Malformed Packets and Sharing Something

In Cybersecurity: Sniffing Attacks & Defenses, the Share Something Personal – Unencrypted? activity involved testing unencrypted transmission of emoji from one micro:bit to another. 

In this activity, the application is a little more versatile, allowing you to scroll through the emoji with the micro:bit module’s A button and send it with the B button. 

This application also has a routine for sending a malformed packet.  In this activity, you will again study how the malformed packet can cause problems, mitigate them, and then also encrypt the communication.

Parts:

• Two micro:bit modules
• Two USB A to micro-B cables

Script: radio_send_receive_images_w_buttons

You can either connect each micro:bit to a separate computer, or both to separate USB ports on the same computer.

• Connect the two micro:bit modules to two USB ports with two USB cables.
• Open two separate browsers and navigate each one to python.microbit.org.
• If you are part of a class, and have been assigned a channel, make sure to adjust the script’s channel=7 argument to your assigned channel before you save and flash the scripts.
• Enter, name, save, and flash the radio_send_receive_images_w_buttons script into both micro:bit modules.
• Before continuing, find the # Sends malformed packet comment and examine how the packet is changed before transmitting.  

# radio_send_receive_images_w_buttons

from microbit import *
import radio

radio.on()
radio.config(channel=7)

n = 0
emoji = [ 'Image.YES', 'Image.NO', 'Image.HEART', 'Image.SKULL' ]
image = eval(emoji[n])
display.show(image)

while True:
    if button_a.was_pressed():
        n = n + 1
        n = n % len(emoji)
        image = eval(emoji[n])
        display.show(image)

    if button_b.was_pressed():
        packet = emoji[n]
        print('packet:', packet)
        if image is Image.SKULL:              # Sends malformed packet
            packet = 'malformed packet'       # Sends malformed packet
        radio.send(packet)
        
    packet = radio.receive()

    if packet:
        print('packet:', packet)

        n = emoji.index(packet, 0, len(emoji))
        image = eval(packet)
        display.show(image)