SD-AEI: An advanced encryption technique for images

In this paper, the author propose a method, SD-AEI, for image encryption, which is an upgraded module for SD-EI combined image encryption technique and basically has three stages: 1) In first stage, each pixel of image is converted to its equivalent eight bit binary number and in that eight bit number, the number of bits, which are equal to the length of password are rotated and then reversed; 2) In second stage, extended hill cipher technique is applied by using involutory matrix, which is generated by same password used in second stage of encryption to make it more secure; 3) In third stage, the whole image file is randomized multiple number of times using Modified MSA Randomization encryption technique and the randomization is dependent on an unique number, which is generated from the password provided for encryption. This proposed technique, SD-AEI, is very effective in encrypting any type of images and the results were very satisfactory. SD-AEI method is also compared with various other image encryption techniques and it was found that SD-AEI cryptographic method takes optimal amount of time when compared to other encryption techniques, for encrypting and decrypting an image file. This method can be used to encrypt any type of image file, especially secret images, where steganography has been applied, so that the contents in the image file can be kept more secure.