Page restriction with simple password

Hi,

I want to restrict the access (read-access) to my wp by using a simple password, shared by a large number of users. There are many plugins doing so, but only with user/password combination. For the sake of simplicity many user should share only one login but without beeing able to change password and so. Does anybody know such a plugin?

At best I would like to have only a simple password field without any username – such as if you restrict just one post. But this password should enable access to the whole site.

Thanks four your help!

Regards,
Peter