Add checking int the client to check the magic values which are

set by a 1.3 server when it downgrades to tls 1.2 or 1.1 as per
RFC 8446 section 4.1.3

ok jsing@

1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib/libssl/tls13_lib.c b/src/lib/libssl/tls13_lib.c
index de3e840a84..5d8c359014 100644
--- a/src/lib/libssl/tls13_lib.c
+++ b/src/lib/libssl/tls13_lib.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: tls13_lib.c,v 1.23 2020/01/23 05:08:30 jsing Exp $ */
+/*      $OpenBSD: tls13_lib.c,v 1.24 2020/01/23 07:30:55 beck Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2019 Bob Beck <beck@openbsd.org>
@@ -24,6 +24,14 @@
 #include "ssl_locl.h"
 #include "tls13_internal.h"
 
+/*
+ * RFC 8446 section 4.1.3, magic values which must be set by the
+ * server in server random if it is willing to downgrade but supports
+ * tls v1.3
+ */
+uint8_t tls13_downgrade_12[8] = {0x44, 0x4f, 0x57, 0x4e, 0x47, 0x52, 0x44, 0x01};
+uint8_t tls13_downgrade_11[8] = {0x44, 0x4f, 0x57, 0x4e, 0x47, 0x52, 0x44, 0x00};
+
 const EVP_AEAD *
 tls13_cipher_aead(const SSL_CIPHER *cipher)
 {