LAMPS M. Sahni, Ed. Internet-Draft Palo Alto Networks Updates: 6960 (if approved) September 10, 2020 Intended status: Standards Track Expires: March 14, 2021 OCSP Nonce Extension 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 to cryptographically bind an OCSP response message to a particular OCSP request message. This document updates RFC 6960. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on March 14, 2021. Copyright Notice Copyright (c) 2020 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 (https://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 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Sahni Expires March 14, 2021 [Page 1]
Internet-Draft OCSP Nonce Extension September 2020 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 2 2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3 3. Security Considerations . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 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]. [RFC6960] does not mention any minimum and maximum length of nonce in the Nonce extension. Lacking limits on the length of nonce in the Nonce extension, 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, and possible evasions using the Nonce extension 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 [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 OCSP request and response is defined in [RFC6960]. [RFC6960] also defines the standard extensions for OCSP messages based on the extension model employed in X.509 version 3 Sahni Expires March 14, 2021 [Page 2]
Internet-Draft OCSP Nonce Extension September 2020 certificates (see [RFC5280]). This document only specifies the new format for Nonce extension and does not change specification of any of the other standard 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 minimum nonce length of 1 octet is defined to provide backward compatibility with older clients that follow [RFC6960]. Newer OCSP clients that support this document MUST use a length of 32 octets for the nonce in Nonce extension. OCSP responders MUST accept lengths of at least 16 octets, and MAY choose to ignore the Nonce extension for requests where the length of the nonce is less than 16 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 [RFC6960]. 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, 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. Sahni Expires March 14, 2021 [Page 3]
Internet-Draft OCSP Nonce Extension September 2020 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 nonce used by a client in OCSP request is 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 nonce is too small e.g. 1 octet then an on-path attacker can prefetch responses with all the possible values of 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 Appendix B.1 and Appendix B.2 of [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 Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax. NEW Syntax: Nonce ::= OCTET STRING(SIZE(1..32)) Sahni Expires March 14, 2021 [Page 4]
Internet-Draft OCSP Nonce Extension September 2020 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>. Sahni Expires March 14, 2021 [Page 5]
Internet-Draft OCSP Nonce Extension September 2020 [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 Sahni Expires March 14, 2021 [Page 6]
