Question

Background:
You can create a simple form of encryption using the xor Boolean operator. For example, if you want to encrypt the letter 'A':

1. Choose another letter as a "key", say 'X'
2. Encrypt 'A' with the xor function: encrypted = 'A' xor 'X'
3. Now you can decrypt by xor'ing your encrypted value with 'X' again: decrypted = encrypted xor 'X'

Your task:
Write a C++ program that meets the following requirements:

1. Asks the user for the name of an input file and a "key" character
2. Encrypt each character in the file using the provided key and the xor function. (Note: The program should handle all standard alphanumeric characters.)
3. Your program should save the results of the encryption into a new file with the same base name, but with a ".xor" file extension.
4. The program should also provide an option to decrypt a given file.
5. Include appropriate error checking.

Submit:

• Fully documented source code

Documentation should include:

• Pseudocode
• Top comment block (The name of the program, The name of the programmer, The date of the program, and A brief description of the purpose of the program)
• Function comments (Description, pre and post conditions)
• Internal comments for all functions

Answer 1

// C++ program to implement XOR encryption and decryption

#include <iostream>

#include <fstream>

#include <cctype>

using namespace std;

string encrypt(string line, char key);

string decrypt(string line, char key);

int main() {

       char key;

       string filename;

       ifstream fin;

       cout<<"Enter the filename : ";

       getline(cin,filename); // provide full path to file

       filename = filename.substr(0,filename.length()-1);

       cout<<"Enter the key character : ";

       cin>>key;

       fin.open(filename.c_str());

       if(fin.is_open())

       {

             string outFile = filename.substr(0,filename.find('.'))+".xor";

             ofstream fout(outFile.c_str());

             string line;

             char option;

             while(!fin.eof())

             {

                    getline(fin,line);

                    fout<<encrypt(line,key);

             }

             fin.close();

             fout.close();

             cout<<"Do you want to decrypt the file (y/n) ? ";

             cin>>option;

             if(tolower(option) == 'y')

             {

                    cout<<"Decrypted file : "<<endl;

                    fin.open(outFile.c_str());

                    if(fin.is_open())

                    {

                           while(!fin.eof())

                           {

                                 getline(fin,line);

                                 cout<<decrypt(line,key);

                           }

                    }

                    fin.close();

             }

       }else

             cout<<"Unable to open file : "<<filename<<endl;

       return 0;

}

// function to encrypt a line using XOR

// Pre-condition : line is not null and key is not empty

// Post-condition : line and key is unchanged

// Returns : string which is obtained by XOR encryption of the standard alphanumeric characters and key

string encrypt(string line, char key)

{

       string encryptedLine="";

       for(size_t i=0;i<line.length();i++)

       {

             encryptedLine += line.at(i)^key;

       }

       return encryptedLine;

}

// function to decrypt a line using XOR

// Pre-condition : line is not null and key is not empty

// Post-condition : line and key is unchanged

// Returns : string which is obtained by XOR decryption of the standard alphanumeric characters and key

string decrypt(string line, char key)

{

       string decryptedLine="";

       for(size_t i=0;i<line.length();i++)

       {

             decryptedLine += (line.at(i)^key);

       }

       return decryptedLine;

}

//end of program

Output:

Input file:

Output file:

Console: