Block mode image encryption technique using two-fold operations based on chaos, MD5 and DNA rules

An innovative image encryption scheme named Two-Fold confusion operation is proposed in the block mode. A gray image is permuted using Logistic map and then Most and Least Significant parts of the image are separated known as MSB and LSB. These LSB and MSB parts are transformed into separate 1-Dimensional arrays and are divided into non-overlapped blocks of fixed size. These blocks are then encoded into DNA bases where each block of LSB and MSB gets a different DNA rule selected dynamically using Chen’s hyper chaotic sequence. The innovation in this scheme is that each selective part of digital image is confused with different operations in DNA algebraic mode: Exclusive-OR for MSB blocks and addition operation for LSB blocks in the first phase. In 2nd phase of confusion, operations are exchanged for LSB and MSB. At last, confused LSB blocks are combined randomly with confused MSB blocks to form blocks of image pixels. These blocks of pixels are decoded back to digital domain by different DNA rules using chaotic pseudo-random numbers. The secret keys for chaotic maps are made dependent on MD5 digest of plain image to avoid launch of chose-plaintext attack. The simulation results show that NPCR score is >99.60%, UACI score > 33.40% and Chi-square is <255, hence proposed system is highly robust against statistical and differential attacks.