4. (20 points) The S-Box of the AES ByteSub step uses the following nonlinear function G: F2s → F2s, where G(r) = 25-2=254. In fact, G(x) = 1 if x ≠0, and G(0) = 0. For any nonzero a, b ∈ F2s, define a set Tab = {x ∈ F28 | G(x) + G(x + a) = b}. Find all possible values of |Tab| for all a, b ∈ F2s - {0}, where |T| means the number of elements in the set T.