#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

/* http://www.freecx.co.uk/crypto/SBox8/Definition_SBox8.php.
 * See that page for licensing information */

/* It has been modified to compute a histogram of byte values in the SBox[]
 * array after the KSA has been run */

// gcc -std=c99 -O3 -fomit-frame-pointer -mtune=native sbox8_v2.testksa2.c -o sbox8_v2.testksa2


#define swap(X,Y) { uint8_t T = X; X = Y; Y = T; }

static uint8_t  a, b, c, d, j;
static uint8_t  SBox[256];
 
void SBox8_INIT();
void SBox8_KSA(uint8_t key[], uint8_t keyLen);
uint8_t  SBox8_PRGA();

//-----------------------------------------
// INIT = Initialise the Internal State
//
void SBox8_INIT() {
	// SBox initalisation
  for (int i=0; i<256; i++) {
  	SBox[i] = i;
	}

	a = b = c = d = j = 0;
}


//-----------------------------------------
// KSA = Key Schedule Algorithm
//
void SBox8_KSA(uint8_t key[], uint8_t keyLen) {
	uint8_t t, k = 0;
	
	// Shuffle the Key into the Permutation
	for (int i=0; i<256; i++) {
		k  = i % keyLen;
		
    for (int n=0; n<8; n++) t = SBox8_PRGA();
    t += SBox[i] + key[k];
    swap(SBox[i], SBox[t]);
	}
}


//-----------------------------------------
// PRGA = Pseudo-Random Generation Algorithm
//
uint8_t SBox8_PRGA() {
	a += SBox[b];
	b += SBox[a];
	c += a + b + j + SBox[j];
	
	swap(SBox[c], SBox[j]);		

	d  = SBox[(SBox[c] + SBox[d]) &0xff];
	
	j++;

	return ((a + b) ^ (c + d));
}

/* Test harness code below */

int main(int argc, char ** argv) {

  /* 75, 124, 88 were picked at random */
  uint8_t key[4] = {75, 0, 0, 0};

  unsigned int sbox_histogram[256][256];
  memset(&sbox_histogram, 0, sizeof(int)*256*256);

	uint16_t maxruns = 256;

  for (int y=0; y<maxruns; y++) {
    key[1] = y & 0xff;
    for (int x=0; x<maxruns; x++) {
      key[2] = x & 0xff;
      for (int i=0; i<maxruns; i++) {
        SBox8_INIT();
        key[3] = i & 0xff;
        SBox8_KSA(key, 4);
        for (int idx=0; idx<maxruns; idx++) {
          sbox_histogram[idx][SBox[idx]]++;
        }
      }
    }  
	}

  printf("Histogram of SBox[] after KSA for key[2-3] from 0x0 to 0xffff:\n");
  printf("       SBox[i]:\n     ");
  for (int i=0; i<256; i++) {
    printf("%10d ", i);
  }
  printf("\nVal: ");
   for (int i=0; i<256; i++) {
    printf("===========");
   }
   printf("\n");
   for (int byte=0; byte<256; byte++) {
     printf("%02x:  ", byte);
     for (int idx=0; idx<256; idx++) {
     	if ( sbox_histogram[idx][byte] > 90000 ){
	      printf("***%7d ", sbox_histogram[idx][byte]);
	    	}
     	else if ( sbox_histogram[idx][byte] < 24000 ){
	      printf("---%7d ", sbox_histogram[idx][byte]);
	    	}
	    else {
	      printf("%10d ", sbox_histogram[idx][byte]);	    
	    }
     }
     printf("\n");
   }
}