ciphers.base64

Attributes

B64_CHARSET

Functions

base64_decode(→ bytes)	Decodes data according to RFC4648.
base64_encode(→ bytes)	Encodes data according to RFC4648.

Module Contents

ciphers.base64.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

ciphers.base64.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'

ciphers.base64.B64_CHARSET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'