Online Certificate Status Protocol (OCSP) Nonce Extension

Introduction This document updates the usage of the Nonce extension in OCSP request and response messages. This extension was previously defined in Section 4.4.1 of and updated in . defines OCSP extensions as optional extension, and defines condition for different extension options. Nonce extension is defined as an optional extension and that provides the freedom to OCSP responders to ignore the nonce extension regardless of its existence or value in OCSP request, whereas language directs the OCSP responders to MUST take action based on Nonce value in OCSP requests. For example it directs OCSP responder to MUST respond with the malformedRequest OCSPResponseStatus in case of zero or longer nonce values. OCSP responder SHOULD be able to ignore the nonce values (valid or invalid) as it is an optional extension. Ignoring the longer nonce value helps OCSP responder to achieve the better backward compatibility as it wont impact the existing OCSP client that has already been sending longer nonce values. This document updates the Nonce extension section of by removing the instruction to OCSP responder to reject the OCSP response that violates the nonce length requirment, provides an example of Nonce value and reinstate the backward compatibility while clearly differentiating the OCSP client and responder expectations.

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 when, and only when, they appear in all capitals, as shown here.

OCSP Extensions The message formats for OCSP requests and responses are defined in and Nonce extension was updated in . also defines the standard extensions for OCSP messages based on the extension model employed in X.509 version 3 certificates (see ). replaces this section to enforce minimum and maximum length for Nonce value. This document updates the Nonce extension section of with clearly define the behavior of OCSP responder and client under precondition of support of Nonce extension while ignoring the OCSP request with longer Nonce length of 32 octets. This document doesn't change the length requirement for Nonce value and does not change the specifications of any of the other standard extensions defined in or .

Nonce Extension This section updates the Section 2.1 of , 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 32 octets.

Newer OCSP client that supports Nonce extension MUST use the length of 32 octets.

Newer OCSP responder that supports the Nonce extension MUST support the nonce value with minimum length of 16 octets to maximum length of 32 octets.
OCSP responder MAY choose to ignore nonces that are less than 16 octets or violates nonce length defined in , and MUST leave out the nonce extension in the response.

The value of the nonce MUST be generated using a cryptographically strong pseudorandom number generator (see ). The minimum nonce length of 1 octet is defined to provide backward compatibility with older clients that follow . id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp } id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 } Nonce ::= OCTET STRING(SIZE(1..32)) Raw Nonce Example: 1FA16041C0E2D739898EC69972A4B967DFD3488148E6DA61CF3AF2DC32383383 OCSP Nonce Octet String: 04201FA16041C0E2D739898EC69972A4B967DFD3488148E6DA61CF3AF2DC32383383

IANA Considerations This memo includes no request to IANA.

Security Considerations This document should not affect the security of the Internet.