Citizenship is a simple gem that allows validation of Portuguese documents or common identifiers, such as citizen card numbers, bank account numbers (NIB), fiscal numbers (NIF) and more. As most of these IDs have some kind of checksum, Citizenship calculates and verifies them accordingly. We also provide some convenient methods for validating local phone numbers and email addresses.

http://www.runtime-revolution.com/runtime/blog/citizenship-simple-yet-useful-validation-of-portuguese-cards-and-more