[Q] : verify an encrypted signed file.

[Werner Koch]

On Mon, 20 Aug 2001 12:07:27 -0400, Justin R Miller said:

> sign it?  I mean, I do this, but I don't understand it.  I would think
> that the encryption would both assure authenticity and intactness.  

Like all other encryption protocols OpenPGP has a flaw here:  Without
signing the data, it is possible to _modify_ the message.  The recipient
will notice some strange characters in the outbut but most users are
naively assuming that this is due to noise on the wire.  There is even
an *theoretical* attack involving some social engineering which allows
to decrypt the message.

The next revision of OpenPGP has a countermeasure against that.  This
new mode is already used by GnuPG and PGP 7 if you are using
AES/RIJNDAEL or Twofish (i.e the recipient hast this algorithm in his
preferences).

  Werner

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Werner Koch        Omnis enim res, quae dando non deficit, dum habetur
g10 Code GmbH      et non datur, nondum habetur, quomodo habenda est.
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