On 25.03.16 12:03, flapflap wrote: > Hi, > > (using Enigmail 1.8.2 from Debian stable) > > For some time already, Enigmail provides Message Filters that allow the > user to permanently decrypt a message or to create an encrypted copy of > a message. > That is quite a nice feature for my long term email archive which is > stored on encrypted disk. > > However, I noted that using these filters emails are not only decrypted > but also the signature (if available) is stripped. I know this affects > PGP/MIME emails but I didn't test Inline PGP. > > o Is it possible to keep a signature after decryption? > o Or is this an inherent property of PGP/MIME/Inline PGP emails, that > the email cannot be /only/ encrypted?
It depends on the used protocol. If mails are signed and encrypted in two steps (RF 3156, section 6.1), then Enigmail would only remove the encryption, but leave the signature intact. However, Enigmail and many other mail clients use the "combined" method. That is, mails are signed and encrypted in one step. This case, there is no extra signature. In theory it should be possible to extract the signature from the encrypted data, and re-create a signed message from it. However, GnuPG does not offer functionality to extract a signature from a signed+encrypted message, and it's not likely that such functionality will ever be implemented [1]. -Patrick [1] http://lists.gnupg.org/pipermail/gnupg-users/2004-April/022352.html
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