class ByteUtils {

    public static byte[] paddingZeroOnHead(byte[] input, int byteLength) {
        if (input.length > byteLength) {
            throw new IllegalArgumentException("input byte array must have length which is less than byteLength you want to be.");
        }
        byte[] padding = new byte[byteLength - input.length];
        return join(padding, input);
    }

}