Brad Klee <bradklee@gmail.com> wrote:

https://0x0.st/zwRU.txt

Easy to brute force if you get the gist of the permutation scheme but looks difficult to reverse engineer otherwise.

That looks very familiar. I notice that common letters remain common, that common digrams either remain common or are reversed, and that words and reversed words sometimes appear. I've seen that before, when I played around with taking a block of text and using each successive possible ASCII character in turn as a delimeter and reversing the text between every instance of that character, treating the end as being followed by the beginning (a "necklace"). For instance: reverse [e] revesre [r] rsevere [s] esrerev [v] erersev But I tried that, and it didn't work. Nor did running through the ASCII sequence in reverse order. Maybe another one of the 128! possible orders for seven-bit ASCII. It doesn't help that there are two non-ASCII characters in the text. Some years ago it occurred to me that exclusive-oring a text with a subset of the square roots, in binary, of the first N primes, followed by the above scrambling algorithm (in ASCII order), followed by the same exclusive-oring again, would be a pretty good encryption algorithm. Does anyone disagree?