, , DES. :
- (Electronic Codebook) - ECB;
- (Cipher Block Chaining) - CBC;
- (Cipher Feedback) - CFB;
- (Output Feedback) - OFB.
, , , . , , . , : DES-CBC DES-CFB , , " , ".
DES-ECB
M 64- ( 8 ): M = M(1)M(2)...M(n). (.5). - . - .
.5. DES ECB
, EXE , - , .
, .
DES-CBC
M , ECB, 64- : M = M(1)M(2)...M(n). M(1) 2 64- IV, . DES, , . 64- C(1) 2 , 64- C(2) .. , (.6).
.6. CBC
i = 1...n C(i) :
C(i) = DES(M(i) xor C(i-1)), C(0) = IV - , . |
:
M(i) = C(i-1) xor DES-1(C(i)), C(0) = IV - , . |
, . M(i) C(i-1) C(i). .
DES-CFB
64. M t- (t <= 64): M = M(1)M(2)...M(n) ( ).
|
|
64- ( ) IV, . IV.
i = 1...n C(i) :
C(i) = M(i) xor P(i-1),
P(i-1) - t DES((i-1)), C(0)=IV.
t C(i).
: P(i-1) C(i)
M(i) = C(i) xor P(i-1).
- CFB .7.
.7. DES CFB
DES-OFB
OFB CFB.
CFB . t P(i-1) (.8).
.8. - DES OFB
, .
ECB . CBC CFB . CFB, , . OFB .