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

@@ -140,6 +140,14 @@ 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
 ----
 
@@ -147,7 +155,6 @@ venv
   activating virtual environments under PowerShell Core 6.1.
   (Contributed by Brett Cannon in :issue:`32718`.)
 
-
 Optimizations
 =============
 

Lib/ssl.py

@@ -777,6 +777,9 @@ class SSLObject:
         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 @@ class SSLSocket(socket):
         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 @@ class ThreadedEchoServer(threading.Thread):
                             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 @@ class ThreadedTests(unittest.TestCase):
                                  '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

+Add SSLContext.post_handshake_auth and
+SSLSocket.verify_client_post_handshake for TLS 1.3's post
+handshake authentication feature.

Modules/_ssl.c

@@ -421,6 +421,9 @@ typedef struct {
      */
     unsigned int hostflags;
     int protocol;
+#ifdef TLS1_3_VERSION
+    int post_handshake_auth;
+#endif
 } PySSLContext;
 
 typedef struct {
@@ -2643,6 +2646,30 @@ _ssl__SSLSocket_get_channel_binding_impl(PySSLSocket *self,
     return PyBytes_FromStringAndSize(buf, len);
 }
 
+/*[clinic input]
+_ssl._SSLSocket.verify_client_post_handshake
+
+Initiate TLS 1.3 post-handshake authentication
+[clinic start generated code]*/
+
+static PyObject *
+_ssl__SSLSocket_verify_client_post_handshake_impl(PySSLSocket *self)
+/*[clinic end generated code: output=532147f3b1341425 input=6bfa874810a3d889]*/
+{
+#ifdef TLS1_3_VERSION
+    int err = SSL_verify_client_post_handshake(self->ssl);
+    if (err == 0)
+        return _setSSLError(NULL, 0, __FILE__, __LINE__);
+    else
+        Py_RETURN_NONE;
+#else
+    PyErr_SetString(PyExc_NotImplementedError,
+                    "Post-handshake auth is not supported by your "
+                    "OpenSSL version.");
+    return NULL;
+#endif
+}
+
 #ifdef OPENSSL_VERSION_1_1
 
 static SSL_SESSION*
@@ -2819,6 +2846,7 @@ static PyMethodDef PySSLMethods[] = {
     _SSL__SSLSOCKET_SELECTED_ALPN_PROTOCOL_METHODDEF
     _SSL__SSLSOCKET_COMPRESSION_METHODDEF
     _SSL__SSLSOCKET_SHUTDOWN_METHODDEF
+    _SSL__SSLSOCKET_VERIFY_CLIENT_POST_HANDSHAKE_METHODDEF
     {NULL, NULL}
 };
 
@@ -2862,7 +2890,7 @@ static PyTypeObject PySSLSocket_Type = {
  */
 
 static int
-_set_verify_mode(SSL_CTX *ctx, enum py_ssl_cert_requirements n)
+_set_verify_mode(PySSLContext *self, enum py_ssl_cert_requirements n)
 {
     int mode;
     int (*verify_cb)(int, X509_STORE_CTX *) = NULL;
@@ -2882,9 +2910,13 @@ _set_verify_mode(SSL_CTX *ctx, enum py_ssl_cert_requirements n)
                         "invalid value for verify_mode");
         return -1;
     }
+#ifdef TLS1_3_VERSION
+    if (self->post_handshake_auth)
+        mode |= SSL_VERIFY_POST_HANDSHAKE;
+#endif
     /* keep current verify cb */
-    verify_cb = SSL_CTX_get_verify_callback(ctx);
-    SSL_CTX_set_verify(ctx, mode, verify_cb);
+    verify_cb = SSL_CTX_get_verify_callback(self->ctx);
+    SSL_CTX_set_verify(self->ctx, mode, verify_cb);
     return 0;
 }
 
@@ -2966,13 +2998,13 @@ _ssl__SSLContext_impl(PyTypeObject *type, int proto_version)
     /* Don't check host name by default */
     if (proto_version == PY_SSL_VERSION_TLS_CLIENT) {
         self->check_hostname = 1;
-        if (_set_verify_mode(self->ctx, PY_SSL_CERT_REQUIRED) == -1) {
+        if (_set_verify_mode(self, PY_SSL_CERT_REQUIRED) == -1) {
             Py_DECREF(self);
             return NULL;
         }
     } else {
         self->check_hostname = 0;
-        if (_set_verify_mode(self->ctx, PY_SSL_CERT_NONE) == -1) {
+        if (_set_verify_mode(self, PY_SSL_CERT_NONE) == -1) {
             Py_DECREF(self);
             return NULL;
         }
@@ -3065,6 +3097,11 @@ _ssl__SSLContext_impl(PyTypeObject *type, int proto_version)
 #endif
     X509_VERIFY_PARAM_set_hostflags(params, self->hostflags);
 
+#ifdef TLS1_3_VERSION
+    self->post_handshake_auth = 0;
+    SSL_CTX_set_post_handshake_auth(self->ctx, self->post_handshake_auth);
+#endif
+
     return (PyObject *)self;
 }
 
@@ -3319,7 +3356,10 @@ _ssl__SSLContext__set_alpn_protocols_impl(PySSLContext *self,
 static PyObject *
 get_verify_mode(PySSLContext *self, void *c)
 {
-    switch (SSL_CTX_get_verify_mode(self->ctx)) {
+    /* ignore SSL_VERIFY_CLIENT_ONCE and SSL_VERIFY_POST_HANDSHAKE */
+    int mask = (SSL_VERIFY_NONE | SSL_VERIFY_PEER |
+                SSL_VERIFY_FAIL_IF_NO_PEER_CERT);
+    switch (SSL_CTX_get_verify_mode(self->ctx) & mask) {
     case SSL_VERIFY_NONE:
         return PyLong_FromLong(PY_SSL_CERT_NONE);
     case SSL_VERIFY_PEER:
@@ -3344,7 +3384,7 @@ set_verify_mode(PySSLContext *self, PyObject *arg, void *c)
                         "check_hostname is enabled.");
         return -1;
     }
-    return _set_verify_mode(self->ctx, n);
+    return _set_verify_mode(self, n);
 }
 
 static PyObject *
@@ -3550,7 +3590,7 @@ set_check_hostname(PySSLContext *self, PyObject *arg, void *c)
     if (check_hostname &&
             SSL_CTX_get_verify_mode(self->ctx) == SSL_VERIFY_NONE) {
         /* check_hostname = True sets verify_mode = CERT_REQUIRED */
-        if (_set_verify_mode(self->ctx, PY_SSL_CERT_REQUIRED) == -1) {
+        if (_set_verify_mode(self, PY_SSL_CERT_REQUIRED) == -1) {
             return -1;
         }
     }
@@ -3558,6 +3598,43 @@ set_check_hostname(PySSLContext *self, PyObject *arg, void *c)
     return 0;
 }
 
+static PyObject *
+get_post_handshake_auth(PySSLContext *self, void *c) {
+#if TLS1_3_VERSION
+    return PyBool_FromLong(self->post_handshake_auth);
+#else
+    Py_RETURN_NONE;
+#endif
+}
+
+#if TLS1_3_VERSION
+static int
+set_post_handshake_auth(PySSLContext *self, PyObject *arg, void *c) {
+    int (*verify_cb)(int, X509_STORE_CTX *) = NULL;
+    int mode = SSL_CTX_get_verify_mode(self->ctx);
+    int pha = PyObject_IsTrue(arg);
+
+    if (pha == -1) {
+        return -1;
+    }
+    self->post_handshake_auth = pha;
+
+    /* client-side socket setting, ignored by server-side */
+    SSL_CTX_set_post_handshake_auth(self->ctx, pha);
+
+    /* server-side socket setting, ignored by client-side */
+    verify_cb = SSL_CTX_get_verify_callback(self->ctx);
+    if (pha) {
+        mode |= SSL_VERIFY_POST_HANDSHAKE;
+    } else {
+        mode ^= SSL_VERIFY_POST_HANDSHAKE;
+    }
+    SSL_CTX_set_verify(self->ctx, mode, verify_cb);
+
+    return 0;
+}
+#endif
+
 static PyObject *
 get_protocol(PySSLContext *self, void *c) {
     return PyLong_FromLong(self->protocol);
@@ -4461,6 +4538,13 @@ static PyGetSetDef context_getsetlist[] = {
                      (setter) set_sni_callback, PySSLContext_sni_callback_doc},
     {"options", (getter) get_options,
                 (setter) set_options, NULL},
+    {"post_handshake_auth", (getter) get_post_handshake_auth,
+#ifdef TLS1_3_VERSION
+                            (setter) set_post_handshake_auth,
+#else
+                            NULL,
+#endif
+                            NULL},
     {"protocol", (getter) get_protocol,
                  NULL, NULL},
     {"verify_flags", (getter) get_verify_flags,

Modules/clinic/_ssl.c.h

@@ -342,6 +342,24 @@ exit:
     return return_value;
 }
 
+PyDoc_STRVAR(_ssl__SSLSocket_verify_client_post_handshake__doc__,
+"verify_client_post_handshake($self, /)\n"
+"--\n"
+"\n"
+"Initiate TLS 1.3 post-handshake authentication");
+
+#define _SSL__SSLSOCKET_VERIFY_CLIENT_POST_HANDSHAKE_METHODDEF    \
+    {"verify_client_post_handshake", (PyCFunction)_ssl__SSLSocket_verify_client_post_handshake, METH_NOARGS, _ssl__SSLSocket_verify_client_post_handshake__doc__},
+
+static PyObject *
+_ssl__SSLSocket_verify_client_post_handshake_impl(PySSLSocket *self);
+
+static PyObject *
+_ssl__SSLSocket_verify_client_post_handshake(PySSLSocket *self, PyObject *Py_UNUSED(ignored))
+{
+    return _ssl__SSLSocket_verify_client_post_handshake_impl(self);
+}
+
 static PyObject *
 _ssl__SSLContext_impl(PyTypeObject *type, int proto_version);
 
@@ -1175,4 +1193,4 @@ exit:
 #ifndef _SSL_ENUM_CRLS_METHODDEF
     #define _SSL_ENUM_CRLS_METHODDEF
 #endif /* !defined(_SSL_ENUM_CRLS_METHODDEF) */
-/*[clinic end generated code: output=e2417fee28666f7c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=c4e73b70ac3618ba input=a9049054013a1b77]*/

Tools/ssl/multissltests.py

@@ -45,16 +45,16 @@ OPENSSL_OLD_VERSIONS = [
 ]
 
 OPENSSL_RECENT_VERSIONS = [
-    "1.0.2o",
-    "1.1.0h",
-    # "1.1.1-pre7",
+    "1.0.2p",
+    "1.1.0i",
+    "1.1.1",
 ]
 
 LIBRESSL_OLD_VERSIONS = [
 ]
 
 LIBRESSL_RECENT_VERSIONS = [
-    "2.7.3",
+    "2.7.4",
 ]
 
 # store files in ../multissl