 Hello, so I'm Matt Smith, I'm from the University of Oxford and this is some work in conjunction with Daniel Moser from ETH, Martin Strohmeier and Yvan Martinovic also from Oxford and Vincent Lenders from Armistice. So whilst this is probably going to be the most crypto lightweight talk of the workshop, hopefully it's going to make you think a little bit when you get on your flights home. So the system in question here is ACARS. Now ACARS is the aircraft communications addressed in a reporting system and it's widely used in both commercial and non-commercial aviation. It's been around for quite a long time since the late 1970s and it's now used for very different purposes to what it was originally intended. But since then it's kind of multi-medium and multi-purpose and one of the key things here is it's now easy to collect with a $10 SDR. So to look a little bit more closely at this, this is kind of a representation of the system. It's now presented over satellite, very high frequency and high frequency subcarriers and it's kind of like text messaging for aircraft. So we have this kind of service provider that handles messages and it's operated in a kind of cellular fashion and in terms of who uses it, well it could be air traffic control to do their air traffic control duties over data link rather than voice or it could be airline operations centres so they do things like updating about passengers or gate information. And in terms of where we come in, well we kind of stand at the side, we use our SDRs and over about nine months we collected a million messages and we did this just on satellite and VHF I should say. So you would think with this in mind that obviously this is probably carrying some sensitive information so you'd have some sort of security in place. Well actually ACARS doesn't have security as standard, it does have post hoc standardised security but no one really uses it. It costs extra on top and so we have this kind of situation where whilst many users require privacy, nobody really wants to pay. So we collected all these messages and we noticed that a business aircraft was sending these scramble messages and when you organise these by the first two characters you realise very quickly that this is a mono alphabetic substitution cypher. So it gets better. Nine static keys were used by all aircraft using the cypher. These were shared and so obviously we got our pen and paper out, we did some frequency analysis and some deduction and we got about three quarters of the keys substitutions. We didn't get 100% because of standard phraseology limits the characters effectively that are used. And the key thing here is we narrowed this down to one particular avionics suite called the Honeywell Primus avionics suite. Some example aircraft that use this are on the right and when we look a little bit more detailer who uses it and the manufacturing year, it kind of goes back to 2002, that's the earliest example that we saw of it, but a particular type of aircraft manufactured on average in 2014, we're also still using this and even some of those were manufactured in 2016 so it's still in use today. So this is all well and good but why do we actually care? Well a big trunk of these aircraft have something called a flight tracking block in place and to give you an idea of what this means, say for example we look at this is an aircraft that was flying last night on flight radar and you can see there's quite a bit of information there about where it's going from, where it's going to, who it is, but for some aircraft all you can find is this and actually when you look on a flight tracker, the flight tracker will deny it that this plane has ever actually flown. So from this we can kind of infer that there's some sort of privacy sensitivity going on and this has been undermined by the weak cipher. So actually 90% of the aircraft observed on VHF in 94% on SATCOM had one of these flight tracking blocks in place and to give you an idea of what this means in practice, well 30% of the messages were status reports and this reveals position, departure and arrival information. So for one aircraft we could see it took off from Turkey where it was at these two particular times when it was landing in Farnborough and according to flight radar, well this aircraft never actually flew anywhere at all. So just to close, oh sorry no I should just add very quickly, blocked aircraft were responsible for 90% of all the status reports so clearly some sort of privacy issue there. Just to close, we did disclose this to Honeywell, they said it wasn't a problem, they said that the cipher isn't encryption but obfuscation is not a security risk. I'll just leave you with the quote down the bottom there where apparently obfuscation becomes encryption when it's good enough. So thank you, we do have a financial crypto paper by the way that explains it in full but thank you. Anyone flying back on a jet? A private jet? Hold on, aviation expert is going to ask a question, Greg. Actually I'm putting on my civil liberties hat, a lot of those flights are rendition flights and there are civil liberties organisations that would really like to know that. Yes, so we do have some more work that looks at the wider issue of ACARS and privacy. This can be anywhere from business aircraft flying around to intelligence aircrafts, there's a whole range of stuff in there. Okay, let's thank the speaker again for a cool talk.