Provably secure threshold public-key encryption with adaptive security and short ciphertexts

Threshold public-key encryption is a cryptographic primitive allowing decryption control in group-oriented encryption applications. Existing TPKE schemes suffer from long ciphertexts with size linear in the number of authorized users or can only achieve non-adaptive security, which is too weak to capture the capacity of the attackers in the real world. In this paper, we propose an efficient TPKE scheme with constant-size ciphertexts and adaptive security. Security is proven under the decision Bilinear Diffie-Hellman Exponentiation assumption in the standard model. Then we extend our basic construction with efficient trade-offs between the key size and the ciphertext size. Finally, we illustrate improvements to transmit multiple secret session keys in one session with almost no extra cost. (C) 2012 Elsevier Inc. All rights reserved.