data encryption standerd

Design of Secure Computer Systems CSI4138/CEG4394
Notes on the Data Encryption Standard (DES)
The Data Encryption Standard (DES) has been developed as a cryptographic standard for
general use by the public. DES was designed with the following objectives in mind [NIS77, Pfl89]:
1. High level of security
2. Completely specified and easy to understand
3. Cryptographic security do not depend on algorithm secrecy
4. Adaptable to diverse applications
5. Economical hardware implementation
6. Efficient (e.g. high data rates)
7. Can be validated
8. Exportable
1 Data Encryption Algorithm
² Substitution-permutation algorithm:
– 64-bit input and output blocks
– 56-bit key (with an additional 8 parity bits)
– information data is cycled 16 times through a set of substitution and permutation transformations:
highly non-linear input-output relationship
² Very high throughput rates achievable (up to 100 Mbits=s)
² Availability of economical hardware to implement DES
² Low to medium security applications (e.g. secure speech communications)
1








4
4
4
4
4
4
4
4 S1
S2
S3
S4
S5
S6
S7
S8
6
6
6
6
6
6
6
6








32 48 P
6
6
32
32 L
Temp
L





A
A A
E
?
48
?
(((((((
hhhh 6 hhh
R32
?
L32  32
-
32
32 32
```` ```` ```` 32 632
IP IP?1
?
6
32 32
?64 664
Input 64 Output 64 Key 56(+8)
?
64
PC1
A
AA





? ?
28 28
C28 D28
28 28
? ?
PC2
A
AA






48
Figure 1: DES encryption/decryption algorithm.
2
?
Initial permutation IP
?
? ?
L0 R0
?
K1
?
© f(R0;K1  ) 
hhhhhhhhhhhhhhhhhhhhh
(((( (((( (((( (((( (((((
? ?
L1 = R0 R1 = L0 © f(R0;K1)
?
K2
?
©  f(R1;K2) 
hhhhhhhhhhhhhhhhhhhhh
(((( (((( (((( (((( (((((
? ?
...
...
? ?
L15 = R14 R15 = L14 © f(R14;K15)
?
K16
?
©  f(R15;K16) 
hhhhhhhhhhhhhhhhhhhhh
(((( (((( (((( (((( (((((
? ?
L16 = R15 R16 = L15 © f(R15;K16)
? ?
?
Final permutation IP?1
?
Figure 2: DES sequence of substitution and permutation transformations.
3
Table 1: Initial IP and inverse initial IP?1 permutation tables.
Initial permutation IP
58 50 42 34 26 18 10 2
60 52 44 36 28 20 12 4
62 54 46 38 30 22 14 6
64 56 48 40 32 24 16 8
57 49 41 33 25 17 9 1
59 51 43 35 27 19 11 3
61 53 45 37 29 21 13 5
63 55 47 39 31 23 15 7
Final permutation IP?1
40 8 48 16 56 24 64 32
39 7 47 15 55 23 63 31
38 6 46 14 54 22 62 30
37 5 45 13 53 21 61 29
36 4 44 12 52 20 60 28
35 3 43 11 51 19 59 27
34 2 42 10 50 18 58 26
33 1 41 9 49 17 57 25
Table 2: Expansion permutation E and permutation P tables.
Expansion permutation E
32 1 2 3 4 5
4 5 6 7 8 9
8 9 10 11 12 13
12 13 14 15 16 17
16 17 18 19 20 21
20 21 22 23 24 25
24 25 26 27 28 29
28 29 30 31 32 1
Permutation P
16 7 20 21
29 12 28 17
1 15 23 26
5 18 31 10
2 8 24 14
32 27 3 9
19 13 30 6
22 11 4 25
4
Table 3: S-boxes (substitution boxes) tables.
Column
Box Row 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
S1 0 14 4 13 1 2 15 11 8 3 10 6 12 5 9 0 7
1 0 15 7 4 14 2 13 1 10 6 12 11 9 5 3 8
2 4 1 14 8 13 6 2 11 15 12 9 7 3 10 5 0
3 15 12 8 2 4 9 1 7 5 11 3 14 10 0 6 13
S2 0 15 1 8 14 6 11 3 4 9 7 2 13 12 0 5 10
1 3 13 4 7 15 2 8 14 12 0 1 10 6 9 11 5
2 0 14 7 11 10 4 13 1 5 8 12 6 9 3 2 15
3 13 8 10 1 3 15 4 2 11 6 7 12 0 5 14 9
S3 0 10 0 9 14 6 3 15 5 1 13 12 7 11 4 2 8
1 13 7 0 9 3 4 6 10 2 8 5 14 12 11 15 1
2 13 6 4 9 8 15 3 0 11 1 2 12 5 10 14 7
3 1 10 13 0 6 9 8 7 4 15 14 3 11 5 2 12
S4 0 7 13 14 3 0 6 9 10 1 2 8 5 11 12 4 15
1 13 8 11 5 6 15 0 3 4 7 2 12 1 10 14 9
2 10 6 9 0 12 11 7 13 15 1 3 14 5 2 8 4
3 3 15 0 6 10 1 13 8 9 4 5 11 12 7 2 14
S5 0 2 12 4 1 7 10 11 6 8 5 3 15 13 0 14 9
1 14 11 2 12 4 7 13 1 5 0 15 10 3 9 8 6
2 4 2 1 11 10 13 7 8 15 9 12 5 6 3 0 14
3 11 8 12 7 1 14 2 13 6 15 0 9 10 4 5 3
S6 0 12 1 10 15 9 2 6 8 0 13 3 4 14 7 5 11
1 10 15 4 2 7 12 9 5 6 1 13 14 0 11 3 8
2 9