From 98be64a81196992b247eb02dff4d393fdf748556 Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Mon, 22 May 2023 16:24:05 +0300
Subject: [PATCH] Add better error message for untrusted devices

---
 main.go           |  3 +++
 messagehandler.go | 25 +++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/main.go b/main.go
index 0d5e71d..9833f69 100644
--- a/main.go
+++ b/main.go
@@ -16,6 +16,7 @@ import (
 	"maunium.net/go/mautrix"
 	"maunium.net/go/mautrix/crypto/cryptohelper"
 	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/id"
 	"maunium.net/go/mautrix/synapseadmin"
 	"maunium.net/go/mautrix/util"
 	"maunium.net/go/mautrix/util/dbutil"
@@ -128,6 +129,8 @@ func main() {
 	syncer.OnEventType(event.StateMember, handleMember)
 	syncer.OnEventType(event.EventMessage, handleMessage)
 	syncer.OnSync(cli.MoveInviteState)
+	cryptoHelper.Machine().SendKeysMinTrust = id.TrustStateCrossSignedTOFU
+	cryptoHelper.Machine().ShareKeysMinTrust = id.TrustStateCrossSignedTOFU
 	cryptoHelper.DecryptErrorCallback = func(evt *event.Event, err error) {
 		_, _ = cli.SendMessageEvent(evt.RoomID, event.EventMessage, &event.MessageEventContent{
 			MsgType:   event.MsgNotice,
diff --git a/messagehandler.go b/messagehandler.go
index c201344..d9e6c8d 100644
--- a/messagehandler.go
+++ b/messagehandler.go
@@ -34,6 +34,14 @@ func replyErr(ctx context.Context, err error, message string) {
 }
 
 func reply(ctx context.Context, message string, args ...any) id.EventID {
+	return replyOpts(ctx, ReplyOpts{}, message, args...)
+}
+
+type ReplyOpts struct {
+	DontEncrypt bool
+}
+
+func replyOpts(ctx context.Context, opts ReplyOpts, message string, args ...any) id.EventID {
 	evt := getEvent(ctx)
 	if len(args) > 0 {
 		message = fmt.Sprintf(message, args...)
@@ -47,7 +55,9 @@ func reply(ctx context.Context, message string, args ...any) id.EventID {
 	} else {
 		content.RelatesTo = (&event.RelatesTo{}).SetReplyTo(evt.ID)
 	}
-	resp, err := cli.SendMessageEvent(evt.RoomID, event.EventMessage, &content)
+	resp, err := cli.SendMessageEvent(evt.RoomID, event.EventMessage, &content, mautrix.ReqSendEvent{
+		DontEncrypt: opts.DontEncrypt,
+	})
 	if err != nil {
 		zerolog.Ctx(ctx).Err(err).Msg("Failed to send reply")
 		return ""
@@ -86,7 +96,18 @@ func handleMessage(source mautrix.EventSource, evt *event.Event) {
 			Str("trust_state", evt.Mautrix.TrustState.String()).
 			Bool("forwarded_keys", evt.Mautrix.ForwardedKeys).
 			Msg("Dropping message with insufficient verification level")
-		reply(ctx, "Insufficient verification level %s (forwarded keys: %t)", evt.Mautrix.TrustState, evt.Mautrix.ForwardedKeys)
+		msg := "Your device is not trusted"
+		switch evt.Mautrix.TrustState {
+		case id.TrustStateCrossSignedUntrusted:
+			msg += " (cross-signing keys changed after using the bot)"
+		case id.TrustStateForwarded:
+			msg += " (keys were forwarded from an unknown device, try `/discardsession`?)"
+		case id.TrustStateUnknownDevice:
+			msg += " (device info not found)"
+		case id.TrustStateUnset:
+			msg += " (unverified)"
+		}
+		replyOpts(ctx, ReplyOpts{DontEncrypt: true}, msg)
 	} else {
 		handleCommand(ctx, evt)
 	}