Chengqing Li Shujun Li Kwok-Tung Lo Kyandoghere Kyamakya A Differential Cryptanalysis of Yen-Chen-Wu Multimedia Cryptography System (MCS) http://arxiv.org/abs/0908.2496 2009 CoRR abs/0908.2496 db/journals/corr/corr0908.html#abs-0908-2496 informal publication