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B requests for A's certificate and verifies with the key sent to him/her.

There is an attack exists as follows:

  1. A sends message, cert and cert key to B.
  2. A sends cert revocation request to CA after confirming the cert and key were successfully accepted.
  3. B receives the revocation information from CA.
  4. A repudiate the message.

It is totally possible that a private key owner keeps using the key before they find that it has been compromised. So, in the above case A can successfully make repudiation.

My question is, can the above attack really be applied? If so, how can it be avoided?

Edit: If it was an intentional attack by the private key owner, it would be totally different from the case of the attacker using the time difference between A's revocation request and B's receipt of the updated CRL information, which can be mitigated by OCSP.

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  • $\begingroup$ "suppose A owns the private key, and its correspondent certificate locates in site of CA. B request for A's certificate from CA for verifying the signature sent to him/her" that's not generally how PKI-X works, the CA signs the certificate which can then be freely distributed to entities trusting the CA (certificate). $\endgroup$
    – Maarten Bodewes
    Commented Jan 26, 2018 at 10:26
  • $\begingroup$ Note that time-stamping and notaries may be used to enhance the signing process. It would probably be interesting to look at e.g. XAdES for more enhanced signing / verification schemes. $\endgroup$
    – Maarten Bodewes
    Commented Jan 26, 2018 at 10:28
  • $\begingroup$ OK, maybe this is the simplest theoretical certificate use model, but this is not the key point of my question, right? I think @Meir Maor's examples just hit the point. $\endgroup$
    – lihui
    Commented Jan 26, 2018 at 11:47
  • $\begingroup$ I've helped Meir with the formatting and upvoted the answer even before that. The fact that I didn't post above comments as answer probably tells enough. The first comment is just to take away a misunderstanding in the first lines of your question, and the second is to indicate that there is more to non-repudiation than basic X.509 certificate based signatures. Your "key point" certainly can stand on it's own: this is not a critique on the question or answer. $\endgroup$
    – Maarten Bodewes
    Commented Jan 26, 2018 at 12:34

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Yes one could do this, the repudiation wouldn't be very convincing.

The CRL really isn't very relevant. A person can always claim his private key was stolen. His credit card was stolen or his car was stolen. We see people commit hit and run, realize what they have done park the car somewhere and report it stolen. Denying a credit card transaction etc. If the car is reported stolen well before the hit and run that would be convincing proof.

As with CRL it would be convincing if the revocation is clearly before the transaction. But a revocation very close in time to the transaction doesn't provide a very convincing repudation though theft is plausible it is not common. And the private key owner could still be held responsible for his private key.

CRLs should not waive responsibility the second they are posted.

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