Question

Do all cycles share the same key in DES?

Answer 1

Answer:

DES consists of 16 rounds of the form:

Li+1=Ri,Ri+1=Li⊕F(Ri,Ki),Li+1=Ri,Ri+1=Li⊕F(Ri,Ki),which are identical except for the round subkeys KiKi.

(The last round is slightly different, in that the half-blocks LL and RRare not swapped as they are after all other rounds, but that makes no cryptanalytic difference.)

The subkeys KiKi are derived from the encryption key KK using the DES key schedule, which takes the form:

KL∥KR=P1(K)KL‖KR=P1(K)Ki=P2(KL⋘ni,

KR⋘ni)Ki=P2(KL⋘ni,KR⋘ni)

DES consists of 16 rounds of the form:

Li+1=Ri,Ri+1=Li⊕F(Ri,Ki),Li+1=Ri,Ri+1=Li⊕F(Ri,Ki),

which are identical except for the round subkeys KiKi.

(The last round is slightly different, in that the half-blocks LL and RRare not swapped as they are after all other rounds, but that makes no cryptanalytic difference.)

The subkeys KiKi are derived from the encryption key KK using the DES key schedule, which takes the form:

KL∥KR=P1(K)KL‖KR=P1(K)Ki=P2(KL⋘ni,

KR⋘ni)Ki=P2(KL⋘ni,KR⋘ni)where KL

KL and K

Answer 2

Answer:

which are identical except for the round subkeys KiKi. (The last round is slightly different, in that the half-blocks LL and RR are not swapped as they are after all other rounds, but that makes no cryptanalytic difference.)

The subkeys KiKi are derived from the encryption key KK using the DES key schedule, which takes the form:

KL∥KR=P1(K)KL‖KR=P1(K)

Ki=P2(KL⋘ni,KR⋘ni)Ki=P2(KL⋘ni,KR⋘ni)

where KLKL and KRKR are the left and right halves of the permuted key P1(K)P1(K), the functions P1P1 and P2P2 are fixed maps that basically just shuffle the bits around, and ⋘ni⋘ni denotes bit rotation by the fixed number of positions.

hope it helps ❤