diff --git a/lib/diaspora_federation/entities/message.rb b/lib/diaspora_federation/entities/message.rb
index 11332e7..e24e20c 100644
--- a/lib/diaspora_federation/entities/message.rb
+++ b/lib/diaspora_federation/entities/message.rb
@@ -8,9 +8,6 @@ module DiasporaFederation
       # @deprecated
       LEGACY_SIGNATURE_ORDER = %i(guid parent_guid text created_at author conversation_guid).freeze
 
-      # The {Message} parent is a {Conversation}
-      PARENT_TYPE = "Conversation".freeze
-
       include Relayable
 
       # @!attribute [r] text
@@ -28,6 +25,40 @@ module DiasporaFederation
       #   @see Conversation#guid
       #   @return [String] conversation guid
       property :conversation_guid
+
+      # It is only valid to receive a {Message} from the author itself,
+      # or from the author of the parent {Conversation} if the author signature is valid.
+      # @deprecated remove after {Message} doesn't include {Relayable} anymore
+      def sender_valid?(sender)
+        sender == author || (sender == parent_author && verify_author_signature)
+      end
+
+      private
+
+      # @deprecated remove after {Message} doesn't include {Relayable} anymore
+      def verify_author_signature
+        pubkey = DiasporaFederation.callbacks.trigger(:fetch_public_key, author)
+        raise PublicKeyNotFound, "author_signature author=#{author} guid=#{guid}" if pubkey.nil?
+        raise SignatureVerificationFailed, "wrong author_signature" unless verify_signature(pubkey, author_signature)
+        true
+      end
+
+      # @deprecated remove after {Message} doesn't include {Relayable} anymore
+      def parent_author
+        parent = DiasporaFederation.callbacks.trigger(:fetch_related_entity, "Conversation", conversation_guid)
+        raise Federation::Fetcher::NotFetchable, "Conversation:#{conversation_guid} not found" unless parent
+        parent.author
+      end
+
+      # Default implementation, don't verify signatures for a {Message}.
+      # @see Entity.populate_entity
+      # @deprecated remove after {Message} doesn't include {Relayable} anymore
+      # @param [Nokogiri::XML::Element] root_node xml nodes
+      # @return [Entity] instance
+      def self.populate_entity(root_node)
+        new({parent_guid: nil, parent: nil}.merge(entity_data(root_node)))
+      end
+      private_class_method :populate_entity
     end
   end
 end
diff --git a/lib/diaspora_federation/validators/message_validator.rb b/lib/diaspora_federation/validators/message_validator.rb
index bb3aa04..84650d3 100644
--- a/lib/diaspora_federation/validators/message_validator.rb
+++ b/lib/diaspora_federation/validators/message_validator.rb
@@ -4,8 +4,8 @@ module DiasporaFederation
     class MessageValidator < Validation::Validator
       include Validation
 
-      include RelayableValidator
-
+      rule :author, %i(not_empty diaspora_id)
+      rule :guid, :guid
       rule :conversation_guid, :guid
     end
   end
diff --git a/spec/lib/diaspora_federation/entities/conversation_spec.rb b/spec/lib/diaspora_federation/entities/conversation_spec.rb
index 93d2158..0bcb251 100644
--- a/spec/lib/diaspora_federation/entities/conversation_spec.rb
+++ b/spec/lib/diaspora_federation/entities/conversation_spec.rb
@@ -35,7 +35,7 @@ XML
 
     it_behaves_like "an Entity subclass"
 
-    it_behaves_like "an XML Entity"
+    it_behaves_like "an XML Entity", %i(parent parent_guid)
 
     context "default values" do
       let(:minimal_xml) {
diff --git a/spec/lib/diaspora_federation/entities/message_spec.rb b/spec/lib/diaspora_federation/entities/message_spec.rb
index e0497b8..04769d1 100644
--- a/spec/lib/diaspora_federation/entities/message_spec.rb
+++ b/spec/lib/diaspora_federation/entities/message_spec.rb
@@ -25,8 +25,84 @@ XML
 
     it_behaves_like "an Entity subclass"
 
-    it_behaves_like "an XML Entity"
+    it_behaves_like "an XML Entity", %i(parent parent_guid)
 
     it_behaves_like "a relayable Entity"
+
+    describe "#sender_valid?" do
+      let(:entity) { Entities::Message.new(data) }
+
+      it "allows the author" do
+        expect(entity.sender_valid?(alice.diaspora_id)).to be_truthy
+      end
+
+      it "allows parent author if the signature is valid" do
+        expect_callback(:fetch_related_entity, "Conversation", entity.conversation_guid).and_return(data[:parent])
+        expect_callback(:fetch_public_key, alice.diaspora_id).and_return(alice.private_key)
+        expect(entity.sender_valid?(bob.diaspora_id)).to be_truthy
+      end
+
+      it "does not allow any other person" do
+        expect_callback(:fetch_related_entity, "Conversation", entity.conversation_guid).and_return(data[:parent])
+        invalid_sender = FactoryGirl.generate(:diaspora_id)
+        expect(entity.sender_valid?(invalid_sender)).to be_falsey
+      end
+
+      it "does not allow the parent author if the signature is invalid" do
+        expect_callback(:fetch_related_entity, "Conversation", entity.conversation_guid).and_return(data[:parent])
+        expect_callback(:fetch_public_key, alice.diaspora_id).and_return(alice.private_key)
+        invalid_entity = Entities::Message.new(data.merge(author_signature: "aa"))
+        expect {
+          invalid_entity.sender_valid?(bob.diaspora_id)
+        }.to raise_error Entities::Relayable::SignatureVerificationFailed, "wrong author_signature"
+      end
+
+      it "raises NotFetchable if the parent Conversation can not be found" do
+        expect_callback(:fetch_related_entity, "Conversation", entity.conversation_guid).and_return(nil)
+        expect {
+          entity.sender_valid?(bob.diaspora_id)
+        }.to raise_error Federation::Fetcher::NotFetchable
+      end
+    end
+
+    context "relayable signature verification" do
+      it "does not verify the signature" do
+        data.merge!(author_signature: "aa", parent_author_signature: "bb")
+        xml = Entities::Message.new(data).to_xml
+
+        expect {
+          Entities::Message.from_xml(xml)
+        }.not_to raise_error
+      end
+    end
+
+    describe ".populate_entity" do
+      it "adds a nil parent" do
+        xml = Entities::Message.new(data).to_xml
+        parsed = Entities::Message.from_xml(xml)
+        expect(parsed.parent).to be_nil
+      end
+
+      it "uses the parent_guid from the parsed xml" do
+        xml = Entities::Message.new(data).to_xml
+        parsed = Entities::Message.from_xml(xml)
+        expect(parsed.parent_guid).to eq(data[:parent_guid])
+      end
+
+      it "uses nil for parent_guid if not in the xml" do
+        xml = <<-XML
+<message>
+  <author>#{data[:author]}</author>
+  <guid>#{data[:guid]}</guid>
+  <text>#{data[:text]}</text>
+  <created_at>#{data[:created_at]}</created_at>
+  <conversation_guid>#{data[:conversation_guid]}</conversation_guid>
+</message>
+XML
+
+        parsed = Entities::Message.from_xml(Nokogiri::XML::Document.parse(xml).root)
+        expect(parsed.parent_guid).to be_nil
+      end
+    end
   end
 end
diff --git a/spec/lib/diaspora_federation/validators/message_validator_spec.rb b/spec/lib/diaspora_federation/validators/message_validator_spec.rb
index 17adfb1..90b5d23 100644
--- a/spec/lib/diaspora_federation/validators/message_validator_spec.rb
+++ b/spec/lib/diaspora_federation/validators/message_validator_spec.rb
@@ -3,7 +3,16 @@ module DiasporaFederation
     let(:entity) { :message_entity }
     it_behaves_like "a common validator"
 
-    it_behaves_like "a relayable validator"
+    it_behaves_like "a diaspora id validator" do
+      let(:property) { :author }
+      let(:mandatory) { true }
+    end
+
+    describe "#guid" do
+      it_behaves_like "a guid validator" do
+        let(:property) { :guid }
+      end
+    end
 
     describe "#conversation_guid" do
       it_behaves_like "a guid validator" do
diff --git a/spec/support/shared_entity_specs.rb b/spec/support/shared_entity_specs.rb
index 83e5598..105e6dc 100644
--- a/spec/support/shared_entity_specs.rb
+++ b/spec/support/shared_entity_specs.rb
@@ -66,21 +66,21 @@ shared_examples "an XML Entity" do |ignored_props=[]|
     end
   end
 
-  def check_entity(entity, parsed_entity, ignored_props=[])
-    entity.class.class_props.each do |name, type|
-      validate_values(entity.send(name), parsed_entity.send(name), type) unless ignored_props.include?(name)
+  def check_entity(entity, parsed_entity, ignored_props)
+    entity.class.class_props.reject {|name| ignored_props.include?(name) }.each do |name, type|
+      validate_values(entity.send(name), parsed_entity.send(name), type, ignored_props)
     end
   end
 
-  def validate_values(value, parsed_value, type)
+  def validate_values(value, parsed_value, type, ignored_props)
     if value.nil?
       expect(parsed_value).to be_nil
     elsif type == String
       expect(parsed_value.to_s).to eq(value.to_s)
     elsif type.instance_of?(Array)
-      value.each_with_index {|entity, index| check_entity(entity, parsed_value[index]) }
+      value.each_with_index {|entity, index| check_entity(entity, parsed_value[index], ignored_props) }
     elsif type.ancestors.include?(DiasporaFederation::Entity)
-      check_entity(value, parsed_value)
+      check_entity(value, parsed_value, ignored_props)
     end
   end
 end