ksnctfの第２問を解くためのスクリプト

ksnctf-q2-decode.scm

(define (ksnctf-q2-decode str)
  (define (decode c)
    (let ((s (x->string c)))
      (if (rxmatch #/[a-zA-Z]/ s)
	  (if (rxmatch #/[a-mA-M]/ s)
	      (integer->char (+ (char->integer c) 26 -13))
	      (integer->char (- (char->integer c) 13)))
	  c)))
  (list->string (map decode (string->list str))))