Android : Wordpress outside autentification

I have an android application that need to connet to a wordpress db.

i'm new to this kind of connection and i discovered that wordpress dont enctry as usually the password with md5.

My application has to register a new users to the blog and also to autentificate them.

What i try :

I have a php script on server side :

include ('../wp-includes/wp-db.php'); 
include ('../wp-includes/class-phpass.php'); 
$my_hasher = new PasswordHash(8, TRUE);
echo  $my_hasher->HashPassword("1234");

But on every refresh the result change. So ...that's not the way.

Can you please help me find the best, correct way to register a user password in a wordpress blog and also to compare the password for future autentification?

Thanks,