An oblivious transfer protocol with log-squared communication

Abstract. We propose a one-round 1-out-of-n computationally-private information retrieval protocol for ℓ-bit strings with low-degree polylogarithmic receivercomputation, linear sender-computation and communication Θ(k · log 2 n + ℓ · log n), where k is a possibly non-constant security parameter. The new protocol is receiver-private if the underlying length-flexible additively homomorphic public-key cryptosystem is IND-CPA secure. It can be transformed to a one-round computationally receiver-private and information-theoretically sender-private 1out-of-n oblivious-transfer protocol for ℓ-bit strings, that has the same asymptotic communication and is private in the standard complexity-theoretic model. Keywords. Computationally-private information retrieval, length-flexible additively homomorphic public-key cryptosystem, oblivious transfer.