Poetic Coding

Private Feed Key adds a 32bit (or 40bit) key for each of your users, creating a unique feed url for every registered user on the site. This allows you to restrict access to your feeds, to registered users only. The plugin will also work with plugins that filter access to posts to certain user levels, only allowing the user to see that content .

Private Feed Key

Private Feed Key adds a 32bit (or 40bit) key for each of your users, creating a unique feed url for every registered user on the site.

P. Chandra

Adds copyright notice at end of articles in full text RSS feeds, with back links to the blog and original article.
A notice gets attached at the bottom of feed articles like this 
Original Article: Title of Article (linked to permalink) 
Copyright Year. Blog Title (linked). All Rights Reserved
Your Blog title is linked to your blog Url. Your article title is linked to the article permalink.
Blog copyright notices are important as your feed gets freely distributed across the web and is republished without permission by RSS scrappers and autoblogs. After using this plugin, now RSS scrappers will link back to your site, which will suggest to search engines that your blog and article was the original source.

Simple Feed Copyright

Adds copyright notice at end of articles in full text RSS feeds, with back links to the blog and original article.

Private Feed Key vs Simple Feed Copyright