1. Department of Computer Science and Engineering; Shanghai Jiao Tong University; Shanghai 200240 China
2. ESAT/COSIC and IBBT; Katholieke Universiteit Leuven; Leuven Belgium
3. Department of Computer Science and Engineering; University of Shanghai for Science and Technology; Shanghai 200093 China
4. School of Computer Science and Technology; Donghua University; Shanghai 201620 China