Imrove strict-kex interoperability

This commit changes AsyncSSH to no longer send MSG_IGNORE during a key
exchange (both initial and when rekeying). With the strict-kex feature,
MSG_IGNORE is no longer allowed during initial kex exchange, but some
implementations also error out if they see MSG_IGNORE during rekeying.
This change should improve interoperability in that case.

Thanks go to GitHub user emeryalden for reporting this issue and helping
to track down the specific issue that caused rekeying to fail!

Author: ronf

asyncssh/connection.py

@@ -1741,7 +1741,7 @@ def send_packet(self, pkttype: int, *args: bytes,
             self._send_kexinit()
             self._kexinit_sent = True
 
-        if (((pkttype in {MSG_SERVICE_REQUEST, MSG_SERVICE_ACCEPT} or
+        if (((pkttype in {MSG_DEBUG, MSG_SERVICE_REQUEST, MSG_SERVICE_ACCEPT} or
               pkttype > MSG_KEX_LAST) and not self._kex_complete) or
                 (pkttype == MSG_USERAUTH_BANNER and
                  not (self._auth_in_progress or self._auth_complete)) or
@@ -1751,7 +1751,7 @@ def send_packet(self, pkttype: int, *args: bytes,
 
         # If we're encrypting and we have no data outstanding, insert an
         # ignore packet into the stream
-        if self._send_encryption and pkttype not in (MSG_IGNORE, MSG_EXT_INFO):
+        if self._send_encryption and pkttype > MSG_KEX_LAST:
             self.send_packet(MSG_IGNORE, String(b''))
 
         orig_payload = Byte(pkttype) + b''.join(args)