I think simply put. However fast multiplication is, simple bitwise operations are even faster - and can be executed sometimes out of order, and in parallel by multiple execution units in the CPU.

I think simply put. However fast multiplication is, simple bitwise operations are even faster - and can be executed sometimes out of order, and in parallel by multiple execution units in the CPU. Moreover - major criteria of any algorithm design is the ability to implement it in hardware. Simplicity and ability to parallelise operation, thus lowering the cycles per byte number - is the key here.