Breaking an image encryption scheme based on a spatiotemporal chaotic system

• A cryptanalysis of an image encryption scheme based on spatiotemporal chaos is presented.
• We gave a complete and partial break of the cryptosystem under study.
• We prove that the studied cryptosystem is not sufficiently secure against chosen plaintext attack.
• Results suggest that a partial attach needs smaller number of plain/ciphered images with acceptable perceptual qualities.

In this paper, we describe a cryptanalysis of image encryption scheme recently proposed by Chun-Yan Song, Yu-Long Qiao, and Xing-Zhou Zhang. The scheme is based on a spatiotemporal chaos with a dynamic keystream generator, and its security is claimed to rely in utilized the plainimage in the keystream generation process to obtain a different keystream for every plainimage/cipherimage pair. However, two flaws are investigated and prove that the security of the proposal against chosen plaintext attack is groundless. Simulations conducted demonstrate that the plainimage can be recovered under partial attack with an acceptable perceptual quality. Moreover, a total break is possible, but a large number of plain-image/cipher-image pairs is needed.