56 lines
1.2 KiB
C
56 lines
1.2 KiB
C
//
|
|
// Example for a 16-bit NFLSR
|
|
//
|
|
|
|
#include <stdio.h>
|
|
#include <stdint.h>
|
|
#include <string.h>
|
|
|
|
#define NLFSR_SIZE 16
|
|
#define DEFAULT_START_STATE 0xACE1 // Default initial state for NLFSR
|
|
|
|
uint16_t nlfsr;
|
|
uint8_t used[65535];
|
|
|
|
uint8_t non_linear_feedback(uint16_t state) {
|
|
// Example non-linear function: XOR of specific bits and AND of others
|
|
uint8_t bit1 = (state >> 0) & 1;
|
|
uint8_t bit2 = (state >> 2) & 1;
|
|
uint8_t bit3 = (state >> 3) & 1;
|
|
uint8_t bit4 = (state >> 5) & 1;
|
|
uint8_t bit5 = (state >> 9) & 1;
|
|
return (bit1 ^ bit2) | (bit3 & bit4) ^ bit5;
|
|
}
|
|
|
|
uint8_t clock_and_shift_nlfsr() {
|
|
uint8_t ret = nlfsr & 1;
|
|
uint8_t new_bit = non_linear_feedback(nlfsr);
|
|
nlfsr = (nlfsr >> 1) | (new_bit << (NLFSR_SIZE - 1));
|
|
|
|
return ret;
|
|
}
|
|
|
|
int main() {
|
|
uint16_t input;
|
|
uint16_t cycle = 0;
|
|
memset(used, sizeof(used), 0);
|
|
|
|
printf("Enter IV for NLFSR: "); scanf("%hd", &input);
|
|
input = input & 0xFFFF;
|
|
nlfsr = input;
|
|
|
|
while (1) {
|
|
cycle++;
|
|
printf("%d", clock_and_shift_nlfsr());
|
|
if (used[nlfsr] > 0)
|
|
break;
|
|
else
|
|
used[nlfsr] = 1;
|
|
// printf("%d\n", nlfsr);
|
|
}
|
|
|
|
printf("\nCycle length: %d bits.\n", cycle);
|
|
return 0;
|
|
}
|
|
|