A secure symmetric image encryption based on linear geometry

Transmission of image as secret over unreliable communication media is the demanding need of the day. But some intrinsic features like bulk data size, correlation among pixels are not properly addressed by conventional encryption algorithms such as DES, Triple-DES, RSA etc. To address the deficiency of conventional encryption algorithms, we propose a symmetric encryption technique based on linear geometry. Though the basic idea is block ciphering (size of each block is 4 bytes), here we have introduced the fundamental concept of linear geometry for ciphering. The ciphered bytes are again shuffled among N positions (N is size of secret file in bytes). The scheme is basically combination of substitution as well as transposition techniques, which provides better protection for secret image. It may be mentioned that there is no change in size after encryption. The proposed image encryption algorithm is described in detail along with its security analysis, such as key sensitivity analysis, statistical analysis, and differential analysis. Comparisons in terms of correlation between the secret and encrypted images, number of pixels change rate and unified average changing intensity are also presented. The present algorithm has been tested using different images to establish that the technique is quite robust and has a great potential to meet the security needs for digital images.