Secure multi–level permutation operation based multiple colour image encryption

In recent days, there is a high demand of encryption of multiple digital images for secure transmission of multiple images. This paper proposes a multi-level permutation operation based secure multiple colour image encryption technique which is totally different than the currently used multiple image encryption techniques. The proposed encryption technique uses three levels of permutation operation: the first level of permutation operation performs pixel-shuffling operations in R, G, and B components, itself; the second level of permutation operation performs row-shuffling operations in between the pixel-shuffled R, G, and B components; the third level of permutation operation performs column-shuffling operations in between the row-shuffled components. At last, the proposed encryption algorithm performs block-diffusion operations to get the final encrypted images. Multi-level permutation operations and diffusion operation only use PWLCM systems multiple times to make the algorithm more secure and stronger. Multiple PWLCM systems in multi-level permutation operations not only produces larger key space and higher key sensitivity but also generates greater randomness of pixels and weaker correlation of adjacent pixels in images as compared to the currently used multiple image encryption techniques. In addition the secret keys which are used in this proposed algorithm not only depends on the original key values but also depends on the original colour images. This protects the algorithm against known-plaintext attack and chosen-plaintext attack. The simulation results and the security analysis indicate that the proposed algorithm has good encryption results, large secret-key space, higher sensitivity towards secret keys and the plaintext, weaker correlation of adjacent pixels, greater randomness of pixels, and enough resistance against various common attacks.