How can I harden/secure my install of Cassandra?

The Last Pickle (a well-known Cassandra consulting company) has a number of great posts on hardening your environment including:

• http://thelastpickle.com/blog/2015/09/30/hardening-cassandra-step-by-step-part-1-server-to-server.html
• http://www.slideshare.net/planetcassandra/the-last-pickle-hardening-apache-cassandra-for-compliance-or-paranoia