Abstract We propose two efficient universally composable adaptivek‐out‐of‐N protocols, secure in the presence of malicious adversary in static corruption model under the Decision Linear and q‐Strong Diffie–Hellman assumptions. Our second scheme additionally requires the hardness of Decision Bilinear Diffie‐Hellman problem. Non‐interactive Groth–Sahai proofs are employed for the verification of pairing product equations. More interestingly, our first scheme facilitates the receiver to verify the correctness of messages recovered. The proposed protocols exhibit significant computational and communication efficiency compared with existing similar schemes in the literature. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract In today's Internet world, security, privacy and efficiency are three prime concerns in designing any cryptographic protocol. Adaptive oblivious transfer with access policy (AOT‐AP) is widely used in oblivious search of privacy preserving databases in which each message is associated with an access policy and only authorized receivers can access the databases. All the existing AOT‐AP protocols assume a trusted third party called issuer apart from a sender and multiple receivers and are secure under the restriction that the issuer never colludes with a collection of receivers. We propose the first issuer‐freeAOT‐AP in universal composable (UC) framework. Our issuer‐free AOT‐AP is UC secure under standard assumptions assuming malicious adversary in static corruption model. More interestingly, our scheme exhibits significant improvements over the existing schemes. Copyright © 2015 John Wiley & Sons, Ltd.

We propose an efficient adaptive oblivious transfer protocol with hidden access policies. This scheme allows a receiver to anonymously recover a message from a database which is protected by hidden attribute based access policy if the receiver's attribute set satisfies the associated access policy implicitly. The proposed scheme is secure in the presence of malicious adversary under the q-Strong Diffie-Hellman (SDH), q-Power Decisional Diffie-Hellman (PDDH) and Decision Bilinear Diffie-Hellman (DBDH) assumption in full-simulation security model. The scheme covers disjunction of attributes. The proposed protocol outperforms the existing similar schemes in terms of both communication and computation.