Returns the binary XOR of the 2 provided strings s1 and s2. s1 and s2
    must be of same length.

def strxor(s1, s2):
    """
    Returns the binary XOR of the 2 provided strings s1 and s2. s1 and s2
    must be of same length.
    """
    return b"".join(map(lambda x, y: chb(orb(x) ^ orb(y)), s1, s2))