For an image of 4096 x 4096, the encryption time is only 59% of the Wang’s for R = 1, and 43% for R=2.Ĭhaper 2 An overview of chaotic cryptosystemsĘģ.2 Converting an image into bit-planesĒ2ģ.3 Proposed encryption/decryption algorithmĒ4 Based on the above observations, our proposed scheme is very efficient.Įxperimental result shows that the propsed encryption scheme under the security requirement NPCR=99.5973% and UACI=33.45785% has better speed efficiency as compared with the Wang’s. Since the size of each transformed subimage is just 1/8 of that of the plain image and same diffusion masks and new posistions are used for every subimage, only 1/8 numbers of diffusion masks and new positions should be calculated. The lower part is highly informative which needs encryption of higher computational effort.
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The upper part is nearly random and unrecgonizable and therefore needs encryption of lower computational effort. These transformed subimages consist of two parts. The new format could be seen as 8 independent transformed subimages stacking together. Besides, we incorporates an idea which transforms the plain image into a new format.
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An improvement direction is to combine permutation and diffusion to avoid duplicating scanning and to raise the efficiency.īased on the Wang’s system, this thesis proposed an efficient image encryption scheme which maintains the advantages of dividing the plain image into blocks type and utilizing spatiotemporal chaos with NCML to perform permutation and diffusion simultaneously. In recent years, various chaos-based cryptosystems with permutation and diffusion have been proposed.
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