I need open .p7m message from my old PC, but I lost my old certs. Is there any method how to decrypt it without key?

  • If the crypto is good there is no way. Jul 21, 2016 at 16:18
  • And if crypto isn't good? Jul 21, 2016 at 16:26
  • 2
    It depends on the key size. S/MIME is old enough that it might use rsa keys less the 1024 bits, which are crack-able with enough effort.
    – AstroDan
    Jul 21, 2016 at 20:23

1 Answer 1


Theoretically, you could brute-force it. Decryption will take somewhere between "immediate" and "The end of the universe", so it depends on how lucky you are.

Practically, no. It's not going to happen.

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