**4. Conclusion**

In this chapter, an image encryption algorithm based on spectral fusion of multiple watermarked images and new chaotic generators is proposed. Logistic-May (LM), Gaussian-Gompertz (GG), and May-Gaussian (MG) systems were used as chaotic generators in the processes of confusion and diffusion. The target images were firstly combined in two multiplex images of same size through DCT and a lowpass filter. Secondly, the previous images are scrambled by permuting the blocks size of (4 4) of each multiplex image. Finally, the later scrambled images are fused by a nonlinear mathematical expression based on Cramer's rule to obtain two hybrid encrypted images. At the decryption step, the watermark hidden in one of the target images is recovered without loss of information. The evaluation metrics of the proposed cryptosystem NCPR, UACI, correlation coefficient, entropy, key space, and NMSE, are among the best values in literature. More interestingly, the proposed cryptosystem can encrypt 32 target images simultaneously with a small NMSE≈4*:*<sup>16</sup> <sup>10</sup><sup>3</sup><sup>≈</sup> 3.7 <sup>10</sup><sup>3</sup> , and encrypted images are sensitive to the key. The proposed encryption algorithm can surely guarantee security and speed of all types of digital data (text and images) transfer in a digital network.

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