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

score 60 · Accepted Answer · answered Jul 31 '16 at 11:31

60

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 '16 at 11:31

Daniel

42,087
4
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3

the output object is a byte, how do I get it to be string? – ScipioAfricanus Jul 24 '19 at 02:44
2

@ScipioAfricanus: you have to decode it, with the correct encoding. – Daniel Jul 24 '19 at 07:00

score 11 · Answer 2 · edited May 23 '17 at 11:46

11

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'

edited May 23 '17 at 11:46

Community

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1

answered Jul 31 '16 at 11:31

Saurav Gupta

535
3
11

1

The answer I gave adds the appropriate padding based on length of the encoded string. Please accept the answer if you found it helpful. – Saurav Gupta Jul 31 '16 at 12:58

score 1 · Answer 3 · answered Jul 31 '16 at 11:47

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=

score 0 · Answer 4 · answered Jul 31 '16 at 11:31

0

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'

answered Jul 31 '16 at 11:31

janbrohl

2,626
1
17
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How to decode base64 in python3

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