From: Eric Hughes <hughes@soda.berkeley.edu>
Date: Fri, 22 Jan 93 08:11:25 PST
To: cypherpunks@toad.com
Subject: PGP on BBS
In-Reply-To: <9301211702.AA11275@xanadu.xanadu.com>
Message-ID: <9301221609.AA24776@soda.berkeley.edu>
MIME-Version: 1.0
Content-Type: text/plain


I wrote:
>>The solution is cooperative processing systems, where both the host
>>and the terminal cooperate to perform some task.  

Dean asks:
>What would the two systems be cooperating about?  I'm not sure to what
>you are pointing.

Here are two basic examples:

1. Session key creation.  I regularly log in remotely to my account at
soda.  I'd like to have that modem link encrypted, with session keys
generated on the fly.  So I'll want to use some implementation of
Diffie-Hellman key exchange to make a session key.  The nature of this
protocol means that both my terminal program and my host have to do
calculations and exchange data.  Therefore I need software on my PC at
home and software on the host that work together.

2. Digital signatures.  I read and send my e-mail on the host.  When I
send PGP-encrypted mail, I have to compose the message on the PC,
encrypt it with a PGP command line, upload it to the host with zmodem,
and read it in to my mailer.  I'm certainly not going to put my secret
key on the host.  

What would be ideal is a cooperative protocol that initiated (in the
background, away from my main connection) a channel, sent just the
data to be signed (an IDEA key, for example), have my PC sign the data
and send it back.  This not only entails software on each end, but
also a line multiplexer so that the signing can take place on a
separate channel.  If it doesn't occur on a separate channel, then I
have to see it, probably move to the shell in order to start it
properly, and in general make it non-automatic.

Eric