Using the idea of caesar cipher, we create our own custom caesar cipher.

caesar_custom_encryption.py

"""
Author: Rafeh Qazi
Program: Encryption and Decryption
Resource: http://www.practicalcryptography.com/ciphers/caesar-cipher/
"""

KEY = 17


def caesar_encryption(letter, key):
    """
    Letter in the first 256 ascii is shifted 'key' positions.
    :param letter: str
    :param key: int
    :return: int
    """
    # mod 256 to create a world of [0,255] integers.
    return (ord(letter) + key) % 256


def caesar_decryption(encrypted_letter, key):
    """
    Used to reverse the destruction caused by caesar_encryption.
    :param letter: int
    :param key: int
    :return: str
    """
    return chr((encrypted_letter - key) % 256)


# decrypt(encrypt(x)) should give you back x.
assert caesar_decryption(caesar_encryption('e', 20), 20) == 'e'

encrypted_message = []
for letter in 'bananas':
    encrypted_message.append(caesar_encryption(letter, KEY))

print(encrypted_message)

decrypted_message = []
for encrypted_letter in encrypted_message:
    decrypted_message.append(caesar_decryption(encrypted_letter, KEY))

print(''.join(decrypted_message))