Re: [openpgp] Message padding in OpenPGP

Justus Winter <justuswinter@gmail.com> Wed, 25 September 2019 09:03 UTC

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From: Justus Winter <justuswinter@gmail.com>
Date: Wed, 25 Sep 2019 11:03:24 +0200
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To: Jon Callas <joncallas@icloud.com>
Cc: openpgp@ietf.org
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Subject: Re: [openpgp] Message padding in OpenPGP
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On Tue, Sep 24, 2019 at 11:00 PM Jon Callas <joncallas@icloud.com> wrote:
> Am I correct in understanding that you're proposing adding in decoy traffic to pad out compressed data to its uncompressed length?

No.  I'm proposing not to compress the data at all, and then add some
padding data according to some policy.  The compression container is
only a means to add the padding within the constraints of the current
ecosystem.

> If I'm missing something, what problem are you trying to solve with this?

There is a correlation between the size of the encrypted message and
the size of the plaintext.  On first sight, compression helps with
that, but that makes the size dependent on the entropy of the
plaintext, which also leads to problems as discussed previously.
Padding alleviates this problem, the tradeoff being an increased
message size.

Cheers,
Justus