Interoperability
+   Consideration.
+
+   Nicolas Williams and Jeffrey Hutzelman provided comments that
+   improved the document.
+
+8.  Normative References
+
+   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
+        Levels", BCP 14, RFC 2119, March 1997.
+
+   [2]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
+        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
+
+   [3]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos
+        Network Authentication Service (V5)", RFC 4120, July 2005.
+
+
+Appendix A.  Copying conditions
+
+   Copyright (C) 2005, 2006 Simon Josefsson
+
+   Regarding this entire document or any portion of it, the author makes
+   no guarantees and is not responsible for any damage resulting from
+   its use.  The author grants irrevocable permission to anyone to use,
+   modify, and distribute it in any way that does not diminish the
+   rights of anyone else to use, modify, and distribute it, provided
+   that redistributed derivative works do not contain misleading author
+   or version information.  Derivative works need not be licensed under
+   similar terms.
+
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+Josefsson               Expires November 11, 2006               [Page 5]
+
+Internet-Draft          Kerberos V5 TCP extension               May 2006
+
+
+Author's Address
+
+   Simon Josefsson
+   SJD
+
+   Email: simon@josefsson.org
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+Josefsson               Expires November 11, 2006               [Page 6]
+
+Internet-Draft          Kerberos V5 TCP extension               May 2006
+
+
+Intellectual Property Statement
+
+   The IETF takes no position regarding the validity or scope of any
+   Intellectual Property Rights or other rights that might be claimed to
+   pertain to the implementation or use of the technology described in
+   this document or the extent to which any license under such rights
+   might or might not be available; nor does it represent that it has
+   made any independent effort to identify any such rights.  Information
+   on the procedures with respect to rights in RFC documents can be
+   found in BCP 78 and BCP 79.
+
+   Copies of IPR disclosures made to the IETF Secretariat and any
+   assurances of licenses to be made available, or the result of an
+   attempt made to obtain a general license or permission for the use of
+   such proprietary rights by implementers or users of this
+   specification can be obtained from the IETF on-line IPR repository at
+   http://www.ietf.org/ipr.
+
+   The IETF invites any interested party to bring to its attention any
+   copyrights, patents or patent applications, or other proprietary
+   rights that may cover technology that may be required to implement
+   this standard.  Please address the information to the IETF at
+   ietf-ipr@ietf.org.
+
+
+Disclaimer of Validity
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
+   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
+   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
+   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
+   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+
+Copyright Statement
+
+   Copyright (C) The Internet Society (2006).  This document is subject
+   to the rights, licenses and restrictions contained in BCP 78, and
+   except as set forth therein, the authors retain all their rights.
+
+
+Acknowledgment
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
+
+
+
+Josefsson               Expires November 11, 2006               [Page 7]
+

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+
+
+
+NETWORK WORKING GROUP                                             L. Zhu
+Internet-Draft                                             K. Jaganathan
+Expires: March 17, 2006                                        K. Lauter
+                                                   Microsoft Corporation
+                                                      September 13, 2005
+
+
+                         ECC Support for PKINIT
+                        draft-zhu-pkinit-ecc-00
+
+Status of this Memo
+
+   By submitting this Internet-Draft, each author represents that any
+   applicable patent or other IPR claims of which he or she is aware
+   have been or will be disclosed, and any of which he or she becomes
+   aware will be disclosed, in accordance with Section 6 of BCP 79.
+
+   Internet-Drafts are working documents of the Internet Engineering
+   Task Force (IETF), its areas, and its working groups.  Note that
+   other groups may also distribute working documents as Internet-
+   Drafts.
+
+   Internet-Drafts are draft documents valid for a maximum of six 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."
+
+   The list of current Internet-Drafts can be accessed at
+   http://www.ietf.org/ietf/1id-abstracts.txt.
+
+   The list of Internet-Draft Shadow Directories can be accessed at
+   http://www.ietf.org/shadow.html.
+
+   This Internet-Draft will expire on March 17, 2006.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2005).
+
+Abstract
+
+   This document describes the use of Elliptic Curve certificates,
+   Elliptic Curve signature schemes and Elliptic Curve Diffie-Hellman
+   (ECDH) key agreement within the framework of PKINIT - the Kerberos
+   Version 5 extension that provides for the use of public key
+   cryptography.
+
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 1]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+Table of Contents
+
+   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
+   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
+   3.  Using Elliptic Curve Certificates and Elliptic Curve
+       Signature Schemes  . . . . . . . . . . . . . . . . . . . . . .  3
+   4.  Using ECDH Key Exchange  . . . . . . . . . . . . . . . . . . .  4
+   5.  Choosing the Domain Parameters and the Key Size  . . . . . . .  6
+   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
+   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
+   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
+   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
+     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
+     9.2.  Informative References . . . . . . . . . . . . . . . . . .  9
+   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
+   Intellectual Property and Copyright Statements . . . . . . . . . . 11
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 2]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+1.  Introduction
+
+   Elliptic Curve Cryptography (ECC) is emerging as an attractive
+   public-key cryptosystem that provides security equivalent to
+   currently popular public-key mechanisms such as RSA and DSA with
+   smaller key sizes [LENSTRA] [NISTSP80057].
+
+   Currently [PKINIT] permits the use of ECC algorithms but it does not
+   specify how ECC parameters are chosen and how to derive the shared
+   key for key delivery using Elliptic Curve Diffie-Hellman (ECDH)
+   [IEEE1363].
+
+   This document describes how to use Elliptic Curve certificates,
+   Elliptic Curve signature schemes, and ECDH with [PKINIT].  However,
+   it should be noted that there is no syntactic or semantic change to
+   the existing [PKINIT] messages.  Both the client and the KDC
+   contribute one ECDH key pair using the key agrement protocol
+   described in this document.
+
+
+2.  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].
+
+
+3.  Using Elliptic Curve Certificates and Elliptic Curve Signature
+    Schemes
+
+   ECC certificates and signature schemes can be used in the
+   Cryptographic Message Syntax (CMS) [RFC3369] content type
+   'SignedData'.
+
+   X.509 certificates [RFC3280] containing ECC public keys or signed
+   using ECC signature schemes MUST comply with [RFC3279].
+
+   The elliptic curve domain parameters recommended in [X9.62],
+   [FIPS186-2], and [SECG] SHOULD be used.
+
+   The signatureAlgorithm field of the CMS data type SignerInfo can
+   contain one of the following ECC signature algorithm identifiers:
+
+      ecdsa-with-Sha1   [ECCPKALGS]
+      ecdsa-with-Sha256 [ECCPKALGS]
+      ecdsa-with-Sha384 [ECCPKALGS]
+      ecdsa-with-Sha512 [ECCPKALGS]
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 3]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+   The corresponding digestAlgorithm field contains one of the following
+   hash algorithm identifiers respectively:
+
+      id-sha1           [RFC3279]
+      id-sha256         [ECCPKALGS]
+      id-sha384         [ECCPKALGS]
+      id-sha512         [ECCPKALGS]
+
+   Namely id-sha1 MUST be used in conjunction with ecdsa-with-Sha1, id-
+   sha256 MUST be used in conjunction with ecdsa-with-Sha256, id-sha384
+   MUST be used in conjunction with ecdsa-with-Sha384, and id-sha512
+   MUST be used in conjunction with ecdsa-with-Sha512.
+
+   Implementations of this specfication MUST support ecdsa-with-Sha256
+   and SHOULD support ecdsa-with-Sha1.
+
+
+4.  Using ECDH Key Exchange
+
+   This section describes how ECDH can be used as the AS reply key
+   delivery method [PKINIT].  Note that the protocol description is
+   similar to that of Modular Exponential Diffie-Hellman (MODP DH), as
+   described in [PKINIT].
+
+   If the client wishes to use ECDH key agreement method, it encodes its
+   ECDH public key value and the domain parameters [IEEE1363] for its
+   ECDH public key in clientPublicValue of the PA-PK-AS-REQ message
+   [PKINIT].
+
+   As described in [PKINIT], the ECDH domain parameters for the client's
+   public key are specified in the algorithm field of the type
+   SubjectPublicKeyInfo [RFC3279] and the client's ECDH public key value
+   is mapped to a subjectPublicKey (a BIT STRING) according to
+   [RFC3279].
+
+   The following algorithm identifier is used to identify the client's
+   choice of the ECDH key agreement method for key delivery.
+
+        id-ecPublicKey (Elliptic Curve Diffie-Hellman [IEEE1363])
+
+   If the domain parameters are not accepted by the KDC, the KDC sends
+   back an error message [RFC4120] with the code
+   KDC_ERR_DH_KEY_PARAMETERS_NOT_ACCEPTED [PKINIT].  This error message
+   contains the list of domain parameters acceptable to the KDC.  This
+   list is encoded as TD-DH-PARAMETERS [PKINIT], and it is in the KDC's
+   decreasing preference order.  The client can then pick a set of
+   domain parameters from the list and retry the authentication.
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 4]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+   Both the client and the KDC MUST have local policy that specifies
+   which set of domain parameters are acceptable if they do not have a
+   priori knowledge of the chosen domain parameters.  The need for such
+   local policy is explained in Section 6.
+
+   If the ECDH domain parameters are accepted by the KDC, the KDC sends
+   back its ECDH public key value in the subjectPublicKey field of the
+   PA-PK-AS-REP message [PKINIT].
+
+   As described in [PKINIT], the KDC's ECDH public key value is encoded
+   as a BIT STRING according to [RFC3279].
+
+   Note that in the steps above, the client can indicate to the KDC that
+   it wishes to reuse ECDH keys or to allow the KDC to do so, by
+   including the clientDHNonce field in the request [PKINIT], and the
+   KDC can then reuse the ECDH keys and include serverDHNonce field in
+   the reply [PKINIT].  This logic is the same as that of the Modular
+   Exponential Diffie-Hellman key agreement method [PKINIT].
+
+   If ECDH is negotiated as the key delivery method, both the KDC and
+   the client calculate the shared secret value and derive the reply key
+   as follows:
+
+   1) Let DHSharedSecret be the x-coordinate of the shared secret value
+      (an elliptic curve point).  DHSharedSecret is the output of
+      operation ECSVDP-DH as described in Section 7.2.1 of [IEEE1363].
+
+   2) DHSharedSecret is first padded with leading zeros such that the
+      size of DHSharedSecret in octets is the same as that of the
+      modulus, then represented as a string of octets in big-endian
+      order.
+
+   3) The DHSharedSecret value derived above is used as input to the
+      octetstring2key() function to derive the AS reply key k, as
+      described in Section 3.2.3.1 of [PKINIT].
+
+   Both the client and KDC then proceed as described in [PKINIT] and
+   [RFC4120].
+
+   Lastly it should be noted that ECDH can be used with any certificates
+   and signature schemes.  However, a significant advantage of using
+   ECDH together with ECC certificates and signature schemes is that the
+   ECC domain parameters in the client or KDC certificates can be used.
+   This obviates the need of locally preconfigured domain parameters as
+   described in Section 6.
+
+
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 5]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+5.  Choosing the Domain Parameters and the Key Size
+
+   The domain parameters and the key size should be chosen so as to
+   provide sufficient cryptographic security [RFC3766].  The following
+   table, based on table 2 on page 63 of NIST SP800-57 part 1
+   [NISTSP80057], gives approximate comparable key sizes for symmetric-
+   and asymmetric-key cryptosystems based on the best-known algorithms
+   for attacking them.
+
+
+                 Symmetric    |  ECC       |   RSA
+                 -------------+----------- +------------
+                    80        |  160 - 223 |   1024
+                   112        |  224 - 255 |   2048
+                   128        |  256 - 383 |   3072
+                   192        |  384 - 511 |   7680
+                   256        |  512+      |  15360
+
+                Table 1: Comparable key sizes (in bits)
+
+   Thus, for example, when securing a 128-bit symmetric key, it is
+   prudent to use 256-bit Elliptic Curve Cryptography (ECC), e.g. group
+   P-256 (secp256r1) as described below.
+
+   A set of ECDH domain parameters is also known as a curve.  A curve is
+   a named curve if the domain paratmeters are well known and can be
+   identified by an Object Identifier, otherwise it is called a custom
+   curve.  [PKINIT] supports both named curves and custom curves, see
+   Section 6 on the tradeoff of choosing between named curves and custom
+   curves.
+
+   The named curves recommended in this document are also recommended by
+   NIST [FIPS186-2].  These fifteen ECC curves are given in the
+   following table [FIPS186-2] [SECG].
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 6]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+              Description                      SEC 2 OID
+              -----------------                ---------
+
+              ECPRGF192Random  group P-192     secp192r1
+              EC2NGF163Random  group B-163     sect163r2
+              EC2NGF163Koblitz group K-163     sect163k1
+
+              ECPRGF224Random  group P-224     secp224r1
+              EC2NGF233Random  group B-233     sect233r1
+              EC2NGF233Koblitz group K-233     sect233k1
+
+              ECPRGF256Random  group P-256     secp256r1
+              EC2NGF283Random  group B-283     sect283r1
+              EC2NGF283Koblitz group K-283     sect283k1
+
+              ECPRGF384Random  group P-384     secp384r1
+              EC2NGF409Random  group B-409     sect409r1
+              EC2NGF409Koblitz group K-409     sect409k1
+
+              ECPRGF521Random  group P-521     secp521r1
+              EC2NGF571Random  group B-571     sect571r1
+              EC2NGF571Koblitz group K-571     sect571k1
+
+
+6.  Security Considerations
+
+   Kerberos error messages are not integrity protected, as a result, the
+   domain parameters sent by the KDC as TD-DH-PARAMETERS can be tampered
+   with by an attacker so that the set of domain parameters selected
+   could be either weaker or not mutually preferred.  Local policy can
+   configure sets of domain parameters acceptable locally, or disallow
+   the negotiation of ECDH domain parameters.
+
+   Beyond elliptic curve size, the main issue is elliptic curve
+   structure.  As a general principle, it is more conservative to use
+   elliptic curves with as little algebraic structure as possible - thus
+   random curves are more conservative than special curves such as
+   Koblitz curves, and curves over F_p with p random are more
+   conservative than curves over F_p with p of a special form (and
+   curves over F_p with p random might be considered more conservative
+   than curves over F_2^m as there is no choice between multiple fields
+   of similar size for characteristic 2).  Note, however, that algebraic
+   structure can also lead to implementation efficiencies and
+   implementors and users may, therefore, need to balance conservatism
+   against a need for efficiency.  Concrete attacks are known against
+   only very few special classes of curves, such as supersingular
+   curves, and these classes are excluded from the ECC standards such as
+   [IEEE1363] and [X9.62].
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 7]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+   Another issue is the potential for catastrophic failures when a
+   single elliptic curve is widely used.  In this case, an attack on the
+   elliptic curve might result in the compromise of a large number of
+   keys.  Again, this concern may need to be balanced against efficiency
+   and interoperability improvements associated with widely-used curves.
+   Substantial additional information on elliptic curve choice can be
+   found in [IEEE1363], [X9.62] and [FIPS186-2].
+
+
+7.  IANA Considerations
+
+   No IANA actions are required for this document.
+
+
+8.  Acknowledgements
+
+   The following people have made significant contributions to this
+   draft: Paul Leach, Dan Simon, Kelvin Yiu, David Cross and Sam
+   Hartman.
+
+
+9.  References
+
+9.1.  Normative References
+
+   [ECCPKALGS]
+              RFC-Editor: To be replaced by RFC number for draft-ietf-
+              pkix-ecc-pkalgs.  Work in Progress.
+
+   [FIPS186-2]
+              NIST, "Digital Signature Standard", FIPS 186-2, 2000.
+
+   [IEEE1363]
+              IEEE, "Standard Specifications for Public Key Cryptography",
+              IEEE 1363, 2000.
+
+   [NISTSP80057]
+              NIST, "Recommendation on Key Management", 
+              http://csrc.nist.gov/publications/nistpubs/, SP 800-57,
+              August 2005.
+                            
+   [PKINIT]   RFC-Editor: To be replaced by RFC number for draft-ietf-
+              cat-kerberos-pk-init.  Work in Progress.
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 8]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
+              Identifiers for the Internet X.509 Public Key
+              Infrastructure Certificate and Certificate Revocation List
+              (CRL) Profile", RFC 3279, April 2002.
+
+   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
+              X.509 Public Key Infrastructure Certificate and
+              Certificate Revocation List (CRL) Profile", RFC 3280,
+              April 2002.
+
+   [RFC3369]  Housley, R., "Cryptographic Message Syntax (CMS)",
+              RFC 3369, August 2002.
+
+   [RFC3766]  Orman, H. and P. Hoffman, "Determining Strengths For
+              Public Keys Used For Exchanging Symmetric Keys", BCP 86,
+              RFC 3766, April 2004.
+
+   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
+              Kerberos Network Authentication Service (V5)", RFC 4120,
+              July 2005.
+              
+   [X9.62]    ANSI, "Public Key Cryptography For The Financial Services
+              Industry: The Elliptic Curve Digital Signature Algorithm
+              (ECDSA)", ANSI X9.62, 1998.
+
+9.2.  Informative References
+
+   [LENSTRA]  Lenstra, A. and E. Verheul, "Selecting Cryptographic Key 
+              Sizes", Journal of Cryptology 14 (2001) 255-293.
+
+   [SECG]     SECG, "Elliptic Curve Cryptography", SEC 1, 2000,
+              <http://www.secg.org/>.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                 [Page 9]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+Authors' Addresses
+
+   Larry Zhu
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: lzhu@microsoft.com
+
+
+   Karthik Jaganathan
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: karthikj@microsoft.com
+
+
+   Kristin Lauter
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: klauter@microsoft.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                [Page 10]
+
+Internet-Draft           ECC Support for PKINIT           September 2005
+
+
+Intellectual Property Statement
+
+   The IETF takes no position regarding the validity or scope of any
+   Intellectual Property Rights or other rights that might be claimed to
+   pertain to the implementation or use of the technology described in
+   this document or the extent to which any license under such rights
+   might or might not be available; nor does it represent that it has
+   made any independent effort to identify any such rights.  Information
+   on the procedures with respect to rights in RFC documents can be
+   found in BCP 78 and BCP 79.
+
+   Copies of IPR disclosures made to the IETF Secretariat and any
+   assurances of licenses to be made available, or the result of an
+   attempt made to obtain a general license or permission for the use of
+   such proprietary rights by implementers or users of this
+   specification can be obtained from the IETF on-line IPR repository at
+   http://www.ietf.org/ipr.
+
+   The IETF invites any interested party to bring to its attention any
+   copyrights, patents or patent applications, or other proprietary
+   rights that may cover technology that may be required to implement
+   this standard.  Please address the information to the IETF at
+   ietf-ipr@ietf.org.
+
+
+Disclaimer of Validity
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
+   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
+   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
+   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
+   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+
+Copyright Statement
+
+   Copyright (C) The Internet Society (2005).  This document is subject
+   to the rights, licenses and restrictions contained in BCP 78, and
+   except as set forth therein, the authors retain all their rights.
+
+
+Acknowledgment
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
+
+
+
+Zhu, et al.              Expires March 17, 2006                [Page 11]
+
+

doc/standardisation/draft-zhu-pkinit-ecc-01.txt

@@ -0,0 +1,611 @@
+
+
+
+NETWORK WORKING GROUP                                             L. Zhu
+Internet-Draft                                             K. Jaganathan
+Expires: September 3, 2006                                     K. Lauter
+                                                   Microsoft Corporation
+                                                           March 2, 2006
+
+
+                         ECC Support for PKINIT
+                        draft-zhu-pkinit-ecc-01
+
+Status of this Memo
+
+   By submitting this Internet-Draft, each author represents that any
+   applicable patent or other IPR claims of which he or she is aware
+   have been or will be disclosed, and any of which he or she becomes
+   aware will be disclosed, in accordance with Section 6 of BCP 79.
+
+   Internet-Drafts are working documents of the Internet Engineering
+   Task Force (IETF), its areas, and its working groups.  Note that
+   other groups may also distribute working documents as Internet-
+   Drafts.
+
+   Internet-Drafts are draft documents valid for a maximum of six 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."
+
+   The list of current Internet-Drafts can be accessed at
+   http://www.ietf.org/ietf/1id-abstracts.txt.
+
+   The list of Internet-Draft Shadow Directories can be accessed at
+   http://www.ietf.org/shadow.html.
+
+   This Internet-Draft will expire on September 3, 2006.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2006).
+
+Abstract
+
+   This document describes the use of Elliptic Curve certificates,
+   Elliptic Curve signature schemes and Elliptic Curve Diffie-Hellman
+   (ECDH) key agreement within the framework of PKINIT - the Kerberos
+   Version 5 extension that provides for the use of public key
+   cryptography.
+
+
+
+
+
+Zhu, et al.             Expires September 3, 2006               [Page 1]
+
+Internet-Draft           ECC Support for PKINIT               March 2006
+
+
+Table of Contents
+
+   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
+   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
+   3.  Using Elliptic Curve Certificates and Elliptic Curve
+       Signature Schemes  . . . . . . . . . . . . . . . . . . . . . .  3
+   4.  Using ECDH Key Exchange  . . . . . . . . . . . . . . . . . . .  4
+   5.  Choosing the Domain Parameters and the Key Size  . . . . . . .  5
+   6.  Interoperability Requirements  . . . . . . . . . . . . . . . .  7
+   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
+   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
+   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
+   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
+     10.1.  Normative References  . . . . . . . . . . . . . . . . . .  8
+     10.2.  Informative References  . . . . . . . . . . . . . . . . .  9
+   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
+   Intellectual Property and Copyright Statements . . . . . . . . . . 11
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+1.  Introduction
+
+   Elliptic Curve Cryptography (ECC) is emerging as an attractive
+   public-key cryptosystem that provides security equivalent to
+   currently popular public-key mechanisms such as RSA and DSA with
+   smaller key sizes [LENSTRA] [NISTSP80057].
+
+   Currently [PKINIT] permits the use of ECC algorithms but it does not
+   specify how ECC parameters are chosen and how to derive the shared
+   key for key delivery using Elliptic Curve Diffie-Hellman (ECDH)
+   [IEEE1363] [X9.63].
+
+   This document describes how to use Elliptic Curve certificates,
+   Elliptic Curve signature schemes, and ECDH with [PKINIT].  However,
+   it should be noted that there is no syntactic or semantic change to
+   the existing [PKINIT] messages.  Both the client and the KDC
+   contribute one ECDH key pair using the key agrement protocol
+   described in this document.
+
+
+2.  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].
+
+
+3.  Using Elliptic Curve Certificates and Elliptic Curve Signature
+    Schemes
+
+   ECC certificates and signature schemes can be used in the
+   Cryptographic Message Syntax (CMS) [RFC3369] content type
+   'SignedData'.
+
+   X.509 certificates [RFC3280] containing ECC public keys or signed
+   using ECC signature schemes MUST comply with [RFC3279].
+
+   The elliptic curve domain parameters recommended in [X9.62],
+   [FIPS186-2], and [SECG] SHOULD be used.
+
+   The signatureAlgorithm field of the CMS data type SignerInfo can
+   contain one of the following ECC signature algorithm identifiers:
+
+      ecdsa-with-Sha1   [ECCPKALGS]
+      ecdsa-with-Sha256 [ECCPKALGS]
+      ecdsa-with-Sha384 [ECCPKALGS]
+      ecdsa-with-Sha512 [ECCPKALGS]
+
+
+
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+   The corresponding digestAlgorithm field contains one of the following
+   hash algorithm identifiers respectively:
+
+      id-sha1           [RFC3279]
+      id-sha256         [ECCPKALGS]
+      id-sha384         [ECCPKALGS]
+      id-sha512         [ECCPKALGS]
+
+   Namely id-sha1 MUST be used in conjunction with ecdsa-with-Sha1, id-
+   sha256 MUST be used in conjunction with ecdsa-with-Sha256, id-sha384
+   MUST be used in conjunction with ecdsa-with-Sha384, and id-sha512
+   MUST be used in conjunction with ecdsa-with-Sha512.
+
+   Implementations of this specfication MUST support ecdsa-with-Sha256
+   and SHOULD support ecdsa-with-Sha1.
+
+
+4.  Using ECDH Key Exchange
+
+   This section describes how ECDH can be used as the AS reply key
+   delivery method [PKINIT].  Note that the protocol description here is
+   similar to that of Modular Exponential Diffie-Hellman (MODP DH), as
+   described in [PKINIT].
+
+   If the client wishes to use ECDH key agreement method, it encodes its
+   ECDH public key value and the domain parameters [IEEE1363] [X9.63]
+   for its ECDH public key in clientPublicValue of the PA-PK-AS-REQ
+   message [PKINIT].
+
+   As described in [PKINIT], the ECDH domain parameters for the client's
+   public key are specified in the algorithm field of the type
+   SubjectPublicKeyInfo [RFC3279] and the client's ECDH public key value
+   is mapped to a subjectPublicKey (a BIT STRING) according to
+   [RFC3279].
+
+   The following algorithm identifier is used to identify the client's
+   choice of the ECDH key agreement method for key delivery.
+
+        id-ecPublicKey (Elliptic Curve Diffie-Hellman [ECCPKALGS])
+
+   If the domain parameters are not accepted by the KDC, the KDC sends
+   back an error message [RFC4120] with the code
+   KDC_ERR_DH_KEY_PARAMETERS_NOT_ACCEPTED [PKINIT].  This error message
+   contains the list of domain parameters acceptable to the KDC.  This
+   list is encoded as TD-DH-PARAMETERS [PKINIT], and it is in the KDC's
+   decreasing preference order.  The client can then pick a set of
+   domain parameters from the list and retry the authentication.
+
+
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+   Both the client and the KDC MUST have local policy that specifies
+   which set of domain parameters are acceptable if they do not have a
+   priori knowledge of the chosen domain parameters.  The need for such
+   local policy is explained in Section 7.
+
+   If the ECDH domain parameters are accepted by the KDC, the KDC sends
+   back its ECDH public key value in the subjectPublicKey field of the
+   PA-PK-AS-REP message [PKINIT].
+
+   As described in [PKINIT], the KDC's ECDH public key value is encoded
+   as a BIT STRING according to [RFC3279].
+
+   Note that in the steps above, the client can indicate to the KDC that
+   it wishes to reuse ECDH keys or to allow the KDC to do so, by
+   including the clientDHNonce field in the request [PKINIT], and the
+   KDC can then reuse the ECDH keys and include serverDHNonce field in
+   the reply [PKINIT].  This logic is the same as that of the Modular
+   Exponential Diffie-Hellman key agreement method [PKINIT].
+
+   If ECDH is negotiated as the key delivery method, then the PA-PK-AS-
+   REP and AS reply key are generated as in Section 3.2.3.1 of [PKINIT]
+   with the following difference: The DHSharedSecret is the x-coordinate
+   of the shared secret value (an elliptic curve point); DHSharedSecret
+   is the output of operation ECSVDP-DH as described in Section 7.2.1 of
+   [IEEE1363].
+
+   Both the client and KDC then proceed as described in [PKINIT] and
+   [RFC4120].
+
+   Lastly it should be noted that ECDH can be used with any certificates
+   and signature schemes.  However, a significant advantage of using
+   ECDH together with ECC certificates and signature schemes is that the
+   ECC domain parameters in the client or KDC certificates can be used.
+   This obviates the need of locally preconfigured domain parameters as
+   described in Section 7.
+
+
+5.  Choosing the Domain Parameters and the Key Size
+
+   The domain parameters and the key size should be chosen so as to
+   provide sufficient cryptographic security [RFC3766].  The following
+   table, based on table 2 on page 63 of NIST SP800-57 part 1
+   [NISTSP80057], gives approximate comparable key sizes for symmetric-
+   and asymmetric-key cryptosystems based on the best-known algorithms
+   for attacking them.
+
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+                 Symmetric    |  ECC       |   RSA
+                 -------------+----------- +------------
+                    80        |  160 - 223 |   1024
+                   112        |  224 - 255 |   2048
+                   128        |  256 - 383 |   3072
+                   192        |  384 - 511 |   7680
+                   256        |  512+      |  15360
+
+                Table 1: Comparable key sizes (in bits)
+
+   Thus, for example, when securing a 128-bit symmetric key, it is
+   prudent to use 256-bit Elliptic Curve Cryptography (ECC), e.g. group
+   P-256 (secp256r1) as described below.
+
+   A set of ECDH domain parameters is also known as a curve.  A curve is
+   a named curve if the domain paratmeters are well known and can be
+   identified by an Object Identifier, otherwise it is called a custom
+   curve.  [PKINIT] supports both named curves and custom curves, see
+   Section 7 on the tradeoff of choosing between named curves and custom
+   curves.
+
+   The named curves recommended in this document are also recommended by
+   NIST [FIPS186-2].  These fifteen ECC curves are given in the
+   following table [FIPS186-2] [SECG].
+
+              Description                      SEC 2 OID
+              -----------------                ---------
+
+              ECPRGF192Random  group P-192     secp192r1
+              EC2NGF163Random  group B-163     sect163r2
+              EC2NGF163Koblitz group K-163     sect163k1
+
+              ECPRGF224Random  group P-224     secp224r1
+              EC2NGF233Random  group B-233     sect233r1
+              EC2NGF233Koblitz group K-233     sect233k1
+
+              ECPRGF256Random  group P-256     secp256r1
+              EC2NGF283Random  group B-283     sect283r1
+              EC2NGF283Koblitz group K-283     sect283k1
+
+              ECPRGF384Random  group P-384     secp384r1
+              EC2NGF409Random  group B-409     sect409r1
+              EC2NGF409Koblitz group K-409     sect409k1
+
+              ECPRGF521Random  group P-521     secp521r1
+              EC2NGF571Random  group B-571     sect571r1
+              EC2NGF571Koblitz group K-571     sect571k1
+
+
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+6.  Interoperability Requirements
+
+   Implementations conforming to this specification MUST support curve
+   P-256 and P-384.
+
+
+7.  Security Considerations
+
+   Kerberos error messages are not integrity protected, as a result, the
+   domain parameters sent by the KDC as TD-DH-PARAMETERS can be tampered
+   with by an attacker so that the set of domain parameters selected
+   could be either weaker or not mutually preferred.  Local policy can
+   configure sets of domain parameters acceptable locally, or disallow
+   the negotiation of ECDH domain parameters.
+
+   Beyond elliptic curve size, the main issue is elliptic curve
+   structure.  As a general principle, it is more conservative to use
+   elliptic curves with as little algebraic structure as possible - thus
+   random curves are more conservative than special curves such as
+   Koblitz curves, and curves over F_p with p random are more
+   conservative than curves over F_p with p of a special form (and
+   curves over F_p with p random might be considered more conservative
+   than curves over F_2^m as there is no choice between multiple fields
+   of similar size for characteristic 2).  Note, however, that algebraic
+   structure can also lead to implementation efficiencies and
+   implementors and users may, therefore, need to balance conservatism
+   against a need for efficiency.  Concrete attacks are known against
+   only very few special classes of curves, such as supersingular
+   curves, and these classes are excluded from the ECC standards such as
+   [IEEE1363] and [X9.62].
+
+   Another issue is the potential for catastrophic failures when a
+   single elliptic curve is widely used.  In this case, an attack on the
+   elliptic curve might result in the compromise of a large number of
+   keys.  Again, this concern may need to be balanced against efficiency
+   and interoperability improvements associated with widely-used curves.
+   Substantial additional information on elliptic curve choice can be
+   found in [IEEE1363], [X9.62] and [FIPS186-2].
+
+
+8.  IANA Considerations
+
+   No IANA actions are required for this document.
+
+
+9.  Acknowledgements
+
+   The following people have made significant contributions to this
+
+
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+   draft: Paul Leach, Dan Simon, Kelvin Yiu, David Cross, Sam Hartman,
+   Tolga Acar, and Stefan Santesson.
+
+
+10.  References
+
+10.1.  Normative References
+
+   [ECCPKALGS]
+              RFC-Editor: To be replaced by RFC number for draft-ietf-
+              pkix-ecc-pkalgs.  Work in Progress.
+
+   [FIPS186-2]
+              NIST, "Digital Signature Standard", FIPS 186-2, 2000.
+
+   [IEEE1363]
+              IEEE, "Standard Specifications for Public Key Cryptography",
+              IEEE 1363, 2000.
+
+   [NISTSP80057]
+              NIST, "Recommendation on Key Management", 
+              http://csrc.nist.gov/publications/nistpubs/, SP 800-57,
+              August 2005.
+
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+   [PKINIT]   RFC-Editor: To be replaced by RFC number for draft-ietf-
+              cat-kerberos-pk-init.  Work in Progress.
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
+              Identifiers for the Internet X.509 Public Key
+              Infrastructure Certificate and Certificate Revocation List
+              (CRL) Profile", RFC 3279, April 2002.
+
+   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
+              X.509 Public Key Infrastructure Certificate and
+              Certificate Revocation List (CRL) Profile", RFC 3280,
+              April 2002.
+
+   [RFC3369]  Housley, R., "Cryptographic Message Syntax (CMS)",
+              RFC 3369, August 2002.
+
+   [RFC3766]  Orman, H. and P. Hoffman, "Determining Strengths For
+              Public Keys Used For Exchanging Symmetric Keys", BCP 86,
+              RFC 3766, April 2004.
+
+   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
+              Kerberos Network Authentication Service (V5)", RFC 4120,
+              July 2005.
+
+   [X9.62]    ANSI, "Public Key Cryptography For The Financial Services
+              Industry: The Elliptic Curve Digital Signature Algorithm
+              (ECDSA)", ANSI X9.62, 1998.
+  
+   [X9.63]    ANSI, "Public Key Cryptography for the Financial Services 
+              Industry: Key Agreement and Key Transport using Elliptic 
+              Curve Cryptography", ANSI X9.63, 2001.
+              
+
+9.2.  Informative References
+
+   [LENSTRA]  Lenstra, A. and E. Verheul, "Selecting Cryptographic Key 
+              Sizes", Journal of Cryptology 14 (2001) 255-293.
+
+   [SECG]     SECG, "Elliptic Curve Cryptography", SEC 1, 2000,
+              <http://www.secg.org/>.
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+Authors' Addresses
+
+   Larry Zhu
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: lzhu@microsoft.com
+
+
+   Karthik Jaganathan
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: karthikj@microsoft.com
+
+
+   Kristin Lauter
+   Microsoft Corporation
+   One Microsoft Way
+   Redmond, WA  98052
+   US
+
+   Email: klauter@microsoft.com
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+Intellectual Property Statement
+
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+
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+Acknowledgment
+
+   Funding for the RFC Editor function is currently provided by the
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+
+
+
+
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+