Efficient Oblivious Transfer for One-Sided Active Adaptive Adversaries

Nargis designed an oblivious transfer protocol secure against erasure-free one-sided active adaptive adversaries (Nargis, AFRICACRYPT 2017). Her protocol uses a two-party lossy threshold public key encryption scheme that is secure in the same setting. We design a new two-party lossy threshold public key encryption scheme secure against erasure-free one-sided active adaptive adversaries. Using this new encryption scheme as a tool, we modify the oblivious protocol of Nargis. The new string OT protocol for string of length linear in the security parameter asymptotically improves the communication complexity, the number of public key encryption operations and the number of exponentiation operations by a factor of the security parameter over the string oblivious transfer protocol of Nargis. The new encryption scheme is of independent interest. It can be used as a tool in other two-party computation protocols for adaptive adversaries.