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Mohamed G. Gouda						CS 386 S
Spring 2008							quiz 8
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Simplify the "fore" and "back" messages in the 1981 David Chaum's Anonymous 
Communication Protocol according to the following assumptions:

1. The sender, say p.i, and receiver, say p.j, of every sent message know 
   one another and they share a session key sk.i.j.  
   (Hint: Note that sk.i.j = sk.j.i.)

2. Each process know a reasonably small number of processes with whom it 
   communicates.

3. The sender and receiver of a message use process mix, that has a public 
   key B, in order defend against an adversary that observes all the traffic 
   in the network and tries to get the following information: Who is sending 
   messages to whom?, what are the contents of the exchanged messages?, and 
   what are the lengths of the exchanged messages?.

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Solution:   

The fore and back msgs, from p.i to p.j, have the same following format:

B<pad',sk.i.j<pad,msg>,q.j>

where msg is either an original msg or a reply to an earlier msg from 
p.j to p.i