Posts Tagged ‘Computer Laboratory’

Communicating with a Firefox extension from Selenium

Monday, May 20th, 2013

Edit: I think this now longer works with more recent versions of Firefox, or at least I have given up on this strategy and gone for extending Webdriver to do what I want instead.

For something I am currently working on I wanted to use Selenium to automatically access some parts of Firefox which are not accessible from a page. The chosen method was to use a Firefox extension and send events between the page and the extension to carry data. Getting this working was more tedious than I was expecting, perhaps mainly because I have tried to avoid javascript whenever possible in the past.

The following code extracts set up listeners with Selenium and the Firefox extension and send one event in each direction. Using this to do proper communication and to run automated tests is left as an exercise for the author but hopefully someone else will find this useful as a starting point. The full code base this forms part of will be open sourced and made public at some future point when it does something more useful.



import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.firefox.FirefoxProfile;

public class App {
private static final String SEND = "\"syncCommandToExtension\"";
private static final String RECV = "\"syncCommandToPage\"";

public static void main(String[] args) throws IOException {
// This is where maven is configured to put the compiled .xpi
File extensionFile = new File("target/extension.xpi");
// So that the relevant Firefox extension developer settings get turned on.
File developerFile = new File("developer_profile-0.1-fn+fx.xpi");
FirefoxProfile firefoxProfile = new FirefoxProfile();
WebDriver driver = new FirefoxDriver(firefoxProfile);
if (driver instanceof JavascriptExecutor) {
AsyncExecute executor = new AsyncExecute(((JavascriptExecutor) driver));
executor.execute("document.addEventListener( " + RECV + ", function(aEvent) { document.title = (" + RECV
+ " + aEvent) }, true);");
"document.dispatchEvent(new CustomEvent(" + SEND + "));");

} else {
System.err.println("Driver does not support javascript execution");

* Encapsulate the boilerplate code required to execute javascript with Selenium
private static class AsyncExecute {
private final JavascriptExecutor executor;

public AsyncExecute(JavascriptExecutor executor) {
this.executor = executor;

public void execute(String javascript) {
executor.executeAsyncScript("var callback = arguments[arguments.length - 1];"+ javascript
+ "callback(null);", new Object[0]);

browserOverlay.js Originally cribbed from the XUL School hello world tutorial.

"syncCommandToExtension", function(aEvent) { window.alert("document syncCommandToExtension" + aEvent);/* do stuff*/ }, true, true);

// do not try to add a callback until the browser window has
// been initialised. We add a callback to the tabbed browser
// when the browser's window gets loaded.
window.addEventListener("load", function () {
// Add a callback to be run every time a document loads.
// note that this includes frames/iframes within the document
gBrowser.addEventListener("load", pageLoadSetup, true);
}, false);

function syncLog(message){
Application.console.log("SYNC-TEST: " + message);

function sendToPage(doc) {
doc.dispatchEvent(new CustomEvent("syncCommandToPage"));

function pageLoadSetup(event) {
// this is the content document of the loaded page.
let doc = event.originalTarget;

if (doc instanceof HTMLDocument) {
// is this an inner frame?
if (doc.defaultView.frameElement) {
// Frame within a tab was loaded.
// Find the root document:
while (doc.defaultView.frameElement) {
doc = doc.defaultView.frameElement.ownerDocument;
// The event listener is added after the page has loaded and we don't want to trigger
// the event until the listener is registered.
setTimeout(function () {sendToPage(doc);},1000);

21st International Workshop on Security Protocols

Wednesday, March 20th, 2013

For the last couple of days I have been at the Security Protocols Workshop which was conveniently located a short cycle ride away. I thoroughly enjoyed it and will definitely be coming back next year (hopefully with a short paper to present). I want to mention some of my  favourite new (to me) ideas which were presented. I am only covering them briefly so if it looks interesting go and read the paper (when it comes out at some unspecified point in the future or find someone with a copy of the pre-proceedings).

Towards new security primitives based on hard AI problems – Bin B. Zhu, Jeff Yan

The core idea here is that if there are problems which computers can’t solve but humans can (e.g. 2D Captchas) then these can be used to allow humans to input their passwords etc. in such a way that a computer trying to input passwords in has no idea what password it is inputting (CaRP). This means that on each attempt the attacker gains nothing because they don’t know what password they tried as they just sent a random selection of click events which the server then interpreted as a password using information that the attacker does not have without human assistance. This helps against online brute force attacks, particularly distributed attacks which are hard to solve with blacklisting without also locking the legitimate user out. It also helps as part of the ‘authentication is machine learning‘ approach as accounts which are flagged as being used suspiciously can be required to login using a CaRP which requires human input and so mitigates automated attacks in a similar way to requiring the use of a mobile number and sending it a text (though it is less strong than that – it does require less infrastructure). Additionally I think that if a particular Captcha scheme is broken then the process of breaking each one will still be computationally intensive and so this should still rate limit the attacker.

Remote device attestation with bounded leakage of secrets – Jun Zhao, Virgil Gligor, Adrian Perrig, James Newsome

This is a neat idea where if the hardware of a device is controlled such that its output bandwidth is strictly limited then it is still possible to be certain that the software on it has not been compromised even if an attacker can install malware on it and has full control of the network. This works by having a large pool of secrets on the device which are updated in a dependent way each epoch and there is not enough bandwidth in an epoch to leak enough data to construct the pool of secrets outside the device. Then the verifier can send the device a new program to fill its working RAM and request a MAC over the memory and secrets storage and this cannot be computed off the device or on the device without filling the RAM with the requested content and so when the MAC is returned the verifier knows the full contents of the hardware’s volatile state and so if it was compromised it no longer is.

Spraying Diffie-Hellman for secure key exchange in MANETs – Ariel Stulman, Jonathan Lahav, and Avraham Shmueli

This idea is for use in providing confidentiality of communication on mobile ad-hoc networks. Since the network is always changing and comprised of many nodes it is hard for an attacker to compromise all the nodes on all paths between two nodes which wish to communicate confidentiality. The idea is to do Diffie-Hellman but split the message into multiple pieces with a hash and send each message via a different route to the recipient. If any one of those pieces gets through without being man-in-the-middled then the attack has failed. In a random dynamically changing network it is hard for an attacker to ensure that. Though not impossible and so a very careful analysis needs to be done to mitigate those risks in practice.

Layering authentication channels to provide covert communication – Mohammed H. Almeshekah, Mikhail Atallah, Eugene H. Spafford

The idea here is that some additional information can be put in the authentication information such as typing <password> <code word> rather than just <password> in the password field and hence transmitting <code word> to the bank which can have many meanings, e.g. have three different code words for 3 levels of access (read only, transactions, administrative) and one for coercion. I particularly liked the idea of being able to tell the bank ‘help someone is coercing me to do this, make everything look as normal but take steps to reverse things afterwards and please send the police’.


There were also lots of other interesting ideas some of which I had seen before in other contexts. I thought I made some useful contributions to discussions and so maybe this whole PhD in computer security thing might work out. There were some really friendly welcoming people there and I already knew a bunch of them as they were CL Security Group people.

Raspberry Pi Entropy server

Thursday, August 23rd, 2012

The Raspberry Pi project is one of the more popular projects the Computer Lab is involved with at the moment and all the incoming freshers are getting one.

One of the things I have been working on as a Research Assistant in the Digital Technology Group is on improving the infrastructure we use for research and my current efforts include using puppet to automate the configuration of our servers.

We have a number of servers which are VMs and hence can be a little short of entropy. One solution to having a shortage of entropy is an ‘entropy key‘ which is a little USB device which uses reverse biased diodes to generate randomness and has a little ARM chip (ARM is something the CL is rather proud of) which does a pile of crypto and analysis to ensure that it is good randomness. As has been done before (with pretty graphs) this can then be fed to VMs providing them with the randomness they want.

My solution to the need for some physical hardware to host the entropy key was a Raspberry Pi because I don’t need very much compute power and dedicated hardware means that it is less likely to get randomly reinstalled. A rPi can be thought of as the hardware equivalent of a small VM.

Unboxed Raspberry Pi with entropy key

I got the rPi from Rob Mullins by taking a short walk down the corridor on the condition that there be photos. One of the interesting things about using rPis for servers is that the cost of the hardware is negligible in comparison with the cost of connecting that hardware to the network and configuring it.

The Raspberry Pi with entropy key temporarily installed in a wiring closet

The rPi is now happily serving entropy to various VMs from the back of a shelf in one of the racks in a server room (not the one shown, we had to move it elsewhere).

Initially it was serving entropy in the clear via the EGD protocol over TCP. Clearly this is rather bad as observable entropy doesn’t really gain you anything (and might lose you everything). Hence it was necessary to use crypto to protect the transport from the rPi to the VMs.
This is managed by the dtg::entropy, dtg::entropy::host and dtg::entropy::client classes which generate the relevant config for egd-linux and stunnel.

This generates an egd-client.conf which looks like this:

; This stunnel config is managed by Puppet.

sslVersion = TLSv1
client = yes

setuid = egd-client
setgid = egd-client
pid = /
chroot = /var/lib/stunnel4/egd-client

socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1
TIMEOUTclose = 0

debug = 0
output = /egd-client.log

verify = 3

CAfile = /usr/local/share/ssl/cafile

accept = 7777
connect =

And a host config like:

; This stunnel config is managed by Puppet.

sslVersion = TLSv1

setuid = egd-host
setgid = egd-host
pid = /
chroot = /var/lib/stunnel4/egd-host

socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1
TIMEOUTclose = 0

debug = 0
output = /egd-host.log

cert = /root/puppet/ssl/stunnel.pem
key = /root/puppet/ssl/stunnel.pem
CAfile = /usr/local/share/ssl/cafile

accept = 7776
connect = 777
cert = /root/puppet/ssl/stunnel.pem
key = /root/puppet/ssl/stunnel.pem
CAfile = /usr/local/share/ssl/cafile

Getting that right was somewhat tedious due to defaults not working well together.
openssl s_client -connect
and a python egd client were useful for debugging. In the version of debian in rasperian the stunnel binary points to an stunnel3 compatibility script around the actual stunnel4 binary which resulted in much confusion when trying to run stunnel manually.

IB Group Projects

Thursday, March 10th, 2011

On Wednesday the Computer Science IB students demonstrated the projects that they have been working on for the last term. This is my thoughts on them.

Some of the projects were really quite interesting, some of them even actually useful in real life, some of them didn’t work, were boring and simply gimmicks.

Alpha: “African SMS Radio” was a project to create a pretty GUI to a “byzantine and buggy” backend. It could allow a radio operator to run polls and examine stats of texts sent to a particular number. However it didn’t look particularly interesting and though there might be use cases for such a system I think only as a component of a larger more enterprise system and only after the “buggy” backend they had to use had been fixed up/rewritten.

Bravo: “Crowd control” was a project to simulate evacuations of buildings. It is a nice use of the Open Room Map project to provide the building data. It looked like it was still a little buggy – in particular it was allowing really quite nasty crushes to occur and the resulting edge effects as people were thrown violently across the room as the system tried to deal with multiple people being in the same place at the same time was a little amusing. With a little more work it could become quite useful as an extension in the Open Room Map ecosystem which could help it gain momentum and take off. I think that the Open Room Map project is really quite cool and useful – it is the way that data on the current structure and contents of buildings can be crowd sourced and kept up to date but then it is a project of my supervisor. ;-)

Charlie: “Digit[Ov]al automated cricket commentary” this was a project to use little location transmitters on necklaces and usb receivers plugged into laptops to determine the location of cricketers while they were playing and then automatically construct commentary on that. It won the prize for best technical project but it didn’t actually work. They hadn’t solved the problem of people being between the transmitter and the receiver reducing transmission strength by 1/3 or the fact that placing a hand over it reduced it by 1/3 or the fact that the transmitters were not omnidirectional and so orientation was a major issue. They were also limited to only four receivers due to only having four suitable laptops. They used a square arrangement to try and detect location. It is possible that a double triangle arrangement with three corners at ground level and then the other triangle higher up (using the ‘stadium’ to gain height) and offset so that the upper vertices lined up with the mid point of the lower edges would have given them a better signal. Calibrating and constructing algorithms to deal with the noise and poor data would probably have been quite difficult and required some significant work – which IB students haven’t really been taught enough for yet.

Delta: “Hand Wave, Hand Wave” was a project to use two sensors with gyroscopes and accelerometers to do gesture recognition and control. It didn’t really work in the demo and since it had reimplemented everything it didn’t manage to do anything particularly interesting. I think using such sensors for gesture control is probably a dead end as kinect and the like makes just using a camera so much easier and more interesting.

Echo: “iZoopraxiscope – Interactive Handheld Projector” this project was about using a phone with a build in pico projector as an interface. This was obviously using very prototype technology – using the projector would drain the phones battery very quickly, in some cases even when the phone was plugged in and fitting it in the (slightly clunky) phone clearly was at the expense of providing the normal processing power that is expected in an Android phone resulting in it being somewhat sluggish. Since the sensors were rather noisy and techniques for coping with that were not as advanced as they might have been (they just used an exponential moving average and manually tweaked the parameter) they had some difficulties with sluggishness in the controls of some of the games. However I think they produced several nice arcade style games (I didn’t play any of them) and so did demonstrate a wide range of uses. With better knowledge of how to deal with sensors (not really covered in any of the courses offered at the CL) and better technology this could be really neat. However getting a battery powered projector to compete with normal lighting is going to be quite a challenge.
The thing I really like about small projectors is that it could help make it easier to interact in lectures. Sometimes when asking a question or making a comment in lectures it might be useful to draw a diagram which the lecturer (and the rest of the audience) can see and currently doing so is really quite hard. (I should take to carrying around a laser pointer for use in these circumstances).

Foxtrot: “Lounge Star” this was a android app for making air passenger’s lives a little easier by telling them information such as which gate to use etc. without them having to go anywhere and integrating with various airlines systems. As someone who has ‘given up flying’ (not in an absolute sense but in a ‘while any other option (including not going) still remains’ sense) this was not vastly interesting but it could really work as a product if the airlines like it. So: “Oh it is another nice little Android app” (but then associated short attention span kicks in and “bored now”).

Golf: The Energy Forecast this was a project I really liked (it pushed the right buttons) it is a project to predict the energy production of all the wind farms in the country based on the predicted wind speed. It integrated various sources of wind speeds, power production profiles for different types of wind farm and the locations and types of many different wind farms (they thought all but I found some they were missing) and they had a very pretty GUI using google maps etc to show things geographically and were using a very pretty graph drawing javascript library. So I did the “oh you should use the SRCF to host that” thing (they were using a public IP on one of their own computers) and I am sort of thinking “I would really like to have your code” (Oh wait I know where that is kept, snarfle, snarfle ;-) It is something I would really like to make into a part of the ReadYourMeter ecosystem (I may try and persuade Andy he wants to get something done with it).
I love wind turbines all my (small) investments are in them, we have one in our back garden etc. this could be really useful. [end fanboyism]

Hotel: “Top Tips” this was a project to see whether the comments traders put on their trading tips actually told you anything about how good the trade was. The answer was no, not really, nothing to see here. Which is a little disappointing and not a particularly interesting project “lets do some data analysis!” etc.

India: “True Mobile Coverage” this was a project to crowd source the collection of real mobile signal strength data. It actually serves a useful purpose and could be really helpful. They needed to work on their display a little as it wasn’t very good at distinguishing between areas they didn’t know much about and areas with weak signal and unfortunately as with all projects it started working in a very last minute manner so they didn’t have that much data to show. Nice crowd sourcing data collection android app of the kind that loads of people in the CL love. Of course there will be large quantities they could do to improve it using the kind of research which has been done in the CL but it is a good start.

Juliet: “Twitter Dashboard” this was so obviously going to win from the beginning – a twitter project (yey bandwagon) which looks pretty. They did do a very good job, it looked pretty, it ate 200% of the SRCF’s CPU continuously during the demo (but was niced to 19 so didn’t affect other services) – there are probably efficiency savings to be made here but that isn’t a priority for a Group Project which is mainly about producing something that looks pretty and as if it works all other considerations are secondary. My thoughts were mainly “Oh another project to make it easier for Redgate to do more of their perpetual advertising. meh.” (they have lovely people working for them but I couldn’t write good enough Java for them)

Kilo: “Walk out of the Underground” this was a project to guide you from the moment you stepped out of the underground to your destination using an arrow on the screen of your phone. It was rather hard to demo inside the Intel Lab where there is both poor signal and insufficient scale to see whether it actually works. It might be useful, it might work, it is yet another app for the app store and could probably drum up a few thousand users as a free app.

Lima: “Who is my Customer?” this was a very enterprise project to do some rather basic Information Retrieval to find the same customer in multiple data sets. The use case being $company has a failsome information system and their data is poor quality and not well linked together. Unfortunately the project gave the impression of being something which one person could hack together in a weekend. I may be being overly harsh but I found it a little boring.

So in summary: I liked “The Energy Forcast” most because it pushed the right buttons, “True mobile coverage” is interesting and useful. Charlie could be interesting if it could be made to work but I think that the ‘cricket’ aspect is a little silly – if you want commentary use a human. iZoopraxiscope (what a silly name) points out some cool tech that will perhaps be useful in the future but really is not ready yet (they might need/be using some of the cool holgrams tech that Tim Wilkinson is working on (he gave a CUCaTS talk “Do We Really Need Pixels?” recently).

Idea for next year: have a competition after the end of the presentations to write up the project in a scientific paper style and then publish the ones that actually reach a sufficiently good standard in a IB Group Project ‘journal’ as this would provide some scientific skills to go with all the Software Engineering skills that the Group project is currently supposed to teach. (No this is so not going to happen in reality)