Scenario: A document is signed with a compromised private key, with a long-term time stamp. The normal expiration date of the key pair is D. The rightful owner of the key pair discovers the compromise 15 days after the fraudulent signature is executed, and has the key revoked.

The evil-doer waits until after the normal expiration date, and presents the document as if it were genuine. As I understand it, CAs remove expired keys from certificate revocation lists and Online Certificate Status Protocol. So a person checking the key sees a key that was valid at the time of the signature, and expired in the normal course of events.

Have I got this scenario right?

Would it make any difference if the certificate had been revoked before the signature was executed?

  • $\begingroup$ That is why you need to check your signature history, $\endgroup$ – kelalaka Jul 28 '20 at 19:40
  • $\begingroup$ @kelalaka thanks for responding. I don't understand what you mean by signature history. $\endgroup$ – Gerard Ashton Jul 29 '20 at 12:45

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