An IBE Scheme with Verifiable Outsourced Key Generation Based on a Single Server

It is well known that private key generation is a computing bottleneck in an identity-based encryption scheme when a large number of users exist. Outsourcing computation can greatly reduce the users' computational cost, but the existing schemes are all based on two servers, which are not feasible in the real cloud environment. In this paper, we first propose a scheme where the PKG outsources the task of private key generation to a single server, and the results can be verified effectively. Moreover, PKG only needs to execute 1 modular exponentiation, so it is more efficient when compared with previous schemes. Meanwhile, we prove the indistinguishability of the ciphertext and verifiability of the outsourcing results in the security model. Finally, the proposed algorithm is realized in a simulation environment. Theoretical analysis and experimental results show that total computing time of PKG and the server in the outsourced algorithm is far less than that of direct computation.