PriVeto: a fully private two round veto protocol.

Veto is a prerogative to unilaterally overrule a decision. A private veto protocol consists of a number of participants who wish to decide whether or not to veto a particular motion without revealing the individual opinions. Essentially all participants jointly perform a multi-party computation (MPC) on a boolean-OR function where an input of "1" represents veto and "0" represents not veto. In 2006, Hao and Zieli´ nski presented a two round veto protocol named Anonymous Veto network (AV-net), which is exceptionally efficient in terms of the number of rounds, computation and bandwidth usage. However, AV-net has two generic issues: 1) a participant who has submitted a veto can find out whether she is the only one who vetoed; 2) the last participant who submits her input can pre-compute the boolean-OR result before submission, and may amend her input based on that knowledge. These two issues generally apply to any multi-round veto protocol where participants commit their input in the last round. In this paper, we propose a novel solution to address both issues within two rounds, which are the best possible round efficiency for a veto protocol. Our new private veto protocol, called PriVeto, has similar system complexities to AV-net, but it binds participants to their inputs in the very first round, eliminating the possibility of runtime changes to any of the inputs. At the end of the protocol, participants are strictly limited to learning nothing more than the output of the boolean-OR function and their own inputs.

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