gistfile1.rb

# Schema:
#
# id               int
# crypted_number   string(255)
# ... anything else ...

class Foo < ActiveRecord::Base
  attr_writer :number
  before_save :encrypt_number
  
  def number
    @number ||= decrypt(crypted_number)
  end
  
  private

  def encrypt_number
    crypted_number = encrypt(@number)
  end
  
  def encrypt(string)
    # super secret crypto algorithm
  end
  
  def decrypt(string)
    # super secret crypto algorithm
  end
end