17 Dec
2003
17 Dec
'03
11:17 p.m.
If the plastic sheet is just a fixed mask, then this scheme yields instantly to chosen plain-text (just send an all-black page), really quickly to known-plaintext, and pretty quickly to multiple cyphertexts. There's got to be more to it than that Simon (defun modexpt (x y n) "computes (x^y) mod n" (cond ((= y 0) 1) ((= y 1) (mod x n)) ((evenp y) (mod (expt (modexpt x (/ y 2) n) 2) n)) (t (mod (* x (modexpt x (1- y) n)) n))))