With the fast evolution of digital data exchange and increased usage of multi media images, it is essential to protect the confidential image data from unauthorized access. In natural images the values and position of the neighbouring pixels are strongly correlated. The proposed method breaks this correlation increasing entropy of the position and entropy of pixel values using block shuffling and encryption by chaotic sequence respectively. The plain-image into blocks and then performs block based shuffling using Arnold Cat transformation. Further, the image is uniformly scrambled, where all the pixels in the same block of scrambled image come from different blocks of original image, after which the image as a whole is shuffled again by the transform. Finally the shuffled image is encrypted using a chaotic sequence generated using symmetric keys, to produce the ciphered image for transmission. The experimental results show that the proposed algorithm can successfully encrypt/decrypt the images with the secret keys, and the analysis of the algorithm also demonstrates that the encrypted images have good information entropy and low correlation coefficients.

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