Improved Non-committing Encryption Schemes Based on a General Complexity Assumption

Non-committing encryption enables the construction of multiparty com-putation protocols secure against an adaptive adversary in the computationalsetting where private channels between players are not assumed. While anynon-committing encryption scheme must be secure in the ordinary seman-tic sense, the converse is not necessarily true. We propose a constructionof non-committing encryption that can be based on any public key systemwhich is secure in the ordinary sense and which has an extra property wecall simulatability. The construction contains an earlier proposed scheme byBeaver based on the Diffie-Hellman problem as a special case, and we proposeanother implementation based on RSA. In a more general setting, our con-struction can be based on any collection of trapdoor one-way permutationswith a certain simulatability property. This offers a considerable efficiencyimprovement over the first non-committing encryption scheme proposed byCanetti et al. Finally, at some loss of efficiency, our scheme can be based ongeneral collections of trapdoor one-way permutations without the simulata-bility assumption, and without the common domain assumption of Canetti etal.