/********************************************************************* * Filename: arcfour.c * Author: Brad Conte (brad AT bradconte.com) * Copyright: * Disclaimer: This code is presented "as is" without any guarantees. * Details: Implementation of the ARCFOUR encryption algorithm. Algorithm specification can be found here: * http://en.wikipedia.org/wiki/RC4 *********************************************************************/ /*************************** HEADER FILES ***************************/ #include <stdlib.h> #include "arcfour.h" /*********************** FUNCTION DEFINITIONS ***********************/ void arcfour_key_setup(BYTE state[], const BYTE key[], int len) { int i, j; BYTE t; for (i = 0; i < 256; ++i) state[i] = i; for (i = 0, j = 0; i < 256; ++i) { j = (j + state[i] + key[i % len]) % 256; t = state[i]; state[i] = state[j]; state[j] = t; } } void arcfour_generate_stream(BYTE state[], BYTE out[], size_t len) { int i, j; size_t idx; BYTE t; for (idx = 0, i = 0, j = 0; idx < len; ++idx) { i = (i + 1) % 256; j = (j + state[i]) % 256; t = state[i]; state[i] = state[j]; state[j] = t; out[idx] = state[(state[i] + state[j]) % 256]; } }