Thread: XOR Encryption & Decrypt.

Please view my code below...

Code:

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

    int main(void)
    {
        char data[100];
        int key;
        int length;
        int i;

        printf("Enter 2 digits key: ");
        scanf("%d", &key);

        flushall();

        printf("\nEnter data to encrypt: ");
        scanf("%[^\n]", &data);

        length = strlen(data);

        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n%s\n", data);

    }

Did my code above encrypt my string successfully? Because I just started working on this so I not sure that did my string has been protected. Also how can I decrypt it after I encrypt it? Very thanks you.

Ok...now i have updated my code...

Code:

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

    int main(void)
    {
        char data[100];
        int key;
        int length;
        int i;

        /* Start Encrypt */

        printf("Enter 2 digits key: ");
        scanf("%d", &key);

        flushall();

        printf("\nEnter data to encrypt: ");
        scanf("%[^\n]", &data);

        length = strlen(data);

        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nEncrypted Data");
        printf("\n==============");
        printf("\n%s\n", data);

        flushall();

        /* Start Decrypt */

        printf("\nEnter unlock key: ");
        scanf("%d", &key);

        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nDecrypted Data");
        printf("\n==============");
        printf("\n%s\n\n", data);



    }

Now my problem is how can I keep looping to lets user input key as long as they have inputed incorrect keys?

Delete the & before the scanf() for data. Data is a string, so it is it's own address.

A while loop is a good loop to use for a repeating effort by the user.

Well, I know that I should use while loop but how can my program determine that the key which input by the user is incorrect?

Put it into a variable, which is itself encoded, perhaps?

Read it from a file?

The thing is, to work, it has to have a good design to it, and that includes key handling/storage. One weak link and your security is *POOF* gone!

Ok, I have updated my code so that the key store into another variable...

Code:

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

    int main(void)
    {
        char data[100];
        int key;
        int length;
        int i, pass;

        /* Start Encrypt */

        printf("Enter 2 digits key: ");
        scanf("%d", &key);
        
        /* Store key into pass */
        pass = key;

        flushall();

        printf("\nEnter data to encrypt: ");
        scanf("%[^\n]", data);

        length = strlen(data);

        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nEncrypted Data");
        printf("\n==============");
        printf("\n%s\n", data);

        flushall();

        /* Start Decrypt */

        do 
        {

            printf("\nEnter unlock key: ");
            scanf("%d", &key);

            for(i=0; i<length; i++)
            {
                data[i] = data[i]^key;
            }

        } while (key != pass);


        printf("\n==============");
        printf("\nDecrypted Data");
        printf("\n==============");
        printf("\n%s\n\n", data);



    }

Now the problem is when the user input invalid key it will loop back then ask again. Now is the main problem, after user input the valid key in the 2nd time. My program accept the key but it still print the encrypt data but not the decrypt data. How could I solve this problem?

I have solve this problems ~ ^^

Please view my code below.

Code:

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

    void encrypt(); 
    void decrypt(char data[], int pass, int length);

    int main(void)
    {
        encrypt();
        decrypt(data[], pass, length);
    }

    void encrypt()
    {
        char data[100];
        int key;
        int i;
        int pass;
        int length;

        /* Start Encrypt */

        printf("Enter 2 digits key: ");
        scanf("%d", &key);
        
        /* Store key into pass */
        pass = key;

        flushall();

        printf("\nEnter data to encrypt: ");
        scanf("%[^\n]", data);

        length = strlen(data);

        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nEncrypted Data");
        printf("\n==============");
        printf("\n%s\n", data);

    }

    void decrypt(char data[], int pass, int length)
    {
        int i, key;

        do 
        {
            flushall();

            printf("\nEnter unlock key: ");
            scanf("%d", &key);

        } while (key != pass);
    
        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nDecrypted Data");
        printf("\n==============");
        printf("\n%s\n\n", data);

    }

error C2065: 'data' : undeclared identifier

Why? I am sure I already pass the data...

Originally Posted by Adak

The thing is, to work, it has to have a good design to it, and that includes key handling/storage. One weak link and your security is *POOF* gone!

... and so is your data.

Declare data[] in main(), and then pass it to all your functions. You're not doing that now.

Code:

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

    void encrypt(); 
    void decrypt(char data[100], int pass, int length, int key, int i);

    int main(char data[100], int pass, int length, int key, int i)
    {
        encrypt();
        decrypt(data, pass, length, key, i);
    }

    void encrypt()
    {
        char data[100];
        int key;
        int i;
        int pass;
        int length;

        /* Start Encrypt */

        printf("Enter 2 digits key: ");
        scanf("%d", &key);
        
        /* Store key into pass */
        pass = key;

        flushall();

        printf("\nEnter data to encrypt: ");
        scanf("%[^\n]", data);

        length = strlen(data);

        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nEncrypted Data");
        printf("\n==============");
        printf("\n%s\n", data);

    }

    void decrypt(char data[100], int pass, int length, int key, int i)
    {
        printf("%d", pass); // Pass already change....why?

        do 
        {
            flushall();

            printf("\nEnter unlock key: ");
            scanf("%d", &key);

        } while (key != pass);
    
        for(i=0; i<length; i++)
        {
            data[i] = data[i]^key;
        }

        printf("\n==============");
        printf("\nDecrypted Data");
        printf("\n==============");
        printf("\n%s\n\n", data);

    }

Now the declare problem has solve...but now is the loop problems. Even when the user input valid key my program continue looping...I wonder why?

Not this:

Code:

int main(char data[100], int pass, int length, int key, int i)

but this:
int main(void) 
{
    char data[100];
    int pass, length, key, i;

    //all your other code for main in here

    return 0;
}

Originally Posted by Siaw Ys

I understand what you mean. All the problem which I post is the problem which I has try to figure by my own but I still can't solve so I need help. I also try to just rely by myself solve it by myself as many as I can but sometimes I really can't solve some problems. Of course, before posting any question, I has also read all my note then I think. I solve some but not all so that why I request help. Yes, some of my coding is guessing, but I also trust that I can learn after what you all have teach me. So, from the guess it will become an knowledge...But I just hope to let you know that I was not beg, at least I sure that I have try my best to solve before request all of you help...

Do you not have a course textbook you can study, for a better understanding.

The problem here is not that you are running into increasingly complex problems as would be expected throughout a course... The problem is that you do not appear to be grasping even the basics of program organization, variable declaration, etc.; day one stuff.

Remember... teaching C is your professor's job... not ours.

You will never learn programming by guesswork, it's never happened before and it's not about to happen anytime soon. All you do is move yourself repeatedly from one screw up to the next and eventually you will become so confused and frustrated you will give up. The only way is as I described above... by deliberate study. (In other words: You can't dumbass your way through this)

There are all kinds of free tutorials on the web. This doesn't need to cost you money you don't have... but you do need to pay attention to the lessons and you need to understand how this works if you are ever to be any good at it.