I agree profoundly with everything except "the concept is superfluous". Yes its just a lack of information, or as I say it "entropy is the name of the bits you

I agree profoundly with everything except "the concept is superfluous". Yes its just a lack of information, or as I say it "entropy is the name of the bits you don't have." That's a profoundly useful thing. You can talk about the password entropy (the bits in the search space for the password you don't have), the mutual entropy (how many bits does Alice have that Bob is missing) etc.