[Standards] [Fwd: [Council] meeting minutes, 2007-11-21]

[Justin Karneges]

On Thursday 22 November 2007 7:39 am, Dave Cridland wrote:
> On Thu Nov 22 10:38:43 2007, Lauri Kaila wrote:
> > What kind of attacks are based on this weakness in XEP-0115? I can
> > only think of DOS by lying capabilities (when the hash of a liar's
> > capabilities collides with someone's real caps). I'd think disabling
> > XEP-0115 is the cure to recover and prevent happening again.
>
> There's a small window for a downgrade attack. For instance, if one
> happened to be able to find out that someone whom the victim usually
> spoke to under some e2e encryption upgraded their client before the
> victim, you could arrange for the victim to query your fake caps by
> disco rather than the target's, allowing you to remove the e2e
> encryption capability.

If you can attack the caps hash then you may as well attack the disco query 
too.  Downgrade attacks are always possible without minimum security 
restraints.  Don't want to worry about talking to your friend non-e2e?  Then 
make e2e a requirement for chatting.

-Justin