Physics gives us some tools to meaningfully talk about "unbreakable" without perfect secrecy. In particular, we can currently reason about "unbreakable on any c

Physics gives us some tools to meaningfully talk about "unbreakable" without perfect secrecy. In particular, we can currently reason about "unbreakable on any classical computer operating in an ambiant temperature no less than the cosmic microwave background, and consuming no more energy than exists in the universe". Physics still has some backdoors (notably reversable computing which, as far as I am aware, has no fundamental limit), but the bigger problem is that complexity theory has not advanced to a point where we can make meaningfull use of this. (The most I have ever seen is computing the lowerbound on energy to enumerate all keys. ) This is probably a solvable problem, but is going to be harder than p vs np.