Int. J. on Recent Trends in Engineering and Technology, Vol. 11, No. 1, July 2014
Shadow Size Reduction of Shared Color Image based on Discrete Cosine Transform Ashwaq T. Hashim1, and Dr. Loay E. George 2 1
Babylon University, College of Science, Dept of Computer Science, Babil, Iraq Name of Institution/Department, City, Country Email:
[email protected] 2 Baghdad University, College of Science, Dept. of Computer Science, Baghdad, Iraq Email:
[email protected]
Abstract—A secret sharing scheme is an intellectual candidate for ensuring secrets as cryptographic keys transmit via Internet. The huge size of a secret image is not only waste the memory space but also requires significant computation for encoding and decoding. During distribution, the unnatural ciphered secret image is hard to deliver and easy to catch interceptors’ attention to decode. Likewise, images containing spatial correlation property are highly correlated with colors of adjacent pixels. This property can reduce the size of secret images in bandwidth and storage space. Several researches have been devoted to develop various sharing schemes for color secret images, and great research efforts spent in reducing the shadow size. This paper presents a new highly resistant algorithm based on Discrete Cosine Transform (DCT) for secret color image sharing. In proposed method, the DCT is used to reduce the secret image size firstly, then it employs the compact linear sharing scheme [1] to generate the shadow images, and then each share is separately encrypted to increase security. Index Terms—Secret sharing, Small shadows, (k, n) Threshold scheme, DCT Transform.
I. INTRODUCTION Secure digital imaging is an important research area combining methods and techniques coming from cryptography and image processing. Visual cryptography and in general secret image sharing techniques enable distributing sensitive visual materials to involved participants through public communication channels, as the generated secure images do not reveal any information if they are not combined in the prescribed way. In visual cryptography, the decoding process is performed directly by the human eyes; while in general, the shared images need some processing to reconstruct the secret image. The increasing number of possibilities to create, publish and distribute images stimulated the need for novel protection methods, offering new sharing and access control mechanisms for the information contained in the published images. Secure image sharing techniques overcome the traditional cryptographic approach, providing new solutions for the development of new and secure imaging applications [2]. Suppose we have a secret color image that we desire to protect. If we employ traditional cryptographic techniques, then we need to encrypt the image and store the image on a secure server. The, we need to pay attention on the security of the key used for encryption. This server would become a single focus of attack from a potential adversary. However, with secure image sharing scheme, we can divide the information in the image into several shares and keep them on separate servers. This would allow for a lot more redundancy in DOI: 01.IJRTET.11.1.28 © Association of Computer Electronics and Electrical Engineers, 2014
the protection since breaking one server will not reveal the secret image.
Figure 1. Principle of Image Sharing
The problem of color image sharing is formally defined as follows. In order to transfer a color image I through a public channel securely, the information of the color image is divided into n pieces and embedded into images Ii, (i = 1, 2, ..., n), and we call the images Ii, (i = 1, 2, ... ,n) as shares. With the knowledge of any k (k
