py2 to 3 base64 issues

[MRAB]

On 2019-08-09 19:21, Larry Martell wrote:
> On Fri, Aug 9, 2019 at 12:23 PM Chris Angelico <rosuav at gmail.com> wrote:
>>
>> On Sat, Aug 10, 2019 at 2:09 AM Larry Martell <larry.martell at gmail.com> wrote:
>> >
>> > I have some python 2 code:
>> >
>> > def decode(key, string):
>> >        decoded_chars = []
>> >        string = base64.urlsafe_b64decode(string)
>> >        for i in range(len(string)):
>> >            key_c = key[i % len(key)]
>> >            encoded_c = chr(abs(ord(string[i]) - ord(key_c) % 256))
>> >            decoded_chars.append(encoded_c)
>> >        decoded_string = "".join(decoded_chars)
>> >        return decoded_string
>> >
>> > and if I call it like this in py2 it works as expected:
>> >
>> > s = 'V3NYVY95iImnnJWCmqphWFFzU1qvqsV6x83Mxa7HipZitZeMxbe709jJtbfW6Y6blQ=='
>> > key = '!@#$VERYsecRet)('
>> > decode(key, s)
>> >
>> > In py3 it fails with
>> >
>> > TypeError: ord() expected string of length 1, but int found
>> >
>> > I know that in py3 base64.urlsafe_b64decode is returning bytes not
>> > chars and that is what that is happening, and I thought the solution
>> > would be to decode it, but what codec would I use for this?
>>
>> Should be safe to decode it as ASCII, since Base 64 uses strictly
>> ASCII characters. But since you're working with bytes, possibly all
>> you need to do is remove the ord calls, since ord(u"x") is the same as
>> b"x"[0]. You'll then need to change the join() at the end to be just
>> "decoded_string = bytes(decoded_chars)", or possibly that followed by
>> a decode-to-text, depending on how your data works.
> 
> That doesn't work:
> 
> -> encoded_c = chr(abs(string[i] - ord(key_c) % 256))
> (Pdb) n
> TypeError: "unsupported operand type(s) for -: 'str' and 'int'"
> (Pdb) string
> 'WsXU\x8fy\x88\x89\xa7\x9c\x95\x82\x9a\xaaaXQsSZ\xaf\xaa\xc5z\xc7\xcd\xcc\xc5\xae\xc7\x8a\x96b\xb5\x97\x8c\xc5\xb7\xbb\xd3\xd8\xc9\xb5\xb7\xd6\xe9\x8e\x9b\x95'
> (Pdb) string[i]
> '\x8f'
> (Pdb) bytes(string[i])
> '\x8f'
> (Pdb) type(string[i])
> <type 'str'>
> 
'string' is a 'str' (in Python 2 that would've been 'unicode'), so 
string[i] is also a 'str' and you need 'ord':

encoded_c = chr(abs(ord(string[i]) - ord(key_c) % 256))