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Class: ActiveSupport::MessageEncryptor

Relationships & Source Files
Namespace Children
Modules:
NullSerializer
Exceptions:
InvalidMessage
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, Messages::Codec
Instance Chain:
self, Messages::Rotator, Messages::Codec, Messages::Metadata
Inherits: ActiveSupport::Messages::Codec
Defined in: activesupport/lib/active_support/message_encryptor.rb

Overview

MessageEncryptor is a simple way to encrypt values which get stored somewhere you don’t trust.

The cipher text and initialization vector are base64 encoded and returned to you.

This can be used in situations similar to the MessageVerifier, but where you don’t want users to be able to determine the value of the payload.

len   = ActiveSupport::MessageEncryptor.key_len
salt  = SecureRandom.random_bytes(len)
key   = ActiveSupport::KeyGenerator.new('password').generate_key(salt, len) # => "\x89\xE0\x156\xAC..."
crypt = ActiveSupport::MessageEncryptor.new(key)                            # => #<ActiveSupport::MessageEncryptor ...>
encrypted_data = crypt.encrypt_and_sign('my secret data')                   # => "NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh..."
crypt.decrypt_and_verify(encrypted_data)                                    # => "my secret data"

The #decrypt_and_verify method will raise an InvalidMessage exception if the data provided cannot be decrypted or verified.

crypt.decrypt_and_verify('not encrypted data') # => ActiveSupport::MessageEncryptor::InvalidMessage

Confining messages to a specific purpose

By default any message can be used throughout your app. But they can also be confined to a specific :purpose.

token = crypt.encrypt_and_sign("this is the chair", purpose: :)

Then that same purpose must be passed when verifying to get the data back out:

crypt.decrypt_and_verify(token, purpose: :)    # => "this is the chair"
crypt.decrypt_and_verify(token, purpose: :shipping) # => nil
crypt.decrypt_and_verify(token)                     # => nil

Likewise, if a message has no purpose it won’t be returned when verifying with a specific purpose.

token = crypt.encrypt_and_sign("the conversation is lively")
crypt.decrypt_and_verify(token, purpose: :scare_tactics) # => nil
crypt.decrypt_and_verify(token)                          # => "the conversation is lively"

Making messages expire

By default messages last forever and verifying one year from now will still return the original value. But messages can be set to expire at a given time with :expires_in or :expires_at.

crypt.encrypt_and_sign(parcel, expires_in: 1.month)
crypt.encrypt_and_sign(doowad, expires_at: Time.now.end_of_year)

Then the messages can be verified and returned up to the expire time. Thereafter, verifying returns nil.

Rotating keys

MessageEncryptor also supports rotating out old configurations by falling back to a stack of encryptors. Call rotate to build and add an encryptor so #decrypt_and_verify will also try the fallback.

By default any rotated encryptors use the values of the primary encryptor unless specified otherwise.

You’d give your encryptor the new defaults:

crypt = ActiveSupport::MessageEncryptor.new(@secret, cipher: "aes-256-gcm")

Then gradually rotate the old values out by adding them as fallbacks. Any message generated with the old values will then work until the rotation is removed.

crypt.rotate old_secret            # Fallback to an old secret instead of @secret.
crypt.rotate cipher: "aes-256-cbc" # Fallback to an old cipher instead of aes-256-gcm.

Though if both the secret and the cipher was changed at the same time, the above should be combined into:

crypt.rotate old_secret, cipher: "aes-256-cbc"

Constant Summary

Messages::Metadata - Included

ENVELOPE_SERIALIZERS, TIMESTAMP_SERIALIZERS

Class Attribute Summary

Messages::Codec - Inherited

.default_serializer

Class Method Summary

Messages::Codec - Inherited

.new

Instance Attribute Summary

Messages::Codec - Inherited

#serializer, #use_message_serializer_for_metadata?

Messages::Metadata - Included

#use_message_serializer_for_metadata, #use_message_serializer_for_metadata?

Instance Method Summary

Messages::Rotator - Included

#fall_back_to, #initialize, #read_message, #rotate, #build_rotation, #catch_rotation_error

Messages::Codec - Inherited

#catch_and_ignore, #catch_and_raise, #decode, #deserialize, #encode, #serialize

Messages::Metadata - Included

#deserialize_from_json, #deserialize_from_json_safe_string, #deserialize_with_metadata, #dual_serialized_metadata_envelope_json?, #extract_from_metadata_envelope, #metadata_envelope?, #parse_expiry, #pick_expiry, #serialize_to_json, #serialize_to_json_safe_string, #serialize_with_metadata, #wrap_in_metadata_envelope, #wrap_in_metadata_legacy_envelope

Constructor Details

.new(secret, sign_secret = nil, **options) ⇒ MessageEncryptor

Initialize a new MessageEncryptor. secret must be at least as long as the cipher key size. For the default ‘aes-256-gcm’ cipher, this is 256 bits. If you are using a user-entered secret, you can generate a suitable key by using KeyGenerator or a similar key derivation function.

The first additional parameter is used as the signature key for MessageVerifier. This allows you to specify keys to encrypt and sign data. Ignored when using an AEAD cipher like ‘aes-256-gcm’.

ActiveSupport::MessageEncryptor.new('secret', 'signature_secret')

Options

:cipher

Cipher to use. Can be any cipher returned by OpenSSL::Cipher.ciphers. Default is ‘aes-256-gcm’.

:digest

Digest used for signing. Ignored when using an AEAD cipher like ‘aes-256-gcm’.

:serializer

The serializer used to serialize message data. You can specify any object that responds to dump and load, or you can choose from several preconfigured serializers: :marshal, :json_allow_marshal, :json, :message_pack_allow_marshal, :message_pack.

The preconfigured serializers include a fallback mechanism to support multiple deserialization formats. For example, the :marshal serializer will serialize using Marshal, but can deserialize using Marshal, ActiveSupport::JSON, or ActiveSupport::MessagePack. This makes it easy to migrate between serializers.

The :marshal, :json_allow_marshal, and :message_pack_allow_marshal serializers support deserializing using Marshal, but the others do not. Beware that Marshal is a potential vector for deserialization attacks in cases where a message signing secret has been leaked. If possible, choose a serializer that does not support Marshal.

The :message_pack and :message_pack_allow_marshal serializers use ActiveSupport::MessagePack, which can roundtrip some Ruby types that are not supported by JSON, and may provide improved performance. However, these require the msgpack gem.

When using Rails, the default depends on config.active_support.message_serializer. Otherwise, the default is :marshal.

:url_safe

By default, MessageEncryptor generates RFC 4648 compliant strings which are not URL-safe. In other words, they can contain “+” and “/”. If you want to generate URL-safe strings (in compliance with “Base 64 Encoding with URL and Filename Safe Alphabet” in RFC 4648), you can pass true.

:force_legacy_metadata_serializer

Whether to use the legacy metadata serializer, which serializes the message first, then wraps it in an envelope which is also serialized. This was the default in Rails 7.0 and below.

If you don’t pass a truthy value, the default is set using config.active_support.use_message_serializer_for_metadata.

[ GitHub ] 

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 183



def initialize(secret, sign_secret = nil, **options)
  super(**options)
  @secret = secret
  @cipher = options[:cipher] || self.class.default_cipher
  @aead_mode = new_cipher.authenticated?
  @verifier = if !@aead_mode
    MessageVerifier.new(sign_secret || secret, **options, serializer: NullSerializer)
  end
end


  







Class Attribute Details



  

    .use_authenticated_message_encryption   (rw)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 93



cattr_accessor :use_authenticated_message_encryption, instance_accessor: false, default: false


  







Class Method Details



  

    .default_cipher  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 96



def default_cipher # :nodoc:
  if use_authenticated_message_encryption
    "aes-256-gcm"
  else
    "aes-256-cbc"
  end
end


  








  

    .key_len(cipher = default_cipher)  
  



  

    

Given a cipher, returns the key length of the cipher to help generate the key of desired size


  



  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 252



def self.key_len(cipher = default_cipher)
  OpenSSL::Cipher.new(cipher).key_len
end


  







Instance Attribute Details



  

    #aead_mode?   (readonly, private)
  



  

    

Alias for #aead_mode.


  



  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 372



alias :aead_mode? :aead_mode


  







Instance Method Details



  

    #aead_mode   (readonly, private)
    Also known as: #aead_mode?
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 371



attr_reader :aead_mode


  








  

    #create_message(value, **options)  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 256



def create_message(value, **options) # :nodoc:
  sign(encrypt(serialize_with_metadata(value, **options)))
end


  








  

    #decrypt(encrypted_message)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 295



def decrypt(encrypted_message)
  cipher = new_cipher
  encrypted_data, iv, auth_tag = extract_parts(encrypted_message)

  # Currently the OpenSSL bindings do not raise an error if auth_tag is
  # truncated, which would allow an attacker to easily forge it. See
  # https://github.com/ruby/openssl/issues/63
  if aead_mode? && auth_tag.bytesize != AUTH_TAG_LENGTH
    throw :invalid_message_format, "truncated auth_tag"
  end

  cipher.decrypt
  cipher.key = @secret
  cipher.iv  = iv
  if aead_mode?
    cipher.auth_tag = auth_tag
    cipher.auth_data = ""
  end

  decrypted_data = cipher.update(encrypted_data)
  decrypted_data << cipher.final
rescue OpenSSLCipherError => error
  throw :invalid_message_format, error
end


  








  

    #decrypt_and_verify(message, **options)  
  



  

    

Decrypt and verify a message. We need to verify the message in order to avoid padding attacks. Reference: www.limited-entropy.com/padding-oracle-attacks/.



Options


:purpose



The purpose that the message was generated with. If the purpose does not match, decrypt_and_verify will return nil.



message = encryptor.encrypt_and_sign("hello", purpose: "greeting")
encryptor.decrypt_and_verify(message, purpose: "greeting") # => "hello"
encryptor.decrypt_and_verify(message)                      # => nil

message = encryptor.encrypt_and_sign("bye")
encryptor.decrypt_and_verify(message)                      # => "bye"
encryptor.decrypt_and_verify(message, purpose: "greeting") # => nil




  



  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 241



def decrypt_and_verify(message, **options)
  catch_and_raise :invalid_message_format, as: InvalidMessage do
    catch_and_raise :invalid_message_serialization, as: InvalidMessage do
      catch_and_ignore :invalid_message_content do
        read_message(message, **options)
      end
    end
  end
end


  








  

    #encrypt(data)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 277



def encrypt(data)
  cipher = new_cipher
  cipher.encrypt
  cipher.key = @secret

  # Rely on OpenSSL for the initialization vector
  iv = cipher.random_iv
  cipher.auth_data = "" if aead_mode?

  encrypted_data = cipher.update(data)
  encrypted_data << cipher.final

  parts = [encrypted_data, iv]
  parts << cipher.auth_tag(AUTH_TAG_LENGTH) if aead_mode?

  join_parts(parts)
end


  








  

    #encrypt_and_sign(value, **options)  
  



  

    

Encrypt and sign a message. We need to sign the message in order to avoid padding attacks. Reference: www.limited-entropy.com/padding-oracle-attacks/.



Options


:expires_at



The datetime at which the message expires. After this datetime, verification of the message will fail.



message = encryptor.encrypt_and_sign("hello", expires_at: Time.now.tomorrow)
encryptor.decrypt_and_verify(message) # => "hello"
# 24 hours later...
encryptor.decrypt_and_verify(message) # => nil


:expires_in



The duration for which the message is valid. After this duration has elapsed, verification of the message will fail.



message = encryptor.encrypt_and_sign("hello", expires_in: 24.hours)
encryptor.decrypt_and_verify(message) # => "hello"
# 24 hours later...
encryptor.decrypt_and_verify(message) # => nil


:purpose



The purpose of the message. If specified, the same purpose must be specified when verifying the message; otherwise, verification will fail. (See #decrypt_and_verify.)




  



  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 220



def encrypt_and_sign(value, **options)
  create_message(value, **options)
end


  








  

    #extract_part(encrypted_message, rindex, length)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 340



def extract_part(encrypted_message, rindex, length)
  index = rindex - length

  if encrypted_message[index - SEPARATOR.length, SEPARATOR.length] == SEPARATOR
    encrypted_message[index, length]
  else
    throw :invalid_message_format, "missing separator"
  end
end


  








  

    #extract_parts(encrypted_message)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 350



def extract_parts(encrypted_message)
  parts = []
  rindex = encrypted_message.length

  if aead_mode?
    parts << extract_part(encrypted_message, rindex, length_of_encoded_auth_tag)
    rindex -= SEPARATOR.length + length_of_encoded_auth_tag
  end

  parts << extract_part(encrypted_message, rindex, length_of_encoded_iv)
  rindex -= SEPARATOR.length + length_of_encoded_iv

  parts << encrypted_message[0, rindex]

  parts.reverse!.map! { |part| decode(part) }
end


  








  

    #inspect  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 264



def inspect # :nodoc:
  "#<#{self.class.name}:#{'%#016x' % (object_id << 1)}>"
end


  








  

    #join_parts(parts)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 336



def join_parts(parts)
  parts.map! { |part| encode(part) }.join(SEPARATOR)
end


  








  

    #length_after_encode(length_before_encode)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 320



def length_after_encode(length_before_encode)
  if @url_safe
    (4 * length_before_encode / 3.0).ceil # length without padding
  else
    4 * (length_before_encode / 3.0).ceil # length with padding
  end
end


  








  

    #length_of_encoded_auth_tag   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 332



def length_of_encoded_auth_tag
  @length_of_encoded_auth_tag ||= length_after_encode(AUTH_TAG_LENGTH)
end


  








  

    #length_of_encoded_iv   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 328



def length_of_encoded_iv
  @length_of_encoded_iv ||= length_after_encode(new_cipher.iv_len)
end


  








  

    #new_cipher   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 367



def new_cipher
  OpenSSL::Cipher.new(@cipher)
end


  








  

    #read_message(message, **options)  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 260



def read_message(message, **options) # :nodoc:
  deserialize_with_metadata(decrypt(verify(message)), **options)
end


  








  

    #sign(data)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 269



def sign(data)
  @verifier ? @verifier.create_message(data) : data
end


  








  

    #verify(data)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/message_encryptor.rb', line 273



def verify(data)
  @verifier ? @verifier.read_message(data) : data
end