Ruby 1.9: fix MessageVerifier#secure_compare

activesupport/Rakefile

@@ -88,7 +88,8 @@ task :release => [ :package ] do
 end
 
 
-require 'lib/active_support/values/time_zone'
+$LOAD_PATH.unshift "#{File.dirname(__FILE__)}/lib"
+require 'active_support/values/time_zone'
 
 namespace :tzinfo do
   desc "Update bundled tzinfo gem. Only copies the subset of classes and definitions required to support Rails time zone features."

activesupport/lib/active_support/message_verifier.rb

@@ -0,0 +1,77 @@
+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
+  # 
+  class MessageVerifier
+    class InvalidSignature < StandardError; end
+
+    def initialize(secret, digest = 'SHA1')
+      @secret = secret
+      @digest = digest
+    end
+
+    def verify(signed_message)
+      data, digest = signed_message.split("--")
+      if secure_compare(digest, generate_digest(data))
+        Marshal.load(ActiveSupport::Base64.decode64(data))
+      else
+        raise InvalidSignature
+      end
+    end
+
+    def generate(value)
+      data = ActiveSupport::Base64.encode64s(Marshal.dump(value))
+      "#{data}--#{generate_digest(data)}"
+    end
+
+    private
+      if "foo".respond_to?(:force_encoding)
+        # constant-time comparison algorithm to prevent timing attacks
+        def secure_compare(a, b)
+          a = a.force_encoding(Encoding::BINARY)
+          b = b.force_encoding(Encoding::BINARY)
+
+          if a.length == b.length
+            result = 0
+            for i in 0..(a.length - 1)
+              result |= a[i].ord ^ b[i].ord
+            end
+            result == 0
+          else
+            false
+          end
+        end
+      else
+        # For 1.8
+        def secure_compare(a, b)
+          if a.length == b.length
+            result = 0
+            for i in 0..(a.length - 1)
+              result |= a[i] ^ b[i]
+            end
+            result == 0
+          else
+            false
+          end
+        end
+      end
+
+      def generate_digest(data)
+        require 'openssl' unless defined?(OpenSSL)
+        OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(@digest), @secret, data)
+      end
+  end
+end