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I sent a valid signed e mail a few weeks ago. Now I reinstalled everything on my computer (including the OS).

Is the certificate now invalid?

  • The answer is going to depend on a lot of factors that you do not talk about. Did you migrate the certificate? – schroeder Nov 17 '15 at 20:03
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    Welcome to security.SE. It may be helpful to add some more data to this question. For example, where was your cert stored (eg: your computer or a keyserver)? Also, are you interested in reusing the cert for new emails or just whether the previously sent email is still valid? – Neil Smithline Nov 17 '15 at 20:07
  • What does migrate mean? The cert was stored on a server afaik. I am not interested in reusing it, the previously sent email should be still valid. – 今天春天 Nov 17 '15 at 20:11
  • A once signed text / email is still valid, verification works with the public key or cert. For siging you need the private key. Did you import the certificate to your cert store? – Daniel Ruf Nov 17 '15 at 20:23
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    No, I do not think so.... – 今天春天 Nov 17 '15 at 20:42
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As schroeder said, we need more information to provide a satisfying answer.

  • Where was the certificate stored?
  • Do you still have access to it and the private key?
  • What do you mean by "invalid"?

I assume that your problem is about not being able to check email signatures anymore.

If the certificate didn't expire during these few weeks, there is no reason for it to be invalid now. A certificate is not linked to a given installation. However, you may have lost your certificate and its private key if you don't have any copy. From what you said, your mail client seems not to be able to check the email signatures; probably because it does not have access to the certificate or does not trust it.

To resolve this issue, you should take a look at the error message given by your mail client. Ensure that your certificate and the actors of the trust chain are present in the cert store of your mail client or your system.

Note that I am only talking about being able to check signature of emails you sent before reinstalling your system.

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