[OTR-users] OTR transport protocol?

[Alex]

On Sun, 4 Apr 2010 19:48:27 -0400
Ian Goldberg <ian at cypherpunks.ca> wrote:

> On Sun, Apr 04, 2010 at 07:23:34PM -0400, Alex wrote:
> > Hi. Would there be any use for an implementation of OTR in a way
> > similar to that of TLS?
> 
> Good question.
> 
> TLS already has the ability to do perfect forward secrecy by using one
> of the ephemeral Diffie-Helman ciphersuites.  It does mutual
> authentication using certificates, but I've seen proposals to include
> PAKE, and even SMP, into TLS.  One would have to figure out exactly
> what deniability/repudiation properties one was looking for to see if
> TLS could be coaxed into doing that.
> 
> That said, if you squint in the right way, you could pretend that
> today's OTR was indeed a transport-level protocol, since you can send
> arbitrary packetized TCP streams over it.  (You'd have to remove the
> specification of how to interpret the decrypted message, though.)
> Its utility would be quite different from TLS, though, since it's
> mainly useful for connecting people who know (and can authenticate)
> each other, whereas TLS can connect strangers, proving they trust the
> PKI-in-the-sky. (See, for example,
> http://government.zdnet.com/?p=8257 )
> 

What do you think of a bank whose branch-employees hand out business
cards containing a fingerprint for use with OTR? The user can go home
and visit the bank's website (using an OTR transport mechanism), at
which point a dialog would ask them if they want to trust the given
fingerprint or not. They can compare it to what is on the business card,
and the server can be authenticated.

The bank's servers (seeing that you are unverified) can ask you a
question only you would know via the shared-secret OTR feature. After
this point, your fingerprint would become trusted on the bank's end and
you won't have to go through that again unless you lose access to the
key (by using a different computer, etc).

Assuming that the code for this was written and incorporated in to
most browsers/OSs, this would be very practical solution to the root
CA problem described in the zdnet article above.

One potential issue is that people are terribly passive and complacent,
and they think that if they aren't doing anything wrong that they have
nothing to hide. I guess we can't code away those problems.

-- 
Alex