Selective encryption for gray images based on chaos and DNA complementary rules

A new block cipher for gray images is proposed in this paper which fully utilizes whole set of DNA complementary rules dynamically for encoding and decoding each pixel of a block. The most significant (MSB) part of each block is added under DNA addition operation with least significant (LSB) while LSB part itself get encrypted by chaotically selecting different DNA rules for each pixel. The initial condition is calculated from 128-bits external input key and then the said key is modified for each subsequent block of an image. An image is permuted by Piecewise Linear Chaotic Map (PWLCM) while logistic sequence is used for the selection of encoding and decoding rules for each pixel of a block. The simulated experimental results and the security analysis in terms of quantitative and qualitative way show that our cipher can not only achieve good encryption effect to resist the exhaustive and statistical attacks but also is a good candidate for encrypting large sized uncompressed gray images.