#include <stdio.h>

#include <string.h>

#include <stdint.h>

#include "utils.h"

static unsigned char lookupTable[31]={ // at 0xFEDB

0x0B, 0x0A, 0x78, 0x0C, 0xE0, 0x29, 0x7B, 0xCF,

0xC3, 0x4B, 0x2B, 0xCC, 0x82, 0x60, 0x80, 0x06,

// from here on the table repeats its values, allowing for an easy

// way to avoid rotate the values of this table based on the round

// counter. just index starting from round_counter

0x0B, 0x0A, 0x78, 0x0C, 0xE0, 0x29, 0x7B, 0xCF,

0xC3, 0x4B, 0x2B, 0xCC, 0x82, 0x60, 0x80};

static unsigned char invertLoNibble2High(unsigned char x) {

return ((x ^ 0xf) << 4) | x;

}

void lfsr(unsigned char state[16], unsigned char newstate[16]) {

char round_counter; // at 0x5c

unsigned char acc, i, tmp;

// advance lfsrs

for(round_counter = 0x1f;round_counter>=0;round_counter--) { // lfsrs are iterated 32 times

unsigned char off = (round_counter & 0xf); // offset, table shifts by one every iteration

acc = 0;

for(i=0;i<16;i ) { // FAC7 in the code this loop is unrolled

acc ^= state[i] & lookupTable[off i];

} // FB43

acc = ((acc >> 1) ^ acc) & 0x55; // FB45..FB4A

// (*round_counter ^ 0xff) & 0xf == is twice the sequence 15..0

tmp=(round_counter ^ 0xff) & 0xf;

// (since the round_counter goes from 31..0, hence twice)

state[tmp] = ((state[tmp] << 1) & 0xAA) | acc;

} // FB63

for(i=0;i<16;i ) newstate[i]=state[i];

}

void init_state(const char key[16], unsigned char state[16]) {

// initialize LFSRs

int i;

for(i=0;i<15;i ) { // FA9E // only 60 bits of entropy

state[i] = invertLoNibble2High(key[i]);

}

state[15]=0xff; // FAB0..FAB4 // not sure why this has to be 0xff, the other bytes are all also guaranteed to not be all == 0

}

uint32_t extract_lfsr(unsigned char state[16]) {

int i;

unsigned char tmp;

unsigned char lfsr_out[4]; // at 0x82

for(i=0;i<4;i ) {

tmp = state[i 7]; // FB68..FB6C

tmp = (tmp << 2) | (tmp >> 6); // 2x rotate left FB6E..FB72 // lfsr_out[i] = rol(lfsr[i 7], 2) ^ lfsr[i]

lfsr_out[i] = tmp ^ state[i]; // FB74 .. FB7A // lfsr_out[0] = rol(lfsr[7],2) ^ lfsr[0]

}

return *((uint32_t*) lfsr_out);

}

int main(void) {

unsigned char state[16];

init_state("\x00\x08\x02\x0e\x0f\x09\x0c\x07\x0a\x03\x02\x02\x09\x0d\x0c\x0f", state);

hexdump("lfsr0", state,16);

unsigned char newstate[16];

lfsr(state, newstate);

hexdump("lfsr1", newstate,16);

printf("x\n",extract_lfsr(newstate));

//printf("x\n",lfsr("\x00\x08\t\x00\x04\t\n\x05\x00\x0c\x02\x08\x0c\n\x08\x00"));

return 0;

}