patches/simulate_tls13_downgrade.patch

diff --git a/third_party/tlslite/tlslite/handshakesettings.py b/third_party/tlslite/tlslite/handshakesettings.py
index 69fc6f455e10..a647af53c13e 100644
--- a/third_party/tlslite/tlslite/handshakesettings.py
+++ b/third_party/tlslite/tlslite/handshakesettings.py
@@ -125,7 +125,15 @@ class HandshakeSettings(object):
     corresponding to the TokenBindingKeyParameters enum in the Token Binding
     Negotiation spec (draft-ietf-tokbind-negotiation-00). Values are in server's
     preference order, with most preferred params first.
-    
+
+    @type simulateTLS13Downgrade: bool
+    @ivar simulateTLS13Downgrade: If true, the server will simulate a TLS 1.3
+    to TLS 1.2 downgrade in the ServerHello random.
+
+    @type simulateTLS12Downgrade: bool
+    @ivar simulateTLS12Downgrade: If true, the server will simulate a TLS 1.2
+    to TLS 1.1 downgrade in the ServerHello random.
+
     Note that TACK support is not standardized by IETF and uses a temporary
     TLS Extension number, so should NOT be used in production software.
 
@@ -153,6 +161,8 @@ class HandshakeSettings(object):
         self.enableExtendedMasterSecret = True
         self.supportedTokenBindingParams = []
         self.alpnProtos = None
+        self.simulateTLS13Downgrade = False
+        self.simulateTLS12Downgrade = False
 
     # Validates the min/max fields, and certificateTypes
     # Filters out unsupported cipherNames and cipherImplementations
@@ -174,6 +184,8 @@ class HandshakeSettings(object):
         other.enableExtendedMasterSecret = self.enableExtendedMasterSecret
         other.supportedTokenBindingParams = self.supportedTokenBindingParams
         other.alpnProtos = self.alpnProtos;
+        other.simulateTLS13Downgrade = self.simulateTLS13Downgrade
+        other.simulateTLS12Downgrade = self.simulateTLS12Downgrade
 
         if not cipherfactory.tripleDESPresent:
             other.cipherNames = [e for e in self.cipherNames if e != "3des"]
diff --git a/third_party/tlslite/tlslite/tlsconnection.py b/third_party/tlslite/tlslite/tlsconnection.py
index 2309d4fa8f3a..cb7160f25cc9 100644
--- a/third_party/tlslite/tlslite/tlsconnection.py
+++ b/third_party/tlslite/tlslite/tlsconnection.py
@@ -1352,8 +1352,16 @@ class TLSConnection(TLSRecordLayer):
             tackExt = TackExtension.create(tacks, activationFlags)
         else:
             tackExt = None
+        serverRandom = getRandomBytes(32)
+        # See https://tools.ietf.org/html/rfc8446#section-4.1.3
+        if settings.simulateTLS13Downgrade:
+            serverRandom = serverRandom[:24] + \
+                bytearray("\x44\x4f\x57\x4e\x47\x52\x44\x01")
+        elif settings.simulateTLS12Downgrade:
+            serverRandom = serverRandom[:24] + \
+                bytearray("\x44\x4f\x57\x4e\x47\x52\x44\x00")
         serverHello = ServerHello()
-        serverHello.create(self.version, getRandomBytes(32), sessionID, \
+        serverHello.create(self.version, serverRandom, sessionID, \
                             cipherSuite, CertificateType.x509, tackExt,
                             alpn_proto_selected,
                             nextProtos)