[Python-Dev] Our responsibilities (was Re: BDFL ruling request: should we block forever waiting for high-quality random bits?)

Nick Coghlan ncoghlan at gmail.com
Thu Jun 16 11:39:48 EDT 2016

On 16 June 2016 at 05:50, Paul Moore <p.f.moore at gmail.com> wrote:
> On 16 June 2016 at 12:34, Donald Stufft <donald at stufft.io> wrote:
>> [1] I don’t think using os.urandom is incorrect to use for security sensitive
>>     applications and I think it’s a losing battle for Python to try and fight
>>     the rest of the world that urandom is not the right answer here.
>> [2] python-dev tends to favor not breaking “working” code over securing existing
>>     APIs, even if “working” is silently doing the wrong thing in a security
>>     context. This is particularly frustrating when it comes to security because
>>     security is by it’s nature the act of taking code that would otherwise
>>     execute and making it error, ideally only in bad situations, but this
>>     “security’s purpose is to make things break” nature clashes with python-dev’s
>>     default of not breaking “working” code in a way that is personally draining
>>     to me.
> Should I take it from these two statements that you do not believe
> that providing *new* APIs that provide better security compared to a
> backward compatible but flawed existing implementation is a reasonable
> approach? And specifically that you don't agree with the decision to
> provide the new "secrets" module as the recommended interface for
> getting secure random numbers from Python?
> One of the aspects of this debate that I'm unclear about is what role
> the people arguing that os.urandom must change see for the new secrets
> module.

The secrets module is great for new code that gets to ignore any
version of Python older than 3.6 - it's the "solve this problem for
the next generation of developers" answer. All of the complicated
"this API is safe for that purpose, this API isn't" discussions get
replaced by "do the obvious thing" (i.e. use random for simulations,
secrets for security).

The os.urandom() debate is about taking the current obvious (because
that's what the entire security community is telling you to do) low
level way to do it and categorically eliminating any and all caveats
on its correctness. Not "it's correct if you use these new flags that
are incompatible with older Python versions". Not "it's not correct
anymore, use a different API". Just "it's correct, and the newer your
Python runtime, the more correct it is".


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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