SUBJECT: RC4 Source Code I've tested this. It is compatible with the RC4 object module that comes in the various RSA toolkits. /* rc4.h */ typedef struct rc4_key { unsigned char state[256]; unsigned char x; unsigned char y; } rc4_key; void prepare_key(unsigned char *key_data_ptr,int key_data_len, rc4_key *key); void rc4(unsigned char *buffer_ptr,int buffer_len,rc4_key * key); /*rc4.c */ #include "rc4.h" static void swap_byte(unsigned char *a, unsigned char *b); void prepare_key(unsigned char *key_data_ptr, int key_data_len, rc4_key *key) { unsigned char swapByte; unsigned char index1; unsigned char index2; unsigned char* state; short counter; state = &key->state[0]; for(counter = 0; counter < 256; counter++) state[counter] = counter; key->x = 0; key->y = 0; index1 = 0; index2 = 0; for(counter = 0; counter < 256; counter++) { index2 = (key_data_ptr[index1] + state[counter] + index2) % 256; swap_byte(&state[counter], &state[index2]); index1 = (index1 + 1) % key_data_len; } } void rc4(unsigned char *buffer_ptr, int buffer_len, rc4_key *key) { unsigned char x; unsigned char y; unsigned char* state; unsigned char xorIndex; short counter; x = key->x; y = key->y; state = &key->state[0]; for(counter = 0; counter < buffer_len; counter ++) { x = (x + 1) % 256; y = (state[x] + y) % 256; swap_byte(&state[x], &state[y]); xorIndex = state[x] + (state[y]) % 256; buffer_ptr[counter] ^= state[xorIndex]; } key->x = x; key->y = y; } static void swap_byte(unsigned char *a, unsigned char *b) { unsigned char swapByte; swapByte = *a; *a = *b; *b = swapByte; }