Optimal Quantum Strong Coin Flipping

Coin flipping is a fundamental cryptographic primitive that enables two distrustful and far apart parties to create a uniformly random bit [Blu81]. Quantum information allows for protocols in the information theoretic setting where no dishonest party can perfectly cheat. The previously best-known quantum protocol by Ambainis achieved a cheating probability of at most 3/4 [Amb01]. On the other hand, Kitaev showed that no quantum protocol can have cheating probability less than 1/ 2 [Kit03]. Closing this gap has been one of the important open questions in quantum cryptography. In this paper, we resolve this question by presenting a quantum strong coin flipping protocol with cheating probability arbitrarily close to 1/ 2. More precisely, we show how to use any weak coin flipping protocol with cheating probability 1/2 + in order to achieve a strong coin flipping protocol with cheating probability 1/ 2 + O(). The optimal quantum strong coin flipping protocol follows from our constructi...

• Type: Conference
• Year: 2009
• Where: FOCS
• Authors: André Chailloux, Iordanis Kerenidis
• Keywords: Cheating Probability, Coin Flipping, Coin Flipping Protocol, FOCS 2009, Theoretical Computer Science