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

/* The code below for SBox8_PIA was copied from
 * 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 */

#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_PIA(uint32_t seed) {

  if (seed == 0) {
    a = 14;
    b = 59;
    c = 23;
    d = 77; 
  } else {  
    a = ( seed        & 0xff);
    b = ((seed >>  8) & 0xff);
    c = ((seed >> 16) & 0xff);
    d = ((seed >> 24) & 0xff);
  }

  // Shifting to the next odd Value of each Variable
  // in Order to generate an alternating Permutation
  uint8_t t = ((b ^ c) + d);
  t |= 1;

  // Initialise the alternating Permutation
  // into the internal State Array
  for (int i=0; i<256; i++) {
    a += t;
    SBox[i] = a;
  }

}

void SBox8_KSA(uint8_t key[], uint8_t keyLen) {

  // Shuffle the Key into the Permutation
  // of the internal State Array
  for (int i=0; i<256; i++) {
    d  = i % keyLen;
    
    a += SBox[b];
    b += SBox[a];
    c  = a + b + i + key[d];
    
    swap(SBox[c], SBox[i]);   
  }
  
  // a,b and c are not explicitly set to zero
  // but keep on carrying over their values
  j=0;
}

/* 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 maxdeeps = 256;

  for (int y=0; y<256; y++) {
    key[1] = y & 0xff;
    for (int x=0; x<256; x++) {
      key[2] = x & 0xff;
      for (int i=0; i<256; i++) {
        SBox8_PIA(0x000000ff);
        key[3] = i & 0xff;
        SBox8_KSA(key, 4);
        for (int idx=0; idx<256; 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("%7d ", 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] > 100000 ){
	      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");
   }
}