code: public Date getGeneralizedTime(int len) throws IOException {
          if (len > available())
              throw new IOException("short read of DER Generalized Time");
  
          if (len < 13 || len > 23)
              throw new IOException("DER Generalized Time length error");
  
          return getTime(len, true);
  
      }
docs: Returns the Generalized Time value that takes up the specified
  number of bytes in this buffer.
  @param len the number of bytes to use