def bytes_xor(byte_seq1, byte_seq2):
    """
    (bytes, bytes) -> (bytes)

    Do bit level XOR or two byte arrays.
    :param byte_seq1: byte sequence (bytes).
    :param byte_seq2: byte sequence (bytes).
    :return: XOR of the byte bytes sequences (bytes).
    """
    assert len(byte_seq1) == len(byte_seq2), "Bytes must be of the same length."
    parts = []
    for byte_seq1, byte_seq2 in zip(byte_seq1, byte_seq2):
        parts.append(bytes([byte_seq1 ^ byte_seq2]))
    return b''.join(parts)