In MixColumn transformations in AES encryption, do we have to Xor the shifted input with 1B only when the leftmost bit is high or is it like the number of times we shift it, and then when a one exceeds power 8 in polynomial form then we have to do it. for eg. if i have to find the transformation 0B.45 i.e. (0000 1011).(0100 0101) Although here the leftmost bit is not high but when i multiply it with 1011 then i have to shift 45 3 times which will make a high bit(here 2nd bit from the left) to exceed power 8. Do I have to XOR with 1B then also?