A Robust Noncryptographic Protocol for Collective Coin Flipping

A new protocol for global coin flipping in the model of Ben-Or and Linial is presented. In this model, global coin flipping is considered to be an asynchronous perfect information game among n players, some of whom are dishonest. Each player possesses a fair coin and they wish to agree on the value of a single bit, which the honest players want to be random. A protocol is $\varepsilon $-robust for t dishonest players if no set of t dishonest players can bias the bit by more than $\varepsilon $. The protocol given here is $\varepsilon $-robust against $\theta (n/\log n)$ dishonest players for any fixed $\varepsilon $, improving on the $\theta (n^{.63 \cdots } )$ robust protocol given by Ben-Or and Linial.