require "openssl" require "base64" require "active_support/core_ext/array/extract_options" require "active_support/message_verifier" module ActiveSupport # 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) # => # # encrypted_data = crypt.encrypt_and_sign('my secret data') # => "NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh..." # crypt.decrypt_and_verify(encrypted_data) # => "my secret data" class MessageEncryptor DEFAULT_CIPHER = "aes-256-cbc" module NullSerializer #:nodoc: def self.load(value) value end def self.dump(value) value end end module NullVerifier #:nodoc: def self.verify(value) value end def self.generate(value) value end end class InvalidMessage < StandardError; end OpenSSLCipherError = OpenSSL::Cipher::CipherError # 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 by # OpenSSL::Cipher.ciphers. Default is 'aes-256-cbc'. # * :digest - String of digest to use for signing. Default is # +SHA1+. Ignored when using an AEAD cipher like 'aes-256-gcm'. # * :serializer - Object serializer to use. Default is +Marshal+. 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 # Encrypt and sign a message. We need to sign the message in order to avoid # padding attacks. Reference: http://www.limited-entropy.com/padding-oracle-attacks. def encrypt_and_sign(value) verifier.generate(_encrypt(value)) end # Decrypt and verify a message. We need to verify the message in order to # avoid padding attacks. Reference: http://www.limited-entropy.com/padding-oracle-attacks. def decrypt_and_verify(value) _decrypt(verifier.verify(value)) end # Given a cipher, returns the key length of the cipher to help generate the key of desired size def self.key_len(cipher = DEFAULT_CIPHER) OpenSSL::Cipher.new(cipher).key_len end private 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 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.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 def new_cipher OpenSSL::Cipher.new(@cipher) end def verifier @verifier end def aead_mode? @aead_mode ||= new_cipher.authenticated? end def resolve_verifier if aead_mode? NullVerifier else MessageVerifier.new(@sign_secret || @secret, digest: @digest, serializer: NullSerializer) end end end end