Improve TLSv1.3 state machine for HelloRetryRequest handling.

The state machine currently handles the HelloRetryRequest case by using
WITH_HRR - in other words, we're explicitly indicating when we transition
to the alternate path. The problem here is that we do not know if we're
going to receive a ServerHello or a HelloRetryRequest until we process
the message. This means that the ServerHello processing code has to handle
both types of messages.

The state machine and associated processing code becomes cleaner if we flip
this around so that we assume we are going to receive a HelloRetryRequest
and upon discovering that it is not, trigger WITHOUT_HRR and hand off to
the ServerHello processing function. In particular, this makes the logic
much more straight forward on the server side, when adding support for HRR.

With feedback from tb@

ok tb@

1 files changed, 4 insertions, 4 deletions

diff --git a/lib/libssl/tls13_handshake.h b/lib/libssl/tls13_handshake.h
index 956d27c61aa..8a08b9fd5bc 100644
--- a/lib/libssl/tls13_handshake.h
+++ b/lib/libssl/tls13_handshake.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_handshake.h,v 1.4 2020/03/10 17:15:02 jsing Exp $ */
+/* $OpenBSD: tls13_handshake.h,v 1.5 2020/04/22 17:05:07 jsing Exp $ */
 /*
  * Copyright (c) 2019 Theo Buehler <tb@openbsd.org>
  *
@@ -24,7 +24,7 @@ __BEGIN_HIDDEN_DECLS
 
 #define INITIAL			0x00
 #define NEGOTIATED		0x01
-#define WITH_HRR		0x02
+#define WITHOUT_HRR		0x02
 #define WITHOUT_CR		0x04
 #define WITH_PSK		0x08
 #define WITH_CCV		0x10
@@ -33,9 +33,9 @@ __BEGIN_HIDDEN_DECLS
 enum tls13_message_type {
 	INVALID,
 	CLIENT_HELLO,
-	SERVER_HELLO,
+	SERVER_HELLO_RETRY_REQUEST,
 	CLIENT_HELLO_RETRY,
-	SERVER_HELLO_RETRY,
+	SERVER_HELLO,
 	SERVER_ENCRYPTED_EXTENSIONS,
 	SERVER_CERTIFICATE_REQUEST,
 	SERVER_CERTIFICATE,