fix implementation of Autocrypt to encrypt if answering to an encrypted message.

Previously, if any of a chat's peers set prefer_encrypt to false
(i.e. "e2ee_enabled=0" in the config, a misnomer btw) then a
previously encrypted chat would drop to cleartext easily.

python/tests/test_account.py

@@ -629,6 +629,45 @@ class TestOnlineAccount:
         ev = ac1._evlogger.get_matching("DC_EVENT_SMTP_MESSAGE_SENT")
         assert not msg.is_encrypted()
 
+    def test_reply_encrypted(self, acfactory, lp):
+        ac1, ac2 = acfactory.get_two_online_accounts()
+
+        lp.sec("ac1: create chat with ac2")
+        chat = self.get_chat(ac1, ac2)
+
+        lp.sec("sending text message from ac1 to ac2")
+        msg_out = chat.send_text("message1")
+        assert not msg_out.is_encrypted()
+
+        lp.sec("wait for ac2 to receive message")
+        ev = ac2._evlogger.get_matching("DC_EVENT_MSGS_CHANGED")
+        msg_in = ac2.get_message_by_id(msg_out.id)
+        assert msg_in.text == "message1"
+        assert not msg_in.is_encrypted()
+
+        lp.sec("create new chat with contact and send back (encrypted) message")
+        chat2b = ac2.create_chat_by_message(msg_in)
+        chat2b.send_text("message-back")
+
+        lp.sec("wait for ac1 to receive message")
+        ev = ac1._evlogger.get_matching("DC_EVENT_INCOMING_MSG")
+        assert ev[1] == chat.id
+        msg_back = ac1.get_message_by_id(ev[2])
+        assert msg_back.text == "message-back"
+        assert msg_back.is_encrypted()
+
+        lp.sec("ac1: e2ee_enabled=0 and see if reply is encrypted")
+        print("ac1: e2ee_enabled={}".format(ac1.get_config("e2ee_enabled")))
+        print("ac2: e2ee_enabled={}".format(ac2.get_config("e2ee_enabled")))
+        ac1.set_config("e2ee_enabled", "0")
+        chat.send_text("message2 -- should be encrypted")
+
+        lp.sec("wait for ac2 to receive message")
+        ev = ac2._evlogger.get_matching("DC_EVENT_INCOMING_MSG")
+        msg_in = ac2.get_message_by_id(ev[2])
+        assert msg_in.text == "message2 -- should be encrypted"
+        assert msg_in.is_encrypted()
+
     def test_saved_mime_on_received_message(self, acfactory, lp):
         ac1, ac2 = acfactory.get_two_online_accounts()
 

src/chat.rs

@@ -259,8 +259,6 @@ impl Chat {
         msg: &mut Message,
         timestamp: i64,
     ) -> Result<MsgId, Error> {
-        let mut do_guarantee_e2ee: bool;
-        let e2ee_enabled: bool;
         let mut new_references = "".into();
         let mut new_in_reply_to = "".into();
         let mut msg_id = 0;
@@ -319,15 +317,12 @@ impl Chat {
                 self.update_param(context)?;
             }
 
-            /* check if we can guarantee E2EE for this message.
+            /* check if we want to encrypt this message.  If yes and circumstances change
-            if we guarantee E2EE, and circumstances change
             so that E2EE is no longer available at a later point (reset, changed settings),
-            we do not send the message out at all */
+            we might not send the message out at all */
-            do_guarantee_e2ee = false;
+            if msg.param.get_int(Param::ForcePlaintext).unwrap_or_default() == 0 {
-            e2ee_enabled = context.get_config_bool(Config::E2eeEnabled);
-            if e2ee_enabled && msg.param.get_int(Param::ForcePlaintext).unwrap_or_default() == 0 {
                 let mut can_encrypt = true;
-                let mut all_mutual = true;
+                let mut all_mutual = context.get_config_bool(Config::E2eeEnabled);
 
                 // take care that this statement returns NULL rows
                 // if there is no peerstates for a chat member!
@@ -377,13 +372,10 @@ impl Chat {
                 if can_encrypt
                     && (all_mutual || last_msg_in_chat_encrypted(context, &context.sql, self.id))
                 {
-                    do_guarantee_e2ee = true;
-                }
-            }
-            if do_guarantee_e2ee {
                     msg.param.set_int(Param::GuaranteeE2ee, 1);
                 }
-            // reset eg. for forwarding
+            }
+            // reset encrypt error state eg. for forwarding
             msg.param.remove(Param::ErroneousE2ee);
 
             // set "In-Reply-To:" to identify the message to which the composed message is a reply;