LAMPS                                                      M. Sahni, Ed.
Internet-Draft                                        Palo Alto Networks
Intended status: Standards Track                          April 23, 26, 2020
Expires: October 25, 28, 2020

                          OCSP Nonce Extension
                     draft-ietf-lamps-ocsp-nonce-00
                     draft-ietf-lamps-ocsp-nonce-01

Abstract

   This document specifies the updated format of the Nonce extension in
   Online Certificate Status Protocol (OCSP) request and response
   messages.  OCSP is used to check the status of a certificate and the
   Nonce extension is used in the OCSP request and response messages to
   avoid replay attacks.  This document updates the RFC 6960

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Nonce Extension . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4   3
     3.1.  Replay Attack . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Nonce Collision . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Changes to Appendix B. of RFC 6960  . . . . . . . . . . . . .   4
     5.1.  Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax  . .   4
     5.2.  Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6   5
     6.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This document updates the usage and format of the Nonce extension
   used in OCSP request and response messages.  This extension was
   previously defined in section 4.1.1 of [RFC6960].  The [RFC6960] does
   not mention any minimum and maximum length of the nonce extension.
   Due to not having an upper or lower limit of the length of the Nonce
   extension, the OCSP responders that follow [RFC6960] may be
   vulnerable to various attacks like Denial of Service attacks
   [RFC4732], chosen prefix attacks to get a desired signature from the
   OCSP responder and possible evasions that can use the Nonce extension
   data for evasion.  This document specifies a lower limit of 1 and an
   upper limit of 32 to the length of the Nonce extension.  This
   document updates the [RFC6960].

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  OCSP Extensions

   The message format for the OCSP request and response is defined in
   the [RFC6960].  It also defines the standard extensions for OCSP
   messages based on the extension model employed in X.509 version 3
   certificates (see [RFC5280]).  Following is the list of standard
   extensions that can be used in the OCSP messages by the OCSP
   responder and OCSP client.

   *  Nonce
   *  CRL References
   *  Acceptable Response Types
   *  Archive Cutoff
   *  CRL Entry Extensions
   *  Service Locator
   *  Preferred Signature Algorithms
   *  Extended Response Definition

   This document only specifies the new format for Nonce extension and
   does not change the specification of any of the other standard
   extensions.

2.1.  Nonce Extension

   This section updates the Section 4.4.1 [1] of [RFC6960] which
   describes the OCSP Nonce extension.

   The nonce cryptographically binds a request and a response to prevent
   replay attacks.  The nonce is included as one of the
   requestExtensions in requests, while in responses it would be
   included as one of the responseExtensions.  In both the request and
   the response, the nonce will be identified by the object identifier
   id-pkix-ocsp-nonce, while the extnValue is the value of the nonce.
   If Nonce extension is present then the length of nonce MUST be at
   least 1 octet and can be up to 32 octets.

   A server MUST reject any OCSP request having a Nonce extension with
   length of more than 32 octets with the malformedRequest
   OCSPResponseStatus as described in section 4.2.1 of [RFC6960]

   The minimum nonce length of 1 octet is defined to provide the
   backward compatibility with clients following [RFC6960].  However the
   newer OCSP clients MUST use length of at least 16 octets for Nonce
   extension and the value of the nonce MUST be generated using a
   cryptographically strong pseudorandom number generator.

      id-pkix-ocsp           OBJECT IDENTIFIER ::= { id-ad-ocsp }

      id-pkix-ocsp-nonce     OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }

      Nonce ::= OCTET STRING(SIZE(1..32))

3.  Security Considerations

   The security considerations of OCSP, in general, are described in the
   [RFC6960].  The Nonce extension is used to avoid replay attacks
   during the interval in which the previous OCSP response for a
   certificate is not expired but the responder has a changed status for
   that certificate.  Including client's Nonce value in the OCSP
   response makes sure that the response is the latest response from the
   server and not an old copy.

3.1.  Replay Attack

   The Nonce extension is used to avoid replay attacks.  Since the OCSP
   responder may choose to not send the Nonce extension in the OCSP
   response even if the client has sent the Nonce extension in the
   request [RFC5019], a man in the middle (MITM) entity can intercept
   the OCSP request and respond with an earlier response from the server
   without the Nonce extension.  This can be mitigated by the server
   using a closer nextUpdate value in the OCSP response.

3.2.  Nonce Collision

   If the value of the nonce used by a client is not random enough, then
   an attacker may prefetch responses with the predicted nonce and can
   replay them, thus defeating the purpose of using nonce.  Therefore
   the client MUST use a nonce value that contains cryptographically
   strong randomness and is freshly generated.  Also if the length of
   the nonce is very small e.g. 1 octet then an attacker can prefetch
   responses with all the possible values of the nonce and replay a
   matching nonce.  A client SHOULD use 32 octets for the nonce length.

4.  IANA Considerations

      This document does not include any new media type registrations
      for OCSP.

5.  Changes to Appendix B. of RFC 6960

   This section updates the ASN.1 definitions of the OCSP Nonce
   extension in the Appendix B.1 and Appendix B.2 of the [RFC6960] The
   Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2
   defines OCSP using ASN.1 - 2008 Syntax

5.1.  Changes to Appendix B.1.  OCSP in ASN.1 - 1998 Syntax

   OLD Syntax:

   The definition of OCSP Nonce Extension is not provided in the
   Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax.

   NEW Syntax:

       Nonce ::= OCTET STRING(SIZE(1..32))

5.2.  Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax

   OLD Syntax:

       re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING IDENTIFIED
           BY id-pkix-ocsp-nonce }

   NEW Syntax:

       re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING(SIZE(1..32))
           IDENTIFIED BY id-pkix-ocsp-nonce }

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", DOI 10.17487/RFC8174, RFC 8174, BCP 14,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC6960]  Santesson, S., Myers, M., Ankney, R., Malpani, A.,
              Galperin, S., and C. Adams, "X.509 Internet Public Key
              Infrastructure Online Certificate Status Protocol - OCSP",
              RFC 6960, DOI 10.17487/RFC6960, June 2013,
              <https://www.rfc-editor.org/info/rfc6960>.

6.2.  Informative References

   [RFC4732]  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
              Denial-of-Service Considerations", RFC 4732,
              DOI 10.17487/RFC4732, December 2006,
              <https://www.rfc-editor.org/info/rfc4732>.

   [RFC5019]  Deacon, A. and R. Hurst, "The Lightweight Online
              Certificate Status Protocol (OCSP) Profile for High-Volume
              Environments", RFC 5019, DOI 10.17487/RFC5019, September
              2007, <https://www.rfc-editor.org/info/rfc5019>.

6.3.  URIs

   [1] https://tools.ietf.org/html/rfc6960#section-4.4.1

Author's Address

   Mohit Sahni (editor)
   Palo Alto Networks
   3000 Tannery Way
   Santa Clara, CA  95054
   US

   Email: msahni@paloaltonetworks.com