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#include<stdio.h>
#include<math.h>

long long int add(long long int a, long long int b,
        long long int G)
{
    if (b == 1)
        return a;

    else
        return (((long long int)(a + b)) % G);
}
int main()
{
    long long int G, x, a, y, b, ka, kb;



    G = 43; //the agreed number
    printf("The value of G : %lld\n\n", G);


    a = 23; //private key for a
    printf("The private key a for A : %lld\n", a);
    x = add(G, a); //gets the generated key


    b = 19; //private key for b
    printf("The private key b for B : %lld\n\n", b);
    y = add(G, b); // gets the generated key

    ka = add(y, a, G); // Secret key for a
    kb = add(x, b, G); // Secret key for b

    printf("Secret key for the A is : %lld\n", ka);
    printf("Secret Key for the B is : %lld\n", kb);

    return 0;
}

this is the flow of the code

THIS IS THE EXPECTED OUTPUT/FLOW OF THE PROGRAM but my code has problems i attached an image to show the problem.

A and B will agree upon a number

G = 43 is the agreed number

A will generate a private number a = 23

B will generate a private number b = 19

A will calculate G=43 + a=23 mod G=43 OR 43 + 23 mod 43 = 66 (let's call it x) x = 66

B will calculate G=43 + b=19 mod G=43 OR 43+19mod43 = 62 (let's call it y) y = 62

for A we get x = 66

for B we get y = 62

They will then exchange x and y

x = 66 will go to B

y = 62 will go to A

A will now calculate y + a mod G OR 62+23 mod 43 = 85 (secret number is ka) ka = 85

B will now calculate x + b mod G OR 66+19 mod 43 = 85 (secret number is kb) kb = 85

This is the error that I get

Naive9
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    So... what is wrong? – Eugene Sh. Apr 11 '22 at 21:43
  • I get errors but I really have no idea where is the problem. any help would be appreciated. – Naive9 Apr 11 '22 at 21:45
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    "get errors" is not an adequate problem description. Please give the expected result vs actual result. Also describe what debugging you did and what/where you find things start going wrong. – kaylum Apr 11 '22 at 21:45
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    Have you tried running your code line by line in a debugger while monitoring the values of all variables, in order to determine at which point your program stops behaving as intended? If you did not try this, then you may want to read this: [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/q/25385173/12149471) You may also want to read this: [How to debug small programs?](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) – Andreas Wenzel Apr 11 '22 at 21:46
  • What errors? You get them when compiling the program? When running? How do they look like? – Eugene Sh. Apr 11 '22 at 21:49
  • the question has been answered. thank you for your response. – Naive9 Apr 12 '22 at 11:23

1 Answers1

1

Your 'add' function is declared as taking 3 arguments

long long int add(long long int a, long long int b, long long int G)

but twice you try to call it only passing 2, here

x = add(G, a); //gets the generated key

and here

y = add(G, b); // gets the generated key

reading the logic you posted those should be

x = add(G, a, G); //gets the generated key

and

y = add(G, b, G); // gets the generated key
pm100
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  • is my code even correct? did I properly declare the "add" function? please help. I'm also confused on that part too. how do i add the modulo on this part x = add(G, a); – Naive9 Apr 11 '22 at 21:55
  • thank you so much I got the expected output. – Naive9 Apr 11 '22 at 23:08