Sidebar: Check out my talk Being Boring - A Survivor's Guide to Ruby Cryptography (describes RbNaCl):
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:
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