Re: [openpgp] Message padding in OpenPGP

[Derek Atkins <[e-mail]>]

Justus Winter <[e-mail]> writes:

> On Tue, Sep 24, 2019 at 11:00 PM Jon Callas <[e-mail]> 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.

Why not just have multiple literal packets inside the encryption?  I.e.:

  ENC{ Lit1{realData} | Lit2{pad} }

Note, of course, that this could provide a covert channel which could
leak other data, theoretically.

> Cheers,
> Justus

-derek
-- 
       Derek Atkins                 617-623-3745
       [e-mail]             www.ihtfp.com
       Computer and Internet Security Consultant