A novel information entropy based randomness test for image encryption

In this paper, a new information entropy based randomness test for image encryption about is proposed. Unlike the conventional information entropy test working on the global image, the new proposed measurement focuses on local image blocks and calculates the sample mean of information entropy over a number of random selected image blocks within a test encrypted image. Reference values are mathematical derived from the ideally encrypted image model. As a result, the randomness of an encrypted image can be easily told by comparing the test values with theoretical ones. Ultimately, a hypothesis test to accept or reject an encrypted image is also derived to accept or reject the null hypothesis that ciphertext image is ideally encrypted/random-like with a significance level α. In such a way, the proposed block entropy test provides both quantitative and qualitative results for image encryption. Experimental results on existing image cipher show the effectiveness of the proposed test. The same idea can be also to other digital data, like videos or audios.