; Use http://cap-lore.com/code/mult/ff.txt for mod-exp and to find primes.
; Use http://cap-lore.com/code/Scheme/eea
(define (inv a p) (mod-exp a (- p 2) p))
(define (mrg p q) (let ((P (* p (inv p q)))(Q (* q (inv q p)))(pq (* p q)))
   (lambda(a b) (modulo (+ (* b P)(* a Q)) pq))))
; RSA below returns a public-private pair of routines given two primes each not 1 mod 17.
(define (RSA p q) (let ((pq (* p q)) (e 17) (mg (mrg p q)) (em (* (- p 1)(- q 1))))
  (if (> (gcd e em) 1) "Bad" (let* ((d (modulo (car (eea e em)) em))
        (pe (modulo d (- p 1)))(qe (modulo d (- q 1))))
    (cons (lambda (p) (mod-exp p e pq))
          (lambda (c) (mg (mod-exp (modulo c p) pe p) (mod-exp (modulo c q) qe q))))))))
; The Java code at http://www.cs.utsa.edu/~wagner/laws/ARSAFast.html seems to use this logic.
; I coded this in 2006 before I saw Wagner's earlier code.