ciphers.xtea
============

.. py:module:: ciphers.xtea

.. autoapi-nested-parse::

   XTEA (eXtended Tiny Encryption Algorithm) is a block cipher designed to
   correct weaknesses in TEA. It was published by David Wheeler and Roger
   Needham in 1997. XTEA operates on 64-bit blocks with a 128-bit key and
   uses a Feistel network with a recommended 64 rounds.

   It's still found in embedded systems and game networking protocols due
   to its simplicity and small code footprint.

   Reference: https://en.wikipedia.org/wiki/XTEA



Attributes
----------

.. autoapisummary::

   ciphers.xtea.DELTA
   ciphers.xtea.MASK


Functions
---------

.. autoapisummary::

   ciphers.xtea.xtea_decrypt
   ciphers.xtea.xtea_encrypt


Module Contents
---------------

.. py:function:: xtea_decrypt(block: bytes, key: bytes, num_rounds: int = 64) -> bytes

   Decrypt a single 64-bit block using XTEA.

   :param block: 8 bytes of ciphertext
   :param key: 16 bytes (128-bit key)
   :param num_rounds: number of Feistel rounds (default 64)
   :return: 8 bytes of plaintext

   Roundtrip test -- encrypt then decrypt returns original plaintext:
   >>> key = b'\x00' * 16
   >>> plaintext = b'\x00' * 8
   >>> xtea_decrypt(xtea_encrypt(plaintext, key), key) == plaintext
   True

   >>> msg = b'hello!!!'
   >>> k = b'sixteenbyteskey!'
   >>> xtea_decrypt(xtea_encrypt(msg, k), k) == msg
   True

   >>> xtea_decrypt(b'short', key)
   Traceback (most recent call last):
       ...
   ValueError: block must be 8 bytes

   >>> xtea_decrypt(b'\x00' * 8, b'short')
   Traceback (most recent call last):
       ...
   ValueError: key must be 16 bytes


.. py:function:: xtea_encrypt(block: bytes, key: bytes, num_rounds: int = 64) -> bytes

   Encrypt a single 64-bit block using XTEA.

   :param block: 8 bytes of plaintext
   :param key: 16 bytes (128-bit key)
   :param num_rounds: number of Feistel rounds (default 64)
   :return: 8 bytes of ciphertext

   >>> key = b'\x00' * 16
   >>> plaintext = b'\x00' * 8
   >>> ciphertext = xtea_encrypt(plaintext, key)
   >>> ciphertext.hex()
   'fc924d124ad0ed50'

   >>> xtea_encrypt(b'hello!!!', b'sixteenbyteskey!')
   b'u\x8d\x00\x17c\xb8\xf0*'

   >>> xtea_encrypt(b'short', key)
   Traceback (most recent call last):
       ...
   ValueError: block must be 8 bytes

   >>> xtea_encrypt(plaintext, b'short')
   Traceback (most recent call last):
       ...
   ValueError: key must be 16 bytes


.. py:data:: DELTA
   :value: 2654435769


.. py:data:: MASK
   :value: 4294967295