Recall the Davies-Meyer compression scheme discussed in class: Hi =H(i1)EMi (H(i1)). Lets say you use DES encryption with this scheme, which has the complementarity property complement(EK (X)) = Ecomplement(K)(complement(X))). a. Show how a message consisting of a block sequence M0; M1; ...; Mn can be altered without altering its hash code. b. Does a similar attack work if the compression scheme is changed to Hi = Mi EH(i-1)(Mi))?