diff --git a/lib/diaspora_federation/entities.rb b/lib/diaspora_federation/entities.rb
index e2748cc..7ab98e9 100644
--- a/lib/diaspora_federation/entities.rb
+++ b/lib/diaspora_federation/entities.rb
@@ -14,3 +14,4 @@ require "diaspora_federation/entities/location"
 require "diaspora_federation/entities/photo"
 require "diaspora_federation/entities/status_message"
 require "diaspora_federation/entities/request"
+require "diaspora_federation/entities/participation"
diff --git a/lib/diaspora_federation/entities/participation.rb b/lib/diaspora_federation/entities/participation.rb
new file mode 100644
index 0000000..a7f99ce
--- /dev/null
+++ b/lib/diaspora_federation/entities/participation.rb
@@ -0,0 +1,12 @@
+module DiasporaFederation
+  module Entities
+    class Participation < Entity
+      property :guid
+      property :target_type
+      property :parent_guid
+      property :parent_author_signature
+      property :author_signature
+      property :diaspora_id, xml_name: :diaspora_handle
+    end
+  end
+end
diff --git a/lib/diaspora_federation/validators.rb b/lib/diaspora_federation/validators.rb
index a84f349..5f4c7f3 100644
--- a/lib/diaspora_federation/validators.rb
+++ b/lib/diaspora_federation/validators.rb
@@ -3,6 +3,7 @@ require "validation/rule/regular_expression"
 require "validation/rule/length"
 require "validation/rule/not_empty"
 require "validation/rule/uri"
+require "validation/rule/numeric"
 
 # +valid+ gem namespace
 module Validation
@@ -37,3 +38,7 @@ require "diaspora_federation/validators/person_validator"
 require "diaspora_federation/validators/profile_validator"
 require "diaspora_federation/validators/web_finger_validator"
 require "diaspora_federation/validators/request_validator"
+require "diaspora_federation/validators/photo_validator"
+require "diaspora_federation/validators/location_validator"
+require "diaspora_federation/validators/status_message_validator"
+require "diaspora_federation/validators/participation_validator"
diff --git a/lib/diaspora_federation/validators/location_validator.rb b/lib/diaspora_federation/validators/location_validator.rb
new file mode 100644
index 0000000..4a2e91d
--- /dev/null
+++ b/lib/diaspora_federation/validators/location_validator.rb
@@ -0,0 +1,10 @@
+module DiasporaFederation
+  module Validators
+    class LocationValidator < Validation::Validator
+      include Validation
+
+      rule :lat, :not_empty
+      rule :lng, :not_empty
+    end
+  end
+end
diff --git a/lib/diaspora_federation/validators/participation_validator.rb b/lib/diaspora_federation/validators/participation_validator.rb
new file mode 100644
index 0000000..e51739b
--- /dev/null
+++ b/lib/diaspora_federation/validators/participation_validator.rb
@@ -0,0 +1,19 @@
+module DiasporaFederation
+  module Validators
+    class ParticipationValidator < Validation::Validator
+      include Validation
+
+      rule :guid, :guid
+
+      rule :target_type, :not_empty
+
+      rule :parent_guid, :guid
+
+      rule :parent_author_signature, :not_empty
+
+      rule :author_signature, :not_empty
+
+      rule :diaspora_id, %i(not_empty diaspora_id)
+    end
+  end
+end
diff --git a/lib/diaspora_federation/validators/photo_validator.rb b/lib/diaspora_federation/validators/photo_validator.rb
new file mode 100644
index 0000000..ffc0680
--- /dev/null
+++ b/lib/diaspora_federation/validators/photo_validator.rb
@@ -0,0 +1,23 @@
+module DiasporaFederation
+  module Validators
+    class PhotoValidator < Validation::Validator
+      include Validation
+
+      rule :guid, :guid
+
+      rule :diaspora_id, %i(not_empty diaspora_id)
+
+      rule :public, :boolean
+
+      rule :remote_photo_path, :not_empty
+
+      rule :remote_photo_name, :not_empty
+
+      rule :status_message_guid, :guid
+
+      rule :height, :numeric
+
+      rule :width, :numeric
+    end
+  end
+end
diff --git a/lib/diaspora_federation/validators/request_validator.rb b/lib/diaspora_federation/validators/request_validator.rb
index 2bd7ec3..fecb7ea 100644
--- a/lib/diaspora_federation/validators/request_validator.rb
+++ b/lib/diaspora_federation/validators/request_validator.rb
@@ -3,8 +3,8 @@ module DiasporaFederation
     class RequestValidator < Validation::Validator
       include Validation
 
-      rule :sender_id, %i(not_nil diaspora_id)
-      rule :recipient_id, %i(not_nil diaspora_id)
+      rule :sender_id, %i(not_empty diaspora_id)
+      rule :recipient_id, %i(not_empty diaspora_id)
     end
   end
 end
diff --git a/lib/diaspora_federation/validators/status_message_validator.rb b/lib/diaspora_federation/validators/status_message_validator.rb
new file mode 100644
index 0000000..04dbb36
--- /dev/null
+++ b/lib/diaspora_federation/validators/status_message_validator.rb
@@ -0,0 +1,13 @@
+module DiasporaFederation
+  module Validators
+    class StatusMessageValidator < Validation::Validator
+      include Validation
+
+      rule :guid, :guid
+
+      rule :diaspora_id, %i(not_empty diaspora_id)
+
+      rule :public, :boolean
+    end
+  end
+end
diff --git a/spec/factories.rb b/spec/factories.rb
index 25fce9b..d68b25d 100644
--- a/spec/factories.rb
+++ b/spec/factories.rb
@@ -8,6 +8,11 @@ FactoryGirl.define do
   sequence(:guid) { UUID.generate :compact }
   sequence(:diaspora_id) {|n| "person-#{n}-#{r_str}@localhost:3000" }
   sequence(:public_key) { OpenSSL::PKey::RSA.generate(1024).public_key.export }
+  sequence(:signature) do |i|
+    abc = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    ltr = abc[i % abc.length]
+    "#{ltr * 6}=="
+  end
 
   factory :person do
     diaspora_id
@@ -83,8 +88,30 @@ FactoryGirl.define do
     remote_photo_path "https://diaspora.example.tld/uploads/images/"
     remote_photo_name "f2a41e9d2db4d9a199c8.jpg"
     text "what you see here..."
-    status_message_guid { guid }
+    status_message_guid { generate(:guid) }
     height 480
     width 800
   end
+
+  factory :participation_entity, class: DiasporaFederation::Entities::Participation do
+    guid
+    target_type "StatusMessage"
+    parent_guid { generate(:guid) }
+    diaspora_id
+    parent_author_signature { generate(:signature) }
+    author_signature { generate(:signature) }
+  end
+
+  factory :status_message_entity, class: DiasporaFederation::Entities::StatusMessage do
+    raw_message "i am a very interesting status update"
+    guid
+    diaspora_id
+    public(true)
+    created_at { Time.zone.now }
+  end
+
+  factory :request_entity, class: DiasporaFederation::Entities::Request do
+    sender_id { generate(:diaspora_id) }
+    recipient_id { generate(:diaspora_id) }
+  end
 end
diff --git a/spec/lib/diaspora_federation/entities/participation_spec.rb b/spec/lib/diaspora_federation/entities/participation_spec.rb
new file mode 100644
index 0000000..5653c41
--- /dev/null
+++ b/spec/lib/diaspora_federation/entities/participation_spec.rb
@@ -0,0 +1,29 @@
+module DiasporaFederation
+  describe Entities::Participation do
+    let(:data) {
+      {guid:                    "0123456789abcdef",
+       target_type:             "Post",
+       parent_guid:             "fedcba9876543210",
+       parent_author_signature: "BBBBBB==",
+       author_signature:        "AAAAAA==",
+       diaspora_id:             "luke@diaspora.example.tld"}
+    }
+
+    let(:xml) {
+      <<-XML
+<participation>
+  <guid>#{data[:guid]}</guid>
+  <target_type>#{data[:target_type]}</target_type>
+  <parent_guid>#{data[:parent_guid]}</parent_guid>
+  <parent_author_signature>#{data[:parent_author_signature]}</parent_author_signature>
+  <author_signature>#{data[:author_signature]}</author_signature>
+  <diaspora_handle>#{data[:diaspora_id]}</diaspora_handle>
+</participation>
+XML
+    }
+
+    it_behaves_like "an Entity subclass"
+
+    it_behaves_like "an XML Entity"
+  end
+end
diff --git a/spec/lib/diaspora_federation/validators/location_validator_spec.rb b/spec/lib/diaspora_federation/validators/location_validator_spec.rb
new file mode 100644
index 0000000..0577d63
--- /dev/null
+++ b/spec/lib/diaspora_federation/validators/location_validator_spec.rb
@@ -0,0 +1,19 @@
+module DiasporaFederation
+  describe Validators::LocationValidator do
+    let(:entity) { :location_entity }
+    it_behaves_like "a common validator"
+
+    context "#lat and #lng" do
+      %i(lat lng).each do |prop|
+        it "must not be empty" do
+          entity = OpenStruct.new(FactoryGirl.attributes_for(:location_entity))
+          entity.public_send("#{prop}=", "")
+
+          validator = Validators::LocationValidator.new(entity)
+          expect(validator).not_to be_valid
+          expect(validator.errors).to include(prop)
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/diaspora_federation/validators/participation_validator_spec.rb b/spec/lib/diaspora_federation/validators/participation_validator_spec.rb
new file mode 100644
index 0000000..9bb8bff
--- /dev/null
+++ b/spec/lib/diaspora_federation/validators/participation_validator_spec.rb
@@ -0,0 +1,42 @@
+module DiasporaFederation
+  describe Validators::ParticipationValidator do
+    let(:entity) { :participation_entity }
+
+    it_behaves_like "a common validator"
+
+    it_behaves_like "a diaspora id validator" do
+      let(:property) { :diaspora_id }
+      let(:mandatory) { true }
+    end
+
+    context "#target_type" do
+      it "must not be empty" do
+        entity = OpenStruct.new(FactoryGirl.attributes_for(:participation_entity, target_type: ""))
+        validator = Validators::ParticipationValidator.new(entity)
+        expect(validator).not_to be_valid
+        expect(validator.errors).to include(:target_type)
+      end
+    end
+
+    context "#guid, #parent_guid" do
+      %i(guid parent_guid).each do |prop|
+        it_behaves_like "a guid validator" do
+          let(:property) { prop }
+        end
+      end
+    end
+
+    context "#author_signature and #parent_author_signature" do
+      %i(author_signature parent_author_signature).each do |prop|
+        it "must not be empty" do
+          p = OpenStruct.new(FactoryGirl.attributes_for(:participation_entity))
+          p.public_send("#{prop}=", "")
+
+          v = Validators::ParticipationValidator.new(p)
+          expect(v).not_to be_valid
+          expect(v.errors).to include(prop)
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/diaspora_federation/validators/person_validator_spec.rb b/spec/lib/diaspora_federation/validators/person_validator_spec.rb
index 753cd9c..b973472 100644
--- a/spec/lib/diaspora_federation/validators/person_validator_spec.rb
+++ b/spec/lib/diaspora_federation/validators/person_validator_spec.rb
@@ -2,13 +2,7 @@ module DiasporaFederation
   describe Validators::PersonValidator do
     let(:entity) { :person_entity }
 
-    it "validates a well-formed instance" do
-      instance = OpenStruct.new(FactoryGirl.attributes_for(:person_entity))
-      validator = Validators::PersonValidator.new(instance)
-
-      expect(validator).to be_valid
-      expect(validator.errors).to be_empty
-    end
+    it_behaves_like "a common validator"
 
     it_behaves_like "a diaspora id validator" do
       let(:property) { :diaspora_id }
diff --git a/spec/lib/diaspora_federation/validators/photo_validator_spec.rb b/spec/lib/diaspora_federation/validators/photo_validator_spec.rb
new file mode 100644
index 0000000..ff1c5e1
--- /dev/null
+++ b/spec/lib/diaspora_federation/validators/photo_validator_spec.rb
@@ -0,0 +1,63 @@
+module DiasporaFederation
+  describe Validators::PhotoValidator do
+    let(:entity) { :photo_entity }
+
+    it_behaves_like "a common validator"
+
+    it_behaves_like "a diaspora id validator" do
+      let(:property) { :diaspora_id }
+      let(:mandatory) { true }
+    end
+
+    context "#guid, #status_message_guid" do
+      %i(guid status_message_guid).each do |prop|
+        it_behaves_like "a guid validator" do
+          let(:property) { prop }
+        end
+      end
+    end
+
+    it_behaves_like "a boolean validator" do
+      let(:property) { :public }
+    end
+
+    context "#remote_photo_path, #remote_photo_name" do
+      %i(remote_photo_name remote_photo_path).each do |prop|
+        it "must not be empty" do
+          p = OpenStruct.new(FactoryGirl.attributes_for(:photo_entity))
+          p.public_send("#{prop}=", "")
+
+          v = Validators::PhotoValidator.new(p)
+          expect(v).not_to be_valid
+          expect(v.errors).to include(prop)
+        end
+      end
+    end
+
+    context "#height, #width" do
+      %i(height width).each do |prop|
+        it "validates an integer" do
+          [123, "123"].each do |val|
+            p = OpenStruct.new(FactoryGirl.attributes_for(:photo_entity))
+            p.public_send("#{prop}=", val)
+
+            v = Validators::PhotoValidator.new(p)
+            expect(v).to be_valid
+            expect(v.errors).to be_empty
+          end
+        end
+
+        it "fails for non numeric types" do
+          [true, :num, "asdf"].each do |val|
+            p = OpenStruct.new(FactoryGirl.attributes_for(:photo_entity))
+            p.public_send("#{prop}=", val)
+
+            v = Validators::PhotoValidator.new(p)
+            expect(v).not_to be_valid
+            expect(v.errors).to include(prop)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/diaspora_federation/validators/request_validator_spec.rb b/spec/lib/diaspora_federation/validators/request_validator_spec.rb
new file mode 100644
index 0000000..79a34c4
--- /dev/null
+++ b/spec/lib/diaspora_federation/validators/request_validator_spec.rb
@@ -0,0 +1,16 @@
+module DiasporaFederation
+  describe Validators::RequestValidator do
+    let(:entity) { :request_entity }
+
+    it_behaves_like "a common validator"
+
+    context "#sender_id, #recipient_id" do
+      %i(sender_id recipient_id).each do |prop|
+        it_behaves_like "a diaspora id validator" do
+          let(:property) { prop }
+          let(:mandatory) { true }
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/diaspora_federation/validators/status_message_validator_spec.rb b/spec/lib/diaspora_federation/validators/status_message_validator_spec.rb
new file mode 100644
index 0000000..1d33a1c
--- /dev/null
+++ b/spec/lib/diaspora_federation/validators/status_message_validator_spec.rb
@@ -0,0 +1,20 @@
+module DiasporaFederation
+  describe Validators::StatusMessageValidator do
+    let(:entity) { :status_message_entity }
+
+    it_behaves_like "a common validator"
+
+    it_behaves_like "a diaspora id validator" do
+      let(:property) { :diaspora_id }
+      let(:mandatory) { true }
+    end
+
+    it_behaves_like "a guid validator" do
+      let(:property) { :guid }
+    end
+
+    it_behaves_like "a boolean validator" do
+      let(:property) { :public }
+    end
+  end
+end
diff --git a/spec/support/shared_validator_specs.rb b/spec/support/shared_validator_specs.rb
index 9b96d30..e3dd4f2 100644
--- a/spec/support/shared_validator_specs.rb
+++ b/spec/support/shared_validator_specs.rb
@@ -4,12 +4,24 @@ def entity_stub(entity, property, val)
   instance
 end
 
+def entity_stub_data(entity, data={})
+  OpenStruct.new(FactoryGirl.attributes_for(entity).merge(data))
+end
+
 ALPHANUMERIC_RANGE = [*"0".."9", *"A".."Z", *"a".."z"]
 
 def alphanumeric_string(length)
   Array.new(length) { ALPHANUMERIC_RANGE.sample }.join
 end
 
+shared_examples "a common validator" do
+  it "validates a well-formed instance" do
+    validator = described_class.new(entity_stub_data(entity))
+    expect(validator).to be_valid
+    expect(validator.errors).to be_empty
+  end
+end
+
 shared_examples "a diaspora id validator" do
   it "must not be nil or empty if mandatory" do
     [nil, ""].each do |val|