DES: What is a meet-in-the-middle attack? For a moment suppose that the best attacks against DES were brute force, that is an attack of trying all possible keys to decrypt the message. Let DES ^Ki(M) denote encrypting message M with key Ki. What is the strength of a DES double encryption (that is, E= DES ^k2(DES ^ki(M)))? Now imagine a triple encryption of DES, E = DES ^k3(DES ^k2(DESKi(M))). How secure is that against a brute-force attack? How do the running times of double DES and triple DES compare with|DES