Modifying of Hill Cipher using Randomized Approach

ABSTRACT: In the modern technological communication networks, where data or image transfer through the communication devices has acquired significance security of the data or image transfer has become a major issue. By means of cryptography, they convert plaintext into ciphertext, or into data that must be unreadable to the attacker. Another approach is to encrypt data of image and then send it to the receiver. Various approaches of modifying Hill Cipher have been discovered earlier, which includes advanced and complicated strategies to overcome the problems faced by using Hill image cipher. This thesis is concerned with a rather simple modification on Hill Cipher using randomized permutation of pixel locations approach and comparing the results with Hill image cipher. The Hill Cipher has advantages in encryption of symmetric data. However, it is insufficient to known plaintext attack. For this reason, the plain image should be processed first to hide its pattern that has the main information. Many researchers used complicated approaches that sometimes depend on matrix mathematics and sometimes on information manipulations. The aim of these complication strategies is to make the encryption approaches in thwart order to any known plaintext and ciphertext attacks. The main object of this thesis is to adjust the original Hill Cipher to decrease the susceptibility to known plaintext attacks and known ciphertext attack. This is achieved by randomizing the information locations for the whole image. So, even if the attacker can guess the key, the decryption still gives false information. Both of Hill image cipher and the proposed modification on it (termed MHill in this thesis) are convenient for all images plaintext block encryption. Results from statistical analysis and comparative studies have shown that Hill Cipher with randomized approach has a correlation coefficient value which is closed to zero and has the maximum deviation value. According to these results Hill Cipher with randomized approach proved that it has better encryption quality compared to Hill image cipher. Keywords: Hill Cipher, randomized approach, modified Hill image cipher, encryption, decryption, Hill Cipher with randomized approach. …………………………………………………………………………………………………………………………