Active Record Encryption

Chapters

1. Why Encrypt Data at the Application Level?
2. Basic Usage
   • Setup
   • Declaration of Encrypted Attributes
   • Deterministic and Non-deterministic Encryption
3. Features
   • Action Text
   • Fixtures
   • Supported Types
   • Ignoring Case
   • Support for Unencrypted Data
   • Support for Previous Encryption Schemes
   • Unique Constraints
   • Filtering Params Named as Encrypted Columns
   • Encoding
4. Key Management
   • Built-in Key Providers
   • Custom Key Providers
   • Model-specific Key Providers
   • Model-specific Keys
   • Rotating Keys
   • Storing Key References
5. API
   • Basic API
6. Configuration
   • Configuration Options
   • Encryption Contexts

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 sits between the database and the application. The application will access unencrypted data, but the database will store it encrypted.

1 Why Encrypt Data at the Application Level?

Active Record Encryption exists to protect sensitive information in your application. A typical example is personally identifiable information from users. But why would you want application-level encryption if you are already encrypting your database at rest?

As an immediate practical benefit, encrypting sensitive attributes adds an additional security layer. For example, if an attacker gained access to your database, a snapshot of it, or your application logs, they wouldn't be able to make sense of the encrypted information. Additionally, encryption can prevent developers from unintentionally exposing users' sensitive data in application logs.

But more importantly, by using Active Record Encryption, you define what constitutes sensitive information in your application at the code level. Active Record Encryption enables granular control of data access in your application and services consuming data from your application. For example, consider auditable Rails consoles that protect encrypted data or check the built-in system to filter controller params automatically.

2 Basic Usage

2.1 Setup

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 values can be stored by copying and pasting the generated values into your existing Rails credentials. Alternatively, these values can be configured from other sources, such as environment variables:

config.active_record.encryption.primary_key = ENV['ACTIVE_RECORD_ENCRYPTION_PRIMARY_KEY']
config.active_record.encryption.deterministic_key = ENV['ACTIVE_RECORD_ENCRYPTION_DETERMINISTIC_KEY']
config.active_record.encryption.key_derivation_salt = ENV['ACTIVE_RECORD_ENCRYPTION_KEY_DERIVATION_SALT']

2.2 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 in the database and will decrypt them upon retrieval:

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

But, under the hood, the executed SQL looks like this:

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

2.2.1 Important: About Storage and Column Size

Encryption requires extra space because of Base64 encoding and the metadata stored along with the encrypted payloads. When using the built-in envelope encryption key provider, you can estimate the worst-case overhead at around 255 bytes. This overhead is negligible at larger sizes. Not only because it gets diluted but because the library uses compression by default, which can offer up to 30% storage savings over the unencrypted version for larger payloads.

There is an important concern about string column sizes: in modern databases the column size determines the number of characters it can allocate, not the number of bytes. For example, with UTF-8, each character can take up to four bytes, so, potentially, a column in a database using UTF-8 can store up to four times its size in terms of number of bytes. Now, encrypted payloads are binary strings serialized as Base64, so they can be stored in regular string columns. Because they are a sequence of ASCII bytes, an encrypted column can take up to four times its clear version size. So, even if the bytes stored in the database are the same, the column must be four times bigger.

In practice, this means:

• When encrypting short texts written in western alphabets (mostly ASCII characters), you should account for that 255 additional overhead when defining the column size.
• When encrypting short texts written in non-western alphabets, such as Cyrillic, you should multiply the column size by 4. Notice that the storage overhead is 255 bytes at most.
• When encrypting long texts, you can ignore column size concerns.

Some examples:

2.3 Deterministic and Non-deterministic Encryption

By default, Active Record Encryption uses a non-deterministic approach to encryption. Non-deterministic, in this context, means that encrypting the same content with the same password twice will result in different ciphertexts. This approach improves security by making crypto-analysis of ciphertexts harder, and 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 non-deterministic approach is recommended unless you need to query the data.

3 Features

3.1 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

3.2 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.

3.2.1 Action Text Fixtures

To encrypt Action Text fixtures, you should place them in fixtures/action_text/encrypted_rich_texts.yml.

3.3 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:

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

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

3.4 Ignoring Case

You might need to ignore casing when querying deterministically encrypted data. Two approaches make accomplishing this easier:

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

3.5 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 option is meant to be used during transition periods while clear data and encrypted data must coexist. Both are set to false by default, which is the recommended goal for any application: errors will be raised when working with unencrypted data.

3.6 Support for Previous Encryption Schemes

Changing encryption properties of attributes can break existing data. For example, imagine you want to make a deterministic attribute non-deterministic. If you just change the declaration in the model, reading existing ciphertexts will fail because the encryption method is 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 so that queries work seamlessly with data encrypted with different schemes. You must set config.active_record.encryption.extend_queries = true to enable this.

You can configure previous encryption schemes:

• Globally
• On a per-attribute basis

3.6.1 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 } ]

3.6.2 Per-attribute Encryption Schemes

Use :previous when declaring the attribute:

class Article
  encrypts :title, deterministic: true, previous: { deterministic: false }
end

3.6.3 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.

Typically, with deterministic encryption, you 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.

3.7 Unique Constraints

3.7.1 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.

3.7.2 Unique Indexes

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

To encourage this, deterministic attributes will always use the oldest available encryption scheme by default when multiple encryption schemes are configured. Otherwise, it's your job to ensure encryption properties don't change for these attributes, or the unique indexes won't work.

class Person
  encrypts :email_address, deterministic: true
end

3.8 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 the following to your application.rb:

config.active_record.encryption.add_to_filter_parameters = false

If filtering is enabled, but you want to exclude specific columns from automatic filtering, add them to config.active_record.encryption.excluded_from_filter_parameters:

config.active_record.encryption.excluded_from_filter_parameters = [:catchphrase]

When generating the filter parameter, Rails will use the model name as a prefix. E.g: For Person#name, the filter parameter will be person.name.

3.9 Encoding

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

Because encoding is stored along with the encrypted payload, values encrypted deterministically will force UTF-8 encoding by default. Therefore the same value with a different encoding will result in a different ciphertext when encrypted. You usually 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

4 Key Management

Key providers implement key management strategies. You can configure key providers globally, or on a per attribute basis.

4.1 Built-in Key Providers

4.1.1 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"])

4.1.2 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 Active Record to use this key provider 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.

4.2 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.

4.3 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

4.4 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

Active Record uses the key to derive the key used to encrypt and decrypt the data.

4.5 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 in which you keep a short list of keys by adding new keys, re-encrypting content, and deleting old keys.

4.6 Storing Key References

You can configure active_record.encryption.store_key_references 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

Doing so makes for more performant decryption because the system can now locate keys directly instead of trying lists of keys. The price to pay is storage: encrypted data will be a bit bigger.

5 API

5.1 Basic API

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

5.1.1 Encrypt and Decrypt

article.encrypt # encrypt or re-encrypt all the encryptable attributes
article.decrypt # decrypt all the encryptable attributes

5.1.2 Read Ciphertext

article.ciphertext_for(:title)

5.1.3 Check if Attribute is Encrypted or Not

article.encrypted_attribute?(:title)

6 Configuration

6.1 Configuration Options

You can configure Active Record Encryption options 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.

6.1.1 config.active_record.encryption.support_unencrypted_data

When true, unencrypted data can be read normally. When false, it will raise errors. Default: false.

6.1.2 config.active_record.encryption.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 config.active_record.encryption.support_unencrypted_data is true) and values encrypted with previous encryption schemes, if any (as provided with the previous: option). Default: false (experimental).

6.1.3 config.active_record.encryption.encrypt_fixtures

When true, encryptable attributes in fixtures will be automatically encrypted when loaded. Default: false.

6.1.4 config.active_record.encryption.store_key_references

When true, a reference to the encryption key is stored in the headers of the encrypted message. This makes for faster decryption when multiple keys are in use. Default: false.

6.1.5 config.active_record.encryption.add_to_filter_parameters

When true, encrypted attribute names are added automatically to config.filter_parameters and won't be shown in logs. Default: true.

6.1.6 config.active_record.encryption.excluded_from_filter_parameters

You can configure a list of params that won't be filtered out when config.active_record.encryption.add_to_filter_parameters is true. Default: [].

6.1.7 config.active_record.encryption.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.

6.1.8 config.active_record.encryption.primary_key

The key or lists of keys used to derive root data-encryption keys. The way they are used depends on the key provider configured. It's preferred to configure it via the active_record_encryption.primary_key credential.

6.1.9 config.active_record.encryption.deterministic_key

The key or list of keys used for deterministic encryption. It's preferred to configure it via the active_record_encryption.deterministic_key credential.

6.1.10 config.active_record.encryption.key_derivation_salt

The salt used when deriving keys. It's preferred to configure it via the active_record_encryption.key_derivation_salt credential.

6.1.11 config.active_record.encryption.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.

6.1.12 config.active_record.encryption.hash_digest_class

The digest algorithm used to derive keys. OpenSSL::Digest::SHA1 by default.

6.1.13 config.active_record.encryption.support_sha1_for_non_deterministic_encryption

Supports decrypting data encrypted non-deterministically with a digest class SHA1. Default is false, which means it will only support the digest algorithm configured in config.active_record.encryption.hash_digest_class.

6.2 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.

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).

6.2.1 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

6.2.2 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

6.2.3 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

6.2.4 Built-in Encryption Contexts

6.2.4.1 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.

6.2.4.2 Protect Encrypted Data

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

ActiveRecord::Encryption.protecting_encrypted_data do
  # ...
end

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

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