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<?php
/*
* Author:
* George Argyros <argyros.george@gmail.com>
*
* Copyright (c) 2012, George Argyros
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of the <organization> nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL GEORGE ARGYROS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*
*
* The function is providing, at least at the systems tested :),
* $len bytes of entropy under any PHP installation or operating system.
* The execution time should be at most 10-20 ms in any system.
*/
function secure_random_bytes($len = 10)
{
/*
* Our primary choice for a cryptographic strong randomness function is
* openssl_random_pseudo_bytes.
*/
$SSLstr = '4'; // http://xkcd.com/221/
if (function_exists('openssl_random_pseudo_bytes') &&
(substr(PHP_VERSION, 0, 3) == '5.4' && version_compare(PHP_VERSION, '5.4.44') >= 0) ||
(substr(PHP_VERSION, 0, 3) == '5.5' && version_compare(PHP_VERSION, '5.5.28') >= 0) ||
(version_compare(PHP_VERSION, '5.6.12') >= 0))
{
$SSLstr = openssl_random_pseudo_bytes($len, $strong);
if ($strong) {
return $SSLstr;
}
}
/*
* If mcrypt extension is available then we use it to gather entropy from
* the operating system's PRNG. This is better than reading /dev/urandom
* directly since it avoids reading larger blocks of data than needed.
* Older versions of mcrypt_create_iv may be broken or take too much time
* to finish so we only use this function with PHP 5.3.7 and above.
* @see https://bugs.php.net/bug.php?id=55169
*/
if (function_exists('mcrypt_create_iv') &&
(version_compare(PHP_VERSION, '5.3.7') >= 0 ||
substr(PHP_OS, 0, 3) !== 'WIN')) {
$str = mcrypt_create_iv($len, MCRYPT_DEV_URANDOM);
if ($str !== false) {
return $str;
}
}
/*
* No build-in crypto randomness function found. We collect any entropy
* available in the PHP core PRNGs along with some filesystem info and memory
* stats. To make this data cryptographically strong we add data either from
* /dev/urandom or if its unavailable, we gather entropy by measuring the
* time needed to compute a number of SHA-1 hashes.
*/
$str = '';
$bits_per_round = 2; // bits of entropy collected in each clock drift round
$msec_per_round = 400; // expected running time of each round in microseconds
$hash_len = 20; // SHA-1 Hash length
$total = $len; // total bytes of entropy to collect
$handle = @fopen('/dev/urandom', 'rb');
if ($handle && function_exists('stream_set_read_buffer')) {
@stream_set_read_buffer($handle, 0);
}
do
{
$bytes = ($total > $hash_len)? $hash_len : $total;
$total -= $bytes;
//collect any entropy available from the PHP system and filesystem
$entropy = rand() . uniqid(mt_rand(), true) . $SSLstr;
$entropy .= implode('', @fstat(@fopen( __FILE__, 'r')));
$entropy .= memory_get_usage() . getmypid();
$entropy .= serialize($_ENV) . serialize($_SERVER);
if (function_exists('posix_times')) {
$entropy .= serialize(posix_times());
}
if (function_exists('zend_thread_id')) {
$entropy .= zend_thread_id();
}
if ($handle) {
$entropy .= @fread($handle, $bytes);
} else {
// Measure the time that the operations will take on average
for ($i = 0; $i < 3; $i++)
{
$c1 = get_microtime();
$var = sha1(mt_rand());
for ($j = 0; $j < 50; $j++) {
$var = sha1($var);
}
$c2 = get_microtime();
$entropy .= $c1 . $c2;
}
// Based on the above measurement determine the total rounds
// in order to bound the total running time.
$rounds = (int) ($msec_per_round * 50 / (int) (($c2 - $c1) * 1000000));
// Take the additional measurements. On average we can expect
// at least $bits_per_round bits of entropy from each measurement.
$iter = $bytes * (int) (ceil(8 / $bits_per_round));
for ($i = 0; $i < $iter; $i++)
{
$c1 = get_microtime();
$var = sha1(mt_rand());
for ($j = 0; $j < $rounds; $j++) {
$var = sha1($var);
}
$c2 = get_microtime();
$entropy .= $c1 . $c2;
}
}
// We assume sha1 is a deterministic extractor for the $entropy variable.
$str .= sha1($entropy, true);
} while ($len > strlen($str));
if ($handle) {
@fclose($handle);
}
return substr($str, 0, $len);
}
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