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Network Working Group                                             L. ZhuRequest for Comments: 4557                                 K. JaganathanCategory: Standards Track                          Microsoft Corporation                                                             N. Williams                                                        Sun Microsystems                                                               June 2006Online Certificate Status Protocol (OCSP) Support forPublic Key Cryptography forInitial Authentication in Kerberos (PKINIT)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   This document defines a mechanism to enable in-band transmission of   Online Certificate Status Protocol (OCSP) responses in the Kerberos   network authentication protocol.  These responses are used to verify   the validity of the certificates used in Public Key Cryptography for   Initial Authentication in Kerberos (PKINIT), which is the Kerberos   Version 5 extension that provides for the use of public key   cryptography.Table of Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................23. Message Definition ..............................................24. Security Considerations .........................................35. Acknowledgements ................................................46. References ......................................................46.1. Normative References .......................................46.2. Informative References .....................................4Zhu, et al.                 Standards Track                     [Page 1]

RFC 4557                OCSP Support for PKINIT                June 20061.  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 the certificates for Kerberos Key Distribution Center   (KDC) in order to avoid transmission of large Certificate Revocation   Lists (CRLs) and therefore save bandwidth on constrained networks   [OCSP-PROFILE].   This document defines a pre-authentication type [RFC4120], where the   client and the KDC MAY piggyback OCSP responses for certificates used   in authentication exchanges, as defined in [RFC4556].   By using this OPTIONAL extension, PKINIT clients and the KDC can   maximize the reuse of cached OCSP responses.2.  Conventions Used in This Document   In this document, the key words "MUST", "MUST NOT", "REQUIRED",   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",   and "OPTIONAL" 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              18   The corresponding padata-value field [RFC4120] contains the DER [X60]   encoding of the following ASN.1 type:          PKOcspData ::= SEQUENCE OF OcspResponse                         -- If more than one OcspResponse is                         -- included, the first OcspResponse                         -- MUST contain the OCSP response                         -- for the signer's certificate.                         -- The signer refers to the client for                         -- AS-REQ, and the KDC for the AS-REP,                         -- respectively.          OcspResponse ::= OCTET STRING                         -- Contains a complete OCSP response,                         -- as defined in [RFC2560].   The client MAY send OCSP responses for certificates used in PA-PK-   AS-REQ [RFC4556] via a PA-PK-OCSP-RESPONSE.Zhu, et al.                 Standards Track                     [Page 2]

RFC 4557                OCSP Support for PKINIT                June 2006   The KDC that receives a PA-PK-OCSP-RESPONSE SHOULD send a PA-PK-   OCSP-RESPONSE containing OCSP responses for certificates used in the   KDC's PA-PK-AS-REP.  The client can request a PA-PK-OCSP-RESPONSE by   using a PKOcspData containing an empty sequence.   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 [RFC4556].   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 be needed   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 its own revocation status verification independently.4.  Security Considerations   The pre-authentication data in this document do not actually   authenticate any principals, but are designed to be used in   conjunction with PKINIT.   There is no binding between PA-PK-OCSP-RESPONSE pre-authentication   data and PKINIT pre-authentication data other than a given OCSP   response corresponding to a certificate used in a PKINIT pre-   authentication data element.  Attacks involving removal or   replacement of PA-PK-OCSP-RESPONSE pre-authentication data elements   are, at worst, downgrade attacks, where a PKINIT client or KDC would   proceed without use of CRLs or OCSP for certificate validation, or   denial-of-service attacks, where a PKINIT client or KDC that cannot   validate the other's certificate without an accompanying OCSP   response might reject the AS exchange or might have to download very   large CRLs in order to continue.  Kerberos V does not protect against   denial-of-service attacks; therefore, the denial-of-service aspect of   these attacks is acceptable.Zhu, et al.                 Standards Track                     [Page 3]

RFC 4557                OCSP Support for PKINIT                June 2006   If a PKINIT client or KDC cannot validate certificates without the   aid of a valid PA-PK-OCSP-RESPONSE, then it SHOULD fail the AS   exchange, possibly according to local configuration.5.  Acknowledgements   This document was based on conversations among the authors, Jeffrey   Altman, Sam Hartman, Martin Rex, and other members of the Kerberos   working group.6.  References6.1.  Normative References   [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.   [RFC4120]      Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The                  Kerberos Network Authentication Service (V5)",RFC4120, July 2005.   [RFC4556]      Zhu, L. and B. Tung, "Public Key Cryptography for                  Initial Authentication in Kerberos (PKINIT)",RFC4556, June 2006.   [X690]         ASN.1 encoding rules: Specification of Basic Encoding                  Rules (BER), Canonical Encoding Rules (CER) and                  Distinguished Encoding Rules (DER), ITU-T                  Recommendation X.690 (1997) | ISO/IEC International                  Standard 8825-1:1998.6.2.  Informative References   [OCSP-PROFILE] Deacon, A. and R. Hurst, "Lightweight OCSP Profile for                  High Volume Environments", Work in Progress, May 2006.Zhu, et al.                 Standards Track                     [Page 4]

RFC 4557                OCSP Support for PKINIT                June 2006Authors' 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.comZhu, et al.                 Standards Track                     [Page 5]

RFC 4557                OCSP Support for PKINIT                June 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   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.Intellectual Property   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 inBCP 78 andBCP 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 athttp://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.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Zhu, et al.                 Standards Track                     [Page 6]