function decrypt(debut, chaine, fin) {
   document.write(decryptJ(debut, chaine, fin));
}

function decryptJ(debut, chaine, fin) {
   var known_letters = new Array("a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q",
		"r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G","H","I",
		"J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z",
		"0","1","2","3","4","5","6","7","8","9","@",".","-");
   var count_known_letters = known_letters.length;
   var key = (chaine.length)%count_known_letters;
   var out = "";
   for ( var i=0; i<chaine.length; i++ ) {
      current = chaine.charAt(i);
      if ( isInArray(current, known_letters) ) {
         for ( var j=0; j<count_known_letters; j++ ) {
            if ( known_letters[j] == current ) break;
         }
         currentIndiceLetter = j;
         newIndiceLetter = (currentIndiceLetter-key)%count_known_letters;
         if ( newIndiceLetter < 0 ) {
            newIndiceLetter += count_known_letters;
         }
         out += known_letters[newIndiceLetter];
      } else {
         out += current;
      }
   }
   return debut+out+fin;
}

function isInArray(needle, arrayHaystack){
   for (x=0; x < arrayHaystack.length; x++) if (arrayHaystack[x] == needle) return true;
   return false;
}