code: public Date getUTCTime(int len) throws IOException {
          if (len > available())
              throw new IOException("short read of DER UTC Time");
  
          if (len < 11 || len > 17)
              throw new IOException("DER UTC Time length error");
  
          return getTime(len, false);
      }
docs: Returns the UTC Time value that takes up the specified number
  of bytes in this buffer.
  @param len the number of bytes to use