For this problem, rely on the fact that in the actual construction of DES the two halves of the output of the nal round of the Feistel network are swapped. That is, if the output of the nal round of the Feistel network is (L16;R16), then the output of DES is (R16;L16). 1. Show that the only difference between computation of DESk and DES^(-1) k is the order in which sub-keys are used. 2. Show that for k = 0^56 it holds that DESk(DESk(x)) = x.