bpo-34670: Add TLS 1.3 post handshake auth (GH-9460)

Add SSLContext.post_handshake_auth and
SSLSocket.verify_client_post_handshake for TLS 1.3 post-handshake
authentication.

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


https://bugs.python.org/issue34670

.travis.yml

@@ -12,7 +12,7 @@ cache:
 
 env:
   global:
-    - OPENSSL=1.1.0h
+    - OPENSSL=1.1.0i
     - OPENSSL_DIR="$HOME/multissl/openssl/${OPENSSL}"
     - PATH="${OPENSSL_DIR}/bin:$PATH"
     # Use -O3 because we don't use debugger on Travis-CI

Doc/library/ssl.rst

@@ -1314,6 +1314,26 @@ SSL sockets also have the following additional methods and attributes:
    returned socket should always be used for further communication with the
    other side of the connection, rather than the original socket.
 
+.. method:: SSLSocket.verify_client_post_handshake()
+
+   Requests post-handshake authentication (PHA) from a TLS 1.3 client. PHA
+   can only be initiated for a TLS 1.3 connection from a server-side socket,
+   after the initial TLS handshake and with PHA enabled on both sides, see
+   :attr:`SSLContext.post_handshake_auth`.
+
+   The method does not perform a cert exchange immediately. The server-side
+   sends a CertificateRequest during the next write event and expects the
+   client to respond with a certificate on the next read event.
+
+   If any precondition isn't met (e.g. not TLS 1.3, PHA not enabled), an
+   :exc:`SSLError` is raised.
+
+   .. versionadded:: 3.8
+
+   .. note::
+      Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3
+      support, the method raises :exc:`NotImplementedError`.
+
 .. method:: SSLSocket.version()
 
    Return the actual SSL protocol version negotiated by the connection
@@ -1929,6 +1949,28 @@ to speed up repeated connections from the same clients.
          >>> ssl.create_default_context().options  # doctest: +SKIP
          <Options.OP_ALL|OP_NO_SSLv3|OP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>
 
+.. attribute:: SSLContext.post_handshake_auth
+
+   Enable TLS 1.3 post-handshake client authentication. Post-handshake auth
+   is disabled by default and a server can only request a TLS client
+   certificate during the initial handshake. When enabled, a server may
+   request a TLS client certificate at any time after the handshake.
+
+   When enabled on client-side sockets, the client signals the server that
+   it supports post-handshake authentication.
+
+   When enabled on server-side sockets, :attr:`SSLContext.verify_mode` must
+   be set to :data:`CERT_OPTIONAL` or :data:`CERT_REQUIRED`, too. The
+   actual client cert exchange is delayed until
+   :meth:`SSLSocket.verify_client_post_handshake` is called and some I/O is
+   performed.
+
+   .. versionadded:: 3.8
+
+   .. note::
+      Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3
+      support, the property value is None and can't be modified
+
 .. attribute:: SSLContext.protocol
 
    The protocol version chosen when constructing the context.  This attribute

Doc/whatsnew/3.8.rst

@@ -140,14 +140,21 @@ pathlib
 contain characters unrepresentable at the OS level.
 (Contributed by Serhiy Storchaka in :issue:`33721`.)
 
+ssl
+---
+
+Added :attr:`SSLContext.post_handshake_auth` to enable and
+:meth:`ssl.SSLSocket.verify_client_post_handshake` to initiate TLS 1.3
+post-handshake authentication.
+(Contributed by Christian Heimes in :issue:`34670`.)
+
 venv
 ----
 
 * :mod:`venv` now includes an ``Activate.ps1`` script on all platforms for
   activating virtual environments under PowerShell Core 6.1.
   (Contributed by Brett Cannon in :issue:`32718`.)
 
-
 Optimizations
 =============
 

Lib/ssl.py

@@ -777,6 +777,9 @@ def version(self):
         current SSL channel. """
         return self._sslobj.version()
 
+    def verify_client_post_handshake(self):
+        return self._sslobj.verify_client_post_handshake()
+
 
 class SSLSocket(socket):
     """This class implements a subtype of socket.socket that wraps
@@ -1094,6 +1097,12 @@ def unwrap(self):
         else:
             raise ValueError("No SSL wrapper around " + str(self))
 
+    def verify_client_post_handshake(self):
+        if self._sslobj:
+            return self._sslobj.verify_client_post_handshake()
+        else:
+            raise ValueError("No SSL wrapper around " + str(self))
+
     def _real_close(self):
         self._sslobj = None
         super()._real_close()

Lib/test/test_ssl.py

@@ -218,7 +218,7 @@ def testing_context(server_cert=SIGNED_CERTFILE):
 
     server_context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
     server_context.load_cert_chain(server_cert)
-    client_context.load_verify_locations(SIGNING_CA)
+    server_context.load_verify_locations(SIGNING_CA)
 
     return client_context, server_context, hostname
 
@@ -2262,6 +2262,23 @@ def run(self):
                             sys.stdout.write(" server: read CB tls-unique from client, sending our CB data...\n")
                         data = self.sslconn.get_channel_binding("tls-unique")
                         self.write(repr(data).encode("us-ascii") + b"\n")
+                    elif stripped == b'PHA':
+                        if support.verbose and self.server.connectionchatty:
+                            sys.stdout.write(" server: initiating post handshake auth\n")
+                        try:
+                            self.sslconn.verify_client_post_handshake()
+                        except ssl.SSLError as e:
+                            self.write(repr(e).encode("us-ascii") + b"\n")
+                        else:
+                            self.write(b"OK\n")
+                    elif stripped == b'HASCERT':
+                        if self.sslconn.getpeercert() is not None:
+                            self.write(b'TRUE\n')
+                        else:
+                            self.write(b'FALSE\n')
+                    elif stripped == b'GETCERT':
+                        cert = self.sslconn.getpeercert()
+                        self.write(repr(cert).encode("us-ascii") + b"\n")
                     else:
                         if (support.verbose and
                             self.server.connectionchatty):
@@ -4148,6 +4165,179 @@ def test_session_handling(self):
                                  'Session refers to a different SSLContext.')
 
 
+@unittest.skipUnless(ssl.HAS_TLSv1_3, "Test needs TLS 1.3")
+class TestPostHandshakeAuth(unittest.TestCase):
+    def test_pha_setter(self):
+        protocols = [
+            ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLS_SERVER, ssl.PROTOCOL_TLS_CLIENT
+        ]
+        for protocol in protocols:
+            ctx = ssl.SSLContext(protocol)
+            self.assertEqual(ctx.post_handshake_auth, False)
+
+            ctx.post_handshake_auth = True
+            self.assertEqual(ctx.post_handshake_auth, True)
+
+            ctx.verify_mode = ssl.CERT_REQUIRED
+            self.assertEqual(ctx.verify_mode, ssl.CERT_REQUIRED)
+            self.assertEqual(ctx.post_handshake_auth, True)
+
+            ctx.post_handshake_auth = False
+            self.assertEqual(ctx.verify_mode, ssl.CERT_REQUIRED)
+            self.assertEqual(ctx.post_handshake_auth, False)
+
+            ctx.verify_mode = ssl.CERT_OPTIONAL
+            ctx.post_handshake_auth = True
+            self.assertEqual(ctx.verify_mode, ssl.CERT_OPTIONAL)
+            self.assertEqual(ctx.post_handshake_auth, True)
+
+    def test_pha_required(self):
+        client_context, server_context, hostname = testing_context()
+        server_context.post_handshake_auth = True
+        server_context.verify_mode = ssl.CERT_REQUIRED
+        client_context.post_handshake_auth = True
+        client_context.load_cert_chain(SIGNED_CERTFILE)
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'FALSE\n')
+                s.write(b'PHA')
+                self.assertEqual(s.recv(1024), b'OK\n')
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'TRUE\n')
+                # PHA method just returns true when cert is already available
+                s.write(b'PHA')
+                self.assertEqual(s.recv(1024), b'OK\n')
+                s.write(b'GETCERT')
+                cert_text = s.recv(4096).decode('us-ascii')
+                self.assertIn('Python Software Foundation CA', cert_text)
+
+    def test_pha_required_nocert(self):
+        client_context, server_context, hostname = testing_context()
+        server_context.post_handshake_auth = True
+        server_context.verify_mode = ssl.CERT_REQUIRED
+        client_context.post_handshake_auth = True
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                s.write(b'PHA')
+                # receive CertificateRequest
+                self.assertEqual(s.recv(1024), b'OK\n')
+                # send empty Certificate + Finish
+                s.write(b'HASCERT')
+                # receive alert
+                with self.assertRaisesRegex(
+                        ssl.SSLError,
+                        'tlsv13 alert certificate required'):
+                    s.recv(1024)
+
+    def test_pha_optional(self):
+        if support.verbose:
+            sys.stdout.write("\n")
+
+        client_context, server_context, hostname = testing_context()
+        server_context.post_handshake_auth = True
+        server_context.verify_mode = ssl.CERT_REQUIRED
+        client_context.post_handshake_auth = True
+        client_context.load_cert_chain(SIGNED_CERTFILE)
+
+        # check CERT_OPTIONAL
+        server_context.verify_mode = ssl.CERT_OPTIONAL
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'FALSE\n')
+                s.write(b'PHA')
+                self.assertEqual(s.recv(1024), b'OK\n')
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'TRUE\n')
+
+    def test_pha_optional_nocert(self):
+        if support.verbose:
+            sys.stdout.write("\n")
+
+        client_context, server_context, hostname = testing_context()
+        server_context.post_handshake_auth = True
+        server_context.verify_mode = ssl.CERT_OPTIONAL
+        client_context.post_handshake_auth = True
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'FALSE\n')
+                s.write(b'PHA')
+                self.assertEqual(s.recv(1024), b'OK\n')
+                # optional doens't fail when client does not have a cert
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'FALSE\n')
+
+    def test_pha_no_pha_client(self):
+        client_context, server_context, hostname = testing_context()
+        server_context.post_handshake_auth = True
+        server_context.verify_mode = ssl.CERT_REQUIRED
+        client_context.load_cert_chain(SIGNED_CERTFILE)
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                with self.assertRaisesRegex(ssl.SSLError, 'not server'):
+                    s.verify_client_post_handshake()
+                s.write(b'PHA')
+                self.assertIn(b'extension not received', s.recv(1024))
+
+    def test_pha_no_pha_server(self):
+        # server doesn't have PHA enabled, cert is requested in handshake
+        client_context, server_context, hostname = testing_context()
+        server_context.verify_mode = ssl.CERT_REQUIRED
+        client_context.post_handshake_auth = True
+        client_context.load_cert_chain(SIGNED_CERTFILE)
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'TRUE\n')
+                # PHA doesn't fail if there is already a cert
+                s.write(b'PHA')
+                self.assertEqual(s.recv(1024), b'OK\n')
+                s.write(b'HASCERT')
+                self.assertEqual(s.recv(1024), b'TRUE\n')
+
+    def test_pha_not_tls13(self):
+        # TLS 1.2
+        client_context, server_context, hostname = testing_context()
+        server_context.verify_mode = ssl.CERT_REQUIRED
+        client_context.maximum_version = ssl.TLSVersion.TLSv1_2
+        client_context.post_handshake_auth = True
+        client_context.load_cert_chain(SIGNED_CERTFILE)
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+                # PHA fails for TLS != 1.3
+                s.write(b'PHA')
+                self.assertIn(b'WRONG_SSL_VERSION', s.recv(1024))
+
+
 def test_main(verbose=False):
     if support.verbose:
         import warnings
@@ -4183,6 +4373,7 @@ def test_main(verbose=False):
     tests = [
         ContextTests, BasicSocketTests, SSLErrorTests, MemoryBIOTests,
         SSLObjectTests, SimpleBackgroundTests, ThreadedTests,
+        TestPostHandshakeAuth
     ]
 
     if support.is_resource_enabled('network'):

Misc/NEWS.d/next/Library/2018-09-14-14-29-45.bpo-34670.17XwGB.rst

@@ -0,0 +1,3 @@
+Add SSLContext.post_handshake_auth and
+SSLSocket.verify_client_post_handshake for TLS 1.3's post
+handshake authentication feature.