Encryption of Gray Images using Scalable Codes

Abstract

In this paper we have used a method for encryption of images using scalable coding. In encryption, a pseudorandom number derived from a secret key is used to encrypt the original pixel values. In encoding block, encrypted data is decomposed into a down sampled sub image and several data sets with a multiple-resolution construction. Thus an encoder quantizes the sub image and calculates the Hadamard coefficients of each data set that will reduce the data amount. Then, this quantized sub image and Hadamard coefficients are regarded as a set of bitstreams. At the receiver end, while decryption of sub image will give the rough information of the original content, the quantized coefficients can be decrypted to regenerate the detailed content with an iteratively updating procedure. At the output we will first obtain a lossy version of image and images of higher resolution can be obtained when more and more bitstreams are received. PSNR of reconstructed images is calculated for all scales. When more number of decomposition levels are used to decompose encrypted data, PSNR performance is good.