This tool runs the first round of DES and creates a text report, revealing all intermediate values. It is useful for studying DES encryption algorithm.
The tool is made for learning purposes only, as it encrypths only an 8-byte block and is not suitable for actual encryption function.
Made by p07010k in March 2020.
bitstring module is needed. Install from pip:
pip install bitstring
There are two options:
- Run all 16 rounds of DES with des.py script, and get cyphertext in hex.
- Run only the 1st round with desvisually.py, and get a text report, revealing all intermediate values and their transformations.
Usage:
des.py [encrypt|decrypt]
Example: We have an 8-byte string November, and would like to encrypt it. The script will invite us to paste the plaintext and a 8-byte key in hex. It is possible to generate a random key by entering empty string:
>des.py encrypt
8-character plaintext: November
HEX key [enter = generate]:
Key used: b742c7238bcca586
Encrypting...
Ciphertext: 67a7d19f8cbb875c
Now we have the 8-byte string encrypted with DES. Copy the key and the ciphertext. Then run des.py in decrypt mode and paste them:
>des.py decrypt
hex ciphertext: 67a7d19f8cbb875c
HEX key [enter = generate]: b742c7238bcca586
Key used: b742c7238bcca586
Decrypting...
Plaintext: November
We have decrypted the initial string.
The desvisually.py script has no arguments.
Usage of the script is kind of similar to the previous. Let's run it with the same plaintext:
>desvisually.py
8-character plaintext: November
HEX key [enter = generate]:
Done. Check des20210408_021014.txt
The example of a text report:
DES Encryption detailed report
2021-04-08 02:10:14.648895
Plaintext (x): November
hex (ASCII):
4e6f76656d626572
bin:
0100111001101111011101100110010101101101011000100110010101110010
64-bit key
hex:
755b210afeb8484b
bin:
0111010101011011001000010000101011111110101110000100100001001011
Overview of Round 1:
k
755b210afeb8484b
↓
x [PC-1]
4e6f76656d626572 ↓
↓ 30d33539a11fa3
[IP] ↓ ↓
↓ C_0 D_0
ff845f5a00fe13a7 30d3353 9a11fa3
↓ ↓ ↓ ↓
L_0 R_0 [LS1] [LS1]
ff845f5a 00fe13a7 ↓ ↓
↓ ↓ k_1 C_1 D_1
↓ [f] ← a2acc92c5ba9 ← [PC-2] ← 61a66a6 3423f47
↓ ↓ ↓ ↓
(XOR) ← d42e5e3d … …
↓
⤷→→→→→→→→⤵
↓
L_1 = R_0 R_1
00fe13a7 2baa0167
↓ ↓
… …
1. Initial Permutation IP(x)
The output value is splited into the halves: L_0, R_0
x = 4e6f76656d626572 → IP(x) = ff845f5a00fe13a7
01 02 03 04 05 06 07 08 58 50 42 34 26 18 10 02
0 1 0 0 1 1 1 0 1 1 1 1 1 1 1 1
09 10 11 12 13 14 15 16 60 52 44 36 28 20 12 04
0 1 1 0 1 1 1 1 1 0 0 0 0 1 0 0
17 18 19 20 21 22 23 24 62 54 46 38 30 22 14 06
0 1 1 1 0 1 1 0 0 1 0 1 1 1 1 1
25 26 27 28 29 30 31 32 64 56 48 40 32 24 16 08
0 1 1 0 0 1 0 1 0 1 0 1 1 0 1 0
33 34 35 36 37 38 39 40 57 49 41 33 25 17 09 01
0 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0
41 42 43 44 45 46 47 48 59 51 43 35 27 19 11 03
0 1 1 0 0 0 1 0 1 1 1 1 1 1 1 0
49 50 51 52 53 54 55 56 61 53 45 37 29 21 13 05
0 1 1 0 0 1 0 1 0 0 0 1 0 0 1 1
57 58 59 60 61 62 63 64 63 55 47 39 31 23 15 07
0 1 1 1 0 0 1 0 1 0 1 0 0 1 1 1
IP(x)
bin:
1111111110000100010111110101101000000000111111100001001110100111
hex:
ff845f5a00fe13a7
L_0 R_0
bin: bin:
11111111100001000101111101011010 00000000111111100001001110100111
hex: hex:
ff845f5a 00fe13a7
2. Permuted choice 1 PC-1(k)
Permutes 64-bit key into 56-bit key
k = 755b210afeb8484b → PC-1(k) = 30d33539a11fa3
01 02 03 04 05 06 07 08 57 49 41 33 25 17 09 01
0 1 1 1 0 1 0 1 0 0 1 1 0 0 0 0
09 10 11 12 13 14 15 16 58 50 42 34 26 18 10 02
0 1 0 1 1 0 1 1 1 1 0 1 0 0 1 1
17 18 19 20 21 22 23 24 59 51 43 35 27 19 11 03
0 0 1 0 0 0 0 1 0 0 1 1 0 1 0 1
25 26 27 28 29 30 31 32 60 52 44 36 63 55 47 39
0 0 0 0 1 0 1 0 0 0 1 1 1 0 0 1
33 34 35 36 37 38 39 40 31 23 15 07 62 54 46 38
1 1 1 1 1 1 1 0 1 0 1 0 0 0 0 1
41 42 43 44 45 46 47 48 30 22 14 06 61 53 45 37
1 0 1 1 1 0 0 0 0 0 0 1 1 1 1 1
49 50 51 52 53 54 55 56 29 21 13 05 28 20 12 04
0 1 0 0 1 0 0 0 1 0 1 0 0 0 1 1
57 58 59 60 61 62 63 64
0 1 0 0 1 0 1 1
PC-1(k)
bin:
00110000110100110011010100111001101000010001111110100011
hex:
30d33539a11fa3
C_0 D_0
bin: bin:
0011000011010011001101010011 1001101000010001111110100011
hex: hex:
30d3353 9a11fa3
3. Transformation 1
Round #1 => the two halves are rotated left by 1 bit
C_i D_i
i=0 0011000011010011001101010011 1001101000010001111110100011
i=1 0110000110100110011010100110 0011010000100011111101000111
C_1 hex: 61a66a6
D_1 hex: 3423f47
PC-2 input: 61a66a63423f47
C_1 and D_1 are used in transformation 2
4. Permuted Choice 2 PC-2
Outputs 48-bit round key k_1
C_1|D_1 = 61a66a63423f47 → PC-2(C_1|D_1) = a2acc92c5ba9
01 02 03 04 05 06 07 08 14 17 11 24 01 05 03 28
0 1 1 0 0 0 0 1 1 0 1 0 0 0 1 0
09 10 11 12 13 14 15 16 15 06 21 10 23 19 12 04
1 0 1 0 0 1 1 0 1 0 1 0 1 1 0 0
17 18 19 20 21 22 23 24 26 08 16 07 27 20 13 02
0 1 1 0 1 0 1 0 1 1 0 0 1 0 0 1
25 26 27 28 29 30 31 32 41 52 31 37 47 55 30 40
0 1 1 0 0 0 1 1 0 0 1 0 1 1 0 0
33 34 35 36 37 38 39 40 51 45 33 48 44 49 39 56
0 1 0 0 0 0 1 0 0 1 0 1 1 0 1 1
41 42 43 44 45 46 47 48 34 53 46 42 50 36 29 32
0 0 1 1 1 1 1 1 1 0 1 0 1 0 0 1
49 50 51 52 53 54 55 56
0 1 0 0 0 1 1 1
k_1
bin:
101000101010110011001001001011000101101110101001
hex:
a2acc92c5ba9
5. f-function
5.1 R_0 Expansion
R_0 → E(R_0)
01 02 03 04 32 01 02 03 04 05
0 0 0 0 1 0 0 0 0 0
05 06 07 08 04 05 06 07 08 09
0 0 0 0 0 0 0 0 0 1
09 10 11 12 08 09 10 11 12 13
1 1 1 1 0 1 1 1 1 1
13 14 15 16 12 13 14 15 16 17
1 1 1 0 1 1 1 1 0 0
17 18 19 20 16 17 18 19 20 21
0 0 0 1 0 0 0 0 1 0
21 22 23 24 20 21 22 23 24 25
0 0 1 1 1 0 0 1 1 1
25 26 27 28 24 25 26 27 28 29
1 0 1 0 1 1 0 1 0 0
29 30 31 32 28 29 30 31 32 01
0 1 1 1 0 0 1 1 1 0
5.2 E(R_0) xor k_1
Then XORed value is splited into 8 6-bit pieces
E(R_0) 100000000001011111111100000010100111110100001110
k_1 101000101010110011001001001011000101101110101001
xor 001000101011101100110101001001100010011010100111
pieces:
001000 101011 101100 110101 001001 100010 011010 100111
5.3 S-boxes
Example on S-box S_1. Other S-boxes applied similarly
piece #1: 001000
left-most bit | right-most bit (row): 00
middle bits (column): 0100
S_1:
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
00 14 4 13 1 2 15 11 8 3 10 6 12 5 9 0 7
01 0 15 7 4 14 2 13 1 10 6 12 11 9 5 3 8
10 4 1 14 8 13 6 2 11 15 12 9 7 3 10 5 0
11 15 12 8 2 4 9 1 7 5 11 3 14 10 0 6 13
Substitution chosen: 2
bin: 10
All substitutions:
0010 1111 0011 0101 0100 1110 1010 0111
S-boxes Output
bin:
00101111001101010100111010100111
hex:
2f354ea7
5.4 Permutation P
This P-box output is f-function output
S-boxes output → f output = d42e5e3d
01 02 03 04 05 06 07 08 16 07 20 21 29 12 28 17
0 0 1 0 1 1 1 1 1 1 0 1 0 1 0 0
09 10 11 12 13 14 15 16 01 15 23 26 05 18 31 10
0 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0
17 18 19 20 21 22 23 24 02 08 24 14 32 27 03 09
0 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0
25 26 27 28 29 30 31 32 19 13 30 06 22 11 04 25
1 0 1 0 0 1 1 1 0 0 1 1 1 1 0 1
f-function output
bin:
11010100001011100101111000111101
hex:
d42e5e3d
6. L_0 xor f-function output
XORed value is R_1
L_0 = ff845f5a
L_0 11111111100001000101111101011010
f output 11010100001011100101111000111101
xor 00101011101010100000000101100111
R_1 = 2baa0167