main.py

#This program is the starter code for the Cracking Caesar's Cipher Project. 
# This code is inspired by Cracking Codes with Python: An Introduction to Building and Breaking Ciphers by Al Sweigart https://www.nostarch.com/crackingcodes (BSD Licensed)

import string

# Global variables
initialPosition = 0
shiftedPosition = 0

lettersLower = string.ascii_lowercase
lettersUpper = string.ascii_uppercase
numbers = string.digits
symbols = string.punctuation
possibleCharacters = lettersLower + lettersUpper + numbers + symbols


# Define the function called decrypt
def decrypt():
  global shiftedPosition
  shiftedPosition = initialPosition - key

# Define the function called wraparound
def wraparound():
  global shiftedPosition
  if shiftedPosition < 0:
    shiftedPosition = shiftedPosition + len(possibleCharacters)

# Run code

# Introduction
print("Welcome! This program will crack the Caesar cipher and figure out any secret message that was encrypted with the Caesar cipher. \n\nType in your encrypted message and this program will print all of the key possibilities of your message below.")

# Receive user input
initialMessage = input("\nWhat is your encrypted message? ")
input("\nPress enter to generate all of the key possibilities for your encrypted message.\n")

# Cycle through all possible keys
for key in range(len(possibleCharacters)):
  shiftedMessage = ""
  
  # Decrypt the message
  for character in initialMessage:
    if character in possibleCharacters:
      initialPosition = possibleCharacters.find(character)
      decrypt()
      wraparound()
  
      shiftedMessage = shiftedMessage + possibleCharacters[shiftedPosition]
  
    else: 
      shiftedMessage = shiftedMessage + character
  
  # Print the shifted message
  print("Key #%s: %s" % (key, shiftedMessage))
  

# Closing message
print("\nNow scroll through all of the key possibilities above and find the readable plaintext message.")