Question

EDIT: SOLVED. zvbra appears to be right. giving only 4 chars to crypt was causing the problem. Gotta see why is that because i was told getline discarded the last character…

Hello fellow stackers.

I want to start by saying I tried to debug and solve my problem by myself but (probably due to my lack of knowledge on assembly and pretty much anything in general) i failed at doing so.
So I’ve came here in the hope you will be able to help me 🙂 .

I decided to code a simple (I think) encryption program, more of a test than anything else.

It’s divided in 2 parts:

Alghorithm.h (Yeah, I know it’s misspelled.) which contains class ‘Crypter’

#include <iostream>
#include <cmath>
using namespace std;

class Crypter
{
private:
    char Crypt[4];

public:
    Crypter()
    {
        getCrypt:
        cout<<"\nEnter a 4 character password: ";
        cin.getline(Crypt,5);
        if (cin.fail())
        {
            cout<<"\n\nError while reading password. 4 CHARACTERS MAXIMUM.\n\n";
            cin.sync(); cin.clear();
            goto getCrypt;
        }
    }

    void Encrypt(string& data)
    {

        for (int i=0; i<data.size();i++)
        {
            int offset=i;
            if (offset>5)
            {
                while (offset>5)
                {
                    offset-=6;
                }
            }
            float base = 2.0f;
            int testbit=pow(base,offset);//gets bit to test. Ex: if offset= 1 (2^1=2=binary 10) test bit is the 2nd least significant bit

            if (data[i]!=(data[i]^testbit)) //if testbit is 1 (tested using xOR)  
                {
                    data[i]= data[i]^Crypt[2];  //-> encrypt using  xOR Crypt[2]

                    testbit=pow(base,offset+2);

                    if(data[i]!=data[i]^testbit)// then if testbit is 1 (tested using xOR)  
                    {
                        data[i]=(data[i]^Crypt[0])+Crypt[3]; //-> encrypt using  xOR Crypt[0] then adding crypt[3]
                    }
                    else
                    {
                        data[i]=(data[i]^Crypt[1])+Crypt[1];//-> encrypt using  xOR Crypt[1] then adding crypt[1]
                    }
                }
            else
            {
                data[i]=((data[i]^Crypt[3])^Crypt[0])+Crypt[2];//-> encrypt using  xOR Crypt[1] then xOR Crypt[0] and finally adding crypt[1]
            }
        }
        return;
    }
};  

and main.cpp

#include "Alghorithm.h"
int main()
{
    string data="This sentence is going to be encrypted";
    Crypter Crypter;
    cout<<"\nEncrypting...";
    Crypter.Encrypt(data);
    cout<<"\n\nEncryption Successful\n\nEncrypted string: "<<data<<endl;
    cin.sync(); cin.clear();
}

Now you programming experts must be thinking how clumsy my algorithm is
and that most parts don’t even make sense for a encryption algorithm(which is possible)
but pretend it’s a nice algorithm that makes total sense.

This is the problem:

It compiles. It runs. It encryptes the sentence and prints the encrypted
version. But right before the program ends (in the screenshots you can see i forgot
to return a value in main, but I’ve fixed that and the problem is did not change a bit) a message pops
up(while running through the compiler) in debug mode [Check Screenshots] and 3 in release mode;

Most of them warn about an error caused by a corruption in the stack around Crypter ‘variable’.

I’m not even close to be considered an experienced programmer so I came here asking for your help.

Since the error only pops up when the program is ending does it mean it is a problem with the cleanup?

I’m totaly lost here. Any responses are appreciated.

NOTE: I’ve also included part of the assembly code (the relevant part) provided by te debugger;
Hope it has some use (check my inline comment on the asm code for the ‘position’ of the error);

Criticise my crappy code at will :)( It seems to have a problem since the resultant encrypted string differes from debug to release mode ?:/?.

-João

Screens:

How the program looks like before i press ENTER(Debug): http://i44.tinypic.com/3ert2.png

How the program looks like before i press ENTER(Release) http://i42.tinypic.com/2nld45f.png

Error shown after pressing ENTER (Debug) http://i41.tinypic.com/bhltoy.png

1st Error shown after pressing ENTER (Release) http://i42.tinypic.com/28lchac.png

2nd Error shown after pressing ENTER (Release) http://i40.tinypic.com/2h3ttmw.png

3rd Error shown after pressing ENTER (Release) http://i41.tinypic.com/2lc5suw.png

ASM Code provided by the debbuger http://pastebin.com/TTXUn0T2

Answer 1

At least one error: you need to reserve 5 characters for the Crypt variable: you need the additional space to null-terminate the string.