C++ Decryptor

[Muhasaresa]

:D Hello,

I am making a C++ console application where the user can encrypt and decrypt text. So far, I have successfully made the encryption part, but am not quite sure how to make the decryption part. For example: abcb -> 128.70.88.70. but I can't make it go back to abcb. Here is my code so far:

#include <conio.h>
#include <stdio.h>
#include <cstdlib>
#include "windows.h"
#include "winuser.h"
#include <cmath>
#include <iostream>
#include <iomanip>
#include <complex>
#include <string>


int main ()
{ 
    using namespace std;
    
    int f;
    char n;
    char b;
    char none;
    string password;
    string nonencr;
    string encr;
    system("color 1f");
    
cout <<"************************************************************************"; cout << endl;
cout <<"****************Welcome to Bashcode Encryptor© v1.0.0.0*****************"; cout << endl;
cout <<"************************************************************************"; cout << endl;
cout << endl;
cout << endl;

cout <<"Enter password: "; do{
     n=char(getch()); 
     
     if(int(n) !=13 && int(n) !=8){ 
                cout<<"x"; 
                password += n; 
                 
                }
                }while(int(n)!=13); 
                                    
cout << endl;
cout << endl;
if ( password == "bashcode"){
             cout <<"ACCESS GRANTED"; Sleep(1500); }
             else {system("CLS"); cout <<"ACCESS DENIED. The program will now shut down."; Sleep(2000) ; return 0;}
cout << endl;
cout << endl;
system("CLS");
cout <<"Select an option:" << endl;

cout << endl;
cout <<"Encrypt (1)" << endl;
cout << endl;
cout <<"Decrypt (2)" << endl;
cout << endl;
cout <<">>>>>>>> "; cin >> f;
if (f == 1){
      system("CLS"); cout <<"Input text to be encrypted: "; do{
     none=char(getch()); 
     
     if(int(none) == 97){ 
                cout<<"a"; 
                encr += "128.";  
                                 
                }
     if(int(none) == 98){ 
                cout<<"b"; 
                encr += "70.";}
     
     
     if(int(none) == 99){ 
                cout<<"c"; 
                encr += "88.";}
                
     if(int(none) == 100){ 
                cout<<"d"; 
                encr += "40.";}
                
     if(int(none) == 101){ 
                cout<<"e"; 
                encr += "54.";}    
     
     if(int(none) == 102){ 
                cout<<"f"; 
                encr += "36.";}                            
     
     if(int(none) == 103){ 
                cout<<"g"; 
                encr += "10.";}           
                }while(int(none)!=13);
     cout << endl;
     cout << endl;
     cout << "Encryped version: ";
     cout << endl;
     cout << endl;
     cout << encr;
}

if (f == 2){
      cout <<"Enter something to decrypt: "; 
     
    
            
               
     
    
      cout << endl;
      cout << endl; 
      cout << nonencr;
}      

cin.clear();
cin.ignore(255, '\n');
cin.get();

return 0; 
}

I would greatly appreciate any help :D

[Computergeek01]

Do you understand the limitations of this method of encryption? This is a subsitution cipher, others call it a "Ceasar Shift" cipher and it is very easily broken with frequency analysis.

[Muhasaresa]

Yes, I started learning C++ a few days ago and I know how feeble my application is, but I'm learning :D

[andywestken]

As coded, you just need to write the reverse function!

Use getch() to get i/p like your encoding function. But add the chars to an array until you reach a '.'. Then you'll need a function to map 128, 70, 88, 80 back to a, b, c, d

You'll also have to renember to handle the last char just after the loop exits.

Andy

P.S. I would split you encode loop out into it's own function before you move on.

[packetpirate]

Those IF statements are horribly redundant and unnecessary... just cast the char to an int. When you cast a char to an integer, the integer is the ASCII value of the character.

[Muhasaresa]

As coded, you just need to write the reverse function!

Thank you for your help, but I'm still not quite sure how I could achieve this because I don't know how I would implement a char array into my code.

Thanks again,

Muhasaresa

[Computergeek01]

I think your problem might be in the encryption you are trying to use. Do you know what it is called? I believe I was wrong when I said this was a Ceasar Shift, it seems that encr is your actual encrypted message but I can't make heads or tails of it. Where did you read up on this?

[Muhasaresa]

You are right, "encr" is the encrypted message and it works just fine. I wrote the code myself and the letters are substituted to a number of my choosing followed by a dot. I'm just trying to get my decryptor working but I have no idea how :(

I can get "abcca" (for example) to go to 128.70.88.88.128.

But I can't get 128.70.88.88.128. to go back to "abcca" :(

Muhasaresa.

[ultifinitus]

Perhaps you may want to do something like this:

unsigned char cryptTable[255];
for (int a = 0; a < sizeof(cryptTable); a++){
    cryptTable[a] = a;
}
//now set up your swaps
cryptTable['a'] = 'b'; //needs the single quotes
cryptTable['b'] = 'a';
//etc. 

(I would put all of this in a class, if I were you, if you know how)

this way you can simply write a function to swap characters directly.
This in conjunction with xor encryption and some simple algorithms (including salting the data) would make a somewhat difficult to break encryption.

[sohguanh]

Encryption/decryption is a very big topic. We have so many algorithm, RSA,Blowfish,AES etc. Seems the current latest is AES.

[Muhasaresa]

Thanks everyone for your help. I appreciate it!

Muhasaresa