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Date: Wed, 6 Jul 2022 15:01:19 -0400
From: Demi Marie Obenour <demi@...isiblethingslab.com>
To: oss-security@...ts.openwall.com
Subject: Re: Re: DO NOT OPEN PREVIOUS MAIL Re:
Denial of service in GnuPG
On Wed, Jul 06, 2022 at 04:50:11PM +0200, Solar Designer wrote:
> On Wed, Jul 06, 2022 at 09:47:28AM -0400, Demi Marie Obenour wrote:
> > On Wed, Jul 06, 2022 at 03:38:10PM +0200, Solar Designer wrote:
> > > On Wed, Jul 06, 2022 at 07:02:59AM -0400, Demi Marie Obenour wrote:
> > > > Was adding compression to PGP even a good idea in the first place?
> > >
> > > I think actually yes, it was, especially back then. It has probably
> > > helped more than it hurt in PGP's lifetime so far.
> >
> > Interesting. Why do you say that?
>
> Oh, I didn't feel this even needed explanation, and I feel silly writing
> the below and don't really have time for it (lesson re-learned: should
> have stayed silent), but well.
>
> PGP is commonly used on compressible data (such as text), and PGP
> messages are then transferred over a network and finally stay in
> people's mailboxes or such. Bandwidth was commonly low back then, and
> storage much more limited than today's.
>
> Some compression existed for unencrypted messages - some network links
> somewhat compressed (e.g., V.42bis), some mail clients supported mailbox
> compression, and of course a mailbox could also be compressed manually.
>
> Obviously, already encrypted content is not compressible.
>
> Without built-in compression in PGP, its messages would be slower to
> transfer and larger to store. Compression would need to be performed
> before PGP, which would be an inconvenience and would lead to similar
> risks, especially if automated, and would often not be done. In PGP,
> it's just one standard way to do it, not more than one.
>
> So compression was of some benefit to a lot of people. We could argue
> that it's little benefit, but multiplied by the number of people it's
> significant. Was compression also a problem for a lot of people?
> Theoretically, yes, but in practice those attacks were not common.
>
> We could also argue that PGP never became popular, MUA integrations are
> poor, etc., and as a consequence that its individual features were not
> of a lot of benefit to computer users at large. While true, that
> argument also means the risks associated with those features did not
> apply to most computer users. So it's irrelevant.
>
> What I say is that for the geeks using PGP, compression was overall of
> more benefit than risk.
>
> Oh, and I'm also grateful for compression in SSH, despite of my own
> criticism of its effect on security.
>
> Alexander
Thanks! I had not considered this at all, and it makes a ton of sense.
Being able to compress data prior to encryption is indeed necessary if
one wants to avoid using more space than a message compressed using
normal methods.
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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