Information Theoretically Secure: Cannot be broken, period Computationally Secure: Cannot be broken without computational power that hopefully nobody has That is kind of what I got from it as well, but RNG's and even PRNG's should have so much randomness (or produce only randomness in the case of RNG) that this is not feasible. Also, my understanding is that all modern ciphers are protected from chosen plaintext attacks, so the randomness of the plaintext should not matter. To the best of my understanding this attack only really matters against non-randomly generated passwords and poorly designed ciphers, but yeah the math is beyond me so I could be way off here. It is indeed debated. Some people think that true randomness is not real and that all things are completely deterministic. I think quantum physics indicates that there is randomness though, again this stuff is a bit beyond my ability to fully comprehend so take what I say for what it is worth. I was just thinking about this the other day. I bet when most people are asked to type randomly on their keyboards it looks something like this: eijfwoejfiewjfioewjfijfiwejfiwjfiwjfijfwejfiwejiofwejifwejfjewiofwj , and that when most people are asked to move their mouse randomly they move it in a circular pattern or up and down pattern. I think it would be better if they were asked to type a short story or to draw a random picture.