def encrypt(message, key): encrypted_message = "" for char in message: if char.isalpha(): if char.isupper(): encrypted_char = chr((ord(char) + key - 65) % 26 + 65) else: encrypted_char = chr((ord(char) + key - 97) % 26 + 97) else: encrypted_char = char encrypted_message += encrypted_char return encrypted_message

def decrypt(encrypted_message, key): decrypted_message = "" for char in encrypted_message: if char.isalpha(): if char.isupper(): decrypted_char = chr((ord(char) - key - 65) % 26 + 65) else: decrypted_char = chr((ord(char) - key - 97) % 26 + 97) else: decrypted_char = char decrypted_message += decrypted_char return decrypted_message

Example usage

message = "Hello, World!" key = 3

encrypted = encrypt(message, key) print("Encrypted message:", encrypted)

decrypted = decrypt(encrypted, key) print("Decrypted message:", decrypted)