How to decode base64 in python3

Question

I have a base64 encrypt code, and I can't decode in python3.5

import base64 code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA" # Unencrypt is 202cb962ac59075b964b07152d234b70 base64.b64decode(code)

Result:

binascii.Error: Incorrect padding

But same website(base64decode) can decode it,

Please anybody can tell me why, and how to use python3.5 decode it?

Thanks

Daniel · Accepted Answer · 2016-07-31 11:31:47Z

65

Base64 needs a string with length multiple of 4. If the string is short, it is padded with 1 to 3 =.

import base64 code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA=" base64.b64decode(code) # b'admin:202cb962ac59075b964b07152d234b70'

answered Jul 31, 2016 at 11:31

Daniel

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2 Comments

ScipioAfricanus Over a year ago

the output object is a byte, how do I get it to be string?

Daniel Over a year ago

@ScipioAfricanus: you have to decode it, with the correct encoding.

Community · Accepted Answer · 2017-05-23 11:46:04Z

According to this answer, you can just add the required padding.

code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA" b64_string = code b64_string += "=" * ((4 - len(b64_string) % 4) % 4) base64.b64decode(b64_string) #'admin:202cb962ac59075b964b07152d234b70'

The answer I gave adds the appropriate padding based on length of the encoded string. Please accept the answer if you found it helpful.

user2853437 · Accepted Answer · 2016-07-31 11:47:21Z

I tried the other way around. If you know what the unencrypted value is:

>>> import base64 >>> unencoded = b'202cb962ac59075b964b07152d234b70' >>> encoded = base64.b64encode(unencoded) >>> print(encoded) b'MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA=' >>> decoded = base64.b64decode(encoded) >>> print(decoded) b'202cb962ac59075b964b07152d234b70'

Now you see the correct padding. b'MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA=

janbrohl · Accepted Answer · 2016-07-31 11:31:47Z

It actually seems to just be that code is incorrectly padded (code is incomplete)

import base64 code = "YWRtaW46MjAyY2I5NjJhYzU5MDc1Yjk2NGIwNzE1MmQyMzRiNzA" base64.b64decode(code+"=")

returns b'admin:202cb962ac59075b964b07152d234b70'

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