[Python-ideas] Pre-PEP Adding A Secrets Module To The Standard Library

Steven D'Aprano steve at pearwood.info
Tue Sep 22 19:47:55 CEST 2015

On Tue, Sep 22, 2015 at 10:26:13AM +0200, Jonas Wielicki wrote:
> On 20.09.2015 02:27, Chris Angelico wrote:
> >>> Also, if you ask for 4 bytes from token_hex, do you get 4 hex
> >>> digits or 8 (four bytes of entropy)?

I think the answer there has to be 8. I interpret Tim's reference to 
"same" as that the intent of token_hex is to call os.urandom(nbytes), 
then convert it to a hex string. So the implementation might be as 
simple as:

def token_hex(nbytes):
    return binascii.hexlify(os.urandom(nbytes))

modulo a call to .decode('ascii') if we want it to return a string.

One obvious question is, how many bytes is enough? Perhaps we should set 
a default value for nbytes, with the understanding that the default 
value will increase in the future.

> > My personal preference for shed colour: token_bytes returns a
> > bytestring, its length being the number provided. All the others
> > return Unicode strings, their lengths again being the number provided.
> > So they're all text bar the one that explicitly says it's in bytes.
> My personal preference would be for the number of bytes to rather
> reflect the entropy in the result. This would be a safer use when
> migrating from using e.g. token_url to token_alpha with the base32
> alphabet [1], for example because you want to have better readable tokens.
> Speaking of which, a token_base32 would probably make sense, too.

Oh oh, scope creep already! And so it begins... *wink*

What you are referring to isn't the standard base32, which already 
exists in the stdlib (in base64.py, together with base16). It's is 
referred to by its creators as z-base-32, and the reasoning they give 
seems sound. It's not intended as a replacement for RFC-3458 base32, but 
an alternative.

If the std lib already included a z-base-32 implementation, I would be 
happy to include token_zbase32 in the same spirit as token_base64. But 
it doesn't. So first you would have to convince somebody to add zbase32 
to the standard library.

>    [1]: https://philzimmermann.com/docs/human-oriented-base-32-encoding.txt


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