Cryptanalyzing an image encryption scheme based on hybrid chaotic system and cyclic elliptic curve

•This paper cryptanalyzed a new image encryption scheme.•The scheme can be broken by known-plaintext and chosen-plaintext attacks.•Some other defects and corresponding improvements are given.•A rough comparison between chaos-based and optics-based image encryption methods is analyzed.

Recently, an image encryption scheme was proposed based on hybrid chaotic system and cyclic elliptic curve. This paper evaluates the security of the scheme and finds that known-plaintext attack can break it with only a pair of plain image/cipher image while chosen-plaintext attack cryptanalyzes it by choosing one plain image with all the zero-value pixels and corresponding cipher image. Meanwhile, experimental results are provided to support the found points. Moreover, some other defects and corresponding improvements are also given. Finally, a rough comparison between chaos theory and optical technique applied to image encryption is done in terms of robustness and statistical analysis. Both of them have own strengths and weaknesses, which motivates the cipher designers to combine their advantages together to construct new-type image encryption schemes.