password for subpages

Hello,
is there a way / plugin that protects subpages with the same password, that the superpage has. I think it’s not a good idea to give all subpages an own password, because if I change the superpage-password, I have to change all the subpages separately…

I looked into the sources, but I am new to WP and not really sure where to change this behaviour. I think the check for a superpage password could be done when loading the page from DB like in the get_post method… But maybe that would be overkill… ??

Thanks for helping
Tobias