class ActiveSupport::MessageEncryptor - activesupport-4.2.3 Documentation

# 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) # => "\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

OpenSSLCipherError

### Public Class Methods

new(secret, *signature_key_or_options) click to toggle source

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 with `OpenSSL::Digest::SHA256.new(user_secret).digest` or similar.

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`.

- `:serializer` - Object serializer to use. Default is `Marshal`.

    # File lib/active_support/message_encryptor.rb, line 45
    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] || 'aes-256-cbc'
      @verifier = MessageVerifier.new(@sign_secret || @secret, digest: options[:digest] || 'SHA1', serializer: NullSerializer)
      @serializer = options[:serializer] || Marshal
    end

### Public Instance Methods

decrypt_and_verify(value) click to toggle source

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 63
    def decrypt_and_verify(value)
      _decrypt(verifier.verify(value))
    end

encrypt_and_sign(value) click to toggle source

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 57
    def encrypt_and_sign(value)
      verifier.generate(_encrypt(value))
    end

### Private Instance Methods

_decrypt(encrypted_message) click to toggle source

    # File lib/active_support/message_encryptor.rb, line 83
    def _decrypt(encrypted_message)
      cipher = new_cipher
      encrypted_data, iv = encrypted_message.split("--").map {|v| ::Base64.strict_decode64(v)}

      cipher.decrypt
      cipher.key = @secret
      cipher.iv  = iv

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

      @serializer.load(decrypted_data)
    rescue OpenSSLCipherError, TypeError, ArgumentError
      raise InvalidMessage
    end

_encrypt(value) click to toggle source

    # File lib/active_support/message_encryptor.rb, line 69
    def _encrypt(value)
      cipher = new_cipher
      cipher.encrypt
      cipher.key = @secret

      # Rely on OpenSSL for the initialization vector
      iv = cipher.random_iv

      encrypted_data = cipher.update(@serializer.dump(value))
      encrypted_data << cipher.final

      "#{::Base64.strict_encode64 encrypted_data}--#{::Base64.strict_encode64 iv}"
    end

new_cipher() click to toggle source

    # File lib/active_support/message_encryptor.rb, line 99
    def new_cipher
      OpenSSL::Cipher::Cipher.new(@cipher)
    end

verifier() click to toggle source

    # File lib/active_support/message_encryptor.rb, line 103
    def verifier
      @verifier
    end