Outsourcing of Verifiable Composite Modular Exponentiations

Modular exponentiation as a basic operation is widely used in discrete-log based cryptographic protocols. Most research has been made for outsourcing exponentiation modular a prime, works for outsourcing composite modular exponentiation are rare. In this paper, we propose two new secure outsourcing protocols for verifiable composite modular exponentiation and batch composite modular exponentiations respectively. We analyze the security and complexity of the protocols. Ours are more efficient.