A Framework for Efficient and Composable Oblivious Transfer
We propose a simple and general framework for constructing oblivious transfer (OT) protocols that are ecient , universally composable, and generally realizable from a variety of standard number-theoretic assumptions, including the decisional Die-Hellman assumption, the quadratic residuosity assumption, and worst-case lattice assumptions. Our OT protocols are round-optimal (one message each way), quite ecient in computation and communication, and can use a single common string for an unbounded number of executions. Furthermore, the protocols can provide statistical security to either the sender or receiver, simply by changing the distribution of the common string. For certain instantiations of the protocol, even a common random string suces. Our key technical contribution is a simple abstraction that we call a dual-mode cryptosystem. We implement dual-mode cryptosystems by taking a unied view of several cryptosystems that have what we call \messy public keys, whose dening