Here it is; bi-directional dining cryptographers

[Phil Fraering <pgf@tyrell.net>]

Bill, I'll probably go down to the notary's this morning to get the
thing registered; I don't want to pay $ 50.00 to surety for what's
likely to be a one-shot deal.

And I've been leaning towards the side of releasing it into the public
domain anyway, so here goes:

(And besides, I can't believe everyone else missed this; one of you
has got to know about this already):

If Alice and Bob are members of a reasonably non-compromised and
free of colluders dining-cryptographers network, with a protocol for
reserving blocks for the transmission of data packets, then if they
both send a data packet in the same block, they can each read what
the other is saying but to the rest of the DC-net it is garbled.

Since what is broadcast is the XOR of Alice's and Bob's data, Alice can
read Bob's data by XOR'ing the output of the DC-net with her attempted
input; Bob can recover her data the same way.

Comments?

(At the very least, it doubles the bandwidth for the two participants...)

Phil