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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3.  
  4. unsigned long long P,Q,E,D;
  5.  
  6. int ExtendedGCD(long long A,long long B, long long *C, long long *D)
  7. {
  8.     int I;
  9.     long long J;
  10.     if (A%B==0)
  11.     {
  12.         (*C)=0;
  13.         (*D)=1;
  14.         return B;
  15.     }
  16.     else
  17.     {
  18.         I = ExtendedGCD(B,A%B,C,D);
  19.         J=(*C);
  20.         (*C)=(*D);
  21.         (*D)=(*D)*(-A/B)+J;
  22.         return I;
  23.     }
  24. }
  25.  
  26. void GenerateKeys()
  27. {
  28.     long long I,J;
  29.     P=6469;  /*944659*/
  30.     Q=5431;  /*817907*/
  31.     E=65537;
  32.     ExtendedGCD((P-1)*(Q-1),E,&I,&J);
  33.     while (J<=0)
  34.         J+=(P-1)*(Q-1);
  35.     D=J;
  36. }
  37.  
  38. unsigned long long ExponentBySquaring(unsigned long long V,unsigned long long Exp)
  39. {
  40.     unsigned long long I;
  41.     if (Exp==0)
  42.     {
  43.         return 1;
  44.     }
  45.     else if (Exp==1)
  46.     {
  47.         return V%(P*Q);
  48.     }
  49.     else
  50.     {
  51.         if (Exp%2==0)
  52.         {
  53.             I=ExponentBySquaring(V,Exp/2);
  54.             I=(I*I)%(P*Q);
  55.         }
  56.         else
  57.         {
  58.             I=ExponentBySquaring(V,Exp/2);
  59.             I=((I*I)%(P*Q))*(V%(P*Q));
  60.         }
  61.         return I%(P*Q);
  62.     }
  63. }
  64.  
  65. unsigned long long MyEncrypt(unsigned long long M)
  66. {
  67.     return ExponentBySquaring(M,E);
  68. }
  69.  
  70. unsigned long long MyDecrypt(unsigned long long C)
  71. {
  72.     return ExponentBySquaring(C,D);
  73. }
  74.  
  75. int main()
  76. {
  77.     GenerateKeys();
  78.     printf("%llu\n",MyDecrypt(MyEncrypt(65)));
  79.     return 0;
  80. }
  81.  
Success #stdin #stdout 0s 2252KB
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65
https://ideone.com/AM70Ot
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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