import binascii


def hex_xor(hex_string_1, hex_string_2):
    """Return the XOR of two hex bytestrings."""
    if len(hex_string_1) != len(hex_string_2):
        raise ValueError('Length of inputs must match.')

    hex_data_1 = binascii.a2b_hex(hex_string_1)
    hex_data_2 = binascii.a2b_hex(hex_string_2)
    return binascii.b2a_hex(
        bytes(
            [char_a ^ char_b for char_a, char_b in zip(hex_data_1, hex_data_2)]
        )
    )