An objective visual security assessment for cipher-images based on local entropy

In recent years, many practical algorithms have been put forward for images and videos encryption. Security analysis on these encryption algorithms focuses research on cryptographic security, and few work relate to visual security. Visual security means that the encrypted video content is unintelligible to human vision. The higher visual security the encryption algorithm can provide, the less information an attacker from the cipher-images to obtain, the greater the difficulty of attack is. Therefore, visual security assessment for cipher-images is a very important indicator in security evaluation of visual media. So far, systematic research on visual security assessment for cipher-images is far from enough. Moreover, there are no practical objective indicators or evaluation methods on visual security have been proposed at present. According to the changes on image information entropy between cipher-images and original images, we present a visual security assessment algorithm based on local entropy. The experiments result shows that the scheme can provide an efficient objective assessment which is match up to subjective assessment, and is also suitable for security assessment of other selective encryption algorithms.