fixup! fixup! fixup! fixup! fixup! wip: single packet decryption (not finished) [no changelog]

core/src/trezor/wire/thp/channel.py

@@ -128,6 +128,11 @@ class Channel:
 
         if self.expected_payload_length + INIT_HEADER_LENGTH == self.bytes_read:
             self._finish_message()
+            if self.fallback_decrypt:
+                # TODO Check CRC and if valid, check tag, if valid update nonces
+                self._finish_fallback()
+                # TODO self.write() failure device is busy - use channel buffer to send this failure message!!
+                return
             return received_message_handler.handle_received_message(self, buffer)
         elif self.expected_payload_length + INIT_HEADER_LENGTH > self.bytes_read:
             self.is_cont_packet_expected = True
@@ -155,9 +160,6 @@ class Channel:
         _, _, payload_length = ustruct.unpack(PacketHeader.format_str_init, packet)
         self.expected_payload_length = payload_length
 
-        # packet_payload = memoryview(packet)[INIT_HEADER_LENGTH:]
-        # The above could be used for single packet decryption
-
         # If the channel does not "own" the buffer lock, decrypt first packet
         # TODO do it only when needed!
         # TODO FIX: If "_decrypt_single_packet_payload" is implemented, it will (possibly) break "decrypt_buffer" and nonces incrementation.
@@ -188,6 +190,9 @@ class Channel:
             # TAG CHECK
             self._handle_fallback_decryption(buf)
 
+            self.bytes_read += to_read_len
+            return
+
         if __debug__ and utils.ALLOW_DEBUG_MESSAGES:
             self._log("handle_init_packet - payload len: ", str(payload_length))
             self._log("handle_init_packet - buffer len: ", str(len(buffer)))
@@ -261,8 +266,22 @@ class Channel:
 
         if not self.is_cont_packet_expected:
             raise ThpError("Continuation packet is not expected, ignoring")
+
         if self.fallback_decrypt:
-            pass  # TODO
+            to_read_len = min(
+                len(packet) - CONT_HEADER_LENGTH,
+                self.expected_payload_length - self.bytes_read,
+            )
+            buf = memoryview(self.buffer)[:to_read_len]
+            utils.memcpy(buf, 0, packet, CONT_HEADER_LENGTH)
+
+            # CRC CHECK
+            self._handle_fallback_crc(buf)
+
+            # TAG CHECK
+            self._handle_fallback_decryption(buf)
+
+            self.bytes_read += to_read_len
             return
         try:
             buffer = memory_manager.get_existing_read_buffer(self.get_channel_id_int())
@@ -281,6 +300,7 @@ class Channel:
         self.expected_payload_length = 0
         self.is_cont_packet_expected = False
 
+    def _finish_fallback(self) -> None:
         self.fallback_decrypt = False
         self.busy_decoder = None
 
@@ -304,6 +324,7 @@ class Channel:
         self.temp_crc = 0
         self.temp_crc_compare = bytearray(4)
         self.temp_tag = bytearray(16)
+        self.bytes_read = INIT_HEADER_LENGTH
 
     def decrypt_buffer(
         self, message_length: int, offset: int = INIT_HEADER_LENGTH