Abstract: Based on the RSA signature and (string) oblivious transfer, an enhanced oblivious transfer protocol is proposed which solves the access control problem for an oblivious transfer protocol. The protocol proposed has the property that only the receiver who has the signture issued by the central authority can open the message which he choose and that the sender can not decide whether the receiver has the signature or not. That is to say, the identity of the receiver can not be confirmed after the protocol. Under the decisional Diffie-Hellman assumption the proposed scheme has provable security.

Key words: access control, Elgamal encryption, oblivious transfer, RSA, decisional Diffie-Hellman assumption