AttrDigest

AttrDigest provides functionality to store a hash digest of an attribute using Argon2.

Argon2 is a password-hashing function that summarizes the state of the art in the design of memory-hard functions and can be used to hash passwords for credential storage, key derivation, or other applications. It is the official winner and recommendation of the Password Hashing Competition (PHC) which ran between 2013 and 2015.

This Gem uses the Ruby Argon2 Gem which provides FFI bindings, and a simplified interface, to the Argon2 algorithm.

AttrDigest provides similar functionality to Rails has_secure_password, but permits any number attributes to be hashed in a model, and obviously you're not limited to just the password attribute.

Installation

To install add the following line to your Gemfile:

gem 'attr_digest'

And run bundle install.

Dependencies

Runtime:

• activerecord (>= 4.2.6)
• activesupport (>= 4.2.6)
• argon2 (= 1.1.3) ** See CHANGELOG.md for version lock reason

Development/Test:

• rake (~> 10.5)
• rspec (~> 3.4)
• sqlite3 (~> 1.3)
• simplecov (~> 0.11.2)
• factory_girl (~> 4.5)

Compatibility

Tested with Ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin16] against ActiveRecord 5.2.0.rc1 on macOS High Sierra 10.13.3 (17D47).

Argon2 requires Ruby 2.2 minimum and an OS platform that supports Ruby FFI Bindings, so unfortunately Windows is out.

Usage

Attributes to be digested are declared using the attr_digest class method in your model:

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.string :security_question, null: false
    t.string :security_answer_digest, null: false
  end
end

class User < ActiveRecord::Base
  attr_digest :security_answer
end

AttrDigest automatically creates the #security_answer getter and #security_answer= setter. The setter creates a digest of the value provided and stores it in the security_answer_digest column.

AttrDigest also defines the method authenticate_security_answer(value) which returns false if the value given does not correspond to the saved digest, or returns true if it does.

Validations

AttrDigest adds some default validations. Using the example above:

• it creates a confirmation validation on security_answer, but only if security_answer is given (for confirmation validations see ActiveRecord Validations).
• it creates a presence validation on security_answer but only on create.
• it creates a presence validation on security_answer_confirmation but only if security_answer has been given; and
• it raises an exception if security_answer_digest is empty on create.

You can disable all validations by passing false to the validations option:

attr_digest :security_answer, validations: false

Case Sensitivity

If you want values passed to be case insensitive, you can pass false to the case_sensitive option:

attr_digest :security_answer, case_sensitive: false

Then differing cases will match, e.g. pizza will match PizzA.

Confirmations

If you prefer to skip confirmations for the attribute you are hashing, you can pass false to the confirmation option:

attr_digest :security_answer, confirmation: false

Format

You can ensure the attribute you are hashing matches a given regular expression by passing a format option:

attr_digest :password, format: { with: /\A[a-zA-Z]+\z/, message: "only allows letters" }

AttrDigest adds the Rails format validator and passes the options hash through as is. See Active Record Validations format validator for options you can pass to the format options hash.

NOTE: The format option is not affected by the validations option. Adding the format option will add a Rails format validator regardless of whether the validations option is set to true or false.

Length

You can ensure the attribute your are hashing meets certain length criteria by passing a length option:

attr_digest :password, length: { minimum: 5 }
attr_digest :password, length: { maximum: 10 }
attr_digest :password, length: { in: 5..10 }
attr_digest :password, length: { is: 8 }

AttrDigest adds the Rails length validator and passes the options hash through as is. See Active Record Validations length validator for options you can pass to the length options hash.

NOTE: The length option is not affected by the validations option. Adding the length option will add a Rails length validator regardless of whether the validations option is set to true or false.

Protected Digest Setter

If you want to prevent the attribute's digest being set directly, you can include the protected option:

attr_digest :security_answer, protected: true

The attribute's digest is not protected from direct setting by default.

Time and Memory Costs

AttrDigest sets a default time and memory cost and expects the following minimum and maximum values:

Option	Minimum Value	Maximum Value	Default Value
:time_cost	1	10	2
:memory_cost	1	31	16

You can change the global defaults by setting the cost options directly on the AttrDigest class:

AttrDigest.time_cost = 3
AttrDigest.memory_cost = 12

You can also change the time and memory cost for a specific attribute by passing the options to the attr_digest class method in your model:

attr_digest :security_answer, time_cost: 3, memory_cost: 12

Secret Key

Argon2 supports an optional secret key value. This should be stored securely on your server, such as alongside your database credentials. Hashes generated with a secret key will only validate when presented that secret.

You can set the optional secret key globally by setting the secret attribute on the AttrDigest class:

AttrDigest.secret =  Rails.application.secrets.secret_key_base

You can also set the optional secret key for a specific attribute by passing the :secret option to the attr_digest class method in your model:

attr_digest :security_answer, secret: Rails.application.secrets.secret_key_base

Tests

Tests are written using Rspec, FactoryGirl and Sqlite3. There are 52 examples with 100% code coverage.

To run the tests, execute the default rake task:

bundle exec rake

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Credit

I would like to thank Panayotis Matsinopoulos for his has_secure_attribute gem which provided a lot of the inspiration and framework for AttrDigest.

I would also like to thank Lawrence Sproul for bringing to light some potential error conditions, providing the motivation to make the gem feature complete and the inspiration for additional validation options.

This gem was written and is maintained by Jurgen Jocubeit, CEO and President Brightcommerce, Inc.

License

The gem is available as open source under the terms of the MIT License.

Copyright

Copyright 2016-2017 Brightcommerce, Inc.