I wanna answer that Plz

Let

K by a 56-bit DES key and L a 64-bit auxiliary key. For any 64-bit

plaintext

M let

DESY

(K k L,M) = DES(K,L ⊕ M)

.

This defines a family of functions

DESY: {0, 1}120 ~ {0, 1}64 → {0, 1}64

.

(a) [8 points]

Show that DESY

is a block cipher.

(b) [22 points]

Let (M1,C1), (M2,C2) be input-output examples of DESY

under a random 120-

bit target key

K k L. Present an attack that given (M1,C1), (M2,C2

) recovers the target

key using at most 2

57 computations of DES or DES−1

. (As usual, the job is actually only to

Let

K by a 56-bit DES key and L

a 64-bit auxiliary key. For any 64-bit

plaintext

M

let

DESY

(K k L,M) = DES(K,L ⊕ M)

.

This defines a family of functions

DESY: {0, 1}120 ~ {0, 1}64 → {0, 1}64

.

(a) [8 points]

Show that DESY

is a block cipher.

(b) [22 points]

Let (M1,C1), (M2,C2) be input-output examples of DESY

under a random 120-

bit target key

K k L. Present an attack that given (M1,C1), (M2,C2

) recovers the target

key using at most 2

57 computations of DES or DES−1

. (As usual, the job is actually only to