Security evaluation of bilateral-diffusion based image encryption algorithm

Recently, a novel bilateral-diffusion image encryption algorithm based on dynamical compound chaos function and LFSR was proposed. The core idea of the algorithm is to introduce the bilateral-diffusion approach. The present paper focuses mainly on security evaluation of this approach. As it is well known, the security of a cryptosystem must depend only on the secrecy of the key rather than the secrecy of the algorithm according to Kerckoff's principle. The security of the original algorithm is determined by two initial keys. Since the keys are fixed, the chaotic keystream keeps unchanged for different images. Thus, our purpose is to reveal the keystream. The cryptanalytic results show that the whole keystream can be broken by using two images including a chosen image and a known image, with a combination of chosen-plaintext attack and known-plaintext attack.