Efficient oblivious transfer with membership verification.

In this article, we introduce a new concept of oblivious transfer with membership verification that allows any legitimate group users to obtain services from a service provider in an oblivious manner. We present two oblivious transfer with membership verification schemes, differing in design. In the first scheme, a trusted group manager issues credentials for a pre-determined group of users so that the group of users with a valid group credential can obtain services from the service provider, while the choices made by group users remain oblivious to the service provider. The second scheme avoids the trusted group manager, which allows any user in the group to be a group manager, thus it is more suitable in distributed systems. In particular, we prove that the two oblivious transfer with membership verification schemes can achieve receiver's privacy and sender's privacy under a half-simulation model. [ABSTRACT FROM AUTHOR]