Multiparty Quantum Coin Flipping

We investigate coin-flipping protocols for multiple parties in a quantum broadcast setting: • We propose and motivate a definition for quantum broadcast. Our model of quantum broadcast channel is new. • We discovered that quantum broadcast is essentially a combination of pairwise quantum channels and a classical broadcast channel. This is a somewhat surprising conclusion, but helps us in both our lower and upper bounds. • We provide tight upper and lower bounds on the optimal bias ε of a coin which can be flipped by k parties of which exactly g parties are honest: for any 1 ≤ g ≤ k, ε = 1 2 − Θ g k . Thus, as long as a constant fraction of the players are honest, they can prevent the coin from being fixed with at least a constant probability. This result stands in sharp contrast with the classical setting, where no non-trivial coin-flipping is possible when g ≤ k 2 .

• Type: Conference
• Year: 2004
• Where: COCO
• Authors: Andris Ambainis, Harry Buhrman, Yevgeniy Dodis, Hein Röhrig
• Keywords: Broadcast Channel, COCO 2004, Quantum Broadcast, Quantum Broadcast Channel