aboutsummaryrefslogtreecommitdiffstats
path: root/activesupport/lib/active_support/message_verifier.rb
blob: 0be13f6f036e4372c027f66e09e883e0053b7779 (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
203
204
205
206
207
208
# frozen_string_literal: true

require "base64"
require_relative "core_ext/object/blank"
require_relative "security_utils"
require_relative "messages/metadata"
require_relative "messages/rotator"

module ActiveSupport
  # +MessageVerifier+ makes it easy to generate and verify messages which are
  # signed to prevent tampering.
  #
  # This is useful for cases like remember-me tokens and auto-unsubscribe links
  # where the session store isn't suitable or available.
  #
  # Remember Me:
  #   cookies[:remember_me] = @verifier.generate([@user.id, 2.weeks.from_now])
  #
  # In the authentication filter:
  #
  #   id, time = @verifier.verify(cookies[:remember_me])
  #   if Time.now < time
  #     self.current_user = User.find(id)
  #   end
  #
  # By default it uses Marshal to serialize the message. If you want to use
  # another serialization method, you can set the serializer in the options
  # hash upon initialization:
  #
  #   @verifier = ActiveSupport::MessageVerifier.new('s3Krit', serializer: YAML)
  #
  # +MessageVerifier+ creates HMAC signatures using SHA1 hash algorithm by default.
  # If you want to use a different hash algorithm, you can change it by providing
  # `:digest` key as an option while initializing the verifier:
  #
  #   @verifier = ActiveSupport::MessageVerifier.new('s3Krit', digest: 'SHA256')
  #
  # === 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 = @verifier.generate("this is the chair", purpose: :login)
  #
  # Then that same purpose must be passed when verifying to get the data back out:
  #
  #   @verifier.verified(token, purpose: :login)    # => "this is the chair"
  #   @verifier.verified(token, purpose: :shipping) # => nil
  #   @verifier.verified(token)                     # => nil
  #
  #   @verifier.verify(token, purpose: :login)      # => "this is the chair"
  #   @verifier.verify(token, purpose: :shipping)   # => ActiveSupport::MessageVerifier::InvalidSignature
  #   @verifier.verify(token)                       # => ActiveSupport::MessageVerifier::InvalidSignature
  #
  # Likewise, if a message has no purpose it won't be returned when verifying with
  # a specific purpose.
  #
  #   token = @verifier.generate("the conversation is lively")
  #   @verifier.verified(token, purpose: :scare_tactics) # => nil
  #   @verifier.verified(token)                          # => "the conversation is lively"
  #
  #   @verifier.verify(token, purpose: :scare_tactics)   # => ActiveSupport::MessageVerifier::InvalidSignature
  #   @verifier.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+.
  #
  #   @verifier.generate(parcel, expires_in: 1.month)
  #   @verifier.generate(doowad, expires_at: Time.now.end_of_year)
  #
  # Then the messages can be verified and returned upto the expire time.
  # Thereafter, the +verified+ method returns +nil+ while +verify+ raises
  # <tt>ActiveSupport::MessageVerifier::InvalidSignature</tt>.
  #
  # === Rotating keys
  #
  # This class also defines a +rotate+ method which can be used to rotate out
  # verification keys no longer in use.
  #
  # This method is called with an options hash where a +:digest+ option and
  # either a +:raw_key+ or +:secret+ option must be defined. If +:raw_key+ is
  # defined, it is used directly for the underlying HMAC function. If the
  # +:secret+ option is defined, a +:salt+ option must also be defined and a
  # +KeyGenerator+ instance will be used to derive a key using +:salt+.  When
  # +:secret+ is used, a +:key_generator+ option may also be defined allowing
  # for custom +KeyGenerator+ instances. This method can be called multiple
  # times and new verifier instances will be added to the rotation stack on
  # each call.
  #
  #   # Specifying the key used for verification
  #   @verifier.rotate raw_key: older_key, digest: "SHA1"
  #
  #   # Specify the digest
  #   @verifier.rotate raw_key: old_key, digest: "SHA256"
  #
  #   # Using a KeyGenerator instance with a secret and salt
  #   @verifier.rotate secret: old_secret, salt: old_salt, digest: "SHA1"
  #
  #   # Specifying the key generator instance
  #   @verifier.rotate key_generator: old_key_gen, salt: old_salt, digest: "SHA256"
  class MessageVerifier
    prepend Messages::Rotator::Verifier

    class InvalidSignature < StandardError; end

    def initialize(secret, options = {})
      raise ArgumentError, "Secret should not be nil." unless secret
      @secret = secret
      @digest = options[:digest] || "SHA1"
      @serializer = options[:serializer] || Marshal
    end

    # Checks if a signed message could have been generated by signing an object
    # with the +MessageVerifier+'s secret.
    #
    #   verifier = ActiveSupport::MessageVerifier.new 's3Krit'
    #   signed_message = verifier.generate 'a private message'
    #   verifier.valid_message?(signed_message) # => true
    #
    #   tampered_message = signed_message.chop # editing the message invalidates the signature
    #   verifier.valid_message?(tampered_message) # => false
    def valid_message?(signed_message)
      return if signed_message.nil? || !signed_message.valid_encoding? || signed_message.blank?

      data, digest = signed_message.split("--".freeze)
      data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
    end

    # Decodes the signed message using the +MessageVerifier+'s secret.
    #
    #   verifier = ActiveSupport::MessageVerifier.new 's3Krit'
    #
    #   signed_message = verifier.generate 'a private message'
    #   verifier.verified(signed_message) # => 'a private message'
    #
    # Returns +nil+ if the message was not signed with the same secret.
    #
    #   other_verifier = ActiveSupport::MessageVerifier.new 'd1ff3r3nt-s3Krit'
    #   other_verifier.verified(signed_message) # => nil
    #
    # Returns +nil+ if the message is not Base64-encoded.
    #
    #   invalid_message = "f--46a0120593880c733a53b6dad75b42ddc1c8996d"
    #   verifier.verified(invalid_message) # => nil
    #
    # Raises any error raised while decoding the signed message.
    #
    #   incompatible_message = "test--dad7b06c94abba8d46a15fafaef56c327665d5ff"
    #   verifier.verified(incompatible_message) # => TypeError: incompatible marshal file format
    def verified(signed_message, purpose: nil, **)
      if valid_message?(signed_message)
        begin
          data = signed_message.split("--".freeze)[0]
          message = Messages::Metadata.verify(decode(data), purpose)
          @serializer.load(message) if message
        rescue ArgumentError => argument_error
          return if argument_error.message.include?("invalid base64")
          raise
        end
      end
    end

    # Decodes the signed message using the +MessageVerifier+'s secret.
    #
    #   verifier = ActiveSupport::MessageVerifier.new 's3Krit'
    #   signed_message = verifier.generate 'a private message'
    #
    #   verifier.verify(signed_message) # => 'a private message'
    #
    # Raises +InvalidSignature+ if the message was not signed with the same
    # secret or was not Base64-encoded.
    #
    #   other_verifier = ActiveSupport::MessageVerifier.new 'd1ff3r3nt-s3Krit'
    #   other_verifier.verify(signed_message) # => ActiveSupport::MessageVerifier::InvalidSignature
    def verify(*args)
      verified(*args) || raise(InvalidSignature)
    end

    # Generates a signed message for the provided value.
    #
    # The message is signed with the +MessageVerifier+'s secret. Without knowing
    # the secret, the original value cannot be extracted from the message.
    #
    #   verifier = ActiveSupport::MessageVerifier.new 's3Krit'
    #   verifier.generate 'a private message' # => "BAhJIhRwcml2YXRlLW1lc3NhZ2UGOgZFVA==--e2d724331ebdee96a10fb99b089508d1c72bd772"
    def generate(value, expires_at: nil, expires_in: nil, purpose: nil)
      data = encode(Messages::Metadata.wrap(@serializer.dump(value), expires_at: expires_at, expires_in: expires_in, purpose: purpose))
      "#{data}--#{generate_digest(data)}"
    end

    private
      def encode(data)
        ::Base64.strict_encode64(data)
      end

      def decode(data)
        ::Base64.strict_decode64(data)
      end

      def generate_digest(data)
        require "openssl" unless defined?(OpenSSL)
        OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data)
      end
  end
end