High security image encryption by two-stage process

The dynamic response of chaotic system is unpredictable and highly sensitive to the variation of initial values of a system. Therefore, the distinguished elements of variables applied to produce encryption codes for the color-image encryption can increase the communication security. This paper proposed a hybrid encryption technique for the color image based on the multi-chaotic-system which combines pixel-chaotic-shuffle (PCS) and image-multi-encryption (IME). This method completely eradicates the outlines of the encrypted images, blurs the distribution characteristics of RGB-level matrices, effectively protects against the decryption of exhaustive attack method, and more over, increases the key space of encrypted images. The test methods involving key space and correlation coefficient r are adopted for the security analysis. Also NPCR (number of pixel change rate) and UACI (unified average changing intensity) are proceeded for the proof of the distinguished characteristic of pixels in the encrypted image. Eventually, empirical images are conducted as illustrations, which show that the proposed method has the great encryption performance and achieves the high confidential security.