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copied!<p>First, it seems that you are using plain <code>md5()</code> to store user passwords... <strong>DO NOT DO THAT, IT IS A <i>SECURITY RISK</i>.</strong> <i>You are putting your users and yourself at risk.</i> Use key strengthening with a stronger hash algorithm or bcrypt. <a href="https://stackoverflow.com/questions/6340105/how-can-we-create-a-fairly-secure-password-hash-in-php/6340197#6340197">See this answer for more information</a>.</p> <hr> <p>It seems that you are actually trying to generate a <code>nonce</code> for email activation.</p> <p>If anything, a <a href="http://en.wikipedia.org/wiki/UUID" rel="nofollow noreferrer">Universally Unique IDentifier (UUID)</a> will do the job. It has a very low change of collision and allows for 3 × 10<sup>38</sup> unique values (once a value is used, you can reuse it for another user anyway for your use case).</p> <p>You can use this function I wrote to generate UUIDs in PHP. What you want for your needs is a v4 UUID.</p> <pre><code>function UUIDv4() { $bytes = str_split(crypto_random_bytes(16)); // Set UUID Version Number $bytes[6] = $bytes[6] & "\x0f" | "\x40"; // Set UUID DCE1.1 varient $bytes[8] = $bytes[8] & "\x3f" | "\x80"; $uuid = bin2hex(implode($bytes)); return sprintf('%08s-%04s-%04s-%04s-%12s', // 32 bits for "time_low" substr($uuid, 0, 8), // 16 bits for "time_mid" substr($uuid, 8, 4), // 16 bits for "time_hi_and_version", // four most significant bits holds version number 4 substr($uuid, 12, 4), // 16 bits, 8 bits for "clk_seq_hi_res", // 8 bits for "clk_seq_low", // two most significant bits holds zero and one for variant DCE1.1 substr($uuid, 16, 4), // 48 bits for "node" substr($uuid, 20, 12) ); } function crypto_random_bytes($count) { static $randomState = null; $bytes = ''; if(function_exists('openssl_random_pseudo_bytes') && (strtoupper(substr(PHP_OS, 0, 3)) !== 'WIN')) { // OpenSSL slow on Win $bytes = openssl_random_pseudo_bytes($count); } if($bytes === '' && is_readable('/dev/urandom') && ($hRand = @fopen('/dev/urandom', 'rb')) !== FALSE) { $bytes = fread($hRand, $count); fclose($hRand); } if(strlen($bytes) < $count) { $bytes = ''; if($randomState === null) { $randomState = microtime(); if(function_exists('getmypid')) { $randomState .= getmypid(); } } for($i = 0; $i < $count; $i += 16) { $randomState = md5(microtime() . $randomState); if (PHP_VERSION >= '5') { $bytes .= md5($randomState, true); } else { $bytes .= pack('H*', md5($randomState)); } } $bytes = substr($bytes, 0, $count); } return $bytes; } </code></pre>

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