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Date: Thu, 20 Oct 2016 18:44:03 +0900
Message-ID: <CAGa2bXazQ74DJgwBh-AuysfQ1T2=MaEfGYytsm4e4w5sPHHqOw@mail.gmail.com>
To: Kalle Sommer Nielsen <kalle@php.net>
Cc: Anatol Belski <anatol.php@belski.net>, Joe Watkins <pthreads@pthreads.org>, 
	Niklas Keller <me@kelunik.com>, Leigh <leight@gmail.com>, 
	PHP Internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] Re: [RFC][DISCUSSION] Improve uniqid() uniqueness
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

Hi Kalle,

I forgot to mention one more thing.

On Thu, Oct 20, 2016 at 6:28 PM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:
> Warnings are based on following facts.
>
> uniqid(); // without entropy
>
> usleep(1) is called to get unique timestamp, but NTP can disturb and
> uniqid() can result in the same ID.
>
> uniqid('', TRUE); // with entropy
>
> It's better, but entropy is based on system timestamp and there is no
> usleep(1), so uniqid() is more sensitive to system clock adjustment by
> NTP, and uniqid() can result in the same ID.
>
> Collision is unlikely, but it not that unlikely with true CSPRNG based
> entropy. Therefore, I made warning a little strong. With CSPRNG, we
> may use more gentle warning. IMO.

Application requires unique ID under across multi process/thread
tasks, it will have more chance to have collided unique ID.

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net