From: Thomas Grant Edwards <tedwards@src.umd.edu>
Date: Mon, 6 Feb 95 20:02:51 PST
To: Wei Dai <weidai@eskimo.com>
Subject: Re: a simple explanation of DC-Net
In-Reply-To: <199502070122.AA01568@mail.eskimo.com>
Message-ID: <Pine.SUN.3.91.950206224622.21262B-100000@thrash.src.umd.edu>
MIME-Version: 1.0
Content-Type: text/plain


On Mon, 6 Feb 1995, Wei Dai wrote:

> P.S.  I realize someone has probably written something like this
> already, but I hope this explanation helps someone who is still
> puzzled.

I've written a test-bed IRC client which uses DC Nets to allow multiple 
people to talk on an IRC channel anonymously.  It operates in a ring, 
with every participant showing his/her random bit stream with the 
neighbor to the "left."  Participants compare their bit stream with the 
one their neighbor shares with them, and broadcasts the differences 
(with lies indicating xmitted "1" bite) to all participants.  The 
difference bits for each round are totalled together modulo 2 by each 
participant, and any anonymous broadcasts can be determined from those 
totals.

My implementation was a quick project for a class and lacks some really 
important features:

1)  used built-in PRNG
2)  does not encrypt private messages for bit stream sharing between 
neighbors
3)  no ALOHA or similar protocol for dealing with message collisions
4)  ring could be expanded to more complex graph to increase number of
    colluding participants needed to break anonymity.

BTW - There have been a few other papers on DC-Nets since Chaum including 
detections of DC-Net disrupters, and protection against a group of active 
attacks.  I include a report with my code now available at 
ftp://ftp.csua.berkeley.edu/pub/cypherpunks/applications/dc-irc.alpha.tar.gz
which goes into more details on these matters and has references.

-Thomas