Re: [openpgp] Disabling compression in OpenPGP

[Jon Callas <[e-mail]>]

> 
> In general, I see two patterns:
> - Compression incidentally thwarts some attacks
> - Compression fundamentally breaks privacy by leaking plaintext entropy (see the Wikimedia Foundation case for a quite convincing example)


In general, compression does the opposite of your second bullet. It *protects* privacy by taking things that are typically not pseudo-random (what you're calling entropic) -- e.g. text -- into something that is highly pseudo-random.

In specific cases, *flaws* in this conversion when combined with an interactive protocol can lead to an attack that is in general, not applicable to a non-interactive protocol with large amounts of compressed data.

But in general, this benefits the defender, as the attacker has no idea what the *actual* plaintext is (the compressed data) unless they know the base plaintext is, and small inaccuracies in the attackers guess lead to large differences.

Of course, I could be wrong. I offered an outline for research where you could come up with some results that would be impressive. Why not do some work on it?

	Jon