caesarcipher.py

import string

LETTERS = string.ascii_lowercase

def choose_key():
    while True:
        key = input('Enter the encryption/decryption key (number 1-25): ')
        if key in [str(x) for x in range(1,26)]:
            return int(key)
        print('\nPick a valid key')

def encrypt(text,key,decrypt=False):
    new = []
    for i, c in enumerate(text.lower()):
        if not c in LETTERS:
            new.append(c)
        else:
            shift = key if not decrypt else -key
            new_char = LETTERS[(LETTERS.index(c) + shift) % 26]
            new.append(new_char.upper() if text[i].isupper() else new_char)
            
    return "".join(new)

def choose_method():
    while True:
        method = input('\nDo you want to encrypt or decrypt the text? (\'e\' or \'d\')').lower()
        if method.startswith('e') or method.startswith('d'):
            return method.startswith('d')
            
        print('\nEnter a valid answer')

def create_text():
    while True:
        text = input('\nEnter the text: ')
        if any(x.isalpha() for x in text):
            return text
        print('\nEnter a valid text with at least one letter')

def crack():
    while True:
        answer = input('\nWould you like to Brute Force the Key? (\'y\' or \'n\'): ').lower()
        if answer.startswith('y') or answer.startswith('n'):
            return answer.startswith('y')
        print('\nCome again?')

def brute_force(text):
    for i in range(1,len(LETTERS)):
        print(f'{i}: {encrypt(text,i,decrypt=True)}')

def solve(key):
    return input('What is the key?: ') == str(key)

def replay():
    while True:
        re = input('Go again? (\'y\' or \'n\'): ')
        if re.startswith('y') or re.startswith('n'):
            return re.startswith('y')
        print('Invalid input')

def main_01():

    print('''Welcome to Caeser's Cryptography Castle!
    
    This program is designed to teach encryption concepts as well as Python code.
    Here is a brief walkthrough of how Caesar Cipher encryption works and how it is implemented in this code:
    
    1. The user must first input a text string
    2. The user must then input a numeric key between 1-25
    4. The user will specify whether to use the encryption or decryption algorithm
    5. The program will then shift each letter of the text according to the uder's choice of key (x steps forward for encryption and x steps back for decryption)
    6. This program returns the ciphertext or plain text to the user
    7. The program includes a simple brute-force algorithm that will cycle all possible keys to crack the code, demonstrating the fragility of Ceasar Cipher
    
    I hope this made sense. Enjoy!\n''')
    
    while True:
        
        key = choose_key()
        
        text = create_text()
        
        method = choose_method()
        
        code = encrypt(text,key,decrypt=method)
        
        print(code)
        
        if not method:
            
            if crack():
        
                print('\nLet\'s crack this code...')
        
                brute_force(code)
            
                guess = solve(key)
            
                if guess:
                    print('Correct!')
                else:
                    print('Wrong!')
                
        re = replay()
        
        if not re:
            break

if __name__ == "__main__":
    main()