My thanks to Tim Newsham and Tim May for sending me information on DC-networks. It appears the modifications that I had been thinking about were not discussed by Chaum in his original paper, which gives me some hope I may have stumbled across something new. Chaum proposes the use of public key cryptography for secure communication between vertices in a DC-net. This leads to the problem of secure key exchange, and the possibility that the public key algorithm is not sound. Instead, the interference properties of a DC-net may be used to give unconditional security. Say Alice wishes to send a message M to Bob. 1. Alice computes the hash of M, and appends it to M to produce a packet P of p bits. 2. Alice transmits on the net "Message of p bits for Bob" 3. Bob receives this message, and prepares a packet R composed of p random bits. 4. Alice transmits packet P. Simultaniously, Bob transmits packet R. The output of the DC­net is now X, where X = P XOR R 5. Bob, computes P = X XOR R. He verifies that the last bits of P are a valid hash for the first portion. If so, he has succesfully recieved M and the transfer is over. If not, there must have been interference from another party. He would then transmit "Alice, resend message", and the procedure would be repeated. All that Carol, another vertex in the net, can see is X. She cannot derive P from X as it has been encrypted with the equivalent of a one-time pad. Thus, P is unconditionally secure. Alice and Bob need no nothing about each other for this transfer to work. Indeed, Alice and Bob may well be pseudonyms. The worst that can happen is that two sites respond to the pseudonym of Bob, and the transfer suffers from interference. Hence the built in hash. Note that only Bob can see the valid hash, and only then if the transfer has worked perfectly. Thus, the hash need not be secure. I have not looked at the efffects of collusion on this protocol. My gut feeling is that sufficient collusion would bring it down in flames. However, this is also true of the basic operation of a DC-net. I cannot claim that I came up with this protocol alone. It was concieved this summer at a seminar I taught on cryptography. After sitting around a table and flipping coins to prove that it actually did work, we started looking at the problems of un-intentional interference. This is the result of half an hour of me trying to remember what little I had read of DC-nets and the students making me look like a fool for not having studied as much as I should have. So, my first question to you is, does it work? The next question is has it been thought of before? And finally, is it useful? -- PGP 2.3a Key by finger