Share Something Personal – Encrypted!

In this activity, you will examine the effects of encrypting your messages on a sniffing cyberattack.  You will leave the sniffer micro:bit’s script the same receiver script, but add Caesar cipher encryption to the transmitter and intended receiver scripts.

Cybersecurity: Encryption Intro has activities introducing the Caesar cipher if you want to learn more about it.

• Repeat the setup from the previous activity, Share Something Personal -Unencrypted.
• Enter, name, save, and flash the radio_send_images_caesar transmitter script into the micro:bit you chose as the transmitter—the one sending the HAPPY/SAD/ANGRY images.  
• The micro:bit you chose to be the sniffer should still be running the radio_receive_images  receiver script from the previous activity.
• Enter, name, save, and flash the radio_receive_images_caesar receiver script into the micro:bit you chose to be the intended receiver.  The receiver script is below the transmitter script.
• Remember, if you only have two micro:bit modules, you can enter flash, save and test the intended receiver script after testing the sniffer.

Transmitter Script: radio_send_images_caesar

# radio_send_images_caesar.py

from microbit import *
import radio

''' Function converts plaintext to ciphertext using key '''

def caesar(key, word):
    alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    result = "

    for letter in word:
        
        letter = letter.upper()
        index = ( alpha.find(letter) + key ) % 26
        result = result + alpha[index]
    
    return result

''' Script starts from here... '''

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

sleep(1000)

string_list = ["HAPPY", "SAD", "ANGRY"]

while True:
    
    for packet in string_list:
        print("packet:", packet)
        display.show(getattr(Image, packet))
        packet = caesar(3, packet)
        print("Send encrypted:", packet)
        radio.send(packet)
        sleep(2500)

Receiver Script: radio_receive_images_caesar

# radio_receive_images_caesar.py

from microbit import *
import radio

''' Function converts plaintext to ciphertext using key '''

def caesar(key, word):
    alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    result = "

    for letter in word:
        
        letter = letter.upper()
        index = ( alpha.find(letter) + key ) % 26
        result = result + alpha[index]
    
    return result

''' Script starts from here... '''

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

sleep(1000)

while True:
    
    packet = radio.receive()

    if packet:
        print("Receive encrypted:", packet)
        packet = caesar(-3, packet)
        print("packet:", packet)
        display.show(getattr(Image, packet))

Test Sniffer and Intended Receiver Responses

• Click the Show serial button in any of the browsers where the serial monitor is not already open.  
• Compare the intended receiver micro:bit’s terminal to the sniffer’s terminal.  
• In this case, the KDSSB instead of HAPPY should cause an exception.  You will correct this in the upcoming activities.
• Compare the intended receiver micro:bit’s LED display to the sniffers as well.
• Reminder: If you are only using two micro:bit modules, test the sniffer first while it’s running the previous activity’s receiver script.  Then, load this activity’s receiver script and compare the difference.