LAMPS                                                      M. Sahni, Ed.
Internet-Draft                                        Palo Alto Networks
Updates: 6960 (if approved)                           September 2, 10, 2020
Intended status: Standards Track
Expires: March 6, 14, 2021

                          OCSP Nonce Extension
                     draft-ietf-lamps-ocsp-nonce-04
                     draft-ietf-lamps-ocsp-nonce-05

Abstract

   This document specifies the updated format of the Nonce extension in
   the 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 to cryptographically bind an OCSP request and response messages
   message to
   avoid replay attacks. a particular OCSP request message.  This document updates the
   RFC 6960.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . .   3   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  . . . . . . . . . . . . .   5   4
     5.1.  Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax  . .   5   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
   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 4.4.1 of [RFC6960].  The  [RFC6960] does not
   mention any minimum and maximum length of the nonce in the Nonce
   extension.
   Due to not having an upper or lower limit of  Lacking limits on the length of nonce in the Nonce
   extension, the an 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 signature, and possible evasions that can use
   using the Nonce extension
   data for evasion. data.  This document specifies a lower
   limit of 1 and an upper limit of 32 to the length of nonce in 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].  [RFC6960] also defines the standard extensions for OCSP
   messages based on the extension model employed in X.509 version 3
   certificates (see [RFC5280]).  The following is a 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. extensions defined in [RFC6960].

2.1.  Nonce Extension

   This section replaces the entirety of the Section 4.4.1 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 in the Nonce
   extension with length of 0 octets or more than 32 octets with the
   malformedRequest OCSPResponseStatus as described in section 4.2.1 of
   [RFC6960].

   The value of the nonce MUST be generated using a cryptographically
   strong pseudorandom number generator (see [RFC4086]).  The OCSP
   clients SHOULD use a length of 32 octets for the Nonce extension.
   The minimum
   nonce length of 1 octet is defined to provide the backward compatibility
   with older clients following [RFC6960]
   however, the newer that follow [RFC6960].  Newer OCSP clients that
   support this document MUST use a length of at least 16 32 octets for the nonce in
   Nonce extension.  The  OCSP responder responders MUST accept lengths of at least 16
   octets, and MAY choose to ignore the Nonce extension for the requests
   where the length of the Nonce extension nonce is less than 16 octets. octets

      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  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. certificate, a copy of that OCSP response can be used
   to indicate that the status of the certificate is still valid.
   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], an on-path attacker can intercept the OCSP request
   and respond with an earlier response from the server without the
   Nonce extension.  This can be mitigated by configuring the server to
   use a short time interval between the thisUpdate and nextUpdate
   fields in the OCSP response.

3.2.  Nonce Collision

   If the value of the nonce used by a client in OCSP request is not
   random enough,
   predictable, then an attacker may prefetch responses with the
   predicted nonce and can replay them, thus defeating the purpose of
   using nonce.  Therefore the value of Nonce extension in the OCSP
   request MUST contain cryptographically strong randomness and MUST be
   freshly generated at the time of creating the OCSP request.  Also if
   the length of the nonce extension is too small e.g. 1 octet then an on-path
   attacker can prefetch responses with all the possible values of the nonce
   and replay a matching nonce.

4.  IANA Considerations

   This document does not call for any IANA actions.

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

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [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>.

Author's Address

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

   Email: msahni@paloaltonetworks.com