WEBVTT 00:00.000 --> 00:23.000 So my name is Kevin Borkner. I'm a PhD student at Cosec. Cosec focuses about everything. 00:23.000 --> 00:27.000 Cryptography related at the University of Kyoliv and Belgium. 00:27.000 --> 00:33.000 And I want to talk about quantum distance bounding, how to advance your proximity. 00:33.000 --> 00:38.000 So the term quantum distance bounding basically divides into two areas. 00:38.000 --> 00:41.000 So you have the quantum part in the distance bounding part. 00:41.000 --> 00:46.000 The distance bounding part is a cryptographic protocol between two communicating parties. 00:46.000 --> 00:52.000 These parties are communicating in such a way that you are able to estimate the physical distance between these two parties. 00:52.000 --> 01:00.000 And quantum in this part basically means that we are relying on quantum mechanics to achieve this physical distance approximation. 01:00.000 --> 01:05.000 Usually when I talk about quantum and cryptography, people confuse these two topics. 01:05.000 --> 01:09.000 So we have quantum cryptography and quantum cryptography. 01:09.000 --> 01:17.000 Post quantum cryptography is basically the development or the upgrade of our current classical cryptography, 01:17.000 --> 01:21.000 because we have the advancements of short algorithm and gross algorithm, 01:21.000 --> 01:25.000 and they currently break our classical systems. 01:25.000 --> 01:28.000 That's why we are developing post quantum cryptography. 01:28.000 --> 01:32.000 It's basically slapping more mathematics on the issues, 01:32.000 --> 01:38.000 and it's not breakable even when we have access to large-scale quantum computers. 01:38.000 --> 01:45.000 On the other hand, we have quantum cryptography, which basically relies on the magic of quantum mechanics. 01:45.000 --> 01:52.000 So these systems are even safe when you have access to unlimited computing power. 01:52.000 --> 01:54.000 In this talk, we're going to focus on the later ones. 01:54.000 --> 02:00.000 So I'm not really, I think I'm the only one in this timetable who focuses on quantum cryptography 02:00.000 --> 02:03.000 and not really on quantum computing in that sense. 02:03.000 --> 02:07.000 All right, I want to start with a problem called a chess grandmaster problem. 02:07.000 --> 02:11.000 So just imagine you have two countries that are involved with each other. 02:11.000 --> 02:14.000 So you have country yellow and country green, 02:14.000 --> 02:20.000 and there's an actual system that got developed during World War II called Identification Friend or Four. 02:20.000 --> 02:21.000 And so how does it work? 02:21.000 --> 02:25.000 So both countries have access to missiles and also two planes. 02:25.000 --> 02:31.000 So what the missile does when it finds a plane flying above the territory, 02:31.000 --> 02:35.000 it gives the plane a challenge, and this plane then responds to this challenge, 02:35.000 --> 02:37.000 so the plane is not shut down. 02:37.000 --> 02:39.000 It's identified as a friend. 02:39.000 --> 02:44.000 So what happens if a missile finds a plane which turns out to be an enemy plane? 02:44.000 --> 02:47.000 The plane, of course, or the pilot is smart, so what they are doing, 02:47.000 --> 02:52.000 they take this challenge, reload it to an airline missile. 02:52.000 --> 02:54.000 This airline missile finds an enemy plane. 02:54.000 --> 02:56.000 The enemy plane doesn't want to get shot, of course. 02:56.000 --> 02:59.000 So it responds to this challenge. 02:59.000 --> 03:05.000 This challenge is really back to the plane and used as the response for the missile from the enemy system. 03:05.000 --> 03:11.000 And with this concept, they're able to circumvent the whole thing and it's actually happened. 03:11.000 --> 03:19.000 So people thought maybe there's an interesting way if we implement clever cryptography 03:19.000 --> 03:23.000 to get rid of this whole problem, turned out that's not the case, 03:23.000 --> 03:30.000 but there is something we can exploit and it's basically the fact that this blue black arrows take way longer 03:30.000 --> 03:33.000 than the communication here on the green side. 03:34.000 --> 03:38.000 So this was kind of the development of distance-bounding protocols, 03:38.000 --> 03:42.000 so it will give you a really high level overview of distance-bounding protocols. 03:42.000 --> 03:47.000 You have a trust-boundary which is pre-determined, so it's basically a physical distance. 03:47.000 --> 03:51.000 You have two communicating parties, the very fire and the prouver. 03:51.000 --> 03:55.000 And these parties are communicating with each other in a challenge response manner, 03:55.000 --> 03:59.000 so what I basically told you, the very fire sensor challenge to the prouver, 03:59.000 --> 04:00.000 the prouver responds to this challenge. 04:01.000 --> 04:05.000 What the very fire does, the very fire stops the time how long it takes for the prouver 04:05.000 --> 04:10.000 to respond to this challenge, once the response is there on the very fire side, 04:10.000 --> 04:14.000 they can estimate the distance between these two parties. 04:14.000 --> 04:19.000 As in this example, the prouver is outside of this trust-boundary, so access is denied. 04:19.000 --> 04:24.000 If we have another party within this trust-boundary, then access is granted. 04:24.000 --> 04:31.000 And if someone tries to trick the system by relaying the challenge, then access is also denied 04:31.000 --> 04:35.000 as basically the slide I showed you before. 04:35.000 --> 04:38.000 And we might be asking where's the quantum party here? 04:38.000 --> 04:42.000 So the traditional or classical distance-bounding protocols, 04:42.000 --> 04:46.000 they usually use as this medium-of-exchange classical bits, 04:46.000 --> 04:50.000 but in our example, we will use Q bits for that. 04:51.000 --> 04:54.000 So you might be asking, why are we doing this? 04:54.000 --> 04:58.000 Why are we not sticking with traditional distance-bounding protocols? 04:58.000 --> 05:01.000 So what's the motivation for quantum distance-bounding protocols? 05:01.000 --> 05:07.000 So there are some issues on the physical layer for classical distance-bounding protocols. 05:07.000 --> 05:11.000 So you have conversion delays from analog to digital communication, 05:11.000 --> 05:16.000 and then you need to do the vice-versa conversion and this introduce some delays. 05:16.000 --> 05:20.000 So the distance measurement isn't as accurate as any more. 05:20.000 --> 05:26.000 Then people thought, okay, maybe switch to full analog processing thing, 05:26.000 --> 05:30.000 so we will get rid of all the digital stuff, to full analog stuff. 05:30.000 --> 05:33.000 Turns out it's also introduced some new attacks, 05:33.000 --> 05:38.000 and people then thought some researchers, okay, how about we change the whole system. 05:38.000 --> 05:43.000 Instead of using radio-frequency, we will use ultrasonic channels to slow the whole protocol down. 05:43.000 --> 05:47.000 Turns out it's also introduced some attack vectors. 05:47.000 --> 05:53.000 So you might be wondering, well, what are some possible applications for quantum distance-bounding? 05:53.000 --> 05:58.000 Usually these two pop up in that case, so you have quantum networks, 05:58.000 --> 06:01.000 which are basically fiber-based quantum networks, 06:01.000 --> 06:05.000 where you have several parties communicating with each other, you have quantum repeater, 06:05.000 --> 06:08.000 and it makes sense to imply quantum distance-bounding there, 06:08.000 --> 06:14.000 to kind of check that these parties are the amount of part, as we expect them, 06:14.000 --> 06:19.000 that they are, so we will kind of have an additional security measurement. 06:19.000 --> 06:23.000 The same can also be applied to satellite to ground communication, 06:23.000 --> 06:28.000 where you have free space links from Earth station and satellites. 06:28.000 --> 06:33.000 And what I want to emphasize on, that to implement quantum distance-bounding protocols, 06:33.000 --> 06:36.000 you don't need a hardware infrastructure upgrade. 06:36.000 --> 06:43.000 If you have quantum networks already in place, it's basically a plug-and-play solution. 06:43.000 --> 06:50.000 So we've talked about entanglement, and usually I'm sure some people already saw this exam, 06:50.000 --> 06:54.000 but I will try to quickly explain entanglement with this one. 06:54.000 --> 07:00.000 So just imagine you have a classical coin flip with two independent coins, 07:00.000 --> 07:03.000 and you flip them at the same time, that's your experiment. 07:03.000 --> 07:08.000 What you are looking for is the outcome, is you have tails tails or heads heads, 07:08.000 --> 07:10.000 so you're looking for the same outcome. 07:10.000 --> 07:14.000 If you have classical coins, you flip them at some stage, 07:14.000 --> 07:18.000 at some point you maybe receive a certain result, tails and heads. 07:18.000 --> 07:24.000 You repeat the whole experiment, and then by some chance you receive heads and heads. 07:24.000 --> 07:30.000 So what I want to point out is that in the classical sense, 07:30.000 --> 07:37.000 if you repeat this experiment a lot of times, then it makes you can have a probability of 50% 07:37.000 --> 07:40.000 to have the same outcome, so tails tails or heads heads. 07:40.000 --> 07:45.000 So what happens if you have some quantum coins that are entangled in a special way? 07:45.000 --> 07:49.000 So you repeat the whole experiment, two coins, you flip them at a time, 07:49.000 --> 07:52.000 then you receive tails tails, then you lie okay, that's crazy. 07:52.000 --> 07:58.000 Let's repeat again, flip them two coins, then you receive heads heads heads. 07:58.000 --> 08:01.000 And if you think like, okay, that's something is off. 08:01.000 --> 08:06.000 Something strange is going on here, then I will congratulate you on this idea, 08:06.000 --> 08:10.000 because you just had a similar idea as Albert Einstein, 93rd or 5. 08:10.000 --> 08:17.000 Where he wrote a paper about it, can quantum mechanical description of physics really be considered complete? 08:17.000 --> 08:22.000 Here the R, yes, that's basically it, you can read about it. 08:22.000 --> 08:27.000 John Stuart Bell came up with the theory about it in 2022. 08:27.000 --> 08:31.000 These three gentlemen's Ellen S. Beck, John F. Gloser and Anton Silinger. 08:31.000 --> 08:36.000 They proved it with the experiments that quantum entanglement is actually a thing. 08:36.000 --> 08:41.000 Okay, with this information, we're able to tackle the quantum distance bounding protocol on a really high level. 08:41.000 --> 08:44.000 So as I told you, you have the two communicating parties. 08:44.000 --> 08:49.000 Here on the left side, we have the very fire and on the right side, we have the proofer. 08:49.000 --> 08:54.000 These two parties agree on a secret key, only known to these two parties. 08:54.000 --> 08:57.000 And as I told you, they are communicating in a challenge response manner, 08:57.000 --> 09:02.000 so the verifier sends the challenge to the proveer, the proveer then responds to this challenge. 09:02.000 --> 09:08.000 The protocol starts by the verifier generating an entangled pair of particles. 09:08.000 --> 09:14.000 Since one half of the particle to the proveer, the other half is kept by the verifier, 09:14.000 --> 09:19.000 what a verifier, that's once this particle leaves the verifier, is it starts the clock. 09:19.000 --> 09:23.000 This is used for this timing measurement that I told you before. 09:23.000 --> 09:29.000 The verifier then, while this particle is flying, the cube is to the proveer, 09:29.000 --> 09:33.000 the verifier measures their own particle and receives some result. 09:33.000 --> 09:38.000 Once this particle reaches the proveer, the proveer also performs the measurement. 09:38.000 --> 09:42.000 And as we learned by the slides before, these two measurements need to be correlated, 09:42.000 --> 09:47.000 because they are basically this quantum coin flip that I just told you about. 09:47.000 --> 09:52.000 So what the proveer then does, the proveer uses this measurement result as the one ingredient, 09:52.000 --> 09:58.000 and the key as the second ingredient, to generate a new cube with this mixture, 09:58.000 --> 10:02.000 then sent over to the verifier as the response. 10:02.000 --> 10:07.000 So this flies to the verifier side, the verifier then stops the clock. 10:07.000 --> 10:13.000 And as I told you this timing component is then used to estimate a distance between these two communicating parties. 10:13.000 --> 10:20.000 So the verifier performs a measurement, and this measurement is determined by the private key. 10:20.000 --> 10:26.000 And if the proveer, generally, did the action on their integral particle, 10:26.000 --> 10:33.000 and if the proveer has access to the secret key, then these two measurement results on the verifier side should be the same, 10:33.000 --> 10:40.000 which means that the proveer was successfully executed, and you can estimate a distance between these two communicating parties. 10:40.000 --> 10:45.000 And you don't do this once, you do this a lot of times, because in quantum mechanics as we already learned, 10:45.000 --> 10:52.000 you have this probabilistic thing, so an attacker has some chance to succeed if you do it only once, 10:52.000 --> 11:01.000 but we repeat this whole proveer a lot of times, and can then use this distance to say how far these two parties are apart. 11:02.000 --> 11:09.000 So in terms of contribution, I use a kiss kit for a lot of my simulations, basically all of them nowadays. 11:09.000 --> 11:15.000 So I first simulated protocols, which are public in this repo. 11:15.000 --> 11:25.000 And I also take, or we also take inspiration from traditional distance bounding protocols, what kinds of attack are applied there, 11:25.000 --> 11:32.000 try to simulate them in our example, to kind of make sure that these do not apply an our protocol is safe, in that sense. 11:32.000 --> 11:37.000 So we've written four papers, I only want, so to be honest. 11:37.000 --> 11:44.000 The rest one is done by my promoters, so the two on the bottom, they do not even use entanglement, 11:44.000 --> 11:52.000 so you only rely on this key, on the secret key, these two parties are sharing with each other. 11:52.000 --> 12:00.000 The second bullet point is a protocol where we have entanglement, and there you have entanglement to have one execution of the whole protocol, 12:00.000 --> 12:07.000 and with that you are able to authenticate not only the sort of verifies not able to authenticate only the proveer, 12:07.000 --> 12:11.000 but also vice versa, so the proveer can authenticate a verifier. 12:11.000 --> 12:21.000 And the first paper, and we will use, we use belts inequality, I won't touch on that, but it's basically an additional security measurement to really see that the proveer generally, 12:21.000 --> 12:26.000 perform the actions on the received particle. 12:26.000 --> 12:32.000 So what are the future plans for now this theoretical idea and theoretical protocol? 12:32.000 --> 12:37.000 First step, should we have a former security analysis? 12:37.000 --> 12:42.000 So what I told you about is that we are looking at some attacks in the traditional distance bounding protocols, 12:42.000 --> 12:47.000 but we want to have a proper security proof in that sense, once this is done, 12:47.000 --> 12:54.000 and we are finally sure that our protocol is secure, we move on to an experimental setup, 12:54.000 --> 13:00.000 so I am in contact with some experimental physicists that already have some experience in that domain, 13:00.000 --> 13:05.000 so we want to have this distance bounding quantum distance bounding protocol on a really small scale, 13:05.000 --> 13:12.000 so in some lab setting, and once this is also working as intended, then we can scale this up to some bigger distance. 13:12.000 --> 13:18.000 So the two final takeaways of this presentation are first with a quantum distance bounding protocol, 13:18.000 --> 13:27.000 you are not only able to ensure who you are talking to, but you also able to identify how far the other party is apart from you, 13:27.000 --> 13:31.000 and the second point is with quantum distance bounding protocol. 13:31.000 --> 13:40.000 It's basically a plug-and-place solution, you have seamless integration in networks where you already have this quantum hardware in place. 13:41.000 --> 13:44.000 That's it from my side, I am happy to take any questions. 13:53.000 --> 13:54.000 Yeah? 14:03.000 --> 14:09.000 So the question is the difference between the classical distance bounding and quantum distance bounding, 14:10.000 --> 14:18.000 maybe I will skip to this slide, so I know I didn't cover all of the details how cubits work, 14:18.000 --> 14:27.000 but I have some really interesting properties, so for classical distance bounding, you are exchanging classical bits, as we know them, 14:27.000 --> 14:34.000 and for the quantum part, you exchange cubits for this part, and they have some interesting properties, as I said, this entanglement thing, 14:34.000 --> 14:45.000 is once that make them unique, they have no cloning theorem, so you are basically not able to copy and paste, as we know it in our usual normal world, 14:45.000 --> 14:52.000 and another property is when you have an eavesdropper that wants to make a measurement on this cubit, it basically destroys it. 14:52.000 --> 14:59.000 So you are not able, if you have an eavesdropper on adversary that sits between these two communicating parties, 14:59.000 --> 15:04.000 wants to pick up a cubit and read it, and then sense it over what this doesn't work. 15:04.000 --> 15:08.000 That's a really fundamental physical thing in quantum mechanics. 15:08.000 --> 15:13.000 So this is some advantage that we use, that's why we are translated to quantum distance bounding, 15:13.000 --> 15:19.000 but the general idea is the same, so that is answer your question. 15:20.000 --> 15:28.000 Can I follow you from there, then I understand that you cannot like to know it, but if you, but if ultimately what you want to do, 15:28.000 --> 15:34.000 extend back the cubit with some additional stuff, or if you want to find that you are the friend of the enemy, 15:34.000 --> 15:43.000 are you not also then able to descend the cubit that goes into you around and kind of do the same thing, as you have it. 15:43.000 --> 15:51.000 So you're basically, what you're trying, the question is if you're not basically able to reflect or incoming cubit right as a challenge, 15:51.000 --> 15:55.000 so it's basically sending a mirror in between. 15:55.000 --> 15:58.000 Yeah, you get sent to like the cubit with some challenge. 15:58.000 --> 16:03.000 Yeah, obviously you are, let's say the enemy in this case, so you know you can return the challenge correctly. 16:03.000 --> 16:11.000 So you just send it to your own missile, which then sends it to you as if it's, oh, this is our own quantum thing, 16:11.000 --> 16:16.000 but you know what I mean, like the same thing that happened in the war in the, yeah, yeah. 16:16.000 --> 16:21.000 I will use maybe this, I don't know if it's answers your question, so basically sending the incoming cubit back, 16:21.000 --> 16:24.000 I don't know if I cover this correctly. 16:24.000 --> 16:25.000 So stop it. 16:25.000 --> 16:33.000 No, what happened in the war war two, that you said was like that you send that challenge around basically to a friend, 16:33.000 --> 16:41.000 so let's say 48, the challenge to 40 people to be kind of like, reply it to the missile that is connected to it, 16:41.000 --> 16:46.000 and then you ask a plane from 48 to basically do this proof and when it sends it back, 16:46.000 --> 16:49.000 kind of disrupted all the way back around. 16:49.000 --> 16:55.000 But that's basically, so the question is if in this example, I showed with missiles and planes, 16:55.000 --> 17:00.000 if it's not able to kind of root the cubit or the challenge in a clever way, right? 17:01.000 --> 17:07.000 To mitigate the whole thing, but that's the timing component component that we have here, which makes it not possible. 17:07.000 --> 17:14.000 So if someone tries to root anything, it's, so you have here sending the cubits or photons in that sense, 17:14.000 --> 17:18.000 so you have to speed up light as fast as possible, so it can go any faster, 17:18.000 --> 17:24.000 and you basically have this timing component, so it's not able for someone. 17:24.000 --> 17:28.000 It would be spotted if you take your the cubit, send it to somewhere else, send it there, 17:28.000 --> 17:30.000 and back and forth and it doesn't work. 17:30.000 --> 17:38.000 So in another point, it's the secret key, so the thing is the proof that that's not only received the cubit, 17:38.000 --> 17:43.000 but the proof also performs this action on the cubit, right? 17:43.000 --> 17:51.000 So therefore, only if they have to access to the key, and also use the entangle cubit they received, 17:51.000 --> 17:54.000 then they are able to send the correct response. 17:55.000 --> 18:01.000 Okay, but also if the timing is kind of what makes the difference, the timing can also be used successfully. 18:01.000 --> 18:07.000 Yeah, the timing is also a thing in the traditional distance bounding protocols. 18:07.000 --> 18:12.000 That's not a unique thing to quantum distance bounding, but maybe we are having some issues, 18:12.000 --> 18:15.000 but we can talk anywhere else after the presentation. 18:15.000 --> 18:17.000 So I have two questions. 18:17.000 --> 18:22.000 First of all, we have a mission to exchange a key at quantum distance bounding protocol. 18:22.000 --> 18:29.000 So how do we have two parties choose the basis in which they imagine a key or a key? 18:29.000 --> 18:32.000 Is it chosen random or in fixed basis? 18:32.000 --> 18:40.000 So in this example, we have the orange basis, you there are fixed, in this example. 18:40.000 --> 18:50.000 So we have this M correlation, and for this part we have the proof of the Peter question. 18:50.000 --> 18:55.000 So the question is how are the basis chosen basically in the protocol? 18:55.000 --> 19:00.000 For this example, the key basically determines the basis. 19:00.000 --> 19:09.000 So if the key is binary, if the key is zero, and this thing then we use the computational basis, 19:09.000 --> 19:16.000 and if it's one, we use the hard amount basis, and with this it verifies 19:16.000 --> 19:21.000 also able to correctly decode the incoming keyword. 19:21.000 --> 19:23.000 And that's like a question as well. 19:23.000 --> 19:26.000 We have like physical properties of the human exchange. 19:26.000 --> 19:30.000 Like at the end of the talk, you mentioned like military applications like IFF. 19:30.000 --> 19:31.000 Yeah. 19:31.000 --> 19:35.000 How would you exchange a coherent keyword stage in such a situation? 19:35.000 --> 19:39.000 Like if you use polarised photons, you have to aim pretty precisely. 19:39.000 --> 19:40.000 Yeah. 19:40.000 --> 19:41.000 Yeah, that's right. 19:41.000 --> 19:49.000 So the question is how to make this cubic exchange, also with regards to this military example, I showed in the beginning. 19:49.000 --> 19:50.000 Yeah, that's right. 19:50.000 --> 19:54.000 It also comes down to these applications of quantum distance bounding protocol. 19:54.000 --> 19:57.000 And I have a lot of slides. 19:57.000 --> 20:00.000 So here it's read forward for quantum networks. 20:00.000 --> 20:01.000 Right. 20:01.000 --> 20:02.000 You have fiber. 20:02.000 --> 20:03.000 They are fiber based. 20:03.000 --> 20:05.000 So it's easy to communicate. 20:05.000 --> 20:10.000 But I get that's of course an interest and good point that you're pointing out here. 20:10.000 --> 20:17.000 That the satellite or ground communication, they need to be really accurate in a certain angle to make this exchange possible. 20:17.000 --> 20:20.000 And also you need to this line of size. 20:20.000 --> 20:22.000 So it's also better dependent. 20:22.000 --> 20:23.000 But yeah. 20:23.000 --> 20:25.000 I'm not really on this physical side. 20:25.000 --> 20:28.000 So I can't give you a satisfying answer on that sense. 20:28.000 --> 20:29.000 But yeah. 20:29.000 --> 20:32.000 Of course, there are, you have quantum key distribution. 20:32.000 --> 20:34.000 I maybe you've heard of that. 20:34.000 --> 20:35.000 Yeah. 20:35.000 --> 20:40.000 There are also, they use this satellite to ground communication over a really, really long distance. 20:40.000 --> 20:42.000 The Chinese did it with like, I don't know. 20:42.000 --> 20:45.000 400, 500 kilometers. 20:45.000 --> 20:46.000 So it's possible. 20:46.000 --> 20:47.000 It's feasible. 20:47.000 --> 20:49.000 But I don't know how they exactly pull this one off. 20:49.000 --> 20:50.000 Yeah. 20:50.000 --> 21:07.000 In our example, we want to have a communication from the ground to the satellite and 21:07.000 --> 21:08.000 forward. 21:08.000 --> 21:09.000 Back and forth. 21:09.000 --> 21:22.000 If you want to authenticate the satellite, yeah. 21:22.000 --> 21:23.000 Yeah. 21:23.000 --> 21:24.000 Yeah. 21:24.000 --> 21:25.000 Yeah. 21:25.000 --> 21:26.000 That's a good point. 21:26.000 --> 21:30.000 We're working on that. 21:30.000 --> 21:35.000 On purpose that we are. 21:36.000 --> 21:38.000 Is it possible to call it the question? 21:38.000 --> 21:45.000 Is it possible to combine our quantum distance bounding protocol with quantum key distribution protocol? 21:45.000 --> 21:47.000 And it is. 21:47.000 --> 21:49.000 But I didn't mention it. 21:49.000 --> 21:55.000 So the thing is the outcome of quantum key distribution protocol is this one time pad that 21:55.000 --> 21:57.000 both parties agreed on. 21:57.000 --> 22:02.000 And basically, you can first have a quantum key distribution protocol in our protocol afterwards. 22:02.000 --> 22:08.000 It didn't mention it in this way because it may look like our quantum distance bounding protocol 22:08.000 --> 22:10.000 depends on QKD, which is not the case. 22:10.000 --> 22:14.000 You can also have some other kind of key exchange. 22:14.000 --> 22:17.000 But of course, it's an easy target. 22:17.000 --> 22:18.000 So it's an easy thing. 22:18.000 --> 22:23.000 You can conclude those two and a really nice thing is that you have to same hardware on both sides. 22:23.000 --> 22:27.000 So for quantum key distribution also for quantum distance bounding, you will use the same hardware. 22:27.000 --> 22:30.000 So if it's already in place, why not also extend it? 22:30.000 --> 22:33.000 Thanks, Kevin.