An Approach to Ensure the Secrecy of Scene Images

Abstract

This thesis proposes a multi-stage encryption technique to enhance the level of secrecy of image to facilitate its secure transmission through the public network. A vast number of researches have been done on image secrecy. The existing image encryption techniques like visual cryptography (VC), steganography, and watermarking etc. while are applied individually; usually they cannot provide unbreakable secrecy. Through combining several separate techniques, a hybrid multi-stage encryption technique is proposed in this thesis, which provides nearly unbreakable image secrecy, while the encryption/decryption time remains almost the same of the exiting techniques. The technique consecutively exploits VC, steganography and one time pad (OTP). At first it encrypts the input image using VC, i.e., splits the pixels of the input image into multiple shares to make it unpredictable. Then after the pixel to binary conversion within each share, the exploitation of steganography detects the least significant bits (LSBs) from each chunk within each share. At last, OTP encryption technique is applied on LSBs along with randomly generated OTP secret key to generate the ultimate cipher image. Besides, prior to sending the OTP key to the receiver, first it is converted from binary to integer and then an asymmetric cryptosystem is applied to encrypt it and thereby the key is delivered securely. Finally, the outcome, the time requirement of encryption and decryption, the security and statistical analyses of the proposed technique are evaluated and compared with existing techniques.