Tukukkk

With the code that I am using, every time there is a "?" on data of the encoded message I get an error back "Incorrect Padding". When using a decoder online I get the correct value for both value1 and value2 below, but for value2 where there should be a "?" I get an exception instead.

The code is:

value1 = "Y29udGludWENCg=="

expected1 = b'continuarn'

value2 = "Y29udGludWE_DQo="

expected2 = b'continua?rn'



data1 = base64.b64decode(value1)

assert data1 == expected1

data2 = base64.b64decode(value2)

assert data2 == expected2

Decoding value2 throws a binascii.Error: Incorrect padding exception, but the data has the right amount of padding (the length of value2 is a multiple of 4).

You do not have standard Base64 data, you have URL-safe base64 data.

Base64 normally uses letters, digits and / and + characters, but the latter two carry special meaning in URLs, so an alternative Base64url encoding is used that uses - and _ characters instead.

Use the base64.urlsafe_b64decode() function to decode these strings:

data2 = base64.urlsafe_b64decode(value2)

Demo:

>>> import base64

>>> value2 = "Y29udGludWE_DQo="

>>> base64.urlsafe_b64decode(value2)

b'continua?rn'