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Active Record Encryption

This guide covers encrypting your database information using Active Record.

After reading this guide you will know:

Active Record supports application-level encryption. It works by declaring which attributes should be encrypted and seamlessly encrypting and decrypting them when necessary. The encryption layer is placed between the database and the application. The application will access unencrypted data but the database will store it encrypted.

1 Basic usage

1.1 Setup

First, you need to add some keys to your rails credentials. Run bin/rails db:encryption:init to generate a random key set:

$ bin/rails db:encryption:init
Add this entry to the credentials of the target environment:

active_record_encryption:
  primary_key: EGY8WhulUOXixybod7ZWwMIL68R9o5kC
  deterministic_key: aPA5XyALhf75NNnMzaspW7akTfZp0lPY
  key_derivation_salt: xEY0dt6TZcAMg52K7O84wYzkjvbA62Hz

These generated keys and salt are 32 bytes length. If you generate these yourself, the minimum lengths you should use are 12 bytes for the primary key (this will be used to derive the AES 32 bytes key) and 20 bytes for the salt.

1.2 Declaration of encrypted attributes

Encryptable attributes are defined at the model level. These are regular Active Record attributes backed by a column with the same name.

class Article < ApplicationRecord
  encrypts :title
end

The library will transparently encrypt these attributes before saving them into the database, and will decrypt them when retrieving their values:

article = Article.create title: "Encrypt it all!"
article.title # => "Encrypt it all!"

But, under the hood, the executed SQL would look like this:

INSERT INTO `articles` (`title`) VALUES ('{\"p\":\"n7J0/ol+a7DRMeaE\",\"h\":{\"iv\":\"DXZMDWUKfp3bg/Yu\",\"at\":\"X1/YjMHbHD4talgF9dt61A==\"}}')

Encryption takes additional space in the column. You can estimate the worst-case overload in around 250 bytes when the built-in envelope encryption key provider is used. For medium and large text columns this overload is negligible, but for string columns of 255 bytes, you should increase their limit accordingly (510 is recommended).

The reason for the additional space are Base 64 encoding and additional metadata stored with the encrypted values.

1.3 Deterministic and non-deterministic encryption

By default, Active Record Encryption uses a non-deterministic approach to encryption. This means that encrypting the same content with the same password twice will result in different ciphertexts. This is good for security, since it makes crypto-analysis of encrypted content much harder, but it makes querying the database impossible.

You can use the deterministic: option to generate initialization vectors in a deterministic way, effectively enabling querying encrypted data.

class Author < ApplicationRecord
  encrypts :email, deterministic: true
end

Author.find_by_email("some@email.com") # You can query the model normally

The recommendation is using the default (non deterministic) unless you need to query the data.

In non-deterministic mode, it uses AES-GCM with a 256-bits key and a random initialization vector. In deterministic mode, it uses AES-GCM too but the initialization vector is generated as a HMAC-SHA-256 digest of the key and contents to encrypt.

You can disable deterministic encryption just by not configuring a deterministic_key.

2 Features

2.1 Action Text

You can encrypt action text attributes by passing encrypted: true in their declaration.

class Message < ApplicationRecord
  has_rich_text :content, encrypted: true
end

Passing individual encryption options to action text attributes is not supported yet. It will use non-deterministic encryption with the global encryption options configured.

2.2 Fixtures

You can get Rails fixtures encrypted automatically by adding this option to your test.rb:

config.active_record.encryption.encrypt_fixtures = true

When enabled, all the encryptable attributes will be encrypted according to the encryption settings defined in the model.

2.2.1 Action text fixtures

To encrypt action text fixtures you should place them in fixtures/action_text/encrypted_rich_texts.yml.

2.3 Supported types

active_record.encryption will serialize values using the underlying type before encrypting them, but they must be serializable as strings. Structured types like serialized are supported out of the box.

If you need to support a custom type, the recommended way is using a serialized attribute. The declaration of the serialized attribute should go before the encryption declaration:

# GOOD
class Article < ApplicationRecord
  serialize :title, Title
  encrypts :title
end

# WRONG
class Article < ApplicationRecord
  encrypts :title
  serialize :title, Title
end

2.4 Ignoring case

You might need to ignore case when querying deterministically encrypted data. There are two options that can help you here.

You can use the :downcase option when declaring the encrypted attribute to downcase the content before encryption occurs.

class Person
  encrypts :email_address, deterministic: true, downcase: true
end

When using :downcase, the original case is lost. In some situations, you might want to ignore the case only when querying, while also storing the original case. For those situations, you can use the option :ignore_case. This requires you to add a new column named original_<column_name> to store the content with the case unchanged:

class Label
  encrypts :name, deterministic: true, ignore_case: true # the content with the original case will be stored in the column `original_name`
end

2.5 Support for unencrypted data

To ease migrations of unencrypted data, the library includes the option config.active_record.encryption.support_unencrypted_data. When set to true:

  • Trying to read encrypted attributes that are not encrypted will work normally, without raising any error
  • Queries with deterministically-encrypted attributes will include the "clear text" version of them, to support finding both encrypted and unencrypted content. You need to set config.active_record.encryption.extend_queries = true to enable this.

This options is meant to be used in transition periods while clear data and encrypted data need to coexist. Their value is false by default, which is the recommended goal for any application: errors will be raised when working with unencrypted data.

2.6 Support for previous encryption schemes

Changing encryption properties of attributes can break existing data. For example, imagine you want to make a "deterministic" attribute "not deterministic". If you just change the declaration in the model, reading existing ciphertexts will fail because they are different now.

To support these situations, you can declare previous encryption schemes that will be used in two scenarios:

  • When reading encrypted data, Active Record Encryption will try previous encryption schemes if the current scheme doesn't work.
  • When querying deterministic data, it will add ciphertexts using previous schemes to the queries so that queries work seamlessly with data encrypted with different scheme. You need to set config.active_record.encryption.extend_queries = true to enable this.

You can configure previous encryption schemes:

  • Globally
  • On a per-attribute basis
2.6.1 Global previous encryption schemes

You can add previous encryption schemes by adding them as list of properties using the previous config property in your application.rb:

config.active_record.encryption.previous = [ { key_provider: MyOldKeyProvider.new } ]
2.6.2 Per-attribute encryption schemes

Use :previous when declaring the attribute:

class Article
  encrypts :title, deterministic: true, previous: { deterministic: false }
end
2.6.3 Encryption schemes and deterministic attributes

When adding previous encryption schemes:

  • With non-deterministic encryption, new information will always be encrypted with the newest (current) encryption scheme.
  • With deterministic encryption, new information will always be encrypted with the oldest encryption scheme by default.

The reason is that, with deterministic encryption, you normally want ciphertexts to remain constant. You can change this behavior by setting deterministic: { fixed: false }. In that case, it will use the newest encryption scheme for encrypting new data.

2.7 Unique constraints

Unique constraints can only be used with data encrypted deterministically.

2.7.1 Unique validations

Unique validations are supported normally as long as extended queries are enabled (config.active_record.encryption.extend_queries = true).

class Person
  validates :email_address, uniqueness: true
  encrypts :email_address, deterministic: true, downcase: true
end

They will also work when combining encrypted and unencrypted data, and when configuring previous encryption schemes.

If you want to ignore case make sure to use downcase: or ignore_case: in the encrypts declaration. Using the case_sensitive: option in the validation won't work.

2.7.2 Unique indexes

To support unique indexes on deterministically-encrypted columns, you need to make sure their ciphertext doesn't ever change.

To encourage this, by default, deterministic attributes will always use the oldest encryption scheme, when multiple encryption schemes are configured. Other than this, it's up to you making sure that encryption properties don't change for these attributes, or the unique indexes won't work.

class Person
  encrypts :email_address, deterministic: true
end

2.8 Filtering params named as encrypted columns

By default, encrypted columns are configured to be automatically filtered in Rails logs. You can disable this behavior by adding this to your application.rb:

config.active_record.encryption.add_to_filter_parameters = false

In case you want exclude specific columns from this automatic filtering, add them to config.active_record.encryption.excluded_from_filter_parameters.

2.9 Encoding

The library will preserve the encoding for string values encrypted non-deterministically.

For values encrypted deterministically, by default, the library will force UTF-8 encoding. The reason is that encoding is stored along with the encrypted payload. This means that the same value with a different encoding will result in different ciphertexts when encrypted. You normally want to avoid this to keep queries and uniqueness constraints working, so the library will perform the conversion automatically on your behalf.

You can configure the desired default encoding for deterministic encryption with:

config.active_record.encryption.forced_encoding_for_deterministic_encryption = Encoding::US_ASCII

And you can disable this behavior and preserve the encoding in all cases with:

config.active_record.encryption.forced_encoding_for_deterministic_encryption = nil

3 Key management

Key management strategies are implemented by key providers. You can configure key providers globally or on a per-attribute basis.

3.1 Built-in key providers

3.1.1 DerivedSecretKeyProvider

A key provider that will serve keys derived from the provided passwords using PBKDF2.

config.active_record.encryption.key_provider = ActiveRecord::Encryption::DerivedSecretKeyProvider.new(["some passwords", "to derive keys from. ", "These should be in", "credentials"])

By default, active_record.encryption configures a DerivedSecretKeyProvider with the keys defined in active_record.encryption.primary_key.

3.1.2 EnvelopeEncryptionKeyProvider

Implements a simple envelope encryption strategy:

  • It generates a random key for each data-encryption operation
  • It stores the data-key with the data itself, encrypted with a primary key defined in the credential active_record.encryption.primary_key.

You can configure by adding this to your application.rb:

config.active_record.encryption.key_provider = ActiveRecord::Encryption::EnvelopeEncryptionKeyProvider.new

As with other built-in key providers, you can provide a list of primary keys in active_record.encryption.primary_key, to implement key-rotation schemes.

3.2 Custom key providers

For more advanced key-management schemes, you can configure a custom key provider in an initializer:

ActiveRecord::Encryption.key_provider = MyKeyProvider.new

A key provider must implement this interface:

class MyKeyProvider
  def encryption_key
  end

  def decryption_keys(encrypted_message)
  end
end

Both methods return ActiveRecord::Encryption::Key objects:

  • encryption_key returns the key used for encrypting some content
  • decryption keys returns a list of potential keys for decrypting a given message

A key can include arbitrary tags that will be stored unencrypted with the message. You can use ActiveRecord::Encryption::Message#headers to examine those values when decrypting.

3.3 Model-specific key providers

You can configure a key provider on a per-class basis with the :key_provider option:

class Article < ApplicationRecord
  encrypts :summary, key_provider: ArticleKeyProvider.new
end

3.4 Model-specific keys

You can configure a given key on a per-class basis with the :key option:

class Article < ApplicationRecord
  encrypts :summary, key: "some secret key for article summaries"
end

The key will be used internally to derive the key used to encrypt and decrypt the data.

3.5 Rotating keys

active_record.encryption can work with lists of keys to support implementing key-rotation schemes:

  • The last key will be used for encrypting new content.
  • All the keys will be tried when decrypting content until one works.
active_record
  encryption:
    primary_key:
        - a1cc4d7b9f420e40a337b9e68c5ecec6 # Previous keys can still decrypt existing content
        - bc17e7b413fd4720716a7633027f8cc4 # Active, encrypts new content
    key_derivation_salt: a3226b97b3b2f8372d1fc6d497a0c0d3

This enables workflows where you keep a short list of keys, by adding new keys, re-encrypting content and deleting old keys.

Rotating keys is not currently supported for deterministic encryption.

Active Record Encryption doesn't provide automatic management of key rotation processes yet. All the pieces are there, but this hasn't been implemented yet.

3.6 Storing key references

There is a setting active_record.encryption.store_key_references you can use to make active_record.encryption store a reference to the encryption key in the encrypted message itself.

config.active_record.encryption.store_key_references = true

This makes for a more performant decryption since, instead of trying lists of keys, the system can now locate keys directly. The price to pay is storage: encrypted data will be a bit bigger in size.

4 API

4.1 Basic API

ActiveRecord encryption is meant to be used declaratively, but it presents an API for advanced usage scenarios.

4.1.1 Encrypt and decrypt
article.encrypt # encrypt or re-encrypt all the encryptable attributes
article.decrypt # decrypt all the encryptable attributes
4.1.2 Read ciphertext
article.ciphertext_for(:title)
4.1.3 Check if attribute is encrypted or not
article.encrypted_attribute?(:title)

5 Configuration

5.1 Configuration options

You can configure Active Record Encryption options by setting them in your application.rb (most common scenario) or in a specific environment config file config/environments/<env name>.rb if you want to set them on a per-environment basis.

All the config options are namespaced in active_record.encryption.config. For example:

config.active_record.encryption.key_provider = ActiveRecord::Encryption::EnvelopeEncryptionKeyProvider.new
config.active_record.encryption.store_key_references = true
config.active_record.encryption.extend_queries = true

The available config options are:

Key Value
support_unencrypted_data When true, unencrypted data can be read normally. When false, it will raise. Default: false.
extend_queries When true, queries referencing deterministically encrypted attributes will be modified to include additional values if needed. Those additional values will be the clean version of the value, when support_unencrypted_data is true) and values encrypted with previous encryption schemes if any (as provided with the previous: option). Default: false (experimental).
encrypt_fixtures When true, encryptable attributes in fixtures will be automatically encrypted when those are loaded. Default: false.
store_key_references When true, a reference to the encryption key is stored in the headers of the encrypted message. This makes for a faster decryption when multiple keys are in use. Default: false.
add_to_filter_parameters When true, encrypted attribute names are added automatically to the list of filtered params that won't be shown in logs. Default: true.
excluded_from_filter_parameters You can configure a list of params that won't be filtered out when add_to_filter_parameters is true. Default: [].
validate_column_size Adds a validation based on the column size. This is recommended to prevent storing huge values using highly compressible payloads. Default: true.
primary_key The key or lists of keys that is used to derive root data-encryption keys. They way they are used depends on the key provider configured. It's preferred to configure it via a credential active_record_encryption.primary_key.
deterministic_key The key or list of keys used for deterministic encryption. It's preferred to configure it via a credential active_record_encryption.deterministic_key.
key_derivation_salt The salt used when deriving keys. It's preferred to configure it via a credential active_record_encryption.key_derivation_salt.
forced_encoding_for_deterministic_encryption The default encoding for attributes encrypted deterministically. You can disable forced encoding by setting this option to nil. It's Encoding::UTF_8 by default.

It's recommended to use Rails built-in credentials support to store keys. If you prefer to set them manually via config properties, make sure you don't commit them with your code (e.g: use environment variables).

5.2 Encryption contexts

An encryption context defines the encryption components that are used in a given moment. There is a default encryption context based on your global configuration, but you can configure a custom context for a given attribute or when running a specific block of code.

Encryption contexts are a flexible but advanced configuration mechanism. Most users should not have to care about them.

The main components of encryption contexts are:

  • encryptor: exposes the internal API for encrypting and decrypting data. It interacts with a key_provider to build encrypted messages and deal with their serialization. The encryption/decryption itself is done by the cipher and the serialization by message_serializer.
  • cipher the encryption algorithm itself (Aes 256 GCM)
  • key_provider serves encryption and decryption keys.
  • message_serializer: serializes and deserializes encrypted payloads (Message).

If you decide to build your own message_serializer, It's important to use safe mechanisms that can't deserialize arbitrary objects. A common supported scenario is encrypting existing unencrypted data. An attacker can leverage this to enter a tampered payload before encryption takes place and perform RCE attacks. This means custom serializers should avoid Marshal, YAML.load (use YAML.safe_load instead) or JSON.load (use JSON.parse instead).

5.2.1 Global encryption context

The global encryption context is the one used by default and is configured as other configuration properties in your application.rb or environment config files.

config.active_record.encryption.key_provider = ActiveRecord::Encryption::EnvelopeEncryptionKeyProvider.new
config.active_record_encryption.encryptor = MyEncryptor.new
5.2.2 Per-attribute encryption contexts

You can override encryption context params by passing them in the attribute declaration:

class Attribute
  encrypts :title, encryptor: MyAttributeEncryptor.new
end
5.2.3 Encryption context when running a block of code

You can use ActiveRecord::Encryption.with_encryption_context to set an encryption context for a given block of code:

ActiveRecord::Encryption.with_encryption_context(encryptor: ActiveRecord::Encryption::NullEncryptor.new) do
  ...
end
5.2.4 Built-in encryption contexts
5.2.4.1 Disable encryption

You can run code without encryption:

ActiveRecord::Encryption.without_encryption do
   ...
end

This means that reading encrypted text will return the ciphertext and saved content will be stored unencrypted.

5.2.4.2 Protect encrypted data

You can run code without encryption but preventing overwriting encrypted content:

ActiveRecord::Encryption.protecting_encrypted_data do
   ...
end

This can be handy if you want to protect encrypted data while still letting someone run arbitrary code against it (e.g: in a Rails console).

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