Expose group ID and allow inspection (#412)

* Expose GroupID on MLSMessage

* Provide handle() complementary to unwrap()

* Add GroupInfo branch; remove redundant checks

* clang-format

* ValidatedContent

* clang-format

* clang-tidy

* clang-tidy

include/mls/messages.h

@@ -570,17 +570,35 @@ struct AuthenticatedContent
   friend struct PrivateMessage;
 };
 
+struct ValidatedContent
+{
+  const AuthenticatedContent& authenticated_content() const;
+
+  friend bool operator==(const ValidatedContent& lhs,
+                         const ValidatedContent& rhs);
+
+private:
+  AuthenticatedContent content_auth;
+
+  ValidatedContent(AuthenticatedContent content_auth_in);
+
+  friend struct PublicMessage;
+  friend struct PrivateMessage;
+  friend class State;
+};
+
 struct PublicMessage
 {
   PublicMessage() = default;
 
+  bytes get_group_id() const { return content.group_id; }
   epoch_t get_epoch() const { return content.epoch; }
 
   static PublicMessage protect(AuthenticatedContent content_auth,
                                CipherSuite suite,
                                const std::optional<bytes>& membership_key,
                                const std::optional<GroupContext>& context);
-  std::optional<AuthenticatedContent> unprotect(
+  std::optional<ValidatedContent> unprotect(
     CipherSuite suite,
     const std::optional<bytes>& membership_key,
     const std::optional<GroupContext>& context) const;
@@ -611,14 +629,15 @@ struct PrivateMessage
 {
   PrivateMessage() = default;
 
+  bytes get_group_id() const { return group_id; }
   epoch_t get_epoch() const { return epoch; }
 
   static PrivateMessage protect(AuthenticatedContent content_auth,
                                 CipherSuite suite,
                                 GroupKeySource& keys,
                                 const bytes& sender_data_secret,
                                 size_t padding_size);
-  std::optional<AuthenticatedContent> unprotect(
+  std::optional<ValidatedContent> unprotect(
     CipherSuite suite,
     GroupKeySource& keys,
     const bytes& sender_data_secret) const;
@@ -649,6 +668,7 @@ struct MLSMessage
   var::variant<PublicMessage, PrivateMessage, Welcome, GroupInfo, KeyPackage>
     message;
 
+  bytes group_id() const;
   epoch_t epoch() const;
   WireFormat wire_format() const;
 

include/mls/state.h

@@ -117,11 +117,16 @@ class State
     const MessageOpts& msg_opts);
 
   ///
-  /// Generic handshake message handler
+  /// Generic handshake message handlers
   ///
   std::optional<State> handle(const MLSMessage& msg);
   std::optional<State> handle(const MLSMessage& msg,
                               std::optional<State> cached_state);
+
+  std::optional<State> handle(const ValidatedContent& content_auth);
+  std::optional<State> handle(const ValidatedContent& content_auth,
+                              std::optional<State> cached_state);
+
   ///
   /// PSK management
   ///
@@ -151,6 +156,11 @@ class State
 
   bytes epoch_authenticator() const;
 
+  ///
+  /// Unwrap messages so that applications can inspect them
+  ///
+  ValidatedContent unwrap(const MLSMessage& msg);
+
   ///
   /// Application encryption and decryption
   ///
@@ -318,7 +328,7 @@ class State
     std::optional<State> cached_state,
     const std::optional<CommitParams>& expected_params);
   std::optional<State> handle(
-    const AuthenticatedContent& content_auth,
+    const ValidatedContent& val_content,
     std::optional<State> cached_state,
     const std::optional<CommitParams>& expected_params);
 
@@ -334,8 +344,6 @@ class State
   template<typename Inner>
   MLSMessage protect_full(Inner&& content, const MessageOpts& msg_opts);
 
-  AuthenticatedContent unprotect_to_content_auth(const MLSMessage& msg);
-
   // Apply the changes requested by various messages
   LeafIndex apply(const Add& add);
   void apply(LeafIndex target, const Update& update);

lib/mls_vectors/src/mls_vectors.cpp

@@ -872,25 +872,26 @@ MessageProtectionTestVector::protect_priv(
 std::optional<GroupContent>
 MessageProtectionTestVector::unprotect(const MLSMessage& message)
 {
-  auto do_unprotect = overloaded{
-    [&](const PublicMessage& pt) {
-      return pt.unprotect(cipher_suite, membership_key, group_context());
-    },
-    [&](const PrivateMessage& ct) {
-      auto keys = group_keys();
-      return ct.unprotect(cipher_suite, keys, sender_data_secret);
-    },
-    [](const auto& /* other */) -> std::optional<AuthenticatedContent> {
-      return std::nullopt;
-    }
-  };
+  auto do_unprotect =
+    overloaded{ [&](const PublicMessage& pt) {
+                 return pt.unprotect(
+                   cipher_suite, membership_key, group_context());
+               },
+                [&](const PrivateMessage& ct) {
+                  auto keys = group_keys();
+                  return ct.unprotect(cipher_suite, keys, sender_data_secret);
+                },
+                [](const auto& /* other */) -> std::optional<ValidatedContent> {
+                  return std::nullopt;
+                } };
 
   auto maybe_auth_content = var::visit(do_unprotect, message.message);
   if (!maybe_auth_content) {
     return std::nullopt;
   }
 
-  auto auth_content = opt::get(maybe_auth_content);
+  auto val_content = opt::get(maybe_auth_content);
+  const auto& auth_content = val_content.authenticated_content();
   if (!auth_content.verify(cipher_suite, signature_pub, group_context())) {
     return std::nullopt;
   }

src/messages.cpp

@@ -464,6 +464,23 @@ AuthenticatedContent::AuthenticatedContent(WireFormat wire_format_in,
 {
 }
 
+const AuthenticatedContent&
+ValidatedContent::authenticated_content() const
+{
+  return content_auth;
+}
+
+ValidatedContent::ValidatedContent(AuthenticatedContent content_auth_in)
+  : content_auth(std::move(content_auth_in))
+{
+}
+
+bool
+operator==(const ValidatedContent& lhs, const ValidatedContent& rhs)
+{
+  return lhs.content_auth == rhs.content_auth;
+}
+
 struct GroupContentTBS
 {
   WireFormat wire_format = WireFormat::reserved;
@@ -526,7 +543,7 @@ PublicMessage::protect(AuthenticatedContent content_auth,
   return pt;
 }
 
-std::optional<AuthenticatedContent>
+std::optional<ValidatedContent>
 PublicMessage::unprotect(CipherSuite suite,
                          const std::optional<bytes>& membership_key,
                          const std::optional<GroupContext>& context) const
@@ -545,11 +562,11 @@ PublicMessage::unprotect(CipherSuite suite,
       break;
   }
 
-  return AuthenticatedContent{
+  return { { AuthenticatedContent{
     WireFormat::mls_public_message,
     content,
     auth,
-  };
+  } } };
 }
 
 bool
@@ -756,7 +773,7 @@ PrivateMessage::protect(AuthenticatedContent content_auth,
   };
 }
 
-std::optional<AuthenticatedContent>
+std::optional<ValidatedContent>
 PrivateMessage::unprotect(CipherSuite suite,
                           GroupKeySource& keys,
                           const bytes& sender_data_secret) const
@@ -813,11 +830,11 @@ PrivateMessage::unprotect(CipherSuite suite,
 
   unmarshal_ciphertext_content(opt::get(content_pt), content, auth);
 
-  return AuthenticatedContent{
+  return { { AuthenticatedContent{
     WireFormat::mls_private_message,
     std::move(content),
     std::move(auth),
-  };
+  } } };
 }
 
 PrivateMessage::PrivateMessage(GroupContent content,
@@ -832,6 +849,21 @@ PrivateMessage::PrivateMessage(GroupContent content,
 {
 }
 
+bytes
+MLSMessage::group_id() const
+{
+  return var::visit(
+    overloaded{
+      [](const PublicMessage& pt) -> bytes { return pt.get_group_id(); },
+      [](const PrivateMessage& ct) -> bytes { return ct.get_group_id(); },
+      [](const GroupInfo& gi) -> bytes { return gi.group_context.group_id; },
+      [](const auto& /* unused */) -> bytes {
+        throw InvalidParameterError("MLSMessage has no group_id");
+      },
+    },
+    message);
+}
+
 epoch_t
 MLSMessage::epoch() const
 {