lib/Dropbox/Security.php
static function getRandomBytes($numBytes)
    {
        Checker::argIntPositive("numBytes", $numBytes);

        // openssl_random_pseudo_bytes had some issues prior to PHP 5.3.4
        if (function_exists('openssl_random_pseudo_bytes')
                && version_compare(PHP_VERSION, '5.3.4') >= 0) {
            $s = openssl_random_pseudo_bytes($numBytes, $isCryptoStrong);
            if ($isCryptoStrong) return $s;
        }

        if (function_exists('mcrypt_create_iv')) {
            return mcrypt_create_iv($numBytes);
        }

        // Hopefully the above two options cover all our users.  But if not, there are
        // other platform-specific options we could add.
        throw new \Exception("no suitable random number source available");
    }
static function getRandomBytes($numBytes)
    {
        Checker::argIntPositive("numBytes", $numBytes);

        // openssl_random_pseudo_bytes had some issues prior to PHP 5.3.4
        if (function_exists('openssl_random_pseudo_bytes')
                && version_compare(PHP_VERSION, '5.3.4') >= 0) {
            $s = openssl_random_pseudo_bytes($numBytes, $isCryptoStrong);
            if ($isCryptoStrong) return $s;
        }

        if (function_exists('mcrypt_create_iv')) {
            return mcrypt_create_iv($numBytes);
        }

        // Hopefully the above two options cover all our users.  But if not, there are
        // other platform-specific options we could add.
        throw new \Exception("no suitable random number source available");
    }
Returns cryptographically strong secure random bytes (as a PHP string).

@param int $numBytes
The number of bytes of random data to return.

@return string