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Date: Tue, 24 Feb 2015 11:08:45 +0000
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To: Pierre Joye <pierre.php@gmail.com>
Cc: Sammy Kaye Powers <me@sammyk.me>, PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] [DISCUSSION] Reliable user-land CSPRNG
From: leight@gmail.com (Leigh)

On 24 February 2015 at 10:55, Pierre Joye <pierre.php@gmail.com> wrote:
> It should use the session.entropy_file setting as it aims to be the exact
> same thing. It also allows custom entropy src (better ones for higher
> demands) as well.

I disagree. We want to take responsibility away from the user to
choose the best source of entropy. The session.entropy_file setting
also does not allow arc4random to be used, which is a source of
cryptographic quality random without using a file descriptor.

In fact I had planned for a future RFC where we allow
session.entropy_file to use using random_bytes(). So the "best" source
is chosen automatically. (If you think there are better sources not
covered by this patch, please let me know, I would like it to be
complete)

There is an aspect of this that has been left for "future work", but
if the list thinks it is important I can implement it for this RFC.
The issue is that on Linux it still does not provide a way of getting
random bytes without using a file descriptor. This is important for a
couple of reasons, 1) It means chroot environments don't require
/dev/*random 2) it prevents fd-exhaustion attacks that force lower
quality randomness. LibreSSL-portable has a very good implementation
of this using the Linux getrandom syscall (Kernel >= 3.17) that I can
phpise and include if we think it is necessary.