OpenSSL certificate revocation check in client program using OCSP stapling 2

Question

Pretty much this is request for additional information for the question: https://stackoverflow.com/questions/9607516/openssl-certificate-revocation-check-in-client-program-using-ocsp-stapling

I want to know how OpenSSL actually handles OCSP stapling response. Questions are:

1. Does the OpenSSL check the signature, issuer key/name hashes of the response?

2. Does the response include OCSP responses for the whole certificate chain? If so, is there a way to know that one of the validations have failed?

3. To sum up, can I simply rely on 'Cert Status: good' field of the response? :)

My concern is that hacker may craft https server using revoked (stolen) certificate but during handshake provide valid stapled OCSP response for a random website that was certified by the same CA issuer. Could the OpenSSL handle such situation?

The sample OCSP response can be found here https://www.feistyduck.com/library/openssl-cookbook/online/ch-testing-with-openssl.html#testing-ocsp-stapling

Answer 1

how OpenSSL actually handles OCSP stapling response

OpenSSL does not do anything by its own in this area. You have to explicitly deal with OCSP stapling in your code, both for signaling that you support stapling and for validating and interpreting the response.

Does the OpenSSL check the signature, issuer key/name hashes of the response?

If the proper functions are used you can do it. Validating a OCSP response is in most ways similar to validating a certificate or a CRL, i.e. validating the trust chain. Apart from that you need to verify that the OCSP response actually is for the correct certificate.

Does the response include OCSP responses for the whole certificate chain? If so, is there a way to know that one of the validations have failed?

This depends on what the server sends and what the client requests (i.e. single OCSP response or multiple). And since you have to implement all the details anyway you have also the information what part of the validation failed.

To sum up, can I simply rely on 'Cert Status: good' field of the response? :)

No, you cannot simply trust any OCSP response sent by the server.
You have to do all the validation of the OCSP response yourself. Apart from the already mentioned parts this involves also checking if the response is stale (too old). And of course the certificate might have been revoked in the last minutes but the response is still valid, i.e. OCSP does not provide real-time information about the status of a certificate.

Note that only very OpenSSL based tools or libraries implement OCSP and/or OCSP stapling at all and even if they do it is usually not enabled by default. This is not much different with other TLS implementations.