bpo-29136: Add TLS 1.3 cipher suites and OP_NO_TLSv1_3 (#1363)

* bpo-29136: Add TLS 1.3 support

TLS 1.3 introduces a new, distinct set of cipher suites. The TLS 1.3
cipher suites don't overlap with cipher suites from TLS 1.2 and earlier.
Since Python sets its own set of permitted ciphers, TLS 1.3 handshake
will fail as soon as OpenSSL 1.1.1 is released. Let's enable the common
AES-GCM and ChaCha20 suites.

Additionally the flag OP_NO_TLSv1_3 is added. It defaults to 0 (no op) with
OpenSSL prior to 1.1.1. This allows applications to opt-out from TLS 1.3
now.

Signed-off-by: Christian Heimes <christian@python.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 747661b..fe9f693 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -170,6 +170,13 @@ class BasicSocketTests(unittest.TestCase):
             ssl.OP_NO_COMPRESSION
         self.assertIn(ssl.HAS_SNI, {True, False})
         self.assertIn(ssl.HAS_ECDH, {True, False})
+        ssl.OP_NO_SSLv2
+        ssl.OP_NO_SSLv3
+        ssl.OP_NO_TLSv1
+        ssl.OP_NO_TLSv1_3
+        if ssl.OPENSSL_VERSION_INFO >= (1, 0, 1):
+            ssl.OP_NO_TLSv1_1
+            ssl.OP_NO_TLSv1_2
 
     def test_str_for_enums(self):
         # Make sure that the PROTOCOL_* constants have enum-like string
@@ -3098,12 +3105,33 @@ class ThreadedTests(unittest.TestCase):
                 self.assertEqual(s.version(), 'TLSv1')
             self.assertIs(s.version(), None)
 
+    @unittest.skipUnless(ssl.HAS_TLSv1_3,
+                         "test requires TLSv1.3 enabled OpenSSL")
+    def test_tls1_3(self):
+        context = ssl.SSLContext(ssl.PROTOCOL_TLS)
+        context.load_cert_chain(CERTFILE)
+        # disable all but TLS 1.3
+        context.options |= (
+            ssl.OP_NO_TLSv1 | ssl.OP_NO_TLSv1_1 | ssl.OP_NO_TLSv1_2
+        )
+        with ThreadedEchoServer(context=context) as server:
+            with context.wrap_socket(socket.socket()) as s:
+                s.connect((HOST, server.port))
+                self.assertIn(s.cipher()[0], [
+                    'TLS13-AES-256-GCM-SHA384',
+                    'TLS13-CHACHA20-POLY1305-SHA256',
+                    'TLS13-AES-128-GCM-SHA256',
+                ])
+
     @unittest.skipUnless(ssl.HAS_ECDH, "test requires ECDH-enabled OpenSSL")
     def test_default_ecdh_curve(self):
         # Issue #21015: elliptic curve-based Diffie Hellman key exchange
         # should be enabled by default on SSL contexts.
         context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
         context.load_cert_chain(CERTFILE)
+        # TLSv1.3 defaults to PFS key agreement and no longer has KEA in
+        # cipher name.
+        context.options |= ssl.OP_NO_TLSv1_3
         # Prior to OpenSSL 1.0.0, ECDH ciphers have to be enabled
         # explicitly using the 'ECCdraft' cipher alias.  Otherwise,
         # our default cipher list should prefer ECDH-based ciphers
@@ -3532,6 +3560,10 @@ class ThreadedTests(unittest.TestCase):
         context2.load_verify_locations(CERTFILE)
         context2.load_cert_chain(CERTFILE)
 
+        # TODO: session reuse does not work with TLS 1.3
+        context.options |= ssl.OP_NO_TLSv1_3
+        context2.options |= ssl.OP_NO_TLSv1_3
+
         server = ThreadedEchoServer(context=context, chatty=False)
         with server:
             with context.wrap_socket(socket.socket()) as s: