On 9 Oct 2019 at 20:05, Brad Klee wrote:
Easy to brute force if you get the gist of the permutation scheme but looks difficult to reverse engineer otherwise.
I remember reading in a issue of Cryptologia, prolly 40 years ago, about an unbreakable permutation cipher. It's point was you permute the *bits* and then regroup them into characters for transmission. They said that you can count the # of 1s and 0s and simply add a block of 1s or 0s at the end so the cleartext is exacts 50/50 1s and 0s. Then permute that. As I remember the argument, since *every* clear text has the same bit-level distribution, in theory any cipher text could, depending on the permutation, become *any* clear text and so it was pretty much unbreakable. [I think the idea was even if you manages to "unscramble" the bits into a clear text, there was no way to tell if it was the *right* clear text. I never saw any mention of it again so I guess it isn't of general interest [or didn't work, although I'm not sure why not]. /Bernie\ Bernie Cosell bernie@fantasyfarm.com -- Too many people; too few sheep --