* * 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 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); }