Shamim Ahmed Laskar and Kattamanchi Hemachandran, Assam University, India

The Internet is a method of communication to distribute information to the masses. Digital image are excellent carriers for hidden information. Steganography and cryptography are technologies that are used for secret and secured communications. In both the methods, secret message is exchanged between two groups, sender and receiver. The main purpose in cryptography is to make massage concept unintelligible, while steganography aims to hide secret message. We propose a method of combining steganography, cryptography for secret data communication. In this paper, we propose a high-performance JPEG steganography along with a substitution encryption methodology. This approach uses the discrete cosine transform (DCT) technique which used in the frequency domain for hiding data within image. It is very difficult to detect hidden message in frequency domain and for this reason we use steganography based on DCT. From the experimental results, we obtain that the proposed method has a larger message capacity. Experimental results show that the correlation and entropy values of the image with encrypted data before the insertion are similar to the values of correlation and entropy after the insertion thus reduces the chance of the confidential message being detected and enables secret communication. The image that contains the hidden data will be used by the receiver to reconstruct the same secret message after extracting it. The effectiveness of the proposed method has been estimated by computing Mean square error (MSE) and Peak Signal to Noise Ratio (PSNR). Experimental results show the method provides high security and the information is safe from various attacks.

Steganography, Cryptography, plaintext, encryption, decryption, ciphertext,substitution cipher, discrete cosine transform, JPEG, quantization, Mean square error and Peak Signal to Noise Ratio.