Re: [openpgp] Disabling compression in OpenPGP

Gregory Maxwell <gmaxwell@gmail.com> Wed, 19 March 2014 21:16 UTC

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Date: Wed, 19 Mar 2014 14:16:16 -0700
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From: Gregory Maxwell <gmaxwell@gmail.com>
To: Jon Callas <jon@callas.org>
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Cc: David Shaw <dshaw@jabberwocky.com>, Peter Todd <pete@petertodd.org>, Alfredo Pironti <alfredo.pironti@inria.fr>, "openpgp@ietf.org OpenPGP" <openpgp@ietf.org>
Subject: Re: [openpgp] Disabling compression in OpenPGP
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On Wed, Mar 19, 2014 at 1:47 PM, Jon Callas <jon@callas.org> wrote:
> What's being leaked by compression? Really, I don't get it.

Some people like a demonstration.

Consider that I'm going to cast one of two ballots in a secret ballot
election. The ballots are just permutations of eachother so they are
the same size.

https://people.xiph.org/~greg/ballot.1
https://people.xiph.org/~greg/ballot.2

I encrypt my secret ballot to the election officials with the public
key at https://people.xiph.org/~greg/openpgp_testpubkey.asc

using the command:
gpg -ear 9C28FC94 --compress-algo ZIP --compress-level 9 ballot.X
(just being explicit for consistency sake, using GPG 1.4.16 in Fedora
19)

And I get the encrypted result of
https://people.xiph.org/~greg/ballot.secret.asc

Which ballot did I cast?   Anyone?