Image encryption technique using improved A5/1 cipher on image bitplanes for wireless data security

With the advancement of wireless communication and popularity of internet, security of transmitted data has become a major area of concern and have attracted many researchers. To prevent unauthorized access, it is important to encrypt 1D either 2D (image) data before transmission over open wireless network. A5/1 ciphering algorithm is one of the highly secure encryption algorithm, widely used in GSM standard over wireless network to provide security for the voice data. In order to achieve high security and efficient utilization of existing technology and available resources, the same algorithm can also be used for image and video encryption over wireless channel. In this paper, Enhanced A5/1 cipher based image encryption technique with image bit plane separation is proposed to enhance the security of image data transmitted over wireless network. In this method gray scale image is separated into eight different biplanes and each separated 2Dbit plane data is converted into 1D data stream. Each data stream is XORed with a key stream generated by stream cipher whose length is equal to the resolution of the image i.e., rows * columns. Enhanced A5/1 stream cipher with improved clock controlling unit and highly nonlinear combining functions is initialized using a 64 bit secret key to generated key stream. For encryption, eight different key streams are used for an image. The proposed method shows high encryption quality, improved differential analysis values, lossless encryption and decryption and fast computations with respect to the standard AES algorithm used as a benchmark.