USBpwn source code for Windows hosts
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Makefile
README.md
host.c
win32kbd.c
win32kbd.h

README.md

USBpwn Windows host

The purpose of this program is to send any (text or binary) file using the LEDs on the keyboard (Num, Caps and Scroll lock). It uses standard C and Win32 API calls and can be run without administrative privileges. The protocol used is the following, implemented in send_frame:

  • the Num and Caps lock state is set to the first two bits to send (in this order)
  • the Scroll lock is turned on
  • the program waits for a newline
  • the Scroll lock is turned off

In other words, Scroll lock is used as a "clock signal", and at raising edge, the two other LEDs can be sampled for data. The newline (that can be achieved by the Enter/Return key) is the acknowledgement signal, making the protocol fully synchronous. For example, sending the bits 1101 can be done in the following way:

            __________________________________
   NUM ____/
                               _______________
  CAPS _______________________/
                ______            ______
SCROLL ________/      \__________/      \_____

                  01                11

Bits are sent from LSB to MSB by send_byte, n bytes are sent from 0 to n-1 by send_bytes. The main program sends the length of the transmission in bytes using ASCII characters, surrounded by two dashes (--) before the raw data.

Usage

> host filename.bin

Compiling

As only standard APIs are used, any decent C compiler can be used. The Makefile takes care of dependencies, you just have to set the compiler used, if you'd like to cross-compile, like me. For example, I used the following commands to compile it under Debian Wheezy:

# apt-get install mingw32
$ CC=i586-mingw32msvc-gcc make

License

The whole project is under MIT license.