Identity-based Threshold Decryption Scheme Without Random Oracles

In this paper, we firstly propose an Identity-based threshold decryption (IBTD) scheme based on truncated decisional Augmented bilinear Diffie-Hellman exponent (ABDHE) assumption, and prove that it is chosen ciphertext secure in the adaptive identity (adaptive- ID) model without random oracles. To the best of our knowledge, it is the first in the literature to achieve such a high security level, tight security reduction and computationally efficiency at the same time. It also enjoys desirable property of non-reconstruction of the private key. In addition, we extend the proposed IBTD scheme into a new mediated identity-based encryption (mIBE) scheme.