My question is about this image. Suppose that client is Alice and Server is Bob. So, basically, I'm trying to setup a scenario... I have a remote Server (Bob) that has an https website. I make: openssl s_client -connect host:443 -status -CApath /etc/ssl/certs/ -CAfile /etc/ssl/certs/ca-certificates.crt that gives me the response about the OCSP. The wireshark only shows packets between me and server... There are not a CA or another thing.

What am I doing wrong or what I am not understanding? Is the CA the OCSP responder? How do I get the answer?

If I'm not doing well, what do I have to change in my setup?

  • The question is unclear for me. If you are asking how you get the OCSP response when no one talks to CA or OCSP, then the answer will be: caching. Web server gets OCSP response from OCSP and uses cached response to staple it for some time (until cached response expires).
    – Crypt32
    May 11 '17 at 20:58
  • But the scenario that I explain... My "bob" is the OCSP responder in this case? No.. It's the server. The server is the service that caches the status? So what is the OCSP Responder? The CA? That is my doubt.
    – PRVS
    May 11 '17 at 21:43
  • The server is the service that caches its own status. OCSP Responder is a service that is authorized to provide revocation information. It is not CA, just is authorized by CA to offer revocation services.
    – Crypt32
    May 11 '17 at 21:46
  • Ok so, I'm only seeing packets between client and server maybe because the status is on the cache of the server. I'm right ?
    – PRVS
    May 11 '17 at 21:51
  • Yes, it is the case.
    – Crypt32
    May 11 '17 at 21:59

One important part of OCSP which you might not be aware of is that the OCSP response is signed and has a limited life time. This means it actually does not matter where the TLS client got the OCSP response from because the OCSP response itself can be verified independently of how the client got it. This property is used within OCSP stapling in that

  • The TLS server (i.e. web server, mail server ...) asks the OCSP responder about the validity of its own certificate.
  • The OCSP responder returns an OCSP response, which is (directly or indirectly) signed by the CA which issued the servers certificate. This OCSP response can be cached for some time by the TLS server.
  • The TLS server can include this OCSP response when doing the TLS handshake with the TLS client. This is called OCSP stapling.
  • The TLS client can treat this stapled OCSP response the same way as if the client would have asked the OCSP responder, i.e. verify the signature and life time on the OCSP response and only use it if the signature is valid and the response is not expired.

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