A chaotic image encryption algorithm based on bit level is proposed. The 8-bit grayscale matrix image is divided into a higher 4-bit matrix image and a lower 4-bit matrix image, which named higher bit image and lower bit image, respectively. Then the encrypted operations are performed on the higher bit and lower bit image. The operations include the mutual disturbing and element exchange operations between them, the scrambling of higher bit image and the diffusion of lower bit images. Simulations and performance analyses show that the proposed scheme has the advantages of large key space, strong system sensitivity, and excellent encryption security, especially good resistance to salt and pepper noise attacks.
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