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Date: Tue, 17 Jan 2017 14:48:55 +0000
Message-ID: <CAPwsocEpGn=Srep4Mqoue1sE-Y7-JDrDk2o09qNSKyTaSLAQNw@mail.gmail.com>
To: Yasuo Ohgaki <yohgaki@ohgaki.net>
Cc: "internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Improving mt_rand() seed
From: leight@gmail.com (Leigh)

On 16 January 2017 at 07:04, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:
> Hi all,
>
> Since I was about to improve uniqid()'s entropy by replacing
> php_combined_lcg() to php_random_int(), I spent time to check other places
> that could be a problem.
>
> mt_rand()'s is seeded as follows by default.
>
> ext/standard/php_rand.h
> #ifdef PHP_WIN32
> #define GENERATE_SEED() (((zend_long) (time(0) * GetCurrentProcessId())) ^
> ((zend_long) (1000000.0 * php_combined_lcg())))
> #else
> #define GENERATE_SEED() (((zend_long) (time(0) * getpid())) ^ ((zend_long)
> (1000000.0 * php_combined_lcg())))
> #endif
>
> We know this kind of seed is guessable. i.e. Our session id is compromised
> by this kind of code.

mt_rand is not advertised as crypto-quality.

Where do you think mt_rand is used in session id generation?

>
> Although it would be rare that raw mt_rand() value is exposed, but
> guessable value is guessable. I'm going to replace the seeding code by
> simple php_random_int() call.
>
> Any comments?
>
> Regards,
>
> --
> Yasuo Ohgaki
> yohgaki@ohgaki.net