Skip to content
This repository
tree: 019df98875
Fetching contributors…

Octocat-spinner-32-eaf2f5

Cannot retrieve contributors at this time

file 69 lines (59 sloc) 2.065 kb
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
require 'base64'
require 'active_support/core_ext/object/blank'

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 < Time.now
  # 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 attribute to
  # something that responds to dump and load, e.g.:
  #
  # @verifier.serializer = YAML
  class MessageVerifier
    class InvalidSignature < StandardError; end

    def initialize(secret, options = {})
      @secret = secret
      @digest = options[:digest] || 'SHA1'
      @serializer = options[:serializer] || Marshal
    end

    def verify(signed_message)
      raise InvalidSignature if signed_message.blank?

      data, digest = signed_message.split("--")
      if data.present? && digest.present? && secure_compare(digest, generate_digest(data))
        @serializer.load(::Base64.decode64(data))
      else
        raise InvalidSignature
      end
    end

    def generate(value)
      data = ::Base64.strict_encode64(@serializer.dump(value))
      "#{data}--#{generate_digest(data)}"
    end

    private
      # constant-time comparison algorithm to prevent timing attacks
      def secure_compare(a, b)
        return false unless a.bytesize == b.bytesize

        l = a.unpack "C#{a.bytesize}"

        res = 0
        b.each_byte { |byte| res |= byte ^ l.shift }
        res == 0
      end

      def generate_digest(data)
        require 'openssl' unless defined?(OpenSSL)
        OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data)
      end
  end
end
Something went wrong with that request. Please try again.