OMEMO: Fail if message keys couldn't be encrypted for any recipient device

If the message (key) can't be encrypted for any device, sending the
message is refused and an informative error message is presented to the
user.

Also, don't encrypt for the same device, since the OMEMO XEP disallows
this.

1 files changed, 20 insertions, 0 deletions

diff --git a/src/omemo/omemo.c b/src/omemo/omemo.c
index a552cd57..495842bf 100644
--- a/src/omemo/omemo.c
+++ b/src/omemo/omemo.c
@@ -705,6 +705,7 @@ omemo_on_message_send(ProfWin* win, const char* const message, gboolean request_
     memcpy(key_tag, key, AES128_GCM_KEY_LENGTH);
     memcpy(key_tag + AES128_GCM_KEY_LENGTH, tag, AES128_GCM_TAG_LENGTH);
 
+    // List of barejids of the recipients of this message
     GList* recipients = NULL;
     if (muc) {
         ProfMucWin* mucwin = (ProfMucWin*)win;
@@ -727,6 +728,7 @@ omemo_on_message_send(ProfWin* win, const char* const message, gboolean request_
 
     omemo_ctx.identity_key_store.recv = false;
 
+    // Encrypt keys for the recipients
     GList* recipients_iter;
     for (recipients_iter = recipients; recipients_iter != NULL; recipients_iter = recipients_iter->next) {
         GList* recipient_device_id = NULL;
@@ -772,6 +774,17 @@ omemo_on_message_send(ProfWin* win, const char* const message, gboolean request_
 
     g_list_free_full(recipients, free);
 
+    // Don't send the message if no key could be encrypted.
+    // (Since none of the recipients would be able to read the message.)
+    if (keys == NULL) {
+        win_println(win, THEME_ERROR, "!", "This message cannot be decrypted for any recipient.\n"
+                "You should trust your recipients' device fingerprint(s) using \"/omemo fingerprint trust FINGERPRINT\".\n"
+                "It could also be that the key bundle of the recipient(s) have not been received. "
+                "In this case, you could try \"omemo end\", \"omemo start\", and send the message again.");
+        goto out;
+    }
+
+    // Encrypt keys for the sender
     if (!muc) {
         GList* sender_device_id = g_hash_table_lookup(omemo_ctx.device_list, jid->barejid);
         for (device_ids_iter = sender_device_id; device_ids_iter != NULL; device_ids_iter = device_ids_iter->next) {
@@ -784,6 +797,12 @@ omemo_on_message_send(ProfWin* win, const char* const message, gboolean request_
                 .device_id = GPOINTER_TO_INT(device_ids_iter->data)
             };
 
+            // Don't encrypt for this device (according to
+            // <https://xmpp.org/extensions/xep-0384.html#encrypt>).
+            if (address.device_id == omemo_ctx.device_id) {
+                continue;
+            }
+
             res = session_cipher_create(&cipher, omemo_ctx.store, &address, omemo_ctx.signal);
             if (res != 0) {
                 log_error("[OMEMO] cannot create cipher for %s device id %d", address.name, address.device_id);
@@ -808,6 +827,7 @@ omemo_on_message_send(ProfWin* win, const char* const message, gboolean request_
         }
     }
 
+    // Send the message
     if (muc) {
         ProfMucWin* mucwin = (ProfMucWin*)win;
         assert(mucwin->memcheck == PROFMUCWIN_MEMCHECK);