HPR4028: Passwords with a Pi Pico

norrist uses a raspberry pi pico to type passwords

Password Managers

• I like using a password managers
• Every site has a different complex password
• I use the browser plugin or copy paste.
• I recently switched from last pass to bit warden.
  • I was one of the users that did not get prompted to increase the number of password iterations from 1000.
• They work basically the same.

My stupid bank

• The normal procedure for changing passwords is
  • fill in old password
  • generate new random password
  • copy paste new password into the new password field
• For some reason, my bank's site uses JavaScript to block paste into the new password fields
• I don't know why banks or anyone disable pasting into a browser field
• The only way I could change my password, was to generate a password simple enough that it could be manually typed into the change fields

First solution

• I wanted to find something like a programmable keyboard where you could input an input string and have the device type out the characters
• I found a few keyboards that used macros, but they seemed too simple to use for a complex password.
• I saw somewhere online that you could use a micro-controller to emulate a keyboard.
• I had a circuit playground express that I wasn't using for anything.
• The circuit playground express has 2 built in buttons
• I found a circuit python tutorial for emulating keystrokes and modified it so it would emulate the keystrokes for a password.
• Button A would output a password and button B would output a different password.

Problems

• The passwords were stored as variables in the code
• The circuit playground express has a lot of built in LED's and touch pads. It was really being wasted to only use it as a keyboard emulation device
• I have another project I want to use the playground express for

Next Solution

• Raspberry Pi Pico - $4 micro controller
• I was able to get circuit python to micro controller a keyboard on the pi pico
• Not many ways to get physically interact with board.
• No buttons and only one LED.
• I decided the best way was to have a count down timer
• blink the led to indicate where the timer was in the countdown
• output the keystrokes when the countdown timer reached zero

More problems

• Circuit python devices work by exposing a small file system when plugged in via USB.
• You can mount the file system and edit the code running on the micro controller
• Once the device is powered on, it starts emulating keystrokes every time the countdown timer cycles
• to keep the micro controller keystrokes from interfering with any work you were doing I would have to mount the device and quickly comment out part of the code so it would stop sending keystrokes
• As a fix, I added a check to only send keystrokes if a file named send_keys exists
• Now, I can work on the code and only add the send_keys file when I an ready.

Storing the password

• I didn't like that the password I want to send as keystrokes was stored as a variable in the code.
• I modified that python to read the password from a separate file named pw.txt

Setup the Pi Pico

Install circuit python

• https://learn.adafruit.com/getting-started-with-raspberry-pi-pico-circuitpython/circuitpython

Bundle

• https://github.com/adafruit/Adafruit_CircuitPython_Bundle -> Releases
• Download adafruit-circuitpython-bundle-py-20231219.zip or current version.
• Create a lib directory on the circuit python drive.
• Copy the directory lib/adafruit_hid from the zip to lib on the circuit python drive.

Code.py

• Circuit python execute code.py
• Copy the code to send the passwords to the file code.py

How to use

• Plug in the pico to your PC and mount the drive
• The LED will blink - 1 second on and 1 second off
• Save the password you want to input as keystrokes in the file pw.txt
• When you are ready for the pico to do the typing, create the file send_keys
• The LED's will blink fast 5 times, then 4 times, ...
• Wait for the LED flashes to count down.
• The pico will send the keystrokes and restart the countdown.
• Remove the file send_keys so stop the input.
• Overwrite pw.txt to be extra secure.

Adapted from Ada fruit circuit python examples

• MIT Licensed
• Keyboard Example

Code

Gitlab Repo

import os
import time

import board
import digitalio
import usb_hid

# https://github.com/adafruit/Adafruit_CircuitPython_Bundle
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS
from adafruit_hid.keycode import Keycode

led = digitalio.DigitalInOut(board.LED)
led.direction = digitalio.Direction.OUTPUT

with open("pw.txt", "r") as pw_file:
    pw = pw_file.read()

a_keys_pressed = [Keycode.A, pw]
control_key = Keycode.SHIFT

# The keyboard object!
time.sleep(1)  # Sleep for a bit to avoid a race condition on some systems
keyboard = Keyboard(usb_hid.devices)
keyboard_layout = KeyboardLayoutUS(keyboard)  # We're in the US :)

def blink_count(i, delay):
    for _ in range(i):
        led.value = True
        time.sleep(delay)
        led.value = False
        time.sleep(delay)
    time.sleep(1)

def countdown_and_send():
    for i in reversed(range(6)):
        print(i)
        blink_count(i, delay=0.2)
    print(f"Sending {a_keys_pressed} as keystrokes")
    for key in a_keys_pressed:
        if isinstance(key, str):  # If it's a string...
            keyboard_layout.write(key)  # ...Print the string

while True:
    print("Hello, CircuitPython!")
    try:
        os.stat("send_keys")
        countdown_and_send()
    except OSError:
        blink_count(1, 1)
        print("touch send_keys to enable keypresses")

Playground express version

# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT

"""CircuitPython Essentials HID Keyboard example"""
import time

import usb_hid
from adafruit_circuitplayground import cp
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS
from adafruit_hid.keycode import Keycode

a_keys_pressed = [Keycode.A, "aaaabbbbccccdddd@@"]
b_keys_pressed = [Keycode.A, "eeeeffffgggghhhh@@"]


control_key = Keycode.SHIFT

time.sleep(1)  # Sleep for a bit to avoid a race condition on some systems
keyboard = Keyboard(usb_hid.devices)
keyboard_layout = KeyboardLayoutUS(keyboard)  # We're in the US :)


print("Waiting for key pin...")

while True:
    if cp.button_a:
        print("A")
        for key in a_keys_pressed:
            if isinstance(key, str):  # If it's a string...
                keyboard_layout.write(key)  # ...Print the string
    elif cp.button_b:
        print("B")
        for key in b_keys_pressed:
            if isinstance(key, str):  # If it's a string...
                keyboard_layout.write(key)  # ...Print the string

    time.sleep(0.1)

Links

• https://circuitpython.org/
• https://learn.adafruit.com/adafruit-circuit-playground-express/overview
• https://www.raspberrypi.com/products/raspberry-pi-pico/

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