ciphers.base64_cipher
=====================

.. py:module:: ciphers.base64_cipher


Attributes
----------

.. autoapisummary::

   ciphers.base64_cipher.B64_CHARSET


Functions
---------

.. autoapisummary::

   ciphers.base64_cipher.base64_decode
   ciphers.base64_cipher.base64_encode


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

.. py:function:: base64_decode(encoded_data: str) -> bytes

   Decodes data according to RFC4648.

   This does the reverse operation of base64_encode.
   We first transform the encoded data back to a binary stream, take off the
   previously appended binary digits according to the padding, at this point we
   would have a binary stream whose length is multiple of 8, the last step is
   to convert every 8 bits to a byte.

   >>> from base64 import b64decode
   >>> a = "VGhpcyBwdWxsIHJlcXVlc3QgaXMgcGFydCBvZiBIYWNrdG9iZXJmZXN0MjAh"
   >>> b = "aHR0cHM6Ly90b29scy5pZXRmLm9yZy9odG1sL3JmYzQ2NDg="
   >>> c = "QQ=="
   >>> base64_decode(a) == b64decode(a)
   True
   >>> base64_decode(b) == b64decode(b)
   True
   >>> base64_decode(c) == b64decode(c)
   True
   >>> base64_decode("abc")
   Traceback (most recent call last):
     ...
   AssertionError: Incorrect padding


.. py:function:: base64_encode(data: bytes) -> bytes

   Encodes data according to RFC4648.

   The data is first transformed to binary and appended with binary digits so that its
   length becomes a multiple of 6, then each 6 binary digits will match a character in
   the B64_CHARSET string. The number of appended binary digits would later determine
   how many "=" signs should be added, the padding.
   For every 2 binary digits added, a "=" sign is added in the output.
   We can add any binary digits to make it a multiple of 6, for instance, consider the
   following example:
   "AA" -> 0010100100101001 -> 001010 010010 1001
   As can be seen above, 2 more binary digits should be added, so there's 4
   possibilities here: 00, 01, 10 or 11.
   That being said, Base64 encoding can be used in Steganography to hide data in these
   appended digits.

   >>> from base64 import b64encode
   >>> a = b"This pull request is part of Hacktoberfest20!"
   >>> b = b"https://tools.ietf.org/html/rfc4648"
   >>> c = b"A"
   >>> base64_encode(a) == b64encode(a)
   True
   >>> base64_encode(b) == b64encode(b)
   True
   >>> base64_encode(c) == b64encode(c)
   True
   >>> base64_encode("abc")
   Traceback (most recent call last):
     ...
   TypeError: a bytes-like object is required, not 'str'


.. py:data:: B64_CHARSET
   :value: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'