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1 | /********************************************************************* |
2 | * Filename: arcfour.c |
3 | * Author: Brad Conte (brad AT bradconte.com) |
4 | * Copyright: |
5 | * Disclaimer: This code is presented "as is" without any guarantees. |
6 | * Details: Implementation of the ARCFOUR encryption algorithm. |
7 | Algorithm specification can be found here: |
8 | * http://en.wikipedia.org/wiki/RC4 |
9 | *********************************************************************/ |
10 | |
11 | /*************************** HEADER FILES ***************************/ |
12 | #include <stdlib.h> |
13 | #include "arcfour.h" |
14 | |
15 | /*********************** FUNCTION DEFINITIONS ***********************/ |
16 | void arcfour_key_setup(BYTE state[], const BYTE key[], int len) |
17 | { |
18 | int i, j; |
19 | BYTE t; |
20 | |
21 | for (i = 0; i < 256; ++i) |
22 | state[i] = i; |
23 | for (i = 0, j = 0; i < 256; ++i) { |
24 | j = (j + state[i] + key[i % len]) % 256; |
25 | t = state[i]; |
26 | state[i] = state[j]; |
27 | state[j] = t; |
28 | } |
29 | } |
30 | |
31 | // This does not hold state between calls. It always generates the |
32 | // stream starting from the first output byte. |
33 | void arcfour_generate_stream(BYTE state[], BYTE out[], size_t len) |
34 | { |
35 | int i, j; |
36 | size_t idx; |
37 | BYTE t; |
38 | |
39 | for (idx = 0, i = 0, j = 0; idx < len; ++idx) { |
40 | i = (i + 1) % 256; |
41 | j = (j + state[i]) % 256; |
42 | t = state[i]; |
43 | state[i] = state[j]; |
44 | state[j] = t; |
45 | out[idx] = state[(state[i] + state[j]) % 256]; |
46 | } |
47 | } |