On the influence of single participant in coin flipping schemes

Iftach Haitner, Nikolaos Makriyannis, Eran Omri

Benny Chor, Mihály Geréb-Graus

We prove that in a one round fair coin flipping scheme with n participants, either the average influence of all participants is at least 3/n - o(l/n), or there is at least one participant whose influence is fI (n- S/ 6).

Iftach Haitner, Nikolaos Makriyannis, Eran Omri

Xie Yumin, Ming Yang, Shi Feng +1 more

Coin flipping by telephone protocol(CFP) is utilized in a system to exchange a binary sequence at random between two person apart far from each other. However, CFP cannot be used in a system with many users like in a group environment system. A transmutation of CFP named T-CFP is proposed in this paper. The precondition of T-CFP is the system's user trusts the system center and center's cheating is meaningless at the same time. The significant difference between CFP and T-CFP is that CFP supports only two users while T-CFP can support many users to exchange special information. The security and efficiency of T-CFP are discussed with a detailed example on T-CFP utilization is demonstrated in this paper.

Guido Berlín, Gilles Brassard A, Félix Bussières +1 more

Coin flipping is a cryptographic primitive in which two spatially separated players, who in principle do not trust each other, wish to establish a common random bit. If we limit ourselves to classical communication, this task requires either assumptions on the computational power of the participants or it requires them to send messages to each other with sufficient simultaneity to force their complete independence. Without such assumptions, all classical protocols are so that one dishonest player can completely bias the outcome to his choosing. If we allow for quantum communication, on the other hand, protocols have been introduced that limit the maximal bias that dishonest players can produce. However, those protocols would be very difficult to implement in practice because they cannot tolerate realistic losses on the quantum channel between the participants or in their quantum storage and measurement apparatus. In this paper, we introduce a novel quantum protocol and we prove its unconditional security even when such losses are taken into account.

Silvio M. Micali, Tal Rabin