 This is SoundFX exploring acoustic cyber weapons with Matt Wixie. Okay, hi everyone. Yeah, so this is SoundFX exploring acoustic cyber weapons. My name is Matt Wixie. I lead security research for PWC UK cyber security practice. I'm also a part-time PhD student at University College London, which is where this work comes from. Prior to joining PWC, I worked in law enforcement in the UK for a few years, and previously spoken at Black Cat and Defconn and other commons as well. So a few disclaimers before we get started. This work was undertaken as part of my PhD research at UCL. I wouldn't have been possible without my supervisors and co-authors for this project, Professor Shane Johnson and Professor Emiliano de Cristofaro. What you're going to see here is presented for educational purposes only. You'll also notice throughout this talk that I mention words like caviar and possibly and potentially quite a lot. That's kind of for two reasons. The first is not to kind of spread fear, uncertainty, and doubt about the topic of this talk, but also because this is really early first stage research in an area where there's often a really blurred line between correlation and causation. So that's why those caveats are there. So why this talk? Why this subject? So a couple of years ago at Defconn, I did a talk called CenoEvil, HenoEvil, which was about using light and sound to exfiltrate data and mess with drones and bypass air gaps and that kind of thing. And as a result of that kind of got really interested in ultrasound and infrasound kind of unconventional uses of sound generally. So why should you care about this talk and this topic? Potentially it's a novel class of attack which we have done some empirical experimentation on. It's an increasing attack surface as well. And it builds on previous work around malware and physical harm, acoustic harm more generally, and digital physical crossover attacks. So a brief bit of background. Probably kind of one of the earliest, one of the early examples of digital physical malware was Stuxnet obviously in 2010. Also things like Mirai, the IoT botnet, more recently some work that was done on things like MRI machines. There have been examples prior to those of malware accidentally or inadvertently affecting physical kit. So the Conficker worm in 2008 infected hospital equipment as did one acquired to some extent. There have been vulnerabilities found in medical implants, things like pacemakers, insulin pumps, that sort of thing. And various vulnerabilities in vehicles as well which potentially will allow an attacker to take control of them and potentially cause harm. But typically with that kind of research there's an indirect relationship between the attack, the effect, and the potential harm that's caused. And to some extent what my research focuses on is trying to take out one of those steps and instead looking at malware or attacks that can directly affect human beings either psychologically or physically. And some examples of the kind of things that would fall under that bracket would be Kevin Paulson's report in 2008 on attackers who uploaded flashing gifts to an epilepsy support forum. And those gifts flashed in patterns consistent with those known to induce photosensitive epileptic seizures and a number of people had seizures as a result. Similarly, Oliver Femi and others in 2013 and Ronan and Shamir in 2016 looked at hacking smart light bulbs and specifically found that they could make those flash again in patterns consistent with photosensitive epileptic seizures. More recently, Reels and Butts in 2017 in their kind of ongoing research on IoT vulnerabilities found that they could attack an IoT car wash and cause it to strike a human being. So when you think about sound as a weapon this isn't my chart. This is a kind of pretty simplistic view of how long you should be exposed to sounds at certain levels. Now this uses decibels. Decibels is an often misunderstood measure of sound because it's not an absolute measure, it's a relative measure. It depends how far away you are from the source of the sound. But you can see when you get up to something like 115 decibels really you can only be exposed to it for around 30 seconds before either temporary or permanent harm starts to occur. And another chart, again not mine just shows you kind of where some of these sounds are categorized in terms of the effects that they can have. So starting with 50 decibels you have a floor fan which is kind of background noise lawnmower and chainsaw, possibly damaging sounds again depends how close you are to it. A jet taking off, again depending how close you are it could cause pain. 200 decibels potentially could be instant death and then the loudest sound known to humanity is the Windows XP startup sound. Okay so acoustics and harm and perceptibility so what can we hear? So you've probably heard the terms ultrasound and infrasound before and traditionally they're defined as being sounds which are either above or below human thresholds of hearing. Traditionally that threshold is 20 hertz to 20 kilohertz. However it's a bit of a misconception as we'll see you can't kind of put these arbitrary cutoff points here. Thresholds very wordly and it depends a lot from person to person what frequencies you're able to hear at what stage in your life as well. In this talk if you see HFN high frequency noise that means between 17 to 21 kilohertz so from near ultrasound just above true ultrasound and if you see LFN that means 60 to 100 hertz. The problem with ultrasound and infrasound is that basing a definition on a lack of a property is a problem because the mechanisms of people understanding high and low frequencies or perceiving high and low frequencies is not fully understood. People have reported being able to hear sounds as low as 1.5 hertz and as high as 25 kilohertz and there's also been some research which suggests that at some level we are aware of sounds even as high as kind of 40 kilohertz whether that's kind of consciously or subconsciously. And there is a significant variation in individuals as to what sounds you can hear. It depends on the volume, it depends on the background noise it depends on the environment you're in so what the walls are made of for example. You may perceive sounds in different ways to other people so with low frequency sounds you may feel it more as vibration than anything else you may perceive what are called audible subharmonics which are kind of, you can think about them as kind of side effects of a dominant frequency and as you grow older your ability to hear higher frequencies declines so younger people, children are much more likely to be able to hear higher frequencies than adults. Now there have been a lot of reported adverse effects with both high and low frequency noise these do come with a lot of caveats so bear that in mind. The susceptibility from person to person will differ as we've said particularly with age as well. There are some reports to suggest that high frequencies can have an adverse effect on hearing they can call something called a temporary threshold shift which is where your kind of audible range will shift temporarily. More increased volumes and amplitudes there have been reported physiological changes as a result of high frequency noise including things like cardiac neurosis, hypertension and functional changes in cardiovascular and central nervous systems. Psychologically high frequency noise has been reported to cause nausea, fatigue and headaches tinnitus and ear pain, irritation and decreased amounts of concentration these are subjective effects so bear that in mind. With low frequency noise it's been associated with temporary threshold shifts with heart ailments and insomnia and with elevated cortisol levels and psychologically the most common reported effect of low frequency noise is annoyance or irritation but it has also been associated with headaches and palpitations deterioration in performance depressive symptoms and distress and interestingly these effects have been reported even at very moderate levels of sound so somewhere between 40 to 45 decibels. The caveats are mentioned with all of these adverse effects if you go back and look at the papers the data is often anecdotal it's often done through the form of questionnaires or surveys after the fact very easily misinterpreted we don't always know the noise dose which is the amount of time that someone's been exposed to these frequencies and at what level and many researchers have found that these effects are not reproducible in a lab environment and there's a number of reasons why that could be the first is that there are ethical restrictions quite rightly placed on researchers exposing human subjects to sounds which they have good reason to believe could cause harm so in a lab environment those levels would be attenuated and therefore might not cause the effects that have been reported in the literature the other example is that some people may have experienced something called a no-see-bub effect so they either believe they're being exposed to a certain level of noise or they are being exposed to it and experiencing these symptoms but the two might not necessarily be related that being said there is a significant base evidence base to suggest that in at least a subset of the population high and low frequencies can cause some adverse effects as a result of that a lot of researchers and organisations have developed exposure guidelines which are basically kind of define the maximum levels at which you should be exposed to sounds at particular frequencies now there are problems with these big differences in the way that they're calculated and implemented typically they focus solely on the workplace so they don't focus on homes or public spaces or schools they're often based on very small samples and those samples are most often adult males so they don't take into account children for example who as I said can hear high frequencies they're much more likely to be able to hear high frequencies in adults this is a compendium of some of these guidelines this was compiled by an academic called Timothy Layton and you can see across the top you've got the various different frequencies now these are not precise frequencies they're the centre of a range of frequencies called a third octave band and then on the left you can see the guidelines that go all the way back from the mid 60s right up to 2015 this isn't necessarily an exhaustive list but just by looking at this you can see two things the first is that as you increase the frequency the maximum exposure then the second is there's big disparities between some of these numbers because they're calculated in different ways so just a quick thing on weighting as well if you've ever done any sound measurement you'll be familiar with weighting sound weighting is a way to either attenuate or emphasise certain frequencies when you're doing a measurement of sound so A weighting is the most commonly used if you buy a sound level meter online or hardware store or something like that it will most probably use A weighting and as you can see A weighting significantly underestimates lower frequency sound because it kind of the curve decays away at the start and then it also underestimates high frequency sound it decays away at the end C weighting is another example you can see there's less of a decay but it still does decay to some extent you've also got Z weighting which is mostly what we used for this experiment because it's a flat frequency response so it doesn't attenuate or emphasise so yeah as I said so with A weighting it's inappropriate for measuring high frequency noise because it underestimates those higher frequencies so Z weighting is probably much more appropriate with low frequency noise there are less guidelines available fewer guidelines available a possible reason for that might be that the main effects of low frequency noise are subjective and moderate levels but again even with the ones that have been published the methodology used to calculate them and implement them differs a lot so for this experiment we used a reference curve proposed by AFRA which took into account a lot of previously published curves measurements of infrasound specifically used something called G weighting which is an ISO standard specifically for infrasound because we were going higher than that we didn't use G weighting so this is the guideline for low frequency noise published by Morehouse and as you can see some of these levels are pretty low particularly when you get to kind of 50 hertz, 63 hertz you're talking about 43, 42 decibels something like that so some previous work looking at sound in security research one of the most common uses of high frequency noise particularly in security research has been as a covert communications channel so Desher Tells in 2014 Hans Back and Gertz also in 2014 looked at kind of covert mesh networks and how devices could communicate silently with each other using high frequency noise in my def contour a couple of years ago I did a similar thing with egg out bypasses and exfiltrating data and an interesting kind of finding from a lot of this research is that many consumer devices are capable of emitting high frequency noise even up to kind of ultrasonic levels there's also been a research looking at the disruption of echolocation systems which use ultrasound so again in that def contour I showed that with drones Jan and others in 2016 looked at for Tesla vehicles Bolton and others in 2018 looked at corrupting data being written to hard disk drives using both high frequency and kind of audible audio and then there's been a number of studies on looking at ultrasonic tracking beacons as well which are used for targeted marketing so some questions I always get asked before we kind of get into the main bit of the the talk first is the brown note I can hear some laughs so I know some people are familiar with the brown note if you're not familiar with it it's this kind of typical tone or mythical frequency that causes people to lose control of their bowels hence the name in reality no one's kind of been able to find this mythical frequency part of the reason for that probably is that any sound potentially if it's loud enough could cause you to feel sick could cause your body to vibrate and potentially have that effect but there's no kind of one frequency that would work for everybody if you're kind of playing sounds at that volume it's not kind of bigger worries basically another one I get asked about as well is the link between infrasound and the paranormal sometimes infrasound is referred to as the ghost frequency or the horror frequency it's often it has been used in things like horror games and horror movies as well I'd kind of direct you to a couple of really interesting papers on this Tandy in 2000 and Parsons and others in 2008 who looked at the possibility of infrasound at resonant frequencies causing people to have hallucinations or to kind of sense of presence in areas associated with paranormal experiences it's a subject that gets debated a lot in that field but it's worth kind of having a read over and the last one is the US Embassy in Cuba and kind of what happened there I would direct you to a paper by Timothy Layton in 2018 which goes into some detail about the sounds that were recorded in that area and the possibility or not of that being a sonic attack so when it comes to kind of acoustic weapons in general there are a lot of misunderstandings around them and a lot of myths as researchers have noted there are kind of significant practical issues associated with actually deploying them which to a large extent applies to this research as well so the fact that attackers can cause something like threshold shifts is probably not of interest to them generally and it's really challenging to cause obstacles kind of directional targeted effects with acoustic weapons with low frequency noise that can propagate very easily it can spread over miles potentially but obviously it's got very low directionality as a result and you would need to build massive audio equipment to be able to do that with high frequency it's got very low propagation it doesn't deal with obstacles well which is why it's used for echolocation because it bounces off of objects so again there's an issue there so moving on to our experiment so this is kind of how we built the hypothesis for this so we said okay given that some high frequencies and some low frequencies might be imperceptible to at least a subset of the population and given that above certain levels they may be associated with adverse effects and given that some consumer equipment has been shown that it can emit at least high frequency noise possibly low frequency noise as well is it possible is it feasible for an attacker to develop malware that can cause a targeted device to emit these frequencies at levels exceeding those in some of these maximum guidelines and therefore potentially cause adverse effects so a rough outline of what we did is we developed attacks in malware pretty kind of trivial malware targeted at certain devices which was able to control the system volume and the speaker output of those devices and as a result play wave files containing certain frequencies which we then measured with a sound level meter and compared that output to maximum permissible levels so we didn't use any human subjects for this experiment because of ethical restrictions quite rightly we did a full risk assessment we had various safety precautions we wore ear defenders we used an anechoic chamber which I'll talk about in a bit and we're not releasing either code of the attacks but we tested these attacks on so some scenarios where an attacker might want to use this and again this is kind of caveated quite heavily if they were seeking to affect the performance or productivity of targeted or generally employees or staff at an organization or at scale targeted harassment of certain individuals or potentially as kind of low grade cyber weapons that could have some physical effect worth noting that if an attacker is in a position to execute code on a device then they're more likely going to be things that they're more interested in doing and even when it comes to sound there may be things that they're more interested in doing than this attack so they may be more interested in C2 channels with that or something else so just a description of some of the devices we tested on the left hand side a laptop, a phone, a bluetooth speaker a smart speaker a pair of overhead phones a vehicle mounted public address system a parametric speaker and a vibration speaker and you can see some of the attack vectors and whether this was kind of remote or local this was our anechoic chamber has anyone ever been in an anechoic chamber before oh well okay quite a few people it's weird right, like really weird so if you haven't been I really recommend you if you get the chance to do it so basically an anechoic chamber is a sound-proofed environment but it's designed specifically to get rid of echoes so these kind of wedges on the walls are fiberglass wedges that bounce echoes back and forth between them so that they dissipate and essentially what this means is you can be in this room and the ambient noise level is below the threshold of human hearing so it is kind of one of the quietest places in the world you can hear your own heart beating if you kind of move your head you can hear like your spine creaking in your neck although that kind of might be more something that I should get checked out yeah so it's really cool and what's kind of really kind of creepy and cool about it is if you kind of close your eyes or you turn the lights off then acoustically an anechoic chamber is an infinite space because there's no walls or obstacles to bounce sound off which I just think is really cool so for our Windows malware which is on laptops we embedded these tones as wave files we had a really trivial C2 channel and all the malware did was it would get a command at a certain frequency it would increase the system volume of the laptop to 100% play the tone for 10 minutes and then restore the volume afterwards Android malware did exactly the same thing our smart speaker the one we used had a known vulnerability that allowed us to control the audio so for this to work in practice the attacker would need to either be on the local network or attack an exposed speaker on the internet or do DNS rebinding or something like that there was a python script we used to scan for speakers on the local network and if an active streamer tone from an attacker controlled web server the headphones were overhead phones connected to the laptop of a bluetooth because they're headphones we placed these much closer to the sound level meter we had vibration speakers which are really cool if you haven't used these before so these don't have a diaphragm cone instead they have like a coil and a movable plate so whatever surface you use whatever surface you put them on that becomes the kind of the source of the sound if you like parametric speakers again these are really cool if you get a chance to play with these so these use ultrasonic carrier waves at 40 kilohertz meaning that you can use them for kind of quite high intensity directional audio so kind of like a beam of sound the one we tested didn't have smart capabilities but given that it was fairly low profile and fairly low cost and that it can be directional it might be attractive to an attacker as like a portable acoustic weapon a vehicle mounted public address system so this didn't have any network interfaces instead it auto plays audio from an inserted storage device so you would need physical access to it some additional attacks that we thought of but didn't test the first is using the html5 audio tag to auto play audio so this would involve like a social engineering attack with an attacker getting a victim to visit a website and they have the sound play automatically this would obviously depend on the currently set system volume so not guaranteed to work and then we also used manipulation of pre-existing audio so this would be either something where an attacker has access to like your I guess your music collection or something or where they're kind of creating a YouTube video that they know people are going to watch and what you would do here is take the legitimate audio lower the amplitude of it and then insert a very high amplitude high frequency or low frequency sound which would look like this second picture here so the kind of intended effect of this is that the victim using their headphones or speakers or whatever would turn the sound up so they can hear the legitimate audio and then inadvertently expose themselves to high levels of whatever frequency it is just another illustration of that there so for measurement we use class 1 sound level meters these are precision grade they're spot calibrated they're really really expensive to buy but we hired them so we hired one for the low frequencies one for the higher frequencies and if you ever feel like you don't have enough excitement in your life have a courier call you and tell them that they don't have any record of you sending this stuff back and that you might owe a company 20,000 pounds and it puts everything else in perspective so we placed each device in anechoic chamber with our sound level meter and then via our attacks we played certain frequencies for 10 minutes we also measured the surface temperature of each device before and after the attack we used some anecdotal evidence or some anecdotes to suggest that particularly with higher frequencies devices could heat up if they were playing high frequency noises so we used Z-waiting for the measurement the only thing we didn't use Z-waiting for was for measurements of 21 kilohertz because that's outside the range of Z-waiting so we used a proprietary high pass filter for that and here's the results for high frequency noise so instances where the levels are above those in maximum guidelines are in bold so you can see the smart speaker at 17 kilohertz and the headphones at 17 kilohertz both exceeded those maximum guidelines and then the parametric speaker did the same for 17 kilohertz for 21 kilohertz and for 40 kilohertz as well now what we're comparing to here is a mean average of that big list of guidelines that I showed you earlier that was in a paper by Timothy Layton so you can see things like the laptop and the phone are not capable of producing sound exceeding those maximum guidelines so it's a minority of devices in a minority of frequencies that are capable of doing this with low frequency noise a similar story so again a minority of devices here it was the Bluetooth speaker at two of those frequencies a smart speaker at all three and the headphones at 100 hertz now particularly when you get to kind of the upper range of this kind of low frequency noise this might be more audible be less suitable as kind of a covert attack and I'll speak a bit about audibility in a minute some other results of interest so the vibration speaker is no good for low frequency because it vibrates so much that it falls over so every time we open the chamber door the speaker was lying on the floor the smart speaker when we open the chamber there's a really strong smell of burning plastic and when we kind of tested this we found that it was actually permanently damaged so this is kind of what happened in the 10 minutes that this smart speaker was being tested you can see the damage starts to occur in like the second minute this was at 17 kilohertz after 5 minutes there's some sort of critical event where a component burns out and then immediately the decibel level drops and never recovers and what we actually found was that we had permanently damaged the speaker and we had made it unable to reproduce frequencies above 5 kilohertz so we took recordings of music before we did the test and after we did the test and looked at the spectrograms and on the top is before the test and on the bottom is after the test so this is a permanent effect as well so we've kind of permanently impaired that speaker I'd love to be able to play it to you because it's copyrighted I can't but it kind of sounds like someone singing underwater in kind of like a metal tank or something like that so it kind of really makes a difference to audio quality so we reported that to the manufacturers who are really responsive and they told us that updates have been rolled out to address it to address it sorry now looking at audible components because this is kind of a key thing for this attack part of kind of the premise of this as a successful attack is relying on the fact that users wouldn't be able to hear it so depending on the device you get more or less audible components in kind of audible ranges if you look at headphones for example this big spike to the right which was 17 kilohertz so that's kind of an intended effect and then you can see to the left you've got kind of different frequencies there which are pretty low so if you're wearing headphones and this happens you might kind of notice something it might appear as kind of distortion or popping or something like that but it wouldn't be that noticeable conversely if you look at the parametric speaker the intended tone is still high but there are much higher levels of other more audible frequencies which means this would be less suited for some kind of stealthy attack so implications of this with the headphones it's a significant concern because headphones are increasingly used particularly by young people high volumes and to some extent a device agnostic so you can kind of plug it into a laptop or a phone or something it might be possible for an attacker to kind of improve that malware by for instance only triggering certain frequencies when headphones are connected so when that kind of device registers with the parametric speaker it does produce a lot of audible components but it might be attractive to some attackers as kind of a portable low cost acoustic weapon in any case the fact that it's using those ultrasonic carrier waves at 40 kHz at pretty high levels means that it could be a public health risk with the Bluetooth and smart speakers more difficult to attack with the Bluetooth speakers you would obviously need to kind of pair with them with the smart speakers though we could permanently damage them with the high frequency noise potentially that burning out of components could be a fire hazard as well and other models might be vulnerable so in terms of feasibility the attacks that we discovered were viable on a minority of devices so out of the kind of 10 tests that we did you're talking about kind of a handful of two to four devices for this attack to succeed on victims not perceiving the sound on them being susceptible to the adverse effects of that sound and for them being exposed for long enough to that sound for it to have an effect remember that our tests were only 10 minutes so for example if I kind of played a 20 kHz tone in this room now at a fairly high level some of you would hear it and not be affected by it some of you would hear it and probably feel uncomfortable some of you wouldn't hear it and wouldn't notice, some of you wouldn't hear it and might feel uncomfortable so it's a real kind of spectrum so yeah it's kind of a lot of obstacles for an attacker to overcome for this attack to work and as I said some attacks require kind of physical or local access as well and crucially attackers might be interested or more interested in other avenues so if they have kind of code execution on a laptop for instance or a phone it's likely that there's other stuff they're interested in okay so moving on to counter measures so uh Descher Tales in 2014 suggested a number of kind of applicable counter measures for these kind of attacks the first is to limit the frequency range of speakers so many speakers have a frequency range that goes up to kind of 20 kHz or above which in most cases is not needed depending on what you're using them for uh visibly alerting users when speakers are in use by an app or a software program doing some kind of filtering during processing to remove high or low frequency noise if it's not needed and uh with mobile specifically some kind of permissions restriction so that if an app wants to use the speaker you have to kind of explicitly grant it permission to do so on the heuristic side um it's very rare that an application, a legitimate application would need access to volume levels we kind of thought of it a few examples so one would be like a muting app for instance and there are some legitimate uses potentially for ultrasound so google nearby messages uses um ultrasound in addition some other commerce channels but generally speaking um there's kind of not many legitimate use cases for that you could monitor the environment for high or low frequency noise um so most consumer sound level meters will not go as high or low um as the levels we tested and you do need specialist equipment that being said there are a couple of android apps that we used in our pilot study ultrasound detector and infrasound detector which we used with a pretty cheap external microphone for the android and there is some studies that suggest um that modern smartphones might be okay for occupational noise measurement at least um as long as you kind of accept that there are caveats without limitations and that you won't necessarily get 100% accurate result uh we developed a proof of concepts uh windows program um that listens to sound uh coming in from your laptop microphone and pops up an alert if it hears frequencies uh above a certain level and above a certain amplitude um it's adapted from another open source application um we are going to kind of release this on github in uh either this evening or tomorrow morning but obviously don't use it to evaluate if there's actual risk of damage or adverse effects to you um or for safety compliance assessments if that's something you want to do then you should really be speaking to a trained professional who's got the right equipment um but the uh application will be available there it does it's accuracy and it's kind of performance does depend a lot on the uh microphone you're using and that kind of stuff um but if you want to have a play with it and kind of see how it works then please do at the um at the policy level um it's really important that I think that these guidelines are reviewed um and that there's some kind of standardization um put in place for these um because as noted before they're often inadequate due to their methodology the fact that they underestimate certain frequencies because of the waiting that's been used um the fact that they are predominantly around occupational contexts and that the samples are very small and based on adult men um and in no way kind of um give you any kind of uh indication if you're somewhere outside of an occupational context as to what sounds are kind of tolerable for health um depending on what area of the country you're sorry but depending on what area of the world you're in um you may have legislation that pertains to uh sound exposure um whether that's low frequency high frequency or just in general um and ideally your employers would um as uh a result of that conduct regular checks so uh to sum up then um this was a first stage bit of research on a very small scale we looked at a very limited number of devices we looked at very short exposure times of 10 minutes um without human experimentation there's also the note that like the smart speaker uh if a device is forced to continually play higher low frequency noise then it may burn out anyway um but it may take kind of several days for that to happen um so we also didn't do any human experimentation on uh perceptibility as to whether uh humans will be actually be able to hear this sound and that's just the kind of limitation of research in this field generally um because of kind of ethical concerns so more research is definitely needed on uh the risk of high frequency and low frequency noise um that could include like a wider range of equipment um so in addition to testing um the devices that we tested you could look at things like IP phones for example and it wouldn't necessarily have to be an attack against them it might just be kind of injecting uh tones into a conversation um you could look at kind of uh attacks on a larger scale whether that's something like uh a kind of uh worm attack against you know 50 laptops in a sound proofed environment or whether it's looking at kind of big devices like um public address systems um on a big scale though logistically obviously that would come with some challenges um testing these overheating effects on other devices would be really cool to see if that um that's something that's common across a lot of speakers um some more work on counter measures so you know one of the encouraging things about this research is the uh whilst the attacks we developed are pretty trivial there are a lot of caveats around it and the counter measures are also trivial um in many um cases so that's kind of encouraging as well obviously the ethical restrictions do make kind of extrapolation to real world effects pretty challenging um it's difficult to be able to say whether or not these attacks would actually allow you uh allow an attacker to have any effect on people um because there are so many variables um so we've only kind of really scratched the surface in terms of what can be done in this field um so definitely if you're kind of interested in this field you want to kind of chat about it a bit more then get in touch with me so just to sum up um so it's likely that um attackers might become increasingly interested in leveraging vulnerabilities against humans um and kind of having digital physical effects certainly the attack surface for these devices is likely to grow and potentially any device with a speaker um obviously depending on on kind of its sound card and um complexity could be used for this kind of attack um and crucially the lack of consensus around kind of adequate safety guidelines is a real challenge however as I said kind of counter measures are available they will work um consequences of his attack are something that's yet to be uh ascertained so um thank you very much um if you want to get in touch with me that's my Twitter handle and my email address um I'm going to take questions uh at the far end of the hall in the hallway um if you're interested in any of this stuff there is an exhaustive list of references at the end of this slide um at the end of this slide deck um which cover kind of acoustic weapons ultrasound, infrasound, human effects and various other bits and pieces as well um I can supply you with more references if you're interested um but there you go some somewhere reading for you so um thank you very much for listening um and as I said I'll take questions out the back and thank you very much