code: public static String decode(String rot, int offset, boolean isDecodeNumber) {
  		final int len = rot.length();
  		final char[] chars = new char[len];
  
  		for (int i = 0; i < len; i++) {
  			chars[i] = decodeChar(rot.charAt(i), offset, isDecodeNumber);
  		}
  		return new String(chars);
  	}
docs: RotN解码
  
  @param rot 被解码的消息密文
  @param offset 位移，常用位移13
  @param isDecodeNumber 是否解码数字
  @return 解码后的字符串