This is the full ISO-7812 implementation, in ruby! This is battle tested, production ready. Use at will.
The project is 100% documented and you shouldn't have any problem understanding the standard just by reading the comments.
I recommend that you copy those files into your own project and not use this as a gem.
Add this line to your application's Gemfile:
gem 'iso7812'
And then execute:
$ bundle
Or install it yourself as:
$ gem install iso7812
require 'iso7812'
include Iso7812::CardNumber
# See available methods on card_number.rb