Globally set a password for all password protected posts and pages.
You can install this plugin directly from your WordPress dashboard:
Now whenever you write or edit a post or page you'll be able to switch password protection on or off with one click, instead of having to manually type in a password for each post. You can change the password whenever you like from the 'Settings -> Global Post Password' menu.
For manual installation, see the guide to Manually Installing Plugins.