Question

Data Encryption (Strings and Bitwise Operators)

Write a C program that uses bitwise operators (e.g. bitwise XOR) to encrypt/decrypt a message. The program will prompt the user to select one of the following menu options:

1. Enter and encrypt a message

2. View encrypted message

3. Decrypt and view the message (NOTE: password protected)

4. Exit

If the user selects option 1, he/she will be prompted to enter a message (a string up to 50 characters long). The program will next encrypt/modify each character of this message before it will be stored into the memory.

If selecting option 2, the user will be able to view on the screen the decrypted message that is stored in the memory.

If the user selects option 3, he/she will then be prompted to enter a password in order to view the original message. (Use “PRG255” as a password.) The user should be limited to three attempts to enter the password. If the user enters the correct password, the program will decrypt the encrypted message and display the original message. If an incorrect password is entered three times the program should show an appropriate message (e.g. “Incorrect password entered three times! Program will terminate now!”) and terminate.

This process will continue until the user chooses the Exit option 4 to terminate the program

NOTE: One of the methods of data encryption uses the XOR bitwise operator with a mask value (an integer number) to encrypt every character of the message and the same operation should be used to decrypt the message.

It is required to submit your source code file, i.e. Lab4.c file as well as a file with your program's run screen captures.

BONUS MARKS:

When message and password are entered by the user the program should NOT display these strings on the screen when they are entered, instead the program will print on the screen a single asterisk (*) representing each character entered. Please note that the actual characters entered by the user will be properly stored in the memory.

A sample run of the program with bonus marks could be as follows:

1. Enter and encrypt a message

2. View encrypted message

3. Decrypt and view the message (NOTE: password protected)

4. Exit

Please select an option => 1

Enter a message => ***********

Please select an option => 3

Enter Password => ******

Message entered: LAB4 PRG255

Answer 1

HERE IS THE CODE AS PER YOUR REQUIREMENT

RAWCODE:

#include<stdio.h>
#include<conio.h>
#include<string.h>
int main(void){
char password[55];
int option;
printf("1. Enter and encrypt a message\n2. View encrypted message\n3. Decrypt and view the message (NOTE: password protected)\n4. Exit\n");
// do-while loop for continuous execution
do{
   printf("\nPlease select an option => ");
   scanf("%d",&option);
   char encrypt[55];
   int p=0;
  
//     if statements for each option
//       To enter a message and encrypt it using xor;

   if(option == 1){
       printf("\nEnter a message => ");
       do{
//         get char method for each character of message
       encrypt[p]=getch();
       if(encrypt[p]!='\r'){
//           printing the "*" character instead of message
       printf("*");
       encrypt[p] = encrypt[p]^1;
       }
       p++;
       }while(encrypt[p-1]!='\r');
       encrypt[p-1]='\0';   
       }
      
//       printing encrypted message
       if(option == 2){
           printf("\n %s ",encrypt);
       }
      
//       printing decrypted message using password
       if(option == 3){
           int count=0;
          
//           continuous while loop for asking password upto 3 times
           while(1){
               int a = 0;
               printf("\nenter the password => ");
               do{
           password[a]=getch();
           if(password[a]!='\r'){
           printf("*");
           }
           a++;
           }while(password[a-1]!='\r');
           password[a-1]='\0';
          
//           password comparison, if okay, prints the decrypted message
               if(strcmp(password,"PRG255") == 0){
                   int i;
                   for(i=0; i<strlen(encrypt); i++){
                       encrypt[i] = encrypt[i]^1;
                   }
                   printf("\n %s",encrypt);
                   break;
               }
//               after 3 iterations, if password still incorrect, the while loop terminates
               else{
                   count++;
                   if(count == 3){
                       printf("\nIncorrect password entered three times! Program will terminate now!");
                       break;
                   }  
               }
           }
              
       }
   }while(option != 4);
}

SCREENSHOTS:

OUTPUT:

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