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Is there a way to determine the date of encryption or the gpg version of a gpg-encrypted file (with symmetric encryption)?

I lost the password but some rough information about when the file was encrypted would help me. (The oldest could be 5-7 years ago, newest a few months. The file modification time is also lost.)

For example, if I remember right, it could be that old versions of gpg did not have integrity checking. Can I figure this out?

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If the file is ASCII armored, you may find the header at the top.

-----BEGIN PGP MESSAGE----- Version: GnuPG v1.4.11 (GNU/Linux)

jA0EAwMCSPY2a+zUrBBgySD3+GWiPhdcQbtKogerjG/50O9Q6f3FY78qqyxLBw00 RA== =DBXE -----END PGP MESSAGE-----

If it isn't then you can try to review the specification, but it's complicated and after several minutes of reading I don't have a clear answer either. See http://www.ietf.org/rfc/rfc4880.txt.

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Thanks, and according to old package descriptions, gpg 1.4.6, the version I likely had used, if the file is old, is compatible with RFC2440. But I'm still deciding if it's too much effort. (Though, generally also an interesting security question, I think) –  noozoph Dec 4 '12 at 22:28
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