Sample-filecrypt is a project mainly written in Ruby, it's free.
Sample Sinatra App for file upload/encryption & download/decryption
author: cmort, 2011
pre-reqs: Ruby, Sinatra, Git, Heroku
overview: small sample sinatra app for Heroku that handles upload/download of files via encrypted communication (SSL, 128bit) and encrypts/decrypts content (AES, 256bit)
Use the custom_page.vf code w/in SFDC to create a new Tab/and VF page that will expose the Ruby app w/in SFDC.
This can be customized for various asset stores, user auth and key mgmt.
Still needs: Get class authorization