diff --git a/lib/diaspora_federation/salmon/exceptions.rb b/lib/diaspora_federation/salmon/exceptions.rb
index 349c7b2..9dd0f96 100644
--- a/lib/diaspora_federation/salmon/exceptions.rb
+++ b/lib/diaspora_federation/salmon/exceptions.rb
@@ -33,6 +33,10 @@ module DiasporaFederation
     class InvalidSignature < RuntimeError
     end
 
+    # Raised, if the parsed Magic Envelope specifies an unhandled data type.
+    class InvalidDataType < RuntimeError
+    end
+
     # Raised, if the parsed Magic Envelope specifies an unhandled algorithm.
     class InvalidAlgorithm < RuntimeError
     end
diff --git a/lib/diaspora_federation/salmon/magic_envelope.rb b/lib/diaspora_federation/salmon/magic_envelope.rb
index dcd9822..be1979c 100644
--- a/lib/diaspora_federation/salmon/magic_envelope.rb
+++ b/lib/diaspora_federation/salmon/magic_envelope.rb
@@ -110,19 +110,20 @@ module DiasporaFederation
       # @raise [ArgumentError] if any of the arguments is of invalid type
       # @raise [InvalidEnvelope] if the envelope XML structure is malformed
       # @raise [InvalidSignature] if the signature can't be verified
-      # @raise [InvalidEncoding] if the data is wrongly encoded
-      # @raise [InvalidAlgorithm] if the algorithm used doesn't match
+      # @raise [InvalidDataType] if the data is missing or unsupported
+      # @raise [InvalidEncoding] if the data is wrongly encoded or encoding is missing
+      # @raise [InvalidAlgorithm] if the algorithm is missing or doesn't match
       def self.unenvelop(magic_env, sender=nil, cipher_params=nil)
         raise ArgumentError unless magic_env.instance_of?(Nokogiri::XML::Element)
 
-        raise InvalidEnvelope unless envelope_valid?(magic_env)
+        validate_envelope(magic_env)
+        validate_type(magic_env)
+        validate_encoding(magic_env)
+        validate_algorithm(magic_env)
 
         sender ||= sender(magic_env)
         raise InvalidSignature unless signature_valid?(magic_env, sender)
 
-        raise InvalidEncoding unless encoding_valid?(magic_env)
-        raise InvalidAlgorithm unless algorithm_valid?(magic_env)
-
         data = read_and_decrypt_data(magic_env, cipher_params)
 
         logger.debug "unenvelop message from #{sender}:\n#{data}"
@@ -165,11 +166,20 @@ module DiasporaFederation
       end
 
       # @param [Nokogiri::XML::Element] env magic envelope XML
-      private_class_method def self.envelope_valid?(env)
-        (env.instance_of?(Nokogiri::XML::Element) &&
-          env.name == "env" &&
-          !env.at_xpath("me:data").content.empty? &&
-          !env.at_xpath("me:sig").content.empty?)
+      # @raise [InvalidEnvelope] if the envelope XML structure is malformed
+      private_class_method def self.validate_envelope(env)
+        raise InvalidEnvelope unless env.instance_of?(Nokogiri::XML::Element) && env.name == "env"
+        validate_element(env, "me:data")
+        validate_element(env, "me:sig")
+      end
+
+      # @param [Nokogiri::XML::Element] env magic envelope XML
+      # @param [String] xpath the element to validate
+      # @raise [InvalidEnvelope] if the element is missing or empty
+      private_class_method def self.validate_element(env, xpath)
+        element = env.at_xpath(xpath)
+        raise InvalidEnvelope, "missing #{xpath}" unless element
+        raise InvalidEnvelope, "empty #{xpath}" if element.content.empty?
       end
 
       # @param [Nokogiri::XML::Element] env magic envelope XML
@@ -207,15 +217,27 @@ module DiasporaFederation
       end
 
       # @param [Nokogiri::XML::Element] magic_env magic envelope XML
-      # @return [Boolean]
-      private_class_method def self.encoding_valid?(magic_env)
-        magic_env.at_xpath("me:encoding").content == ENCODING
+      # @raise [InvalidDataType] if the data is missing or unsupported
+      private_class_method def self.validate_type(magic_env)
+        type = magic_env.at_xpath("me:data")["type"]
+        raise InvalidDataType, "missing data type" if type.nil?
+        raise InvalidDataType, "invalid data type: #{type}" unless type == DATA_TYPE
       end
 
       # @param [Nokogiri::XML::Element] magic_env magic envelope XML
-      # @return [Boolean]
-      private_class_method def self.algorithm_valid?(magic_env)
-        magic_env.at_xpath("me:alg").content == ALGORITHM
+      # @raise [InvalidEncoding] if the data is wrongly encoded or encoding is missing
+      private_class_method def self.validate_encoding(magic_env)
+        enc = magic_env.at_xpath("me:encoding")
+        raise InvalidEncoding, "missing encoding" unless enc
+        raise InvalidEncoding, "invalid encoding: #{enc.content}" unless enc.content == ENCODING
+      end
+
+      # @param [Nokogiri::XML::Element] magic_env magic envelope XML
+      # @raise [InvalidAlgorithm] if the algorithm is missing or doesn't match
+      private_class_method def self.validate_algorithm(magic_env)
+        alg = magic_env.at_xpath("me:alg")
+        raise InvalidAlgorithm, "missing algorithm" unless alg
+        raise InvalidAlgorithm, "invalid algorithm: #{alg.content}" unless alg.content == ALGORITHM
       end
 
       # @param [Nokogiri::XML::Element] magic_env magic envelope XML
diff --git a/spec/lib/diaspora_federation/salmon/magic_envelope_spec.rb b/spec/lib/diaspora_federation/salmon/magic_envelope_spec.rb
index 1d1c72e..b7b305d 100644
--- a/spec/lib/diaspora_federation/salmon/magic_envelope_spec.rb
+++ b/spec/lib/diaspora_federation/salmon/magic_envelope_spec.rb
@@ -110,11 +110,6 @@ module DiasporaFederation
           ).and_return(privkey.public_key)
         end
 
-        def re_sign(env, key)
-          new_sig = Base64.urlsafe_encode64(key.sign(OpenSSL::Digest::SHA256.new, sig_subj(env)))
-          env.at_xpath("me:sig").content = new_sig
-        end
-
         it "works with sane input" do
           expect {
             Salmon::MagicEnvelope.unenvelop(envelope.envelop(privkey), sender)
@@ -135,6 +130,14 @@ module DiasporaFederation
           }.to raise_error Salmon::InvalidEnvelope
         end
 
+        it "raises if missing signature" do
+          bad_env = envelope.envelop(privkey)
+          bad_env.at_xpath("me:sig").remove
+          expect {
+            Salmon::MagicEnvelope.unenvelop(bad_env, sender)
+          }.to raise_error Salmon::InvalidEnvelope, "missing me:sig"
+        end
+
         it "verifies the signature" do
           other_sender = FactoryGirl.generate(:diaspora_id)
           other_key = OpenSSL::PKey::RSA.generate(512)
@@ -146,22 +149,60 @@ module DiasporaFederation
           }.to raise_error Salmon::InvalidSignature
         end
 
+        it "raises if missing data" do
+          bad_env = envelope.envelop(privkey)
+          bad_env.at_xpath("me:data").remove
+          expect {
+            Salmon::MagicEnvelope.unenvelop(bad_env, sender)
+          }.to raise_error Salmon::InvalidEnvelope, "missing me:data"
+        end
+
+        it "raises if missing encoding" do
+          bad_env = envelope.envelop(privkey)
+          bad_env.at_xpath("me:encoding").remove
+          expect {
+            Salmon::MagicEnvelope.unenvelop(bad_env, sender)
+          }.to raise_error Salmon::InvalidEncoding, "missing encoding"
+        end
+
         it "verifies the encoding" do
           bad_env = envelope.envelop(privkey)
           bad_env.at_xpath("me:encoding").content = "invalid_enc"
-          re_sign(bad_env, privkey)
           expect {
             Salmon::MagicEnvelope.unenvelop(bad_env, sender)
-          }.to raise_error Salmon::InvalidEncoding
+          }.to raise_error Salmon::InvalidEncoding, "invalid encoding: invalid_enc"
+        end
+
+        it "raises if missing algorithm" do
+          bad_env = envelope.envelop(privkey)
+          bad_env.at_xpath("me:alg").remove
+          expect {
+            Salmon::MagicEnvelope.unenvelop(bad_env, sender)
+          }.to raise_error Salmon::InvalidAlgorithm, "missing algorithm"
         end
 
         it "verifies the algorithm" do
           bad_env = envelope.envelop(privkey)
           bad_env.at_xpath("me:alg").content = "invalid_alg"
-          re_sign(bad_env, privkey)
           expect {
             Salmon::MagicEnvelope.unenvelop(bad_env, sender)
-          }.to raise_error Salmon::InvalidAlgorithm
+          }.to raise_error Salmon::InvalidAlgorithm, "invalid algorithm: invalid_alg"
+        end
+
+        it "raises if missing data type" do
+          bad_env = envelope.envelop(privkey)
+          bad_env.at_xpath("me:data").attributes["type"].remove
+          expect {
+            Salmon::MagicEnvelope.unenvelop(bad_env, sender)
+          }.to raise_error Salmon::InvalidDataType, "missing data type"
+        end
+
+        it "verifies the data type" do
+          bad_env = envelope.envelop(privkey)
+          bad_env.at_xpath("me:data")["type"] = "invalid_type"
+          expect {
+            Salmon::MagicEnvelope.unenvelop(bad_env, sender)
+          }.to raise_error Salmon::InvalidDataType, "invalid data type: invalid_type"
         end
       end