/** * @brief Generates a Universally Unique IDentifier, version 4. * * This function generates a truly random UUID. The built in CakePHP String::uuid() function * is not cryptographically secure. You should uses this function instead. * * @see http://tools.ietf.org/html/rfc4122#section-4.4 * @see http://en.wikipedia.org/wiki/UUID * @return {string} A UUID, made up of 32 hex digits and 4 hyphens. */ static function uuid() { if (!self::$urand) { self::$urand = @fopen('/dev/urandom', 'rb'); } $pr_bits = false; if (is_resource(self::$urand)) { $pr_bits .= @fread(self::$urand, 16); } if (!$pr_bits) { $fp = @fopen('/dev/urandom', 'rb'); if ($fp !== false) { $pr_bits .= @fread($fp, 16); @fclose($fp); } else { // If /dev/urandom isn't available (eg: in non-unix systems), use mt_rand(). $pr_bits = ""; for ($cnt = 0; $cnt < 16; $cnt++) { $pr_bits .= chr(mt_rand(0, 255)); } } } $time_low = bin2hex(substr($pr_bits, 0, 4)); $time_mid = bin2hex(substr($pr_bits, 4, 2)); $time_hi_and_version = bin2hex(substr($pr_bits, 6, 2)); $clock_seq_hi_and_reserved = bin2hex(substr($pr_bits, 8, 2)); $node = bin2hex(substr($pr_bits, 10, 6)); /** * Set the four most significant bits (bits 12 through 15) of the * time_hi_and_version field to the 4-bit version number from * Section 4.1.3. * @see http://tools.ietf.org/html/rfc4122#section-4.1.3 */ $time_hi_and_version = hexdec($time_hi_and_version); $time_hi_and_version = $time_hi_and_version >> 4; $time_hi_and_version = $time_hi_and_version | 0x4000; /** * Set the two most significant bits (bits 6 and 7) of the * clock_seq_hi_and_reserved to zero and one, respectively. */ $clock_seq_hi_and_reserved = hexdec($clock_seq_hi_and_reserved); $clock_seq_hi_and_reserved = $clock_seq_hi_and_reserved >> 2; $clock_seq_hi_and_reserved = $clock_seq_hi_and_reserved | 0x8000; return sprintf('%08s-%04s-%04x-%04x-%012s', $time_low, $time_mid, $time_hi_and_version, $clock_seq_hi_and_reserved, $node); }