Make a unique filesystem path, without creating the file

Steven D'Aprano steve at pearwood.info
Mon Feb 22 19:33:09 EST 2016


On Tue, 23 Feb 2016 06:32 am, Marko Rauhamaa wrote:

> Jon Ribbens <jon+usenet at unequivocal.co.uk>:
> 
>> Suppose you had code like this:
>>
>>   filename = binascii.hexlify(os.urandom(16)).decode("ascii")
>>
>> Do we really think that is insecure or that there are any practical
>> attacks against it? It would be basically the same as saying that
>> urandom() is broken, surely?
> 
> urandom() is not quite random and so should not be considered
> cryptographically airtight.
> 
> Under Linux, /dev/random is the way to go when strong security is
> needed. Note that /dev/random is a scarce resource on ordinary systems.

That's actually incorrect, but you're not the only one to have been mislead
by the man pages.

http://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers/


On non-Linux Unixes, the difference between urandom and random is mostly, or
entirely, gone, in favour of urandom's non-blocking behaviour. And it's a
myth that the output of random is "more random" or "more pure" than
urandom's. In reality, on Linux both urandom and random use exactly the
same CSPRNG.

See also:

http://www.2uo.de/myths-about-urandom/


for a good explanation of how random and urandom actually work on Linux.






-- 
Steven



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