; RC4 in Scheme.
; See note at http://cap-lore.com/code/Scheme/reposIntro/rc4.html .

(define (Do n p) (if (> n 0) (let ((u (- n 1))) (p u) (Do u p))))

(define (grc4 key)(let ((s (make-string 256))(i 0)(j 0))
 (Do 256 (lambda(n) (string-set! s n (integer->char n))))
 (let ((len (string-length key))(j 0))
   (Do 256 (lambda (k) (let ((i (- 255 k)))
     (set! j (modulo (+ j (char->integer (string-ref s i))
        (char->integer (string-ref key (modulo i len)))) 256))
     (let ((t (string-ref s i))) (string-set! s i (string-ref s j))
       (string-set! s j t))))))
  (lambda (n)(let ((v 0)) (Do n (lambda (dm)
    (set! i (if (= i 255) 0 (+ i 1)))
    (let* ((a (string-ref s i))(A (char->integer a)))
      (set! j (modulo (+ j A) 256))
      (let* ((b (string-ref s j))(B (char->integer b)))
        (string-set! s i b)(string-set! s j a)
        (set! v (+ (* 256 v) (char->integer
           (string-ref s (modulo (+ A B) 256))))))))) v))))


(define pr (let ((px (lambda (h) (display (string-ref "0123456789abcdef" h)))))
  (lambda (s) (let ((l (string-length s))) (newline) (Do l
  (lambda (n) (let ((k (char->integer (string-ref s (- (- l 1) n)))))
  (px (quotient k 16))(px (modulo k 16)))))))))

(define (rd x) (let* ((l (/ (string-length x) 2)) (n (make-string l))
      (hx (lambda (j) (let ((u (char->integer (string-ref x j))))
         (- u (if (< u 58) 48 87))))))
   (Do l (lambda (j) (string-set! n j (integer->char 
       (+ (* 16 (hx (+ j j))) (hx (+ j j 1))))))) n))

(define xx (grc4 "keytext"))
(newline) ; => (179)(69)(136)(154)(208)(235)(123)(244)(57)(47)(193)(120)(186)(128)(235)(213)(86)(173)(69)(216)(182)(133)(211)(184)(203)(226)(114)(56)(200)(27)
(define xx (grc4 "keytext"))
(Do 400 (lambda (dm) (xx 256)))
(Do 30 (lambda(x)(write (list (xx 1)))))(newline) ; => (28)(43)(69)(134)(42)(184)(169)(248)(67)(151)(87)(172)(232)(186)(70)(164)(94)(112)(237)(106)(199)(205)(73)(109)(244)(107)(60)(62)(97)(200)