CRYPTOLOGY - Hacking: The Art of Exploitation - page 444

int key[13] = {1, 2, 3, 4, 5, 66, 75, 123, 99, 100, 123, 43, 213};
int seed[16];
int N = 256;
int i, j, k, t, x, A;
int keystream, keybyte;
int max_result, max_count;
int results[256];
int known_j, known_S;
if(argc < 2) {
printf("Usage: %s <keybyte to attack>\n", argv[0]);
exit(0);
}
A = atoi(argv[1]);
if((A > 12) || (A < 0)) {
printf("keybyte must be from 0 to 12.\n");
exit(0);
}
for(k=0; k < 256; k++)
results[k] = 0;
IV[0] = A + 3;
IV[1] = N - 1;
for(x=0; x < 256; x++) {
IV[2] = x;
keystream = RC4(IV, key);
printf("Using IV: (%d, %d, %d), first keystream byte is %u\n",
IV[0], IV[1], IV[2], keystream);
printf("Doing the first %d steps of KSA.. ", A+3);
//Seed = IV + key;
for(k=0; k<3; k++)
seed[k] = IV[k];
for(k=0; k<13; k++)
seed[k+3] = key[k];
// -= Key Scheduling Algorithm (KSA) =-
//Initialize the arrays.
for(k=0; k<256; k++) {
S[k] = k;
K[k] = seed[k%16];
}
j=0;
for(i=0; i < (A + 3); i++) {
j = (j + S[i] + K[i])%256;
t = S[i];