rom-encrypted_attribute

ROM::EncryptedAttribute

This gem adds support for encrypted attributes to ROM.

Traditionally ROM team suggested to put encryption logic in repository code (more precisely, in the mapper from database struct to an entity). I personally think this is not the greatest idea. Repository lies logically in the application layer (or even domain layer), while encryption and decryption of data is a purely infrastructure concern. As such, it should be as low-level and hidden as possible.

In ROM terms it means doing it in a relation. The gem leverages custom types to achieve encryption and decryption.

The scheme is compatible with Rails' default settings for ActiveRecord encryption, so you can still read records encrypted with ActiveRecord from ROM (and vice versa) as long as you provide the same primary key and key derivation salt.

Installation

Install the gem and add to the application's Gemfile by executing:

$ bundle add rom-encrypted_attribute

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install rom-encrypted_attribute

Usage

There are two ways to use this library: via a ROM schema plugin or by a "bare metal" approach.

ROM plugin

Somewhere in you code set the config for the gem. This is done using Dry::Configurable, so you can use all options available there. For example:

ROM::EncryptedAttribute.configure do |config|
  config.primary_key = "your-primary-key" # required
  config.key_derivation_salt = "your-derivation-salt" # required
  config.hash_digest_class = OpenSSL::Digest::SHA256 # SHA1 by default
end

Then use the plugin in your ROM relation:

class SecretNotes < ::ROM::Relation[:sql]
  schema(:secret_notes, infer: true) do
    use :encrypted_attributes
    encrypt :content
  end
end

You can override individual configuration values if, for example, one database table uses different primary key:

class SecretNotes < ::ROM::Relation[:sql]
  schema(:secret_notes, infer: true) do
    use :encrypted_attributes, primary_key: ENV["SPECIAL_PRIMARY_KEY"]
    encrypt :content
  end
end

If you specify all configuration options, or use defaults, you can skip setting the global config.

You can also override global per-schema settings on a per-field level:

class SecretNotes < ::ROM::Relation[:sql]
  schema(:secret_notes, infer: true) do
    use :encrypted_attributes
    encrypt :content
    encrypt :title, :hash_digest_class: OpenSSL::Digest::SHA256
  end
end

"Bare metal"

In your relation, define custom types using a helper method from the gem. You need to provide the credentials to it somehow. This might be done via environmental variables, Hanami settings (if you're using Hanami) or any other means, really.

class SecretNotes < ROM::Relation[:sql]
  EncryptedString, EncryptedStringReader =
    ROM::EncryptedAttribute.define_encrypted_attribute_types(
      primary_key: ENV["ENCRYPTION_PRIMARY_KEY"],
      key_derivation_salt: ENV["ENCRYPTION_KEY_DERIVATION_SALT"]
    )
    
  schema(:secret_notes, infer: true) do
    attribute :content, EncryptedString, read: EncryptedStringReader
  end
end

With this approach you can define the types globally in your application and reuse it, without having to pass primary_key and key_derivation_salt every time in the schema.

Other considerations

By default the gem uses SHA1 for key derivation (same as Rails' default), but you can configure it by passing custom hash_digest_class option.

class SecretNotes < ROM::Relation[:sql]
  EncryptedString, EncryptedStringReader =
    ROM::EncryptedAttribute.define_encrypted_attribute_types(
      primary_key: ENV["ENCRYPTION_PRIMARY_KEY"],
      key_derivation_salt: ENV["ENCRYPTION_KEY_DERIVATION_SALT"],
      hash_digest_class: OpenSSL::Digest::SHA256
    )
    
  schema(:secret_notes, infer: true) do
    attribute :content, EncryptedString, read: EncryptedStringReader
  end
end

Caveats

• Due to a bug in rom-sql, reading unencrypted data is always supported, which means that if there's a plain not-encrypted data in your database already, it will be read correctly. This might or might not be desirable, but for the time being there's no choice in configuring this behaviour.
• Support for deterministic encryption from ActiveRecord::Encryption is not (yet) implemented
• Support for key rotation is not (yet) implemented

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/katafrakt/rom-encrypted_attribute.