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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <math.h>
  4. #include <stdint.h>
  5. #include <stdlib.h>
  6. #include <time.h>
  7.  
  8.  
  9. // Additive constant
  10. uint8_t c[8]= {1,1,0,0,0,1,1,0};
  11.  
  12. //Global S Box
  13. uint8_t sbox[256] = {0};
  14.  
  15. //Powers of 
  16. int powersoftwo[11]= {1,2,4,8,16,32,64,128,256,512,1024};
  17.  
  18. //Calculates x such that ax mod m = 1 using extended euclid's algorithm. 
  19. int modInverse(int a, int m){
  20.     int x, y;
  21.     int g = gcdExtended(a, m,&x,&y);
  22.     if (g != 1)
  23.         printf("no inverse\n");
  24.     else{
  25.         int res = (x%m + m) % m;
  26.         return res;
  27.     }
  28. }
  29.  
  30. int gcdExtended(int a, int b, int *x, int *y)
  31. {
  32.     if (a == 0){
  33.         *x = 0, *y = 1;
  34.         return b;
  35.     }
  36.     int x1, y1; // To store results of recursive call
  37.     int gcd = gcdExtended(b%a, a, &x1, &y1);
  38.     // Update x and y using results of recursive
  39.     // call
  40.     *x = y1 - (b/a) * x1;
  41.     *y = x1;
  42.     return gcd;
  43. }
  44.  
  45. void getbinary(uint8_t n,uint8_t *a){
  46.     int i=0;
  47.     while(n > 0){
  48.         a[i++] = n%2;
  49.         n = n/2;
  50.     }
  51.     return;
  52. }
  53.  
  54. int getdecimal(uint8_t *a){
  55.     int i,n=0;
  56.     for(i=0;i<8;i++)
  57.         n = n + a[i]*powersoftwo[i];
  58.     return n;
  59. }
  60.  
  61. //generates sbox
  62. void generate_sbox(){
  63.     int i,j;
  64.     //loop for all 0-255 entries.
  65.     //special case = 0
  66.     for(i=1;i!=16*16;i++){
  67.         uint8_t tmp[8] = {0};			//stores binary of inverse.
  68.         uint8_t y;
  69.         int inv = modInverse(i,283);	//inverse.
  70.         getbinary(inv,tmp);
  71.         uint8_t newtmp[8];
  72.         //Affine transformation
  73.         for(j=0;j<8;j++)
  74.             newtmp[j] = (tmp[j]^tmp[(j+4)%8]^tmp[(j+5)%8]^tmp[(j+6)%8]^tmp[(j+7)%8]^c[j]);
  75.         //decimal to binary conversion.
  76.         int num = getdecimal(newtmp);
  77.         sbox[i] = num;
  78.     }
  79.     return ;
  80. }
  81.  
  82.  
  83. int main(){
  84.     generate_sbox();
  85.     return 0;
  86. }
Success #stdin #stdout 0s 9296KB
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https://ideone.com/zJUjup
language:
C (gcc 8.3)
created:
8 years ago
visibility:
public

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