How to implement a DES algorithm
Original: Matthew Fischer
The Data Encryption Standard algorithm has been formally licensed by the US government in 1977, which is a method of encrypting 64-bit data with a 56-bit key. The DES algorithm is applied to many applications that need secure encryption. (, Such as: UNIX's password algorithm is based on the DES algorithm). Here is a language description of how to implement the DES algorithm. If you want its source code, you can download http // assassin.yeah.net, you have any questions, you can write to me (Assassin@ynmail.com) .
1-1. Transform key
The 64-bit key is obtained, each of which is a parity bit.
1-2. Transform key
1-2-1
Dip the parity bit in the 64-bit key, and the key change is obtained according to the following table (PC-1) to get 56-bit keys, in the transformation, the parity bit is discarded.
Permute Choice 1 (PC-1)
57 49 41 33 25 17 9
1 58 50 42 34 26 18
10 2 59 51 43 35 27
19 11 3 60 52 44 36
63 55 47 39 31 23 15
7 62 54 46 38 30 22
14 6 61 53 45 37 29
21 13 5 28 20 12 4
1-2-2
The transformed key is divided into two parts, and the 28th starting is called C [0], and the last 28 is called D [0].
1-2-3
Generate 16 sub-keys, initial I = 1.
1-2-3
-1. At the same time, C [I], D [i] left shift 1 or 2 bits, determines the number of digits left-shifted according to the I value. See the table below
I: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Left displacement zone: 1 2 2 2 2 2 2 2 2 2 2 2 2 1
1-2-3
-2. Press the C [I] D [i] as a whole according to the following table (PC-2) transformation, get 48-bit K [i]
Permutech 2 (PC-2)
14 17 11 24 1 5
3 28 15 6 21 10
23 19 12 4 26 8
16 7 27 20 13 2
41 52 31 37 47 55
30 40 51 45 33 48
44 49 39 56 34 53
46 42 50 36 29 32
1-2-3
-3. From 1-2-3-1, it is performed until K [16] is calculated.
2. Handle 64-bit data
2-1. Take 64-bit data, if the data length is less than 64 bits, it should be extended to 64 bits (eg, 补 零)
2-2. Press 64-bit data to transform (IP)
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
2-3. Divide the transformed data into two parts, starting 32-bit called L [0], the last 32-bit is called R [0].
2-4. Encrypt data with 16 sub-key, initial I = 1.
2-4-1
32-bit R [i-1] is expanded to 48-bit E [I-1]
Expansion (e)
32 1 2 3 4 5
4 5 6 7 8 98 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
2-4-2
. Different or E [I-1] and K [i], that is, E [i-1] xor k [i]
2-4-3
Divide the different or post-secondary part of the eight 6-digit part, and the first to 6th is called B [1], and the 7th to the 12th is called B [2], and so on, 43-bit to 48th is called B [8].
2-4-4
Press the S table transform all B [J], initial J = 1. All values in the S table are treated as 4-bit lengths.
2-4-4
-1. Combine the first bit and 6 bits of B [J] into a variable M, M as a line number in S [J].
2-4-4
-2. Combine B [J] of the second bits to the 5th bits, as a 4-bit length variable N, N as the number in S [J].
2-4-4
-3. Use S [J] [M] [N] to replace B [J].
Substitution
Box
1
(S [1])
14 4 13 1 2 15 11 8 3 10 6 12 5 9 0 7
0 15 7 4 14 2 13 1 10 6 12 11 9 5 3 8
4 1 14 8 13 6 2 11 15 12 9 7 3 10 5 0
15 12 8 2 4 9 1 7 5 11 3 14 10 0 6 13
S [2]
15 1 8 14 6 11 3 4 9 7 2 13 12 0 5 10
3 13 4 7 15 2 8 14 12 0 1 10 6 9 11 5
0 14 7 11 10 4 13 1 5 8 12 6 9 3 2 15
13 8 10 1 3 15 4 2 11 6 7 12 0 5 14 9
S [3]
10 0 9 14 6 3 15 5 1 13 12 7 11 4 2 8
13 7 0 9 3 4 6 10 2 8 5 14 12 11 15 1
13 6 4 9 8 15 3 0 11 1 2 12 5 10 14 7
1 10 13 0 6 9 8 7 4 15 14 3 11 5 2 12
S [4]
7 13 14 3 0 6 9 10 1 2 8 5 11 12 4 15
13 8 11 5 6 15 0 3 4 7 2 12 1 10 14 9
10 6 9 0 12 11 7 13 15 1 3 14 5 2 8 4
3 15 0 6 10 1 13 8 9 4 5 11 12 7 2 14
S [5]
2 12 4 1 7 10 11 6 8 5 3 15 13 0 14 9
14 11 2 12 4 7 13 1 5 0 15 10 3 9 8 6
4 2 1 11 10 13 7 8 15 9 12 5 6 3 0 14
11 8 12 7 1 14 2 13 6 15 0 9 10 4 5 3
S [6]
12 1 10 15 9 2 6 8 0 13 3 4 14 7 5 11
10 15 4 2 7 12 9 5 6 1 13 14 0 11 3 8
9 14 15 5 2 8 12 3 7 0 4 10 1 13 11 6
4 3 2 12 9 5 15 10 11 14 1 7 6 0 8 13
S [7]
4 11 2 14 15 0 8 13 3 12 9 7 5 10 6 1
13 0 11 7 4 9 1 10 14 3 5 12 2 15 8 6
1 4 11 13 12 3 7 14 10 15 6 8 0 5 9 2
6 11 13 8 1 4 10 7 9 5 0 15 14 2 3 12
S [8]
13 2 8 4 6 15 11 1 10 9 3 14 5 0 12 7
1 15 13 8 10 3 7 4 12 5 6 11 0 14 9 2
7 11 4 1 9 12 14 2 0 6 10 13 15 3 5 82 1 14 7 4 10 8 13 15 12 9 0 3 5 6 11
2-4-4
-4. Circulate from 2-4-4-1 until B [8] is replaced.
2-4-4
-5. Combine B [1] to B [8], press the table (P) to change, get P.
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
2-4-6
The result is placed in R [I], ie R [I] = P xor L [I-1].
2-4-7
. L [i] = r [i-1]
2-4-8
The loop is started from 2-4-1 until K [16] is transformed.
2-4-5
R [16] L [16] after combining transformation (Note: R is started 32 bits), and the final result is obtained in the table (IP-1) transformation.
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
