OCSP Nonce Extension
draft-msahni-lamps-ocsp-nonce-00

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

Status of This Memo

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Table of Contents

• 1. Introduction
• 1.1. Terminology
• 2. OCSP Extensions
• 2.1. Nonce Extension
• 3. Security Considerations
• 4. IANA Considerations
• 5. References
• 5.1. Normative References
• 5.2. Informative References
• Author's Address

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 the 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, chosen prefix attacks to get desired signature of the OCSP responder and other possible evasions which can use nonce extension data. This document specifies a lower limit of 1 and 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] [RFC5280]. 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 specification of any of the other standard extensions.

2.1. 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 atleast 1 byte and can be upto 32 bytes.

   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 responder has a changed status for that certificate. Including client's Nonce value in the OCSP response makes sure that the response is a latest response from the server and not a 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, a man in the middle (MITM) entity can intercept the OCSP request and respond with a earlier response from the server without the Nonce extension. This can be mitigated by server using a closer nextUpdate value in the OCSP response.

4. IANA Considerations

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

5. References

5.1. Normative References

5.2. Informative References

Author's Address