Practical oblivious transfer protocols

We consider 1-out-N Oblivious Transfer (OT) for strings. Oblivious Transfer is a primitive used in a variety of cryptographic protocols and applications (e.g. [11, 1, 10, 17, 12, 13]). We present a new highly efficient two-pass (one-round) protocol for 1-out-N OT. Our protocol has a constant online computational complexity (for the chooser as well as for the sender). This is a surprising property, since in our protocol the sender's computational complexity does not depend on the number N of strings. The privacy of chooser and sender is protected computational under the Decisional Diffie-Hellman assumption. We also sketch how to apply the techniques of [1] to our protocol to get a protocol for priced OT.