RSA Algorithm

 //RSA ALGORITHM  
 #include <stdio.h>  
 int modulo(int e, int n, int pt)  
 {  
   int h;  
   if(e==0)  
     return 1;  
   else if(e==1)  
     return pt%n;  
   else  
   {  
     h = modulo(e/2, n, pt);  
     if(e%2==0)  
       return ((h*h)%n)%n;  
     else  
       return ((h*h)*(pt%n))%n;  
   }  
 }  
 int main()  
 {  
   int p, q, n, z, e, d, pt,ct;  
   printf("Enter p & q values <prime numbers>: ");  
   scanf("%d%d", &p, &q);  
   n = p*q;  
   z = (p-1)*(q-1);  
   printf("\nEnter a relative prime number to %d i.e., e value: ",z);  
   scanf("%d", &e);  
   d = 1;  
   while((d*e)%z!=1)  
     d++;  
   printf("d value is: %d\n", d);  
   printf("Keys are: <e, n>:(%d, %d)\t<d, n>:(%d, %d)",e,n,d,n);  
   printf("\n\nEnter message<pt> such that pt < %d : ",n);  
   scanf("%d", &pt);  
   ct = modulo(e,n,pt);  
   printf("\nCipher Text: %d\n",ct);  
   pt = modulo(d,n,ct);  
   printf("Decrypted Text: %d",pt);  
   return 0;  
 }  
 /*  SAMPLE OUTPUT
 Enter p & q values <prime numbers>: 11 7  
 Enter a relative prime number to 60 i.e., e value: 13  
 d value is: 37  
 Keys are: <e, n>:(13, 77)    <d, n>:(37, 77)  
 Enter message<pt> such that pt < 77 : 5  
 Cipher Text: 26  
 Decrypted Text: 5  
 */