Apply Caesar Cipher to Words from Serial Monitor

This script places the Caesar cipher in a loop.  This will allow you to type entire words for encrypting/decrypting!  It still also works with single characters if that’s all you want to encrypt.  

Example script: caesar_terminal_words

• Change project’s name from  caesar_terminal_letters to caesar_terminal_words.
• Update it to match the script below
• Save the modified script.
• Click the Send to micro:bit button.

# caesar_terminal_words
 
from microbit import *
 
sleep(1000)
 
print("Set your keyboard to CAPS LOCK.")
print()
 
while True:
    text = input("Enter key: ")
    key = int(text)
 
    word = input("Enter character(s) in A...Z range: ")
 
    alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    result = "
 
    for letter in word:
        
        letter = letter.upper()
        index = ( alpha.find(letter) + key ) % 26
        result = result + alpha[index]
 
    print("result:", result)
    print()

• Follow the prompts in the serial monitor.  Valid keys are from -25 to 25.
• Try encrypting HELLO with the key set to 5.
• Try decrypting MJQQT with the key set to -5.
• Write a short message for your friend or lab partner and give them the key to decrypt it.

How caesar_terminal_words Works

Inside the while True loop, the script stores a number you enter into an int variable named key.  Then, it stores a word you type in a string variable named word.

    text = input("Enter key: ")
    key = int(text)

    word = input("Enter character(s) in A...Z range: ")

In addition to the alpha (alphabet) string, a second empty string named result is created to store the result.

    alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    result = "

After that, a for… loop goes through each letter in the plaintext string.  After making sure the letter is upper-case, it applies the Caesar cipher with two lines.  The first finds the index of the new character with index = ( alpha.find(letter) + key ) % 26.  The second adds the character to whatever is already in the ciphertext string with result = result + alpha[index].

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

Before repeating the loop, the ciphertext is printed to the terminal.

    print("result: ", result)