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py2 to 3 base64 issues


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'>