<?php
$parameters = $_GET;

$signature = $parameters['api_sig'];
unset($parameters['api_sig']);
ksort($parameters);

$secretKey      = '01bc7a393c0cb427c0c4d96e5c0d9c65'; // fill here with your personal secret key
$string2compute = '';

foreach ($parameters as $name => $value) {
    $string2compute .= $name . $value;
}

// true if OK, false if not
// if your are using md5 instead of sha1 please replace

if (sha1($string2compute . $secretKey) == $signature) {
    $code    = 0;
    $message = 'OK';
}
else {
    $code    = 1;
    $message = 'KO';
}

//header('Content-Type: text/xml; charset=UTF-8');
echo "string2compute = " . $string2compute;
echo "<br>&nbsp;<br>Signature dans la Notification : " . $signature;
echo "<br>&nbsp;<br>Signature calcule : " . sha1($string2compute . $secretKey);
echo "<br>&nbsp;<br>Résponse : ";
echo '<?xml version="1.0" encoding="UTF-8" ?>';
?>
<response status="1">
 <code><?php echo $code; ?></code>
 <message><?php echo $message; ?></message>
</response>