Passwords and Multiple WPs on Same Domain

Hello,

I have various WPs on the same domain and I want to have a different password for them – although it is the same admin. Is that possible or do all WPs on say http://www.example.com have to be the same? Even if they are http://www.example.com/blog1/wp_login.php and ww.example.com/blog2/wp_login.php etc

Thanks for your time

D