[Python-Dev] BDFL ruling request: should we block forever waiting for high-quality random bits?

Larry Hastings larry at hastings.org
Sat Jun 11 17:58:07 EDT 2016

On 06/11/2016 01:48 PM, Guido van Rossum wrote:
> So I still don't see why we need os.getrandom() -- it has nothing to 
> recommend it over the secrets module (since both won't happen before 3.6).

I have two reasons, neither of which I think are necessarily all that 
persuasive.  Don't consider this an argument--merely some observations.

First, simply as a practical matter: the secrets module is currently 
pure Python.  ISTM that the os module is where we put miscellaneous bits 
of os functionality; getrandom() definitely falls into that category.  
Rather than adding a new _secrets module or whatever it seemed easiest 
just to add it there.

Second, I'd put this under the "consenting adults" rule.  Clearly 
cryptography is a contentious subject with sharply differing opinions.  
There are many, many cryptography libraries available on PyPi; perhaps 
those libraries would like to use getrandom(), or /dev/urandom, or even 
getentropy(), in a way different than how secrets does it.  My thinking 
is, the os module should provide platform support, the secrets module 
should be our codified best-practices, and we encourage everyone to use 
secrets.  I'd go so far as to add that recommendation to the doc *and* 
the docstrings of os.urandom(), random.SystemRandom, and os.getrandom() 
(and os.getentropy()) if we add it.  But by providing the OS 
functionality in a neutral way we allow external cryptographers to write 
what *they* view as best-practices code without wading into 
implementation detalis of secrets, or using ctypes, or whatnot.

But like I said I don't have a strong opinion.  As long as we're not 
adding mysterious flags to os.urandom() I'll probably sit the rest of 
this one out.

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