vendor/rails/activesupport/lib/active_support/message_verifier.rb

   1 module ActiveSupport
   2   # MessageVerifier makes it easy to generate and verify messages which are signed
   3   # to prevent tampering.
   4   #
   5   # This is useful for cases like remember-me tokens and auto-unsubscribe links where the
   6   # session store isn't suitable or available.
   7   #
   8   # Remember Me:
   9   #   cookies[:remember_me] = @verifier.generate([@user.id, 2.weeks.from_now])
  10   #
  11   # In the authentication filter:
  12   #
  13   #   id, time = @verifier.verify(cookies[:remember_me])
  14   #   if time < Time.now
  15   #     self.current_user = User.find(id)
  16   #   end
  17   #
  18   class MessageVerifier
  19     class InvalidSignature < StandardError; end
  20
  21     def initialize(secret, digest = 'SHA1')
  22       @secret = secret
  23       @digest = digest
  24     end
  25
  26     def verify(signed_message)
  27       data, digest = signed_message.split("--")
  28       if digest != generate_digest(data)
  29         raise InvalidSignature
  30       else
  31         Marshal.load(ActiveSupport::Base64.decode64(data))
  32       end
  33     end
  34
  35     def generate(value)
  36       data = ActiveSupport::Base64.encode64s(Marshal.dump(value))
  37       "#{data}--#{generate_digest(data)}"
  38     end
  39
  40     private
  41       def generate_digest(data)
  42         require 'openssl' unless defined?(OpenSSL)
  43         OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(@digest), @secret, data)
  44       end
  45   end
  46 end