Internet-Draft draft-ietf-lamps-ocsp-nonce-update-00 February 2024
Sharma Expires 23 August 2024 [Page]
Internet Engineering Task Force
8954 (if approved)
Intended Status:
Standards Track
H. Sharma, Ed.
Netskope Inc

Online Certificate Status Protocol (OCSP) Nonce Extension


This document updates the Nonce extension section of RFC-8954. Nonce extension is an optional extension for Online Certificate Status Protocol (OCSP) request and response messages. OCSP is used for checking the status of a certificate, and the Nonce extension is used to cryptographically bind an OCSP response message to a particular OCSP request message. Some environments use cryptographic algorithms that generate a Nonce that is longer than 32 octets. This document updates the maximum allowed length of Nonce to 128 octets.

Status of This Memo

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This Internet-Draft will expire on 23 August 2024.

Table of Contents

1. Introduction

Nonce extension was previously defined in Section 4.4.1 of [RFC6960] and updated in [RFC8954]. [RFC8954] enforces the maximum Nonce length to 32 octets. To support cryptographic algorithms that generate a Nonce that is longer than 32 octets, this document updates the maximum allowed size of the Nonce to 128 octets. In addition, this document recommends that the OCSP client and responder use a Nonce with a minimum length of 32 octets.

1.1. Requirements Language

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 formats for OCSP requests and responses are defined in [RFC6960] and Nonce extension was updated in [RFC8954]. [RFC6960] also defines the standard extensions for OCSP messages based on the extension model employed in X.509 version 3 certificates (see [RFC5280]). [RFC8954] replaces this section to enforce the minimum and maximum length for the Nonce value. This document extends the maximum allowed nonce length to 128 octets and does not change the specifications of any of the other standard extensions defined in [RFC6960].

2.1. Nonce Extension

This section replaces the entirety of Section 2.1 of [RFC8954], 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; 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 the Nonce extension is present, then the length of the Nonce MUST be at least 1 octet and can be up to 128 octets.

An OCSP client that implements this document SHOULD use a minimum length of 32 octets for Nonce in the Nonce extension. RFC 8954-compliant implementations will be unable to process nonces generated per the new specification with sizes in excess of what was permitted by RFC 8954.

OCSP resonder that implements this document MUST reject any OCSP request that has a Nonce in the Nonce extension with a length of either 0 octets or more than 128 octets, with the malformedRequest OCSPResponseStatus as described in Section 4.2.1 of [RFC6960]. Responders, supporting the Nonce extension, 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 or more than 32 octets.

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].

    id-pkix-ocsp           OBJECT IDENTIFIER ::= { id-ad-ocsp }
    id-pkix-ocsp-Nonce     OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }
    Nonce ::= OCTET STRING(SIZE(1..128))

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 a 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 not to 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.

4. IANA Considerations

This memo includes no request to IANA.

5. Changes to Appendix B of RFC 6960.

This section updates the ASN.1 definitions of the OCSP Nonce extension in Appendices B.1 and B.2 of [RFC6960]. Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax; 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..128))

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

OLD Syntax:

                                    BY id-pkix-ocsp-nonce }

NEW Syntax:

     re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING(SIZE(1..128))
                                  IDENTIFIED BY id-pkix-ocsp-nonce }

6. References

6.1. Normative References

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, , <>.
Sahni, M., Ed., "Online Certificate Status Protocol (OCSP) Nonce Extension", RFC 8954, DOI 10.17487/RFC8954, , <>.
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, , <>.
Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Deacon, A. and R. Hurst, "The Lightweight Online Certificate Status Protocol (OCSP) Profile for High-Volume Environments", RFC 5019, DOI 10.17487/RFC5019, , <>.

Author's Address

Himanshu Sharma (editor)
Netskope Inc
2445 Augustine Dr 3rd floor
Santa Clara, California 95054
United States of America