attr_keyring

Simple encryption-at-rest plugin for ActiveRecord.


Keywords
activerecord, encryption, keyring, rotation-encryption
License
MIT
Install
gem install attr_keyring -v 0.2.2

Documentation

attr_keyring: Simple encryption-at-rest with key rotation support for ActiveRecord.

Travis-CI Code Climate Test Coverage Gem Gem

N.B.: attr_keyring is not for encrypting passwords--for that, you should use something like bcrypt. It's meant for encrypting sensitive data you will need to access in plain text (e.g. storing OAuth token from users). Passwords do not fall in that category.

This library is heavily inspired by attr_vault but it's not a direct port and same keys won't work here without some manual intervention.

Installation

Add this line to your application's Gemfile:

gem "attr_keyring"

And then execute:

$ bundle

Or install it yourself as:

$ gem install attr_keyring

Usage

Model Configuration

Migration

  1. You'll need a column to track the key that was used for encryption; by default it's called keyring_id.
  2. Every encrypted columns must follow the name encrypted_<column name>.
  3. Optionally, you can also have a <column name>_digest to help with searching (see Lookup section below).

The following example shows how to create a column twitter_oauth_token without the digest, and another one called social_security_number with the digest column.

class CreateUsers < ActiveRecord::Migration[5.2]
  def change
    create_table :users do |t|
      t.citext :email, null: false
      t.timestamps

      # The following columns are used for encryption.
      t.binary :encrypted_twitter_oauth_token
      t.binary :encrypted_social_security_number
      t.text :social_security_number_digest
      t.integer :keyring_id
    end

    add_index :users, :email, unique: true
    add_index :users, :social_security_number_digest, unique: true
  end
end

ActiveRecord

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  include AttrKeyring
end

class User < ApplicationRecord
  attr_keyring ENV["USER_KEYRING"]
  attr_encrypt :twitter_oauth_token, :social_security_number
end

The code above will encrypt your columns with the current key. If you're updating a record, then the column will be migrated to the latest key available.

You can use the model as you would normally do.

user = User.create(
  email: "john@example.com",
  twitter_oauth_token: "TOKEN",
  social_security_number: "SSN"
)

user.twitter_oauth_token
#=> TOKEN

user.keyring_id
#=> 1

user.encrypted_twitter_oauth_token
#=> "\xF0\xFD\xE3\x98\x98\xBBBp\xCCV45\x17\xA8\xF2r\x99\xC8W\xB2i\xD0;\xC2>7[\xF0R\xAC\x00s\x8F\x82QW{\x0F\x01\x88\x86\x03w\x0E\xCBJ\xC6q"

Encryption

By default, AES-128-CBC is the algorithm used for encryption. This algorithm uses 16 bytes keys. Using 16-bytes of random data base64-encoded is the recommended way. You can easily generate keys by using the following command:

$ dd if=/dev/urandom bs=16 count=1 2>/dev/null | openssl base64

Include the result of this in the value section of the key description in the keyring.

You can also use AES-256-CBC, which uses 32-bytes keys. To specify the encryptor when defining the keyring, use encryptor: AttrKeyring::Encryptor::AES256CBC.

class User < ApplicationRecord
  attr_keyring ENV["USER_KEYRING"],
               encryptor: AttrKeyring::Encryptor::AES256CBC
end

To generate keys, use bs=32 instead.

$ dd if=/dev/urandom bs=32 count=1 2>/dev/null | openssl base64

About the encrypted message

Initialization vectors (IV) should be unpredictable and unique; ideally, they will be cryptographically random. They do not have to be secret: IVs are typically just added to ciphertext messages unencrypted. It may sound contradictory that something has to be unpredictable and unique, but does not have to be secret; it is important to remember that an attacker must not be able to predict ahead of time what a given IV will be.

With that in mind, attr_keyring uses unencrypted iv + encrypted message as the value of encrypted_<column>. If you're planning to migrate from other encryption mechanisms or read encrypted values from the database without using attr_keyring, make sure you account for this. The IV length can be retrieved by OpenSSL::Cipher#iv_len, e.g. OpenSSL::Cipher.new("AES-128-CBC").iv_len.

Keyring

Keys are managed through a keyring--a short JSON document describing your encryption keys. The keyring must be a JSON object mapping numeric ids of the keys to the key values. A keyring must have at least one key. For example:

{
  "1": "QSXyoiRDPoJmfkJUZ4hJeQ==",
  "2": "r6AfOeilPDJomFsiOXLdfQ=="
}

The id is used to track which key encrypted which piece of data; a key with a larger id is assumed to be newer. The value is the actual bytes of the encryption key.

Dynamically loading keyring

If you're using Rails 5.2+, you can use credentials to define your keyring. Your credentials.yml must be define like the following:

user_keyring:
  1: "QSXyoiRDPoJmfkJUZ4hJeQ=="
  2: "r6AfOeilPDJomFsiOXLdfQ=="

Then you can setup your model by using attr_keyring Rails.application.credentials.user_keyring.

Other possibilities (e.g. the keyring file is provided by configuration management):

  • attr_keyring YAML.load_file(keyring_file)
  • attr_keyring JSON.parse(File.read(keyring_file)).

Lookup

One tricky aspect of encryption is looking up records by known secret. E.g.,

User.where(twitter_oauth_token: "241F596D-79FF-4C08-921A-A19E533B4F52")

is trivial with plain text fields, but impossible with the model defined as above.

If add a column <attribute>_digest exists, then a SHA1 digest from the value will be saved. This will allow you to lookup by that value instead and add unique indexes.

User.where(twitter_oauth_token_digest: Digest::SHA1.hexdigest("241F596D-79FF-4C08-921A-A19E533B4F52"))

Key Rotation

Because attr_keyring uses a keyring, with access to multiple keys at once, key rotation is fairly straightforward: if you add a key to the keyring with a higher id than any other key, that key will automatically be used for encryption when records are either created or updated. Any keys that are no longer in use can be safely removed from the keyring.

To check if an existing key with id 123 is still in use, run:

# For a large dataset, you may want to index the `keyring_id` column.
User.where(keyring_id: 123).empty?

You may not want to wait for records to be updated (e.g. key leaking). In that case, you can rollout a key rotation:

User.where(keyring_id: 1234).find_each do |user|
    user.keyring_rotate!
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/fnando/attr_keyring. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

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

Icon

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Code of Conduct

Everyone interacting in the attr_keyring project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.