Abstract: Medical image involves privacy and other important information， so encrypting medical images during the storage and transmission is essential. In order to improve the quality of the encryption at a high speed， a segmented medical image was treated using an even scrambling method based on the Arnold mapping combined with logistic mapping for generating quasirandom numbers to control scrambling parameters. The image was further encrypted through NOR/OR operation of the pixel values. Experimental results show that the method is sensitive to the key and covers the information of an image well， and that it resists cropping and tampering attacks simultaneously， compared with the single logistic mapping method. The operations of the method proposed are simpler than that of conventional ones， so， the method meets the requirement of the encryption speed.

Key words: even scrambling, logistic mapping, chaotic mapping, image encryption, medical image