Jess

A simple plugin that allows you to restrict access to certain pages on your website to only logged in users quickly and easily. This plugin can be useful to those who do not need overly complicated membership systems, and to those who want to password protect a group of pages but don’t want to password protect each page individually, forcing the users to log into each one.
It is simple to use. First select whether you want to password protect all pages by default, and want to choose which pages are public. Or choose to allow all pages to be public by default, and choose which pages are password protected.
When non-logged in users try to access a password protected page they will be redirected to the WordPress login screen. Once logged in, they will be redirected back to the requested page and will not be asked to log in again on subsequent pages.

Password Protect Pages

Restrict access to specific pages to only logged in users.

mores

For some reason or other, you might want to allow access to certain posts only to certain people. You can use password-protection on Pages and Posts, but those need to be set individually. 
It’s far simpler to just write a Post, specify a category and all posts in that category are password protected. Or you might decide to protect a lot of old posts. 
Imagine a family blog where certain posts are only visible to people who know the birthday of your first child, or remember your pet’s name. 
Cat-Pass is not for super-sensitive information, it’s for casual use.

Cat-Pass

Cat-Pass lets you password-protect categories. Caution: deactivating the plugin will render your protected posts visible again.

Password Protect Pages vs Cat-Pass