<!DOCTYPE html>
<html>
<body>

<?php
$str = "Hello";
echo sha1($str);

if (sha1($str) == "f7ff9e8b7bb2e09b70935a5d785e0cc5d9d0abf0")
   {
   echo "<br>Hello world!";
   exit;
   }
?>

</body>
</html>