Image Encryption Using Chaotic Map

An image encryption technique using modified perturbed map is proposed. The encryption happens in three phases. The parameters of the proposed chaotic map is generated using a random 128-bit key which generates a chaotic sequence of size 65536 $(\mathbf{256}\times \mathbf{256})$. The sequence generated by the chaotic map is converted into an integer with the maximum value equal to 255. The index values of the chaotic sequence whose pixel value equal to i is placed in block I. By arranging the pixel values 256 blocks are generated. The pixel values of the image are selected one by one based on the index value which is stored in blocks and XORed with the respective chaotic data and the resulting value is stored in the blocks. Average of each block is calculated. A hash value is generated using SHA-256 for each block with the average value as input. The first block hash value is XORed with the first eight pixels of second block. The same process is repeated for all blocks. The first eight pixels of the first block is XORed with hash value of last block. The cipher image is obtained by repeating the same process for one more iteration. The quality of the encryption algorithm is verified using statistical analysis, differential attack analysis and speed analysis. The experimental results shows that the proposed image encryption technique gives better result in terms of entropy, chi square test, correlation coefficient, NPCR and UACI.