Analysis of effect of varying quantization level on the image communication scheme based on combination of compression, cryptography and steganography

Abstract: In [4], we had proposed a new technique for secret communication of a digital image through a network exposed to attackers by combining two popular information security techniques: Cryptography and Steganography. We used a modified version of AES for encryption which uses a key stream generator (W7) and four techniques for steganography (one in spatial and three in frequency domain) which resist some typical statistical attacks. Before encryption we used JPEG compression technique to compress the image. Huffman codes obtained in the entropy coding step are encrypted using AES and hidden in a cover. The stego image is hence transmitted. Introduction of compression reduces the amount of data to be encrypted and hence the encryption time. In this paper, we have tried to find a quantisation level range for JPEG image compression which not only gives a satisfactory decryption result but also a good compression ratio and PSNR for stego image and reduced encryption and steganographic time.