Forget about Bayes Theorem. I meant Bayesian Probability Theory, as described in Probability Theory: the Logic of Science by E. T. Jaynes.

My point was just that to me, noticing in a hard drive a big seemingly random chunk of bytes is very strong Bayesian evidence that the disk holds encrypted data. And if there is encrypted data, the owner of the disk is more likely than not able to access it.

> But how do you determine the frequencies E and R (or their ratio)?

Just ask people in non-adverse situations. With enough effort, that should get you a decent probability distribution over the possible frequencies of E and R.