Unicode Shift Cipher

#!/usr/bin/python3
# -*- coding: utf-8 -*-

import random

code_points = {
    'english': (32, 126),
    'burmese': (1024, 1279),
    'arabic': (1536, 1791),
    'canadian_aboriginal': (5120, 5759),
    'chinese': (19968, 40869),
    'korean': (44032, 55216),
}


def unicodeCipher(
    message,
    mode,
    plaintext=(32, 126),
    ciphertext=(19968, 40869),
    ):
    """Unicode shift cipher

    Args:
        message (str): The plaintext to be enciphered.
        mode (str): 'e' for encryption, 'd' for encryption.
        plaintext (tuple): Tuple of the plaintext unicode start and end points. Defaults to ASCII plaintext. You can use one of the strings defined in the code_points dictionary.
        ciphertext (tuple): Tuple of the ciphertext unicode start and end points. Defaults to Chinese. You can use one of the strings defined in the code_points dictionary.
    """

    if mode != 'e' and mode != 'd':
        raise ValueError('Mode must be e for encryption or d for decryption')

    if type(plaintext) is str:
        plaintext = code_points[plaintext]
    if type(ciphertext) is str:
        ciphertext = code_points[ciphertext]

    plaintext_range = plaintext[1] - plaintext[0] + 1
    ciphertext_range = ciphertext[1] - ciphertext[0]

    ciphertext_size = ciphertext_range / plaintext_range

    if ciphertext_size < 1:
        raise ValueError('Ciphertext code point range needs to be larger than plaintext code point range')

    output = []

    if mode == 'e':
        for letter in message:
            unicode_decimal = ord(letter) - plaintext[0] + ciphertext[0] + plaintext_range * int(random.uniform(0, ciphertext_size) - 1)
            output.append(chr(unicode_decimal))

    elif mode == 'd':
        for letter in message:
            unicode_decimal = (ord(letter) - ciphertext[0]) % plaintext_range + plaintext[0]
            output.append(chr(unicode_decimal))

    return ''.join(output)


if __name__ == '__main__':
    example_plaintext = 'This is a Unicode cipher'

    example_ciphertext = unicodeCipher(example_plaintext, 'e', 'english', 'korean')
    print('Ciphertext: ' + example_ciphertext)

    print('Decrypted: ' + unicodeCipher(example_ciphertext, 'd', 'english', 'korean'))