Practical t-out-n Oblivious Transfer and Its Applications

摘要

General constructions of t-out-n (string) oblivious transfers and millionaire protocol are presented using two-lock crypto-system, which enables Alice to send Bob secret without shared key. In the proposed t-out-n (string) oblivious transfer, Alice cannot determine which t messages Bob received even if she has unlimited computational power while Bob cannot learn the other n - t messages if the discrete logarithm problem is infeasible. The scheme requires constant rounds. Alice needs n + t modular exponentiations and Bob needs 2t modular exponentiations. Furthermore, the basic scheme is improved to meet public verifiability and extended to distributed oblivious transfers. As applications, efficient PIR scheme and millionaire protocol are built.