From: Derek Atkins <warlord@Athena.MIT.EDU>
Date: Tue, 13 Apr 93 02:46:14 PDT
To: karn@qualcomm.com (Phil Karn)
Subject: Re: Modem encryption proposal
In-Reply-To: <9304130721.AA29941@servo>
Message-ID: <9304130945.AA02555@hodge>
MIME-Version: 1.0
Content-Type: text/plain


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> Crypto synchronization seems to be a problem mainly in real-time
> appliations like digital voice, where you don't have a reliable
> protocol underneath you.

Phil, there is more to this than meets the eye.  What happens if I, as
an attacker, start feeding extra characters onto the modem line?
Granted, I wont know what you are saying, since the link is encrypted,
but if I can get an extra character on there, then the decryption will
lose sync, and wont return the proper value...

For example...
	Sender:  	more foo
	Encrypted data:	HaoVwAog

	Received data:	HaooVwAog
	Decrypted:	morOmf&sm

Now what?  The sender and receiver are out of sync....  I believe this
was what Nickey was talking about..  I was discussing this problem
with a few people and haven't come up with a good, viable solution...
yet.

> This is essentially how encrypted Kerberos Telnet works now,
> although I would like to generalize the service to work with any TCP
> client.

Uhh, there is a kstream package somewhere (or am I thinking of
vapor-ware, it's late and I'm tried).  This wouldn't be very hard to
create.  In fact, I was hoping to do something like this with my
Thesis...  Although it might get left for "future work".  This depends
upon having a clearly denoted stream, which neither telnet nor kermit
provide a good interface.  (Trust me on this -- it took me a while to
try to create one for the little I've hacked them for my Thesis).

- -derek

PGP 2 key available upon request on the key-server:
	pgp-public-keys@toxicwaste.mit.edu
- --
  Derek Atkins, MIT '93, Electrical Engineering and Computer Science
     Secretary, MIT Student Information Processing Board (SIPB)
           MIT Media Laboratory, Speech Research Group
           warlord@MIT.EDU       PP-ASEL        N1NWH

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