## Coin Flipping with Constant Bias Implies One-Way Functions. (2011)

###### Iftach Haitner, Eran Omri.

SIAM Journal of Computing 43(2): 389-409 (2014)

Proc. of IEEE 52nd Annual Symposium on Foundations of Computer Science (FOCS), Pages 110–119, 2011.

__Full version draft PDF __| __FOCS version__

###### Abstract

It is well known (cf., Impagliazzo and Luby [FOCS '89]) that the existence of almost all "interesting" cryptographic applications, i.e., ones that cannot hold information theoretically, implies one-way functions. An important exception where the above implication is not known, however, is the case of coin-flipping protocols. Such protocols allow honest parties to mutually flip an unbiased coin, while guaranteeing that even a cheating (efficient) party cannot bias the output of the protocol by much. Impagliazzo and Luby proved that coin-flipping protocols that are safe against negligible bias do imply one-way functions, and, very recently, Maji, Prabhakaran, and Sahai [FOCS '10] proved the same for constant-round protocols (with any non-trivial bias). For the general case, however, no such implication was known. We make progress towards answering the above fundamental question, showing that (strong) coin-flipping protocols safe against a constant bias (concretely, (√2 -1)/2 - o(1)) imply one-way functions.