Merge pull request #3828 from minrk/signature_scheme

signature_scheme lives in Session

not ConnectionFileMixin

prevents empty signature_scheme in connection files

IPython/kernel/connect.py

@@ -391,7 +391,6 b' class ConnectionFileMixin(HasTraits):'
     _connection_file_written = Bool(False)
 
     transport = CaselessStrEnum(['tcp', 'ipc'], default_value='tcp', config=True)
-    signature_scheme = Unicode('')
 
     ip = Unicode(LOCALHOST, config=True,
         help="""Set the kernel\'s IP address [default localhost].
@@ -439,7 +438,8 b' class ConnectionFileMixin(HasTraits):'
             stdin_port=self.stdin_port,
             hb_port=self.hb_port,
             control_port=self.control_port,
-            signature_scheme=self.signature_scheme,
+            signature_scheme=self.session.signature_scheme,
+            key=self.session.key,
         )
 
     def cleanup_connection_file(self):
@@ -476,7 +476,7 b' class ConnectionFileMixin(HasTraits):'
             stdin_port=self.stdin_port, iopub_port=self.iopub_port,
             shell_port=self.shell_port, hb_port=self.hb_port,
             control_port=self.control_port,
-            signature_scheme=self.signature_scheme,
+            signature_scheme=self.session.signature_scheme,
         )
         # write_connection_file also sets default ports:
         for name in port_names:

IPython/kernel/tests/test_kernelmanager.py

@@ -47,4 +47,15 b' class TestKernelManager(TestCase):'
     def test_ipc_lifecycle(self):
         km = self._get_ipc_km()
         self._run_lifecycle(km)
+    
+    def test_get_connect_info(self):
+        km = self._get_tcp_km()
+        cinfo = km.get_connection_info()
+        keys = sorted(cinfo.keys())
+        expected = sorted([
+            'ip', 'transport',
+            'hb_port', 'shell_port', 'stdin_port', 'iopub_port', 'control_port',
+            'key', 'signature_scheme',
+        ])
+        self.assertEqual(keys, expected)