feistel.scm

;; ファイステルネットワーク (JScheme)

(define-method (swap (x Long))
  (+ (>>> x 32) (<< x 32)))

(define-method (round (plain Long) f subkey)
  (^ plain (<< (f (& plain Integer.MAX_VALUE$) subkey) 32)))

(define-method (feistel (plain Long) f subkeys)
  (let lp ((p (round plain f (car subkeys))) (subkeys (cdr subkeys)))
    (if (null? subkeys) p
      (lp (round (swap p) f (car subkeys)) (cdr subkeys)))))

; (feistel 24L (lambda (p k) (^ (>> p 10) k)) '(66 77 88))
; => 111669149781L
; (feistel 111669149781L (lambda (p k) (^ (>> p 10) k)) '(88 77 66))
; => 24L