You are currently browsing the category archive for the ‘wireless’ category.

Earlier this week, Google Scholar highlighted for me a new paper on mobile security. I am familiar with the work of a couple of the authors, so I downloaded it and read the whole thing. It turns out it is, by far, the best overview/compilation of related work in the literature on mobile security research that I have ever seen.

On top of that, the paper analyzes and digests all the literature in a comprehensive way, deriving a methodology to classify attacks by their underlying and root causes, proposed mitigations and solutions, etc.

I strongly recommend folks interested in the area of mobile security to read this paper and as many of the cited works as possible. I’ve given tutorials and workshops on mobile security in the past, and I always include a suggested reading list at the end. From now on, I’ll suggest folks to read the references of this paper, highlighting some of the key ones.

All in all, I strongly recommend downloading this paper. Really good and well organized compilation of published research work on mobile security.

Rupprecht, David, et al. “On Security Research towards Future Mobile Network Generations.” arXiv preprint arXiv:1710.08932(2017).

On a side note, I am slowly progressing in my new research project. Testing a bunch of new attacks, both active and passive, with a modified version of srsLTE. Pretty awesome tool.

Advertisements

Ever since back in 2010 I started investigating what would happen if a radio adversary jammed specific LTE signaling channels – as opposed to barrage jamming of the entire LTE signal -, I have been very interested in what I referred as to Smart Jamming back in 2013 and again in 2014.

smart_jammingA team in Virginia Tech has been one of the main players in the research field of smart jamming, more commonly known as Protocol-Aware Jamming. Starting with their 2013 paper “Vulnerability of LTE to Hostile Interference“, this team has published a bunch of interesting results in this area, including a paper in which I collaborated with them.

The same team just released a pre-print version of their Milcom paper in which they actually implement smart jamming attacks against downlink signaling channels using off-the-shelf software defined radios and open-source software. It makes me happy every time there is a new excellent work in LTE security which implements and tests exploits, attacks and solutions using open-source software. Over a year ago I wrote a short article on how I anticipated a spike in excellent LTE security research work now that the open-source implementations of LTE have reached a high level of maturity.

In the case of the Virginia Tech paper, they implement their protocol-aware jamming use cases on top of the srsLTE tool, which has always been one of the most complete LTE open-source implementation and might currently be the best one. It is also, to the date, the only tool that provides a full implementation of the UE LTE stack.

Read the paper on smart jamming implementation on SDRs running srsLTE here:

R. Rao, S. Ha, V. Marojevic, J.H. Reed, “LTE PHY Layer Vulnerability Analysis and Testing Using Open-Source SDR Tools”, IEEE MILCOM 2017, 23-25 Oct. 2017.

Happy Saturday!

ps. Dembele better be good. Let’s try to get Coutinho now. Though I feel terrible we are just adding more fuel to the fire of the over-inflated and out of control European soccer transfer market…

As I predicted in an article I wrote last year, the increasingly maturity of the open-source implementations of the LTE stack is fueling more and more exciting work in LTE security. I saw two presentations at Blackhat in the area that will most likely make it to the mainstream media.

Ravishankar Borgaonkar and his colleagues at TU Berlin keep producing exciting work in this area and presented some fresh work on new techniques to track devices in mobile networks. Considering that the team under Prof. Jean-Pierre Seifert are responsible for some of the coolest papers I’ve read in the last 6 years, I was really looking forward to this one.

By tracking and analyzing the AKA sequence number and collecting messages by impersonating a target’s IMSI, one can collect RAND.AUTN pairs to be used later to track that victim. Fun stuff and yet another issue in mobile networks that has been carried over from generation to generation and is likely going to impact 5G networks as well. It could be worst, I guess. LTE networks could, for example, add a plain-text identifier, unique per device, in each packet at the PHY layer. Oh, wait, that actually happens and allows tracking devices as well

Very interesting presentation on exploiting CS fallback for voice traffic. Despite a device is well authenticated and secured on LTE, in CS fallback mode, calls will be delivered over, often, GSM. Sniffing the paging channel and replying with spoofed paging response messages, the authors are able to intercept phone calls.

This is a very cool exploit that I was already familiar with. Actually, I am looking forward to seeing the video of the presentation or reading the authors’ paper on this. Based on just the slides, this looks very similar and reminds me a lot to a really cool paper: Let Me Answer That For You: Exploiting Broadcast Information in Cellular Networks. By the way, this paper is by the team under, guess who, Jean-Pierre Seifert. I told you these guys do cool work!

 

As I said last year, more and more exciting research in LTE security and exploits. I wish I could say the same about myself, but having a full-time job (a really good one that I love and with which I am involved now in security of many other wireless technologies as well as corporate network security, data mining and machine learning and other fun stuff), going to a ton of rock concerts (follow me @rgoestotheshows), playing soccer twice a week, never missing an FC Barcelona game (the greatest soccer team in the world) and – specially – being about to become a dad for the first time, keep me VERY busy.

When I find some time, I work on the paper on my radio adventures at the Mobile World Congress scanning 802.11, BLE&Bluetooth, LTE and cloning my badge. I promised myself I would have it ready before next year’s Mobile World Congress 🙂 I am also starting to work in a new project/collaboration testing a whole new bunch of LTE protocol exploits. Some really FUN stuff. This time I have a team with me and we are actually aiming to submit papers to conferences, so things should be happening on this project soon. Stay tuned. Same bat-channel.

Ps. Please, Neymar, do not go to PSG!

I was just reading the newest post by Google’s Project Zero. They just released a report on a massive bug that allows remote code execution by exploiting a vulnerability on the 802.11 Broadcom SoC used in most smartphones.

Actually, the bug is not massive (it is, after all, just a simple buffer overflow because boundaries are not well checked when processing a specific type of packet), but its consequences are massive indeed. The vulnerability is specific to the parsing of certain messages in 802.11z TDLS, a mode of P2P ad-hoc communication. The report published by Gal Beniamini is just the first part of the overall project, and it “just” shows up to remote code execution on the Broadcom wifi SoC, but it hints that it can be leveraged to gain remote code execution ability in the application’s processor:

In the next blog post, we’ll see how we can use our assumed control of the Wi-Fi SoC in order to further escalate our privileges into the application processor, taking over the host’s operating system!

Long story shirt, this vulnerability results in a massive vulnerability. Theoretically (I am eager to see the second part of this report!), an attacker can take over a smartphone’s OS by simply sending malformed WiFi frames, achieving full device takeover by WiFi proximity alone. The good news is that this bug has been patched already both for iOS devices and Android devices, so I’d say you go ahead and update your mobile’s OS if you haven’t in a while.

I strongly recommend folks to read the report by Gal Beniamini, as it is excellently written and easy to understand and follow. It’s actually a great reference/introduction to buffer overflows and how to leverage them for malicious intent. The overall exploit is rather complex, but very nicely explained step by step in the report.

Fun stuff!

I was reading this morning a new paper on the topic of LTE IMSI catchers: https://arxiv.org/pdf/1702.04434.pdf

Mjølsnes, Stig F., and Ruxandra F. Olimid. “Easy 4G/LTE IMSI Catchers for Non-Programmers.” arXiv preprint arXiv:1702.04434 (2017).

Although this is old news, it is exciting to see that the recent discovery and implementation of LTE IMSI catchers by the team of Prof. Seifert at TU Berlin (Oct 2015 – https://arxiv.org/pdf/1510.07563.pdf) has sparked the interest in this area. The paper also mentions the DoS threats that were introduced by the same team in [1]. I have done some work and implementation of LTE IMSI catchers and the DoS exploits myself in the past as well ([2] and [3]).

I was giving a talk on this topic last week at UC Irvine, trying to encourage graduate students to focus their PhD research in this area as there is still a lot of work to be done. We need the talented minds of graduate researchers to come up with new threats and, more importantly, solutions to these threats.

Back to this new paper, it is a great overview of IMSI catchers and it is great that the authors implemented the IMSI catcher using an alternative tool (Open Air Interface). I found interesting, though, that they state that implementing an IMSI cather on openLTE requires source code modification such that it is not a viable option for “non programmers”.

Although the claim of their implementation being for non-programmers is obviously correct, their LTE IMSI catcher uses very similar software and the same computing equipment as the ones in [1,2,3]. I would argue that adding 3 lines of code to openLTE is something a non-programmer could do as well. This is what the authors of [1] did. The only modification required at openLTE (as I have explicitly stated at every talk I have given) is mostly to add an fprintf statement where openLTE parses the AttachRequest message or the TAU/LocationArea Update message. Although one can do slightly fancier things.

Anyhow, maybe I am too optimistic and expecting a non-programmer to add an fprintf statement in openLTE is perhaps asking too much 🙂

Regardless, this new paper is great and very interesting and an excellent reference on this topic. I am wondering if they will be presenting their work at a conference soon?

I look forward to more and more research in this area.

[1] Shaik, Altaf, et al. “Practical attacks against privacy and availability in 4G/LTE mobile communication systems.” arXiv preprint arXiv:1510.07563(2015).

[2] Jover, Roger Piqueras. “LTE security and protocol exploits.” ShmooCon (2016).

[3] Jover, Roger Piqueras. “LTE security, protocol exploits and location tracking experimentation with low-cost software radio.” arXiv preprint arXiv:1607.05171 (2016).

Authentication in mobile networks is executed leveraging a symmetric key system. For each mobile subscriber, there is a secret key that is known only by the mobile device and the network operator. Actually, it is not the device itself holding the key, but the SIM card. On the network side, in the case of LTE, the secret key is stored in the Home Subscriber Server (HSS).

Based on this pre-shared secret key, a mobile device and the network can mutually authenticate itself. Though, this is not necessarily the case. For some reason someone must have thought, when designing 2G-GSM, that having the end point authenticate the mobile network was not a requirement… too bad that not having mutual authentication opens the door to all types of rogue base station MitM attacks. Bad things also happen when this pre-shared “secret” key is sent from the SIM card manufacturer to the mobile operator in the clear in a bunch of DVDs and someone manages to steal them.

After years or security research in mobile networks, identifying, implementing and testing protocol exploits, I started thinking that perhaps it would be a good idea to transition the security architecture of a mobile networks towards a PKI-based system. This is why I really enjoy reading research papers with PKI proposals for mobile networks, which is a rather rare topic in the research community. Thanks to Google Scholar, a very interesting paper showed up in my radar: Chandrasekaran, Varun, and Lakshminarayanan Subramanian. “A Decentralized PKI In A Mobile Ecosystem.

PKI would increase the complexity of each cryptographic operation, but it is not like device and network authenticate each other constantly. Definitively, a lot of research would have to be done to validate whether it would be possible.

With a PKI-based authentication architecture in mobile networks, so many cool things could potentially be done. For example, it is very well understood that, regardless of mutual authentication and strong encryption, a mobile device engages in a substantial exchange of unprotected messages  with *any* LTE base station (malicious or not) that advertises itself with the right broadcast information (and this broadcast information is transmitted in the clear in the SIB broadcast messages). And this is the source of a series of protocol exploits and attacks. Perhaps, by means of PKI, broadcast messages could be “signed” by the operator in a way that mobile devices could verify their freshness (to avoid replay attacks) and verify that the base station is legitimate. This would allow mobile devices to verify the legitimacy of a base station before starting to engage in RACH procedures, RRC connection establishments, NAS attach exchanges, etc.

Anyhow, very interesting paper on cool things that could be done applying PKI to mobile networks. Worth reading it.

 

(Yes, after months? maybe years? I decided to get back to being somehow active on my blog… Most likely I’ll just be posting about security and wireless/mobile interesting stuff)

I was reading this morning a very cool paper from a team at MITRE implementing a jamming mitigation engine leveraging beamforming. The idea is to generate a null in reception at the direction from which the jamming signal is coming from.

Link to the paper: http://ieeexplore.ieee.org/abstract/document/7795331/

It is very interesting that this type of jamming mitigation is becoming popular. It is an area with a lot of potential, specially in the context of 5G, communication at mmWaves and massive arrays of antennas.

My former team and I worked in a very similar idea in the past. We both implemented a beamforming-based mitigation for radio jamming against LTE (details in this paper) and there’s a bunch of patents already public about that technology: beamforming at the eNodeB and beamforming at the UE. In the case of the UE, we also used beamforming to increase the capacity and throughput of the system… a bit of a utopian idea that, actually, now makes much more sense with carrier frequencies in the mmWave range and above and massive arrays of antennas in the context of 5G. I strongly recommend to read Prof. Rappaport’s work in this area for more details.

Anyhow, the paper is VERY interesting and presents some exciting area in this area.

https://static-content.springer.com/image/art%3A10.1186%2F1687-417X-2014-7/MediaObjects/13635_2013_Article_22_Fig7_HTML.jpg

I recently was contacted by someone with questions regarding a document I wrote (LTE PHY fundamentals) a few years ago as part of a class at Columbia University and that is hosted on my website. The confusion was regarding Doppler shift and the time separation of the reference signals in LTE.

Quoting the message:

I was trying to tell you that 500 km/h does not mean a Doppler shift that you wrote in your document. If the carrier frequency is low and the receiver is moving through the transmitter Doppler shift will be zero cos(90).

Please read the LTE documentation carefully: Universal Mobile Telecommunications System (UMTS); LTE; Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN). In chapter 7.3, it is clearly written that this speed can be from 15 to 120 in the best case with a Doppler shift, not 500 as you wrote and even calculated the Doppler shift.

After responding to the question, I thought that it would be a good idea to write a quick post here and reference it from my website to clarify this topic if other people had the same questions.

The 3GPP standards do account mobility of up to 500km/h. Checking ETSI TR 125 913 V9.0.0 (Universal Mobile Telecommunications System (UMTS); LTE; Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN) one can read:

The E-UTRAN shall support mobility across the cellular network and should be optimized for low mobile speed from 0 to 15 km/h. Higher mobile speed between 15 and 120 km/h should be supported with high performance. Mobility across the cellular network shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h depending on the frequency band). Voice and other real-time services supported in the CS domain in R6 shall be supported by EUTRAN via the PS domain with at least equal quality as supported by UTRAN (e.g. in terms of guaranteed bit rate) over the whole of the speed range. The impact of intra E-UTRA handovers on quality (e.g. interruption time) shall be less than or equal to that provided by CS domain handovers in GERAN.

The mobile speed above 250 km/h represents special case, such as high speed train environment. In such case a special scenario applies for issues such as mobility solutions and channel models. For the physical layer parametrization EUTRAN should be able to maintain the connection up to 350 km/h, or even up to 500 km/h depending on the frequency band.

Regarding this topic, Samsung did some very interesting experiments on the high speed case inside a plane flying at 750km/h. Also, a recent paper was presented in a Sigcomm workshop that I was part of the TPC committee. It presented high speed measurements of LTE (check the paper titled “Performance of LTE in a High-velocity Environment: A Measurement Study”).

As for the Doppler shift, the Doppler equation does contain a cos(alfa), but alfa will only be 90 degrees when a mobile is under the cell tower, In general, in mobile communications, one does not consider the special case of alfa=0 (see below for more details). Anyhow, the way system specifications are designed is for the worst case scenario. In the case of LTE, the maximum possible doppler shift is for the highest carrier frequency (~2GHz at the time I wrote the document), V=500km/h and alfa=0 (cos(0)=1). That’s why the separation of the pilot tones in the LTE/OFDMA lattice is 0.5ms (the derivation of the value 0.5ms is in my document). Essentially, the Doppler shift defines the coherence time, which is the duration of time for which the channel does not change “substantially” or, more mathematically defined, the delay for which its autocorrelation is “higher” than a certain value (there is different ways to define coherence time depending on how “strict” one wants to be). Pilot tones or reference signals are used to sample the channel to perform equalization and other tricks. The Doppler shift defines the maximum sampling period that will allow to sample the channel correctly. If the channel can change as fast as every 0.5ms, one needs to have one sample at least ever 0.5ms. Therefore, the reference signals are separated every 0.5ms, tackling this way the worst case scenario for the coherence time.

Generally, in wireless communications for terrestrial applications, one usually does not even consider alfa because the heights of the towers (10 to 50m or so) are much smaller than the distances between the mobile devices and the towers (up to 35km for the biggest supported cells), so the value of alfa is always very small. However, in radar applications they do consider alfa because planes are flying at high altitudes.

Anyways, the best way to read about this concepts and have them explained much better than what I did here, is to check Rappaport’s book.

ReferenceSignal

Check this IEEE ComSoc tutorial on Advances in Coordinated Multi-Cell Multi-User MIMO Systems. Free of charge for a limited time.

Advances in Coordinated Multi-Cell Multi-User MIMO Systems

 

I recently read a very interesting paper that discusses one of the coolest wireless comm-related projects I have seen around for a while. A team of researchers from University of Washington presented this paper at Sigcomm this summer in Hong Kong. The paper was, by the way, awarded with the best paper award.

The idea is simple but could lead to a whole new technology with a great spectrum of applications. These researchers have designed a simple communication system that operates with no need for battery or power. Essentially, the nodes use the signals that are transmitted around them (for example TV signals) and modulate them in such a way that they are able to communicate with each other. Essentially, is a further step more from, for example, RFID tags that use the power of the transmitted signal to power themselves and send a reply. Although ambient backscatter (which is the name the authors give to this technology) has very short range, it could potentially be used for multiple applications, including certain types of wireless sensor networks.

The ambient backscatter project website presents the following video. One can observe the huge antennas these small devices have, which indicate that they operate at not too high frequencies and give an idea of the very low power they operate at. No room for inefficiencies of small twisted or patched antennas. They keep it simple for now with a dipole tuned at the wavelength.

By the way, this project is lead, among others, by Prof. Shyam Gollakota. He was recently awarded with the prestigious ACM Doctoral Dissertation Award and shortly after got a position as Assistant Professor at the University of Washington. Good stuff.

[UPDATE]

While browsing more stuff for this post I found about another project from Gollakota: WiSee. Again, really cool stuff. They are using subtle variations in wireless signals when a person moves to do gesture control. Very interesting. Check it out here.

About me:

Born in Barcelona, moved to Los Angeles at age 24, ended in NYC, where I enjoy life, tweet about music and work as a geek in security for wireless networks.
All the opinions expressed in this blog are my own and are not related to my employer.
About me: http://rogerpiquerasjover.net/

Blog Stats

  • 128,168 hits

Twitter feed

Enter your email address to follow this blog and receive notifications of new posts by email.