Sidebar: Check out my talk Being Boring - A Survivor's Guide to Ruby
Cryptography (describes RbNaCl): http://www.youtube.com/watch?v=e13irYP6WJA

RbNaCl is a Ruby FFI binding to the Networking and Cryptography Library by
Dan Bernstein and his collaborators:

https://github.com/cryptosphere/rbnacl

Version 3.0 includes a new "SimpleBox" API designed to be the most
straightforward API for cryptography possible. It automatically uses a
random nonce per message (using libsodium's randombytes implementation
which pulls from /dev/urandom on *IX and CryptGenRandom on Windows).
Simplebox is usable for both public-key and secret-key cryptography:

https://github.com/cryptosphere/rbnacl/wiki/SimpleBox
http://rubydoc.info/github/cryptosphere/rbnacl/master/RbNaCl/SimpleBox

Full list of changes from 2.0 below:

* Rename RandomNonceBox to SimpleBox (backwards compatibility preserved)
* Reverse documented order of SimpleBox/RandomNonceBox initialize
parameters. Technically backwards compatible, but confusing.
* Ensure all strings are ASCII-8BIT/BINARY encoding prior to use

-- 
Tony Arcieri