In the `traditional' DC Net, how is absence of a message detected?
If this is a seperately distinguishable outcome of a round, each round may
return three outcomes: `0', `1' and `none'. To represent these quantum
mechanically, you need at least a 3-state quantum system (to make the outcomes
perfectly distinguishable).
In the proposals so far (for using quantum physics to protect the anonymity of
the sender), the quarantee is not that the sender is always anonymous. It's
merely that any eavesdropping will be detected. This is a weaker
guarantee. Moreover, it is not clear how in the current proposal, eavesdropping
is distinguished from collisions (ie two cryptographers trying to send
simultaneously).
Also, using a photon circulation scheme implies that _one_ cryptographer is
made responsible for firing the photon. This gives him extra power (eg firing
two photons simultaneously...).
The idea to use quantum physics to get rid of the shared randomness is
nice. I'm not sure that the approach outlined by Hal can be made to work.
Jaap-Henk
--
Jaap-Henk Hoepman | Come sail your ships around me
Dept. of Computer Science | And burn your bridges down
University of Twente | Nick Cave - "Ship Song"
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