pseudo_random_key generates pseudo random surrogate keys for a model using the
Blowfish block cipher and a PostgreSQL sequence generator. The generated keys
will not repeat any value through the entire cycle of the sequence generator.

You should create an initializer in config/initializers/pseudo_random_key.rb:

  PseudoRandomKey.init("0123456789ABCDEF") # and change this secret!

Then you should declare pseudo_random_key in your model:

  class MyModel < ActiveRecord::Base
    pseudo_random_key
  end

The Blowfish cipher uses a 64-bit block size, so the generated surrogate keys
(and foreign keys that reference the surrogate keys) will be 64 bits.