Online Certificate Status Protocol Algorithm Agility
RFC 6277

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Internet Engineering Task Force (IETF)                      S. Santesson
Request for Comments: 6277                                  3xA Security
Updates: 2560                                            P. Hallam-Baker
Category: Standards Track                          Default Deny Security
ISSN: 2070-1721                                                June 2011

          Online Certificate Status Protocol Algorithm Agility

Abstract

   The Online Certificate Status Protocol (OCSP) requires server
   responses to be signed but does not specify a mechanism for selecting
   the signature algorithm to be used.  This may lead to avoidable
   interoperability failures in contexts where multiple signature
   algorithms are in use.  This document specifies rules for server
   signature algorithm selection and an extension that allows a client
   to advise a server that specific signature algorithms are supported.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6277.

Copyright Notice

   Copyright (c) 2011 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
   (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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Santesson & Hallam-Baker     Standards Track                    [Page 1]
RFC 6277                 OCSP Algorithm Agility                June 2011

Table of Contents

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................3
   2. OCSP Algorithm Agility Requirements .............................3
   3. Updates to Mandatory and Optional Cryptographic Algorithms ......4
   4. Client Indication of Preferred Signature Algorithms .............4
   5. Responder Signature Algorithm Selection .........................5
      5.1. Dynamic Response ...........................................5
      5.2. Static Response ............................................6
   6. Acknowledgements ................................................6
   7. Security Considerations .........................................6
      7.1. Use of Insecure Algorithms .................................6
      7.2. Man-in-the-Middle Downgrade Attack .........................7
      7.3. Denial-of-Service Attack ...................................7
   8. References ......................................................7
      8.1. Normative References .......................................7
      8.2. Informative References .....................................8
   Appendix A.  ASN.1 Modules .........................................9
      A.1. ASN.1 Module ...............................................9
      A.2. 1988 ASN.1 Module .........................................10

1.  Introduction

   The Online Certificate Status Protocol (OCSP) [RFC2560] defines a
   protocol for obtaining certificate status information from an online
   service.  An OCSP responder may or may not be issued an OCSP
   responder certificate by the certification authority (CA) that issued
   the certificate whose status is being queried.  An OCSP responder may
   provide pre-signed OCSP responses or may sign responses when queried.

   RFC 2560 [RFC2560] specifies a means for an OCSP responder to
   indicate the signature and digest algorithms used in a response but
   not how those algorithms are specified.  The only algorithm
   requirements established by that protocol specification are that the
   OCSP client SHALL support the Digital Signature Algorithm (DSA) sig-
   alg-oid specified in Section 7.2.2 of [RFC2459] and SHOULD be capable
   of processing RSA signatures as specified in Section 7.2.1 of
   [RFC2459].  The only requirement placed on responders by RFC 2560 is
   that they SHALL support the SHA1 hashing algorithm.

   This document specifies rules for server signature algorithm
   selection and an extension that allows a client to advise a server
   that specific signature algorithms are supported.