diff --git a/IPython/frontend/qt/console/qtconsoleapp.py b/IPython/frontend/qt/console/qtconsoleapp.py
index 29e3597..96fb0ba 100644
--- a/IPython/frontend/qt/console/qtconsoleapp.py
+++ b/IPython/frontend/qt/console/qtconsoleapp.py
@@ -42,6 +42,7 @@ from IPython.frontend.qt.console import styles
 from IPython.frontend.qt.kernelmanager import QtKernelManager
 from IPython.parallel.util import select_random_ports
 from IPython.utils.path import filefind
+from IPython.utils.py3compat import str_to_bytes
 from IPython.utils.traitlets import (
     Dict, List, Unicode, Int, CaselessStrEnum, CBool, Any
 )
@@ -404,7 +405,7 @@ class IPythonQtConsoleApp(BaseIPythonApplication):
                 # not overridden by config or cl_args
                 setattr(self, name, cfg[name])
         if 'key' in cfg:
-            self.config.Session.key = cfg['key']
+            self.config.Session.key = str_to_bytes(cfg['key'])
     
     def init_ssh(self):
         """set up ssh tunnels, if needed."""
diff --git a/IPython/zmq/entry_point.py b/IPython/zmq/entry_point.py
index 9c4e549..c54664e 100644
--- a/IPython/zmq/entry_point.py
+++ b/IPython/zmq/entry_point.py
@@ -15,12 +15,13 @@ from zmq.utils import jsonapi as json
 
 # IPython imports
 from IPython.utils.localinterfaces import LOCALHOST
+from IPython.utils.py3compat import bytes_to_str
 
 # Local imports.
 from parentpoller import ParentPollerWindows
 
 def write_connection_file(fname=None, shell_port=0, iopub_port=0, stdin_port=0, hb_port=0,
-                         ip=LOCALHOST, key=''):
+                         ip=LOCALHOST, key=b''):
     """Generates a JSON config file, including the selection of random ports.
     
     Parameters
@@ -79,7 +80,7 @@ def write_connection_file(fname=None, shell_port=0, iopub_port=0, stdin_port=0, 
                 hb_port=hb_port,
               )
     cfg['ip'] = ip
-    cfg['key'] = key
+    cfg['key'] = bytes_to_str(key)
     
     with open(fname, 'wb') as f:
         f.write(json.dumps(cfg, indent=2))
diff --git a/IPython/zmq/kernelapp.py b/IPython/zmq/kernelapp.py
index b990808..5d536a2 100644
--- a/IPython/zmq/kernelapp.py
+++ b/IPython/zmq/kernelapp.py
@@ -31,6 +31,7 @@ from IPython.core.application import (
 from IPython.utils import io
 from IPython.utils.localinterfaces import LOCALHOST
 from IPython.utils.path import filefind
+from IPython.utils.py3compat import str_to_bytes
 from IPython.utils.traitlets import (Any, Instance, Dict, Unicode, Int, Bool,
                                         DottedObjectName)
 from IPython.utils.importstring import import_item
@@ -176,7 +177,7 @@ class KernelApp(BaseIPythonApplication):
                 # not overridden by config or cl_args
                 setattr(self, name, cfg[name])
         if 'key' in cfg:
-            self.config.Session.key = cfg['key']
+            self.config.Session.key = str_to_bytes(cfg['key'])
     
     def write_connection_file(self):
         """write connection info to JSON file"""