Cookie value encryption

Is there anything built into either Ruby or Rails that can help
encrypt and decrypt values placed in a cookie?

I realize that I could store sensitive data in the server side session
instead I would like to know if cookie encryption is easily doable
(exploring options).

OpenSSL, which is poorly documented. Luckily there's EZCrypto to the
rescue (though I've never used it): http://ezcrypto.rubyforge.org/

Or may be use cookie based session store, which encrypts the data.

Where can I find some docs on how to use the Cookie Based Session
Store? I'm using Rails 1.2.3 The following page makes no mention of
it: http://wiki.rubyonrails.org/rails/pages/HowtoChangeSessionStore

Regards

Oops. Cookie based session store is only in edge rails.