GSoC Report #2 - Avahi network service discover (GNOME Keysign)

Hi !

Last time I had talked about the design of the GUI for Keysign application and how will this app be used to automate key signing process. I ended up with telling you that I had started to work on the network part of the application and that I used avahi to discover services on the network.

Basically, in order to transfer data between two computers we have to implement a client-server model:

•  The client is the Keysign app found on the computer of the person who will sign a key. This will make a request on the ip address and port discovered by avahi.
•  The server is the Keysign app that is found on the person's laptop who wants to get his key signed. When that user selects a key and present it to be signed, it will start up the server that listens for tcp connection.

Now here comes the avahi ' s job, which is to allows us to publish and discover services and hosts running on the local network.
This simple scenario involves only two users connected on the same WIFI network. Later on it might be best to open a secured channel and have all key signing participans connected to it.
Right now, after we 'll establish a connection, the public key can be transferred insecurely but authenticated by using the owner's key fingerprint.

Here is a simplistic example of an event-driven Avahi Publisher using avahi and dbus libraries for python:

1. class AvahiPublisher:
2.     def __init__(self, name, port, stype="_demo._tcp",
3.                  domain="", host="", text=""):
4.         # simple instantiation
6.     def publish(self):
7.         bus = dbus.SystemBus()
8.         server = dbus.Interface(bus.get_object(
9.                                     avahi.DBUS_NAME,
10.                                     avahi.DBUS_PATH_SERVER),
11.                                 avahi.DBUS_INTERFACE_SERVER)
13.         group = dbus.Interface(
14.                     bus.get_object(avahi.DBUS_NAME,
15.                                    server.EntryGroupNew()),
16.                     avahi.DBUS_INTERFACE_ENTRY_GROUP)
17. 
    
18.         group.AddService(avahi.IF_UNSPEC, 
19.                      avahi.PROTO_UNSPEC,dbus.UInt32(0),
20.                      self.name, self.stype, self.domain, self.host,
21.                      dbus.UInt16(self.port), self.text)
23.         group.Commit()
24.         self.group = group
26.     def unpublish(self):
27.         self.group.Reset()

For this to work you need the avahi D-Bus API that uses avahi-daemon and has bindings for other languages than C.

The problem that I had encountered was with the avahi service browsing. D-Bus connections require a main loop to  make asynchronous calls, receive signals or export objects so that whenever a new service is published or unpublished, avahi discovers it and calls the handler method.

The thing is that the default main loop of the Gtk+ application doesn't work with DBus. It seems that DBus is expecting a DBusGMainLoop , not an ordinary loop.
Not only this but the library wraps dbus-glib rather then gio's dbus implementation which we wanted to use.

For now we will stick with these rather old bindings if we want to use avahi. As a temporary solution , we use both GObject Introspection and python-dbus. It is bad but I lack the knowledge for how to make it work in other way.

This is how the service discovering is handled:

1. class AvahiBrowser(GObject.GObject):
2.     __gsignals__ = {
3.         'new_service': (GObject.SIGNAL_RUN_LAST, None,
4.             # name, address (could be an int too (for IPv4)), port
5.             (str, str, int))
6.     }
8.     def __init__(self, loop=None, service='_._tcp'):
9.         GObject.GObject.__init__(self)
10.         self.service = service
11.         # It seems that these are different loops..?!
12.         self.loop = loop or DBusGMainLoop()
13.         self.bus = dbus.SystemBus(mainloop=self.loop)
15.         self.server = dbus.Interface( self.bus.get_object(
16.                avahi.DBUS_NAME, '/'), 'org.freedesktop.Avahi.Server')
18.         self.sbrowser = dbus.Interface(self.bus.get_object(
19.             avahi.DBUS_NAME,self.server.ServiceBrowserNew(avahi.IF_UNSPEC,
20.                 avahi.PROTO_UNSPEC, TYPE, 'local', dbus.UInt32(0))),
21.             avahi.DBUS_INTERFACE_SERVICE_BROWSER)
23.         self.sbrowser.connect_to_signal("ItemNew", self.on_new_item)
24. 
    
25.     def on_new_item(self, interface, protocol, name, stype, 
26.                    domain, flags):
27.         print "Found service '%s' type '%s' domain '%s' " 
28.                % (name, stype, domain)
30.         self.server.ResolveService(interface, protocol, name, stype,
31.             domain, avahi.PROTO_UNSPEC, dbus.UInt32(0),
32.             reply_handler=self.on_service_resolved,
33.             error_handler=self.on_error)

I want to thank my mentor Tobi for helping me on this part, as there were some things a bit too complex for me.
In any case, the app now publishes itself on the network and browse for services until it is stopped. It is not handled properly yet , as to only publish the service only when a key is available to be transferred, but work is in progress.

From now on I will post more frequently as I have done some work but did not post about it yet.
I hope you enjoyed reading this. See you soon :-)

GSoC Report #1 - Have a look at the GUI of Geysigning (GNOME keysigning)

Hello !

I should start by saying that my academic exam period has finally ended and now I can focus on the project which I'm doing for GNOME.

The very basic idea of this project is to help people who attend Key signing Parties and automate the long process it takes to sign each other's key. Afterwards this project can be further extended and integrated with GNOME desktop platform to offer users an easier way to encrypt information and  exchange keys over a local network.

To achieve this we have to start with a simple and minimalist Graphical User Interface (GUI). I am using GTK+ 3 for Python which I found easy to understand and develop applications in it. There is a good tutorial that is continuously updated. Here is the link to it if you want to check it out.

For now this does all that we want which is to develop fast from scratch a program that should work in the following scenario: one person wants to sign another person's key while both of them are physically close (and on the same WiFi network). It must be simple enough to use while also dealing with keys, signatures, revocations, sending emails, authenticating data, etc.
Later when we will want to scale it to work with more users we will probably ditch python and migrate to a very fast language like C.

OK then, let's start with how the GUI looks until this moment. I have chose to use a gtk+3 notebook container so I can make use of the possibility to add pages to it:

Image 1 - "Keys" page (tab)

Here you can see the main notebook container with two pages: "Keys" and "Get Key". The first one will populate a list of keys from the user's list of keys, and the second which is shown below, will give the possibility to enter or scan a key fingerprint encoded as a QR code:

Image 2 - "Get Key" page (tab)

I've constructed this UI by creating a separate class for each page and then put them together into a MainWindow class. The "KeySignSection()" and "GetKeySection()" are objects of specialised classes for "Keys" and "Get Key" pages:

1. class MainWindow(Gtk.Window):
3.     def __init__(self):
4.         Gtk.Window.__init__(self, title="Geysigning")
5.         self.set_border_width(10)
7.         # create notebook container
8.         notebook = Gtk.Notebook()
9.         notebook.append_page(KeySignSection(), Gtk.Label('Keys'))
10.         notebook.append_page(GetKeySection(), Gtk.Label('Get Key'))
11.         self.add(notebook)
13.         # setup signals
14.         self.connect("delete-event", Gtk.main_quit)

The progress bar shown in Image 1 will be filled with each step a user takes to sign a key. Each of these steps represents a page in another notebook container, a child widget of the "Keys" page.

This notebook container have its tab labels hidden. For example after a user selects a key and presses the "Next" button down right , the notebook should change to the second step of the process which shows information about the selected key :

Image 3 -  "Fingerprint" & "QR" sub-page 2

As you can see, the progress bar doesn't change accordingly to the current step of the process. I haven't found a way to fix this but I'm still learning GTK+ :).

For now, me and my mentor Tobias Mueller decided to stop working on the UI and moved on the network part of Geysigning app.
In order to communicate over the network between two or more instances of the same application, the latter must first advertise its existence on the network. It also must discover other services of the same type,  on the network. This means that a computer network must be created and thus it requires implementing the zero-configuration networking.

I have done this using avahi but I will tell you the details in the next post. Until then, I hope you had a good time reading this. See you soon :-)

Google Summer of Code 2014

Hello,

Good news, I have been accepted to Google Summer of Code 2014 , a program dedicated to students that helps them to get involved into open source world.

This is my first GSoC project and I am happy to be part of such a great community like GNOME.

The project that I'll be working on it's called Geysign. This will provide GNOME platform with a tool which will integrate into desktop and will ease up the process of signing Open PGP keys. This is fairly usefull for people attending key signing parties.

I am sure this will be a great experience. Thanks Google and Gnome for this opportunity :-)

"The birth of a blog"

Hello,

I am Andrei Macavei and I’m second year student in The Computer Science Department, at University “POLITEHNICA” of Bucharest.

I am interested in computer science but also in martial arts. I like Bruce Lee and his fighting technique. One of his action movies is called "The way of the Dragon" and I adapted its name for this blog :-) .

There couldn't be a better time to start blogging, than now when I got accepted to GSoC 2014 to work on a project for GNOME organisation. I was asked to post updates about what I am working on a blog and this is what I will do for the next months.

From time to time, I will also write posts related to martial arts :-) .

Hope you will find this interesting for you. Have a fun time reading it.