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

[Robert Kern]

On 2015-09-21 17:22, Steven D'Aprano wrote:
> On Sun, Sep 20, 2015 at 09:00:08AM +0300, Serhiy Storchaka wrote:
>> On 20.09.15 02:40, Tim Peters wrote:

>>>   Token functions
>>>      .token_bytes(nbytes)
>>>          another name for os.urandom()
>>>      .token_hex(nbytes)
>>>          same, but return string of ASCII hex digits
>>>      .token_url(nbytes)
>>>          same, but return URL-safe base64-encoded ASCII
>>>      .token_alpha(alphabet, nchars)
>>>          string of `nchars` characters drawn uniformly
>>>          from `alphabet`
>>
>> token_hex(nbytes) == token_alpha('0123456789abcdef', nchars) ?
>> token_url(nbytes) == token_alpha(
>>      'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_',
>>       nchars) ?
>
> They may be reasonable implementations for the functions, but simple as
> they are, I think we still want to provide them as named functions
> rather than expect the user to write things like the above. If they're
> doing it more than once, they'll want to write a helper function, we
> might as well provide that for them.

Actually, I don't think those are the semantics that Tim intended. Rather, 
token_hex(nbytes) would return a string twice as long as nbytes. The idea is 
that you want to get nbytes-worth of random bits, just encoded in a common 
"safe" format. Similarly, token_url(nbytes) would get nbytes of random bits then 
base64-encode it, not just pick nbytes characters from a URL-safe list of 
characters. This makes it easier to reason about how much entropy you are 
actually using.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco