class ActiveSupport::MessageEncryptor
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.
salt = SecureRandom.random_bytes(64) key = ActiveSupport::KeyGenerator.new('password').generate_key(salt, 32) # => "\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"
Constants
- DEFAULT_CIPHER
- OpenSSLCipherError
Public Class Methods
Given a cipher, returns the key length of the cipher to help generate the key of desired size
# File lib/active_support/message_encryptor.rb, line 88 def self.key_len(cipher = DEFAULT_CIPHER) OpenSSL::Cipher.new(cipher).key_len end
Initialize a new MessageEncryptor.
secret
must be at least as long as the cipher key size. For
the default 'aes-256-cbc' cipher, this is 256 bits. If you are
using a user-entered secret, you can generate a suitable key by using
ActiveSupport::KeyGenerator
or a similar key derivation
function.
First additional parameter is used as the signature key for
MessageVerifier
. This allows you to specify keys to encrypt
and sign data.
ActiveSupport::MessageEncryptor.new('secret', 'signature_secret')
Options:
-
:cipher
- Cipher to use. Can be any cipher returned byOpenSSL::Cipher.ciphers
. Default is 'aes-256-cbc'. -
:digest
- String of digest to use for signing. Default isSHA1
. Ignored when using an AEAD cipher like 'aes-256-gcm'. -
:serializer
- Object serializer to use. Default isMarshal
.
# File lib/active_support/message_encryptor.rb, line 64 def initialize(secret, *signature_key_or_options) options = signature_key_or_options.extract_options! sign_secret = signature_key_or_options.first @secret = secret @sign_secret = sign_secret @cipher = options[:cipher] || DEFAULT_CIPHER @digest = options[:digest] || "SHA1" unless aead_mode? @verifier = resolve_verifier @serializer = options[:serializer] || Marshal end
Public Instance Methods
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.
# File lib/active_support/message_encryptor.rb, line 83 def decrypt_and_verify(value) _decrypt(verifier.verify(value)) end
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.
# File lib/active_support/message_encryptor.rb, line 77 def encrypt_and_sign(value) verifier.generate(_encrypt(value)) end
Private Instance Methods
# File lib/active_support/message_encryptor.rb, line 111 def _decrypt(encrypted_message) cipher = new_cipher encrypted_data, iv, auth_tag = encrypted_message.split("--".freeze).map { |v| ::Base64.strict_decode64(v) } # 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 raise InvalidMessage if aead_mode? && (auth_tag.nil? || auth_tag.bytes.length != 16) 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 @serializer.load(decrypted_data) rescue OpenSSLCipherError, TypeError, ArgumentError raise InvalidMessage end
# File lib/active_support/message_encryptor.rb, line 94 def _encrypt(value) 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(@serializer.dump(value)) encrypted_data << cipher.final blob = "#{::Base64.strict_encode64 encrypted_data}--#{::Base64.strict_encode64 iv}" blob << "--#{::Base64.strict_encode64 cipher.auth_tag}" if aead_mode? blob end
# File lib/active_support/message_encryptor.rb, line 144 def aead_mode? @aead_mode ||= new_cipher.authenticated? end
# File lib/active_support/message_encryptor.rb, line 136 def new_cipher OpenSSL::Cipher.new(@cipher) end
# File lib/active_support/message_encryptor.rb, line 148 def resolve_verifier if aead_mode? NullVerifier else MessageVerifier.new(@sign_secret || @secret, digest: @digest, serializer: NullSerializer) end end
# File lib/active_support/message_encryptor.rb, line 140 def verifier @verifier end