I was reading this paper. Under the section 4.3 and 4.5 they add The Chi-Square Test Analysis of Cipher Image and Information Entropy Analysis respectively. I was interested to know how they manage to get the p-value and calculate Entropy from an encrypted image (theoretical perspective).
Any idea or suggestion or provide a script will be appreciated. Or redirect me to any blog/article where those analyses were discussed in details will be appreciated to. I googled them but didn't get enough information to implement or write a python script to test for an encrypted image.
I was wondering how to test/identify that an encrypted image is good one or hard to decrypt. Is there any theory based on this topic?