Re: The Dining Cryptographers Protocol
My spin on the Dining Cryptographers Protocol is, it's nifty and theoretically strong, but in practice mixes are better for almost all uses. If you have N people in a DC-net, you must exchange N bits of traffic per bit of anonymous message transmitted. If you use mixes and send each message on M hops, you exchange M bits of traffic per bit of anonymous message transmitted. N is typically 100-10000, and M is typically 2-10. Mixes are more efficient. One advantage of DC-nets is that they're instant; with mixes there must be some delays in order to accumulate enough cover messages to defeat traffic analysis. -- Marc Ringuette (mnr@cs.cmu.edu)
Marc.Ringuette writes:
My spin on the Dining Cryptographers Protocol is, it's nifty and theoretically strong, but in practice mixes are better for almost all uses. [...] N is typically 100-10000, and M is typically 2-10. Mixes are more efficient.
Let me continue to be a broken record. Cryptography is all economics. You want unconditional security, you pay. Period. Sometimes it's worth it, sometimes it's not. It is not up to the cryptographer to make the economic judgement, it is up to the user.
One advantage of DC-nets is that they're instant; with mixes there must be some delays in order to accumulate enough cover messages to defeat traffic analysis.
This idea of "delays" providing security for a mix is a common, but incorrect, notion. I don't think Marc is incorrect about this here, merely unclear. In a well used mix system, the latency time to accumulate ten messages would be only a few minutes. It is the reordering of the output messages with respect to the input that provides mix security. Any delay in merely a consequence of the time to collect. Eric
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Eric Hughes -
Marc.Ringuette＠GS80.SP.CS.CMU.EDU