NETWORK WORKING GROUP                                             L. Zhu
Internet-Draft                                             K. Jaganathan
Expires: February 8, May 21, 2005                              Microsoft Corporation
                                                             N. Williams
                                                        Sun Microsystems
                                                         August 10,
                                                       November 20, 2004

                        OCSP Support for PKINIT
                   draft-ietf-krb-wg-ocsp-for-pkinit-01
                 draft-ietf-krb-wg-ocsp-for-pkinit-02

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   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document defines a mechanism to enable in-band transmission of
   OCSP responses.  These responses are used to verify the validity of
   the certificates used in PKINIT - the Kerberos Version 5 extension
   that provides for the use of public key cryptography.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Conventions Used in This Document  . . . . . . . . . . . . . .   4
   3.   Message Definition . . . . . . . . . . . . . . . . . . . . . .   5
   4.   Security Considerations  . . . . . . . . . . . . . . . . . . .   6
   5.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . .   7
   6.   References   Acknowledgement  . . . . . . . . . . . . . . . . . . . . . .   8
   7.   References . . . . 7 . . . . . . . . . . . . . . . . . . . . .   8
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7   8
        Intellectual Property and Copyright Statements . . . . . . . . 9  10

1.  Introduction

   Online Certificate Status Protocol (OCSP) [RFC2560] enables
   applications to obtain timely information regarding the revocation
   status of a certificate.  Because OCSP responses are well-bounded and
   small in size, constrained clients may wish to use OCSP to check the
   validity of KDC certificates in order to avoid transmission of large
   Certificate Revocation Lists (CRLs) and therefore save bandwidth on
   constrained networks. networks [OCSP-PROFILE].

   This document defines a pre-authentication type [CLARIFICATIONS],
   where the client and the KDC MAY piggyback OCSP responses for
   certificates used in authentication exchanges, as defined in
   [PKINIT].

   By using this OPTIONAL extension, PKINIT clients and the KDC can
   maximize the reuse of cached OCSP responses.

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.  Message Definition

   A pre-authentication type identifier is defined for this mechanism:

              PA-PK-OCSP-RESPONSE              16

   The corresponding pre-authentication field contains OCSP data as
   follows:

          PA-PK-OCSP-DATA ::= SEQUENCE OF OcspResponse

          OcspResponse ::= OCTET STRING
                         -- contains a complete OCSP response,
                         -- defined in [RFC2560]

   The client MAY send OCSP responses for certificates used in
   PA-PK-AS-REQ [PKINIT] via a PA-PK-OCSP-RESPONSE.

   The KDC that receives a PA-PK-OCSP-RESPONSE the SHOULD send a
   PA-PK-OCSP-RESPONSE in response.  The client can request a
   PA-PK-OCSP-RESPONSE by using an empty sequence in its request.

   The KDC MAY send a PA-PK-OCSP-RESPONSE when it does not receive a
   PA-PK-OCSP-RESPONSE from the client.

   The PA-PK-OCSP-RESPONSE sent by the KDC contains OCSP responses for
   certificates used in PA-PK-AS-REP [PKINIT].

   Note the lack of integrity protection for the empty or missing OCSP
   response; lack of an expected OCSP response from the KDC for the
   KDC's certificates SHOULD be treated as an error by the client,
   unless it is configured otherwise.

   When using OCSP, the response is signed by the OCSP server, which is
   trusted by the receiver.  Depending on local policy, further
   verification of the validity of the OCSP servers MAY need to be done.

   The client and the KDC SHOULD ignore invalid OCSP responses received
   via this mechanism, and they MAY implement CRL processing logic as a
   fall-back position, if the OCSP responses received via this mechanism
   alone are not sufficient for the verification of certificate
   validity.  The client and/or the KDC MAY ignore a valid OCSP response
   and perform their own revocation status verification independently.

4.  Security Considerations

   The pre-authentication data in this document do not actually
   authenticate any principals, and MUST be used in conjunction with
   PKINIT.

   There is a downgrade attack against clients which want OCSP responses
   from the KDC for the KDC's certificates.  The clients, however, can
   treat the absence of valid OCSP responses as an error, based on their
   local configuration.

5.  IANA Considerations

   This document defines a new pre-authentication type for use with
   PKINIT to encode OCSP responses.  The official value for this padata
   identifier need to be acquired from IANA.

6

6.  Acknowledgements

   This document was based on conversations among the authors, Jeffrey
   Altman, Sam Hartman, Martin Rex and other members of the Kerberos
   working group.

7  References

   [CLARIFICATIONS]
              Neuman, B., Yu, Y., Hartman, S. and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)",
              draft-ietf-krb-wg-kerberos-clarifications, Work in
              progress.

   [OCSP-PROFILE]
              Deacon, A. and R. Hurst, "Lightweight OCSP Profile for
              High Volume Environments",
              draft-ietf-pkix-lightweight-ocsp-profile, Work in
              progress.

   [PKINIT]   Tung, B., Neuman, B. and B. Neuman, S. Medvinsky, "Public Key
              Cryptography for Initial Authentication in Kerberos",
              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.

   [RFC2560]  Myers, M., Ankney, R., Malpani, A., Galperin, S. and C.
              Adams, "X.509 Internet Public Key Infrastructure Online
              Certificate Status Protocol - OCSP", RFC 2560, June 1999.

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
   Nicolas Williams
   Sun Microsystems
   5300 Riata Trace Ct
   Austin, TX  78727
   US

   EMail: Nicolas.Williams@sun.com

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Copyright Statement

   Copyright (C) The Internet Society (2004).  This document is subject
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Acknowledgment

   This document was based on conversations among

   Funding for the authors, Jeffrey
   Altman, Sam Hartman, Martin Rex, and other members of RFC Editor function is currently provided by the Kerberos
   working group.
   Internet Society.