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Modern encryption for Rails
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Lockbox

📦 Modern encryption for Rails

  • Uses state-of-the-art algorithms
  • Works with database fields, files, and strings
  • Makes migrating existing data and key rotation easy

Lockbox aims to make encryption as friendly and intuitive as possible. Encrypted fields and files behave just like unencrypted ones for maximum compatibility with 3rd party libraries and existing code.

Learn the principles behind it, how to secure emails with Devise, and how to secure sensitive data in Rails.

Build Status

Installation

Add this line to your application’s Gemfile:

gem 'lockbox'

Key Generation

Generate a key

Lockbox.generate_key

Store the key with your other secrets. This is typically Rails credentials or an environment variable (dotenv is great for this). Be sure to use different keys in development and production. Keys don’t need to be hex-encoded, but it’s often easier to store them this way.

Set the following environment variable with your key (you can use this one in development)

LOCKBOX_MASTER_KEY=0000000000000000000000000000000000000000000000000000000000000000

or create config/initializers/lockbox.rb with something like

Lockbox.master_key = Rails.application.credentials.lockbox_master_key

Then follow the instructions below for the data you want to encrypt.

Database Fields

Files

Other

Active Record

Create a migration with:

class AddEmailCiphertextToUsers < ActiveRecord::Migration[6.0]
  def change
    add_column :users, :email_ciphertext, :text
  end
end

Add to your model:

class User < ApplicationRecord
  encrypts :email
end

You can use email just like any other attribute.

User.create!(email: "hi@example.org")

If you need to query encrypted fields, check out Blind Index.

Types

Fields are strings by default. Specify the type of a field with:

class User < ApplicationRecord
  encrypts :born_on, type: :date
  encrypts :signed_at, type: :datetime
  encrypts :opens_at, type: :time
  encrypts :active, type: :boolean
  encrypts :salary, type: :integer
  encrypts :latitude, type: :float
  encrypts :video, type: :binary
  encrypts :properties, type: :json
  encrypts :settings, type: :hash
end

Note: Use a text column for the ciphertext in migrations, regardless of the type

Lockbox automatically works with serialized fields for maximum compatibility with existing code and libraries.

class User < ApplicationRecord
  serialize :properties, JSON
  store :settings, accessors: [:color, :homepage]
  attribute :configuration, CustomType.new

  encrypts :properties, :settings, :configuration
end

For StoreModel, use:

class User < ApplicationRecord
  encrypts :configuration, type: Configuration.to_type

  after_initialize do
    self.configuration ||= {}
  end
end

Validations

Validations work as expected with the exception of uniqueness. Uniqueness validations require a blind index.

Fixtures

You can use encrypted attributes in fixtures with:

test_user:
  email_ciphertext: <%= User.generate_email_ciphertext("secret").inspect %>

Be sure to include the inspect at the end or it won’t be encoded properly in YAML.

Migrating Existing Data

Lockbox makes it easy to encrypt an existing column. Add a new column for the ciphertext, then add to your model:

class User < ApplicationRecord
  encrypts :email, migrating: true
end

Backfill the data in the Rails console:

Lockbox.migrate(User)

Then update the model to the desired state:

class User < ApplicationRecord
  encrypts :email

  # remove this line after dropping email column
  self.ignored_columns = ["email"]
end

Finally, drop the unencrypted column.

If adding blind indexes, mark them as migrating during this process as well.

class User < ApplicationRecord
  blind_index :email, migrating: true
end

Mongoid

Add to your model:

class User
  field :email_ciphertext, type: String

  encrypts :email
end

You can use email just like any other attribute.

User.create!(email: "hi@example.org")

If you need to query encrypted fields, check out Blind Index.

Active Storage

Add to your model:

class User < ApplicationRecord
  has_one_attached :license
  encrypts_attached :license
end

Works with multiple attachments as well.

class User < ApplicationRecord
  has_many_attached :documents
  encrypts_attached :documents
end

There are a few limitations to be aware of:

  • Metadata like image width and height are not extracted when encrypted
  • Direct uploads cannot be encrypted

To serve encrypted files, use a controller action.

def license
  user = User.find(params[:id])
  send_data user.license.download, type: user.license.content_type
end

CarrierWave

Add to your uploader:

class LicenseUploader < CarrierWave::Uploader::Base
  encrypt
end

Encryption is applied to all versions after processing.

You can mount the uploader as normal. With Active Record, this involves creating a migration:

class AddLicenseToUsers < ActiveRecord::Migration[6.0]
  def change
    add_column :users, :license, :string
  end
end

And updating the model:

class User < ApplicationRecord
  mount_uploader :license, LicenseUploader
end

To serve encrypted files, use a controller action.

def license
  user = User.find(params[:id])
  send_data user.license.read, type: user.license.content_type
end

Shrine

Generate a key

key = Lockbox.generate_key

Create a lockbox

lockbox = Lockbox.new(key: key)

Encrypt files before passing them to Shrine

LicenseUploader.upload(lockbox.encrypt_io(file), :store)

And decrypt them after reading

lockbox.decrypt(uploaded_file.read)

For models, encrypt with:

license = params.require(:user).fetch(:license)
user.license = lockbox.encrypt_io(license)

To serve encrypted files, use a controller action.

def license
  user = User.find(params[:id])
  send_data box.decrypt(user.license.read), type: user.license.mime_type
end

Local Files

Read the file as a binary string

message = File.binread("file.txt")

Then follow the instructions for encrypting a string below.

Strings

Generate a key

key = Lockbox.generate_key

Create a lockbox

lockbox = Lockbox.new(key: key, encode: true)

Encrypt

ciphertext = lockbox.encrypt("hello")

Decrypt

lockbox.decrypt(ciphertext)

Use decrypt_str get the value as UTF-8

Key Rotation

To make key rotation easy, you can pass previous versions of keys that can decrypt.

Active Record

Update your model:

class User < ApplicationRecord
  encrypts :email, previous_versions: [{key: previous_key}]
end

Use master_key instead of key if passing the master key.

To rotate existing records, use:

Lockbox.rotate(User, attributes: [:email])

Once all records are rotated, you can remove previous_versions from the model.

Mongoid

Update your model:

class User
  encrypts :email, previous_versions: [{key: previous_key}]
end

Use master_key instead of key if passing the master key.

To rotate existing records, use:

Lockbox.rotate(User, attributes: [:email])

Once all records are rotated, you can remove previous_versions from the model.

Active Storage

Update your model:

class User < ApplicationRecord
  encrypts_attached :license, previous_versions: [{key: previous_key}]
end

Use master_key instead of key if passing the master key.

To rotate existing files, use:

User.find_each do |user|
  user.license.rotate_encryption!
end

Once all files are rotated, you can remove previous_versions from the model.

CarrierWave

Update your model:

class LicenseUploader < CarrierWave::Uploader::Base
  encrypt previous_versions: [{key: previous_key}]
end

Use master_key instead of key if passing the master key.

To rotate existing files, use:

User.find_each do |user|
  user.license.rotate_encryption!
end

Once all files are rotated, you can remove previous_versions from the model.

Strings

For strings, use:

Lockbox.new(key: key, previous_versions: [{key: previous_key}])

Auditing

It’s a good idea to track user and employee access to sensitive data. Lockbox provides a convenient way to do this with Active Record, but you can use a similar pattern to write audits to any location.

rails generate lockbox:audits
rails db:migrate

Then create an audit wherever a user can view data:

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])

    LockboxAudit.create!(
      subject: @user,
      viewer: current_user,
      data: ["name", "email"],
      context: "#{controller_name}##{action_name}",
      ip: request.remote_ip
    )
  end
end

Query audits with:

LockboxAudit.last(100)

Note: This approach is not intended to be used in the event of a breach or insider attack, as it’s trivial for someone with access to your infrastructure to bypass.

Algorithms

AES-GCM

This is the default algorithm. It’s:

For users who do a lot of encryptions: You should rotate an individual key after 2 billion encryptions to minimize the chance of a nonce collision, which will expose the key. Each database field and file uploader use a different key (derived from the master key) to extend this window.

XSalsa20

You can also use XSalsa20, which uses an extended nonce so you don’t have to worry about nonce collisions. First, install Libsodium. For Homebrew, use:

brew install libsodium

And add to your Gemfile:

gem 'rbnacl'

Then add to your model:

class User < ApplicationRecord
  encrypts :email, algorithm: "xsalsa20"
end

Make it the default with:

Lockbox.default_options = {algorithm: "xsalsa20"}

You can also pass an algorithm to previous_versions for key rotation.

XSalsa20 Deployment

Heroku

Heroku comes with libsodium preinstalled.

Ubuntu

For Ubuntu 18.04, use:

sudo apt-get install libsodium23

For Ubuntu 16.04, use:

sudo apt-get install libsodium18
Travis CI

On Bionic, add to .travis.yml:

addons:
  apt:
    packages:
      - libsodium23

On Xenial, add to .travis.yml:

addons:
  apt:
    packages:
      - libsodium18
CircleCI

Add a step to .circleci/config.yml:

- run:
    name: install Libsodium
    command: |
      sudo apt-get install -y libsodium18

Hybrid Cryptography

Hybrid cryptography allows servers to encrypt data without being able to decrypt it.

Follow the instructions above for installing Libsodium and including rbnacl in your Gemfile.

Generate a key pair with:

Lockbox.generate_key_pair

Store the keys with your other secrets. Then use:

class User < ApplicationRecord
  encrypts :email, algorithm: "hybrid", encryption_key: encryption_key, decryption_key: decryption_key
end

Make sure decryption_key is nil on servers that shouldn’t decrypt.

This uses X25519 for key exchange and XSalsa20 for encryption.

Key Separation

The master key is used to generate unique keys for each column. This technique comes from CipherSweet. The table name and column name are both used in this process. If you need to rename a table with encrypted columns, or an encrypted column itself, get the key:

Lockbox.attribute_key(table: "users", attribute: "email_ciphertext")

And set it directly before renaming:

class User < ApplicationRecord
  encrypts :email, key: ENV["USER_EMAIL_ENCRYPTION_KEY"]
end

Key Management

You can use a key management service to manage your keys with KMS Encrypted.

class User < ApplicationRecord
  encrypts :email, key: :kms_key
end

For CarrierWave, use:

class LicenseUploader < CarrierWave::Uploader::Base
  encrypt key: -> { model.kms_key }
end

Note: KMS Encrypted’s key rotation does not know to rotate encrypted files, so avoid calling record.rotate_kms_key! on models with file uploads for now.

Data Leakage

While encryption hides the content of a message, an attacker can still get the length of the message (since the length of the ciphertext is the length of the message plus a constant number of bytes).

Let’s say you want to encrypt the status of a candidate’s background check. Valid statuses are clear, consider, and fail. Even with the data encrypted, it’s trivial to map the ciphertext to a status.

lockbox = Lockbox.new(key: key)
lockbox.encrypt("fail").bytesize      # 32
lockbox.encrypt("clear").bytesize     # 33
lockbox.encrypt("consider").bytesize  # 36

Add padding to conceal the exact length of messages.

lockbox = Lockbox.new(key: key, padding: true)
lockbox.encrypt("fail").bytesize      # 44
lockbox.encrypt("clear").bytesize     # 44
lockbox.encrypt("consider").bytesize  # 44

The block size for padding is 16 bytes by default. If we have a status larger than 15 bytes, it will have a different length than the others.

box.encrypt("length15status!").bytesize   # 44
box.encrypt("length16status!!").bytesize  # 60

Change the block size with:

Lockbox.new(padding: 32) # bytes

Binary Columns

You can use binary columns for the ciphertext instead of text columns to save space.

class AddEmailCiphertextToUsers < ActiveRecord::Migration[6.0]
  def change
    add_column :users, :email_ciphertext, :binary
  end
end

You should disable Base64 encoding if you do this.

class User < ApplicationRecord
  encrypts :email, encode: false
end

or set it globally:

Lockbox.default_options = {encode: false}

Compatibility

It’s easy to read encrypted data in another language if needed.

For AES-GCM, the format is:

  • nonce (IV) - 12 bytes
  • ciphertext - variable length
  • authentication tag - 16 bytes

Here are some examples.

For XSalsa20, use the appropriate Libsodium library.

Migrating from Another Library

Lockbox makes it easy to migrate from another library without downtime. The example below uses attr_encrypted but the same approach should work for any library.

Let’s suppose your model looks like this:

class User < ApplicationRecord
  attr_encrypted :name, key: key
  attr_encrypted :email, key: key
end

Create a migration with:

class MigrateToLockbox < ActiveRecord::Migration[6.0]
  def change
    add_column :users, :name_ciphertext, :text
    add_column :users, :email_ciphertext, :text
  end
end

And add encrypts to your model with the migrating option:

class User < ApplicationRecord
  encrypts :name, :email, migrating: true
end

Then run:

Lockbox.migrate(User)

Once all records are migrated, remove the migrating option and the previous model code (the attr_encrypted methods in this example).

class User < ApplicationRecord
  encrypts :name, :email
end

Then remove the previous gem from your Gemfile and drop its columns.

class RemovePreviousEncryptedColumns < ActiveRecord::Migration[6.0]
  def change
    remove_column :users, :encrypted_name, :text
    remove_column :users, :encrypted_name_iv, :text
    remove_column :users, :encrypted_email, :text
    remove_column :users, :encrypted_email_iv, :text
  end
end

Upgrading

0.2.0

0.2.0 brings a number of improvements. Here are a few to be aware of:

  • Added encrypts method for database fields
  • Added support for XSalsa20
  • attached_encrypted is deprecated in favor of encrypts_attached.

Optional

To switch to a master key, generate a key:

Lockbox.generate_key

And set ENV["LOCKBOX_MASTER_KEY"] or Lockbox.master_key.

Update your model:

class User < ApplicationRecord
  encrypts_attached :license, previous_versions: [{key: key}]
end

New uploads will be encrypted with the new key.

You can rotate existing records with:

User.unscoped.find_each do |user|
  user.license.rotate_encryption!
end

Once that’s complete, update your model:

class User < ApplicationRecord
  encrypts_attached :license
end

History

View the changelog

Contributing

Everyone is encouraged to help improve this project. Here are a few ways you can help:

To get started with development and testing:

git clone https://github.com/ankane/lockbox.git
cd lockbox
bundle install
bundle exec rake test
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