aboutsummaryrefslogtreecommitdiffstats
path: root/activesupport/lib/active_support/message_encryptor.rb
blob: 27620f56bec08c723a7c71c4c875636f7240dc6e (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
# frozen_string_literal: true

require "openssl"
require "base64"
require_relative "core_ext/array/extract_options"
require_relative "message_verifier"
require_relative "messages/metadata"

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 <tt>MessageVerifier</tt>, 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"
  #
  # === 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: :login)
  #
  # Then that same purpose must be passed when verifying to get the data back out:
  #
  #   crypt.decrypt_and_verify(token, purpose: :login)    # => "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 upto the expire time.
  # Thereafter, verifying returns +nil+.
  class MessageEncryptor
    class << self
      attr_accessor :use_authenticated_message_encryption #:nodoc:

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

    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-gcm' cipher, this is 256
    # bits. If you are using a user-entered secret, you can generate a suitable
    # key by using <tt>ActiveSupport::KeyGenerator</tt> 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:
    # * <tt>:cipher</tt>     - Cipher to use. Can be any cipher returned by
    #   <tt>OpenSSL::Cipher.ciphers</tt>. Default is 'aes-256-gcm'.
    # * <tt>:digest</tt> - String of digest to use for signing. Default is
    #   +SHA1+. Ignored when using an AEAD cipher like 'aes-256-gcm'.
    # * <tt>:serializer</tt> - 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] || self.class.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: https://www.limited-entropy.com/padding-oracle-attacks/.
    def encrypt_and_sign(value, expires_at: nil, expires_in: nil, purpose: nil)
      verifier.generate(_encrypt(value, expires_at: expires_at, expires_in: expires_in, purpose: purpose))
    end

    # Decrypt and verify a message. We need to verify the message in order to
    # avoid padding attacks. Reference: https://www.limited-entropy.com/padding-oracle-attacks/.
    def decrypt_and_verify(data, purpose: nil)
      _decrypt(verifier.verify(data), purpose)
    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, **metadata_options)
        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(Messages::Metadata.wrap(@serializer.dump(value), metadata_options))
        encrypted_data << cipher.final

        blob = "#{::Base64.strict_encode64 encrypted_data}--#{::Base64.strict_encode64 iv}"
        blob = "#{blob}--#{::Base64.strict_encode64 cipher.auth_tag}" if aead_mode?
        blob
      end

      def _decrypt(encrypted_message, purpose)
        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

        message = Messages::Metadata.verify(decrypted_data, purpose)
        @serializer.load(message) if message
      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