MySQL Prepared statement confusion

Question

Ok, so I am having a lot of trouble with Prepared statements. I've done hours of research and still can't seem to fully understand everything...

I really feel like I need to understand Prepared statements because I was just about to release a few new free APIs on my website (which require API Key to execute API) but I recently realized how insecure everything is.... I can simply use SQL injection to bypass API Key check, eg 'OR'1'='1

Here is how I validate API Key:

$apikey = $_GET['key'];
$sql = "SELECT * FROM `table` WHERE `key` = '$apikey'";
$query = mysqli_query($con, $sql);
if($query)
{
    $fetchrow = mysqli_fetch_row($query);
    if(isset($fetchrow[0]))
    {
        echo "API Key is valid!";
    }
    else
    {
        echo "API KEY is invalid";
    }
}

And like mentioned above this can easily be bypassed by executing my API like this

http://website.com/api.php?key='OR'1'='1

This really scared me at first, but then I did some research and learned a good way to prevent any form of SQL injection is to use prepared statement, so I did a lot of research and it just seems quite complicated to me :/

So I guess my question is, how can I take my above code, and make it function the same way using prepared statements?

Answer 1

Probably everything you need:

class Database {
    private static $mysqli;

Connect to the DB:

public static function connect(){
    if (isset(self::$mysqli)){
        return self::$mysqli;
    }
    self::$mysqli = new mysqli("DB_HOST", "DB_USER", "DB_PASS", "DB_NAME");
    if (mysqli_connect_errno()) {
        /*Log error here, return 500 code (db connection error) or something... Details in $mysqli->error*/
    }
    self::$mysqli->query("SET NAMES utf8");
    return self::$mysqli;
}

Execute statement and get results:

public static function execute($stmt){
    $stmt->execute();
    if ($mysqli->error) {
        /*Log it or throw 500 code (sql error)*/
    }
    return self::getResults($stmt);
}

Bind results to the pure array:

private static function getResults($stmt){
    $stmt->store_result();
    $meta = $stmt->result_metadata();

    if (is_object($meta)){
        $variables = array();
        $data = array();

        while($field = $meta->fetch_field()) {
            $variables[] = &$data[$field->name];
        }

        call_user_func_array(array($stmt, "bind_result"), $variables);

        $i = 0;
        while($stmt->fetch()) {
            $array[$i] = array();
            foreach($data as $k=>$v)
            $array[$i][$k] = $v;
            $i++;
        }
        $stmt->close();
        return $array;
    } else {
        return $meta;
    }
}

Class end :)

}

Example of usage:

public function getSomething($something, $somethingOther){
    $mysqli = Database::connect();
    $stmt = $mysqli->prepare("SELECT * FROM table WHERE something = ? AND somethingOther = ?");
    $stmt->bind_param("si", $something, $somethingOther); // s means string, i means number
    $resultsArray = Database::execute($stmt);
    $someData = $resultsArray[0]["someColumn"];
}

Resolving your problem:

public function isKeyValid($key){
    $mysqli = Database::connect();
    $stmt = $mysqli->prepare("SELECT * FROM table WHERE key = ? LIMIT 1");
    $stmt->bind_param("s", $key);
    $results = Database::execute($stmt);
    return count($results > 0);
}

PHP automatically closes DB connection so no worries about it.

Answer 2

$sql = "SELECT * FROM `table` WHERE `key` = ?";

if(stmt = $mysqli->prepare($sql)) {
    $stmt->bind_param("i", $apikey);

    $stmt->execute();
    $stmt->bind_result($res);
    $stmt->fetch();

    $stmt->close();
}

See more - http://php.net/manual/en/mysqli.prepare.php