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Date: Fri, 14 Feb 2014 15:02:20 +0200
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To: Pierre Joye <pierre.php@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] unify entropy source for all php related functions
From: narf@devilix.net (Andrey Andreev)

On Fri, Feb 14, 2014 at 2:26 PM, Pierre Joye <pierre.php@gmail.com> wrote:
>
> On Feb 14, 2014 7:03 PM, "Andrey Andreev" <narf@devilix.net> wrote:
>> ALL sources
>> say that /dev/urandom is both widely used and considered safe for
>> cryptography. Only a select few mention that it could be a bit weaker
>> in specific cases, in theory.
>
> No urandom (and similar) are not crypto safe. Totally not. They are however
> good enough for most usages but crypto safe related tasks like key
> generation and the likes. Any (good) paper mentions this.
>
> Cheers,
> Pierre

So how does openssl_random_pseudo_bytes() work without blocking then?

    $ cat test.php
    <?php
    $crypto_strong = NULL;
    $orandom = openssl_random_pseudo_bytes(32, $crypto_strong);
    var_dump(bin2hex($orandom), $crypto_strong);
    $mrandom = mcrypt_create_iv(32, MCRYPT_DEV_RANDOM);
    var_dump($mrandom);

    $ php test.php
    string(64) "bc10fe2a302039bc0b1ff85b1da53d1b2dc73be515bc1ab9a4a1f8895da7357b"
    bool(true)
    (blocks)

If it doesn't block, it obviously doesn't use (only) /dev/random, yet
it says that the output is crypto-safe. Or is that a bug?

Cheers,
Andrey.