Using a central node to coordinate the DC-net traffic requires that the participants trust that central node. If the central node is evil, I think there are things it could do to identify message senders. For example, instead of doing a single collation of N messages, it could do N collations of N-1 messages, and find out who sent a message by seeing in which collation that message doesn't show up.
A collation of N-1 nodes will always produce garbage; the whole set is needed for the message to fall out. Example C wishes to broadcast the number 10. A sends 5 to B B sends 11 to C C sends 7 to D D sends 14 to A A sends 14 - 5 = 9 to Central node B sends 5 - 11 = -6 C sends 11 - 7 + 10 = 14 D sends 7 - 14 = -7 Central node computes 9 - 6 + 14 - 7 = 10; Collating the subset ABC yields 17 Collating ABD yields -4 ACD yields 16 BCD yields 1 What Jim McCoy was talking about (I think: please correct me) was that there are attacks on this protocol, that can prevent messages from being transmitted; or alter messages in transit. Example: B wants to jam the transmission. He simply violates the protocol. A sends 14 - 5 = 9 to Central node B sends 5 - 11 + 8 = 2 (the +8 is static) C sends 11 - 7 + 10 = 14 D sends 7 - 14 = -7 Now the message sums up to 18, instead of 10 as C intended. Worse than that; If B knows that 10 is going to be broadcast, he can force the message to be any value he wants, by properly choosing his jamming signal. There's an even nastier trick you can play with the vanilla DC protocol. Two adjacent members can conspire to set up a 3rd. Let's say the DC Cell gets busted by the Feds for posting the illegal number 10 to the Internet. The guilty party is C, but C and D can lie about the number they shared and make it look like A. C testifies, "I received an 11 from B and sent a -3 to D" D testifies, "I received a 3 from C and sent a 4 to A" That makes A's calculation look off by 10, the number of the message. A testifies, "You liar! You gave me 14!" Who's lying? I'm not sure is these constitute bugs or "features" of the DC protocol; since the goal is to obscure the source of the message, allowing jammers and spoofers may preserve plausible deniability at the cost of network reliability; then again, maybe I'm just being lazy. -- You have violated Robot's Rules of Order and will be asked to leave the future immediately. Thank You.