Image Encryption Using Lagrange-Least Squares Interpolation
Mohammed A. Shreef, Haider K. Hoomod · SSRN Electronic Journal · 2013
Today, information security is becoming one of the most important issues in social network era. The fast development of network technology leads to facilitate many aspects of life, but it also gives attackers or unauthorized users an opportunity to violate the privacy of people. Encryption is a common technique that exists to protect information security, thereby deters attackers. Actually, digital images are widely used in storage and communication applications. Therefore, the protection of image data from unauthorized access has attracted much attention recently. This paper adopts a new image cryptosystem, XLLS, which consists of two main parts: encryption/decryption algorithm and ciphered key. The encryption algorithm is composed of two main stages: the diffusion stage and the substitution stage. In the diffusion stage, the pixels values are modified so that a slight change in one pixel is spread out to all pixels in the image. This stage completely depends in its construction on ‘XOR’ operation. For the substitution stage, it mainly composes of two encryption processes: Lagrange Process (LP) and Least Squares Process (LSP). This stage aims at changing the value of each pixel in the diffused image by using the principles of Lagrange interpolation and least squares method. For the decryption algorithm, it is simply the reverse of the encryption algorithm. On the other hand, the proposed cryptosystem introduces two different approaches of initial key. The users have option to choose any one of them to encrypt the plain-image. In the first approach, the proposed cryptosystem uses a key whose length is of 192 bits (24 bytes) in hexadecimal system as its input, and then expands it by using AES-192 key expansion algorithm. Conversely, in the second approach, the proposed cryptosystem uses an image as a key to cipher the plain-image, and then processes and expands the key-image by using the CBI key expansion algorithm.