def size8(parent=None, new_value=None, **kwargs):
    """
    Size getter for rsa key data where the byte size
    of the integer is (parent.parent.bitlen + 7) // 8
    (the + 7 is to round up to the nearest multiple of 8)

    We dont want to have this be a setter since bitlen
    is used by more than one attribute and while it may
    work for some bigints, it may be too small for others.
    """
    if new_value is None:
        return (parent.parent.bitlen + 7) // 8
