On Tue, Mar 19, 2019 at 3:43 PM Giampaolo Rodola' <g.rod...@gmail.com> wrote:
>
> On Tue, Mar 19, 2019 at 6:21 PM Guido van Rossum <gu...@python.org> wrote:
>
> >> On Tue, Mar 19, 2019 at 10:14 AM Giampaolo Rodola' <g.rod...@gmail.com>
> >> wrote:
> >> Technically you cannot make it 100% safe, only less likely to occur.
> > That seems unnecessarily pedantic. A cryptographic random generator, like
> > the one in the secrets module, *is* safe enough for all practical purposes
> > (with a large margin).
> > [...]
> > Hm, the random sequence (implemented in tempfile._RandomNameSequence) is
> > currently derived from the random module, which is not cryptographically
> > secure. Maybe all we need to do is replace its source of randomness with
> > one derived from the secrets module. That seems a one-line change.
>
> Seems to make sense to me. Currently the random string is 8 chars
> long, meaning (if I'm not mistaken) max 40320 possible combinations:
>
> >>> len(list(itertools.permutations('wuoa736m'))))
> 40320
It's 8 chars taken from a-z0-9_, so there are 37**8 ~= 10**12 possible
names, or ~41 bits.
> We may use 9 chars and get to 362880 and increase "security".
> Regardless, it seems to me the original deprecation warning for
> mktemp() was not really justified and should be removed.
Historically, mktemp variants have caused *tons* of serious security
vulnerabilities. It's not a theoretical issue. See e.g.
https://www.owasp.org/index.php/Insecure_Temporary_File
I believe that if we used sufficient unguessable randomness to
generate the name, then that would resolve the issues and let us
un-deprecate it. Though like Brett I would like to double-check this
with security specialists :-).
This would also simplify the implementation a *lot*, down to just:
def mktemp(suffix='', prefix='tmp', dir=None):
if dir is None:
dir = gettempdir()
return _os.path.join(dir, prefix +
secrets.token_urlsafe(ENTROPY_BYTES) + suffix)
The choice of ENTROPY_BYTES is an interesting question. 16 (= 128
bits) would be a nice "obviously safe" number, and gives 22-byte
filenames. We might be able to get away with fewer, if we had a
plausible cost model for the attack. This is another point where a
security specialist might be helpful :-).
-n
--
Nathaniel J. Smith -- https://vorpus.org
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
https://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
