Restricted adaptive oblivious transfer
In this work we consider the following primitive, that we call restricted adaptive oblivious transfer. On the one hand, the owner of a database wants to restrict the access of users to this data according to some policy, in such a way that a user can only obtain information satisfying the restrictions imposed by the owner. On the other hand, a legitimate user wants to privately retrieve allowed parts of the data, in a sequential and adaptive way, without letting the owner know which part of the data is being obtained.After having formally described the components and required properties of a protocol for restricted adaptive oblivious transfer, we propose two generic ways to realize this primitive. The first one uses a cryptographic tool which has received a lot of attention from the literature in recent years: cryptosystems which are both multiplicatively and additively homomorphic. Our second generic construction is based on secret sharing schemes.