Re: Applicability of signed messages as proof of sending

[Richard Laager <rlaager@xxxxxxxxxx>]

On Fri, 2005-08-12 at 10:39 +0100, Ian G wrote:
> Len Sassaman wrote:
> > On Thu, 11 Aug 2005, Ian G wrote:
 
> > Right. I'm one of those people. This does, however, leave one open to MITM
> > attacks -- which are probably not that large of a threat in the general
> > case, but when dealing with centralized, proprietary IM systems, could
> > very well be a realistic problem. (This is why Trillian's SecureIM
> > solution fails my sniff test.)
> 
> Right.  That's an interesting point.  So GAIM
> uses AIM which is a proprietary IM system.  Now,
> if that was all it was, *and* one assumed that
> MITM in AIM was a real threat, then this would
> be plausible logically, but still weak in terms
> of validation.

Gaim (please not GAIM) supports a variety of protocols besides AIM, so
that does change the threat model a bit. It'd be significantly easier to
do a MITM attack on more documented and decentralized protocols.

I'll admit that MITM attacks are rare and sophisticated, but if you're
not guarding against them, the only take you prevent is casual snooping
on the wire. If you're only going to worry about casual snooping, you
could just as well use rot13 as your "encryption". (Granted, I'm
exaggerating a little, but why bother with something as complex and
secure as OpenPGP to prevent casual snooping.) Your points about
keyloggers, etc. are very valid.

Richard Laager