I'm working on one of those unsolved puzzles, and one theory I have is that one or more sections of it are using digits of pi, e, or some other irrational number as a one-time pad.
(The obvious approach would just be to try well-known irrational numbers, but I've tried that without success and if it is that there must be some other complication.)
Are there any cryptanalysis methods that that allows for that wouldn't apply to a one-time pad composed of letters? One thing that occurred to me is that since letters can't be shifted by more than 9 places, it ought to show very small peaks in its frequency distribution, one-tenth the size of ones for plain text and displaced about five letters to the right along the alphabet. But I don't know how much practical use that would be.
The question is probably equivalent to whether a Gronsfeld cipher has any weaknesses that a Vigenere cipher doesn't.