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A few weeks ago I wrote a blog post about a 3GPP SA3 proposal to leverage Digital Certificates in cellular networks. Despite some aspects in the proposal being far from ideal (as I discussed in the blog post), that proposal was and is very good news. It is the first time I have seen an actual proposal to leverage PKI to address inherent security issues in cellular networks on both LTE and 5G.

Today, a new revision of that proposal has been published, and I am now one of the co-authors (under my Softhandover affiliation). The new revision of 3GPP SA3 S3-202630 can be found here.


This is a proposal for Non-Public Networks (NPN), which are essentially “private” 5G deployments commonly used for critical applications such as first responders, tactical networks, utilities and industrial plants, etc. As such, this proposal is not aimed at commercial 5G deployments. However, the technology proposed could fairly easily be applied to commercial 5G networks by expanding the Certificate Authority network. For example, a TelCo operator could sign certificates for foreign operators with which it has trusted roaming agreements, such that devices roaming could verify the certificate chain that a roaming base station presents to the UE.

One of my main concerns with the previous revision was that it proposed to encrypt broadcast messages as opposed to sign them.

The newest revision proposes to actually sign broadcast messages along with a digest that includes a time stamp and, potentially, some form of geo-location in order to prevent for those messages to be replayed. Along with the message, each base station passes to the UE a certificate signed by the core network which attests the base station’s public key.

By leveraging digital certificates and a root of trust pre-loaded on the UEs (in the case of private 5G networks, the core network as Certificate Authority) both broadcast messages (SIBx) and signaling messages (RRC, NAS, etc) can present a certificate to the UE. Then, the UE can cryptographically verify that they originated at a real and trusted base station.

I am not too familiar yet on how 3GPP procedures work when it comes to such proposals, so I am not sure why the introduction of the document still alludes to encrypting broadcast messages, tough. But the body of the proposal is updated with the aforementioned improvements.

I have been advocating for years for leveraging PKI-like technology in cellular as a solution to the many vulnerabilities that leverage pre-authentication messages. Back in February, during my talk at ShmooCon, I made the case once more. I am glad to see that things are finally starting to move in that direction. And I am a coauthor!

If this proposal is approved, it will be part of the actual 5G standard. Exciting to know that I might be able to contribute to the global standard for cellular communications to improve its security. Hopefully we can bring such a proposal to commercial 5G deployments as well.

A few months ago, before the world as we knew it changed entirely into this “new normal” we live in, I rode the Acela to DC for a couple of days to give a talk in 5G security at SchmooCon. During the talk, given the obvious time limitations, I was not able to go in depth in the security analysis of 5G traffic.

I am done reading a book I was reading and I am out of things I want to watch on Netflix, so on nights I do not run or exercise, I started doing a bit of writing as part of my (pandemic+fatherhood)-induced Revenge Bedtime Procrastination. My plan is to eventually publish a paper with the full security analysis of 5G traffic but, meanwhile, I thought I would post some further analysis and ramblings here. Also, I was able to get some new traffic captures to analyze.


All captures analyzed here are from actual 5G devices (Release 15 compliant) communicating over 5G standalone mode (5G-SA). The traffic was captured with the Sanjole Wavejudge tool. The analysis has been done with the Sanjole Wavejudge v5.3.1 software analyzer. In the figure above we can see this particular capture is for a Release 15.4.0-compliant device.


This is a pretty good capture that contains the expected broadcast messages (MIB and SIB1) plus the attach handshake for a given UE. If we filter out everything and focus strictly on the messages between the UE and the gNodeB, we have the following:


This particular capture contains the PRACH handshake (without contention resolution) and the RRC handshake. However, we can notice that the DL MAC-RAR message is missing as well as the UL RRCSetupRequest. And the information transfer messages appear to have been retransmitted a few times, indicating perhaps issues at decoding those messages at the UE or the gNodeB. In a follow up post I will analyze another interesting capture of a UE initially connected to LTE that transitions to 5G via an RCCConnectionReconfiguration message sent by the NodeB. That capture is much cleaner and with all messages.

Note that 5G captures are massive and, unlike LTE captures that can be dumped in real time onto a pcap file, very short in duration. This particular capture is just 1.6 seconds long. This is why there is so few user messages in it.

One of the main things I argued in LTE and, as I discussed during my talk, is still an issue in 5G, is the potential for user tracking leveraging the RNTI. The T-RNTI derived during the RACH handshake, which is eventually upgraded to CRNTI, stays constant for long duration of times and allows to tell apart traffic between multiple users regardless of encryption. It is not that interesting in this capture as there is only one UE communicating. Plus in this capture there is no MAC-RAR message, which is the packet that allows to map an RNTI to a target user by triggering the target’s device to connect to the network at a known time. This can be achieved in many ways and the only requirement is to trigger a paging message for the target.


In the capture I analyzed for my ShmooCon talk, however, I was capable of dissecting the DL MAC-RAR message. As shown on the figure above, the T-CRNTI field in this message indicates the id to “track” to be able to tell apart traffic from a given target from the traffic of all other users. This is, for example, one of the setup steps of the aLTEr attack in order to identify DNS requests for a given UE. As I always highlight, this trick has been one of the stepping stones for a number of exploits demonstrated by academic teams over the last 3 years, however it was initially deemed not a security risk by 3GPP a few years ago after I introduced this issue.


Similarly to LTE, the 5G SIB1 broadcast message, shown directly above, discloses certain information, such as the identity of the operator of the tower. This has been identified as a potential issue in tactical or ad-hoc cellular deployments for critical applications, such as first responders. However, it is not really doable or feasible to encrypt this information in the broadcast messages, so this should be part of the overall threat model and attack surface evaluation of the 5G protocol. These messages should be signed using a digital certificate, though, as I argued in my ShmooCon talk.

Something interesting in cellular protocols is the amount of padding bits left in most messages in order to make room for potential new additions to the protocol. The SIB1 message, for example, has 13 bytes of padding always set to 0x00. When running fuzzing tests, I always like to add garbage in there to see how the cellular modem treats that. In some private deployments, it is not rare to see opportunistic usage of padding bytes for certain applications and, if the custom firmware does not properly treat those extra bytes, things get interesting.

These extra bytes have also been used recently to demonstrate the implementation of X.509 digital certificates in cellular in what was, in my humble opinion, the greatest and most promising paper in cellular security of the last few years.

Although the software does not allow me to decode some of the payloads embedded in certain RRC packets in this capture because the MAC layer appears to have been in developer mode in the UE+gNodeB, there is many things we can analyze. The raw bytes of the NAS payload can easily be decoded manually, though. I will work on that when I have some time.

Among the many pre-authentication messages that are exchanged in the 5G attach process, the devices exchange their capabilities reports in the clear (which this talk from BlackHat 2019 leverages to fingerprint devices). The message below, obfuscated, lists the capabilities of the UE in the ue-CapabilityRAT-Container payload.


Then the devices finally settle the cipher and integrity protection algorithms to be used in the SecurityModeCommand message.


In the context of LTE, in the event that UE is connecting for the first time, or in any event in which the serving network does not have the TMSI/GUTI of the UE, this one will transmit its IMSI in the clear. In the case of 5G, when the optional feature of protecting the SUPI is enabled (which I suspect will rarely be the case), the UE will disclose its SUCI (encrypted version of the SUPI). The capture above of an RRCSetupComplete message indeed contains a SUCI (obfuscated), indicating that this feature is enabled in this test network.


The SUPI encryption process, which is an optional feature, is well designed and does prevent identity tracking of devices, with a different SUCI being generated each time the SUPI is encrypted. Therefore, being able to capture SUCIs should not lead to fingerprinting a given user or device.

As I discussed during my talk, despite interesting new security features such as SUPI encryption, 5G protocols still leverage a number of handshakes that are not encrypted, not authenticated and not integrity protected. And, by means of abusing these messages, an attacker could launch similar attacks to the ones I started implementing 10 years ago, with a small subset of them being what I was able to demonstrate during my 2015 ShmooCon talk.

If you are interested in this type of security research, feel free to reach out. I know a few of groups in academia (UC Irvine, VATech, Mississippi State University, etc) that are looking for students to work in 5G protocol security. Also, the folks at the CCI 5G Security Initiative are also actively searching for security researchers (PhD grads and postdocs) and engineers to work in running and leveraging their security research 5G testbed.

When I have time I will post a follow up to this with an analysis of a capture of a UE initially camped in an LTE cell moving into a 5G cell. As part of this analysis, I will revisit a number of security issues that are present in LTE protocols.

Time to go to bed now. I’ll schedule this to publish tomorrow around lunch time so bon appetit!


I finally had some time, once I finished reading Do What You Want (highly recommended! Especially if you are a fan of the band like myself), to write a few notes on the first proposal I have ever seen in 3GPP to leverage digital certificates in cellular communications.

S3-202161 was among the many proposals discussed during the August 2020 meeting of 3GPP SA3. As I mentioned a few days ago, this proposal is beyond great news as it is the first proposal to leverage digital certificates in cellular that I have ever seen.

It is important to note that this proposal is strictly aimed at private 5G deployments, which has very different implications than commercial networks. The threat model is similar, though the solution can be slightly simple as there is no need for a full-fledged PKI infrastructure with CAs and sub-CAs and the need to validate certificate chains. As I mention below, if this proposal was for commercial 5G networks, it would be very incomplete and far from optimal or secure.

In general, anything that leverages digital certificates in 5G is a good idea compared to the current security specifications, period. However, there was a few items I wanted to discuss about this proposal that I summarize in this post.

  • Encryption: This proposal appears to be hyper-focused in leveraging PKI to encrypt (as opposed to sign) pre-authentication messages. This is interesting. In general, assuming that the feature to encrypt the SUPI is always enabled (wishful thinking, I know…), encrypting pre-authentication messages does not address much of the threat model in cellular networks. After all, there is not much that an attacker can do by eavesdropping signaling messages as long as they cannot be spoofed or modified. Things like the RNTI are in the header of the outermost packet/payload, so that would likely never be encrypted. Otherwise each UE would have to (attempt to) decrypt every single packet it receives in the DL and run crypto on it. This way the radio would never be able to shut down to save battery. In general, aiming to encrypt the pre-authentication messages sounds like a sub-optimal strategy.
  • Encryption with asymmetric keys???: It is interesting that the proposal aims at encrypting pre-authentication messages (referred to as unicast messages throughout the document) using asymmetric keys. Given the compute power of a smartphone and current basebands, this might be ok. But, in general, encryption/decryption using secret/public asymmetric keys is not a good idea. Keys are very large (current standards dictate 1024bits if not 2048bits) and encryption is computationally expensive and slow. Asymmetric keys are normally leveraged to secure an initial handshake to establish a secure channel and derive a session symmetric key, using thereafter AES or a similar symmetric cipher to encrypt traffic.
  • Why not signing pre-authentication messages?: The majority of vulnerabilities identified in the LTE protocol over the last 4 years leverage spoofing pre-authentication messages. Although encrypting these messages is, perhaps, achieving a similar outcome to just signing them, it is surprising that the proposal does not aim at signing the messages. Ideally, those messages would be signed – but not necessarily encrypted – using an HMAC (if the UE and gNodeB have derived a symmetric “session” key already) or a digital signature that factors in a hash. The hash component is critical to prevent, among other threats, replay attacks. Note that just signing, for example, SIB1 messages and many RRC messages would not prevent replaying those messages later. In general, one should hash a timestamp and other metrics such that a message cannot be replayed or reused. Many years ago I worked on a project that PoCed something similar to this to protect SIBx messages. Some other items we proposed to hash were a fingerprint of the physical location of the tower and a timestamp.
  • Threats that are not mitigated by this proposal?: Possibly the most interesting aspect of this proposal is section “6.2X.3.3 – Threats that are not mitigated by encrypting unicast signaling messages“, which explicitly mentions preventing UEs from camping on false base stations. I think that this should be the main goal of such a proposal. Even if encrypting signaling messages instead of signing them, I believe this proposal does prevent UEs from camping on malicious base stations, which would not be able to produce signaling messages that the UE can cryptographically verify as legitimate.

Regardless of the above, it is very good news that digital certificates are finally being considered for cellular communication systems as a way to prevent attacks that abuse unprotected pre-authentication messages.

However, such a solution would not suffice for 5G commercial deployments. In such a scenario, in order to support many of today’s use cases, such as roaming, a full-fledged PKI system would be necessary, with multiple CAs and each operator/country deciding what CAs to trust and which ones not to trust. Moreover, logistics such as certificate rotation and, especially, revocation would be very complex. I shared some thoughts on that in a previous blog post.

Done for tonight. Now I need to find myself another book to read. If only all my favorite bands wrote a book about their history… Again, I highly recommend Do What You Want.


For over 10 years I have been identifying and testing a number of exploits in cellular protocols that leverage what I refer to as “pre-authentication message”. In parallel, I have been witnessing the rise of a number of excellent academic teams doing outstanding research in this area and identifying further security issues in cellular protocols, mst of which are root-caused by pre-authentication messages.

This never-ending challenge spawns from the fact that (as I highlighted back in January 2016 during my ShmooCon talk) any mobile device will exchange a number of messages in both directions with any base station, malicious or not, that advertises itself with the right broadcast information. A mobile device has no means to verify cryptographically the legitimacy of a base station until it has gone through a number of insecure (in plain text, no integrity protection, no authentication) message handshakes that occur prior to the establishment of an authenticated and secured connection.

For years I have advocated for the use of a PKI-like system in cellular, leveraging digital certificates to substantially raise the security bar against the threat of rogue base stations in both LTE and 5G.

After all, when I browse Gmail and I am asked to type in my credentials, my browser and, by extension myself, knows that it is indeed “Gmail” who it is speaking with before sending any “messages” to it. This is technology that has been deployed and matured for over 15 years and have made possible things such as eCommerce. However, when my smartphone sees a base station it has no way of verifying its legitimacy prior to exchanging a number of messages that have been proven to be exploitable for Denial of Service, silent downgrade to GSM, IMSI catching, etc.


A couple of years ago, the best thing in years in cellular security research happened. Syed Rafiul and his team at Purdue University published a paper detailing neat and really promising results of their application of digital certificates to LTE. In a nutshell, they did a PoC embedding X.509 certificates in the broadcast LTE messages, using srsLTE for it.


From that moment I have been waiting for the day someone would propose using digital certificates in cellular. And it seems that day has finally come. In this month’s 3GPP SA3 meeting, a number of proposals were presented. Among them, two that discuss leveraging Digital Certificates to substantially raise the bar against rogue base station attacks. This is a goal clearly stated from the get-go, with one of the documents entitled “Study on 5G security enhancement against false base stations“. These documents can be found in this link, by searching (ctrl+f) for “Mitre”.

  • Study on 5G security enhancement against false base stations:

Interestingly, this first proposal discusses encrypting messages, not signing them, which is not exactly what I was expecting. Nevertheless, this proposal is mainly geared towards Non-Public Networks, eg. private cellular deployments, so that might be why its a proposal slightly different than what I have been advocating and recommending for years. The proposal goes on stating that X.509 certificates will be pre-loaded for the gNBs a given UE is allowed to connect, which would obviously never scale in a commercial network.

  • Study on authentication enhancements in 5GS:

This second proposal is very similar to the previous one, both in its scope and in that it seems to place most highlight in encryption as opposed to authentication. Interestingly, this proposal covers certificates in both directions, in the sense that both the network (gNBs) and the UEs provide certificates to distribute their public keys.


In general, this is very good news as it is the very first time such a proposal ends up in the standards. These two documents are mostly geared for non-public cellular networks and do not scale too well over commercial deployments, but it is a great step in the right direction.


As I discussed in my ShmooCon talk in February, pre-authentication messages still exist in 5G and they can be exploited in similar ways as in LTE to launch DoS attacks, silently downgrade the connection to legacy protocols, etc.

In deploying digital certificates in cellular, one could leverage the existing trust relationships between global operators (eg. roaming agreements) to build and architect the certificate chain and corresponding roots of trust each operator chooses to pre-load on their devices or USIM cards. For example (in very high-level detail):

  • Each mobile operator is a sub-CA and trusts/signs certificates for their own base stations.
  • Each mobile operator has a list of trusted partners/peers (eg. via roaming agreements) and, as such, it signs and certifies the certificates for each of those operators, which can then act as a further sub-CA.
    • Alternatively, the mobile devices of USIM cards could come pre-loaded with the certificates for the national operators a given operator “trusts”.
    • However, it is always best to trust no-one but your own operator and let the chain of certificates, which can be adjusted any time, do the rest.
  • Each country could have a trusted 3rd party be the national trusted CA, which could in turn decide what other countries to “trust” and, thus, sign the certificates for the national CA of these countries.

Looking forward to seeing where do these two new proposals end up.

Edit (08/25/2020):

One of the main challenges in leveraging Digital Certificates in cellular is, as I discussed as well during my ShmooCon talk, certificate revocation. If there has been an update in the certificate revocation list, a UE is not able to get that update until it has successfully connected to the network by, potentially, trusting a network and corresponding certificate that is perhaps in the last certificate revocation list update.


As a result of this, there is a small risk even if leveraging digital certificates. For example, let’s say that while you were on a long-haul flight with your phone off, there was a massive conflict escalating between the US and country X. Because you work in, for example, XYZ government agency, the certificate chain is updated in a way that your phone will not trust anymore certificates signed by the subCA of, for example, country X or any of the operators in that country. Otherwise, it would be a security risk and you could be the target of a malicious gNB at the arrival airport.

At that point, your phone has no means of downloading a certificate revocation list because, by definition, it has not connected to the Internet yet. And, as a result, your phone, upon landing, will still trust the “old” certificate chain and the base stations of any operator in country X.

One potential solution to this would be the following:

  • If your phone has been “off” for a few hours and sees an MCC-MNC combination for, for example, another country the phone enters a “let’s be careful mode” (limited security exposure to a potential rogue base station).
  • Connect to the network normally and attempt to establish a secure channel (mutually authenticated and encrypted) with your home operator.
  • Check whether there is any updates in the certificate revocation list, download any update.
  • Disconnect from the tower/network and start over in “normal” mode with an updated certificate list.

In the event that, upon landing at the airport in country X, my phone connects to a rogue base station, this will be within this “minimal security exposure mode”. In that case, establishing the secure channel with the home operator will fail. Only if the base station I am connecting to is legitimate and operating normally, the UE will be able to download the updated certificate revocation list.

(Originally published as a LinkedIn article – Reposted on this blog)

About 10 years ago, I started working on mobile and cellular security research. While most of my work in the early days leveraged costly network testing equipment and a neat lab set-up, I also experimented with a number of open-source implementations of the LTE (Long Term Evolution) PHY layer, which were critical for the work on protocol-aware jamming back in 2011. Everything changed in 2012, though. On December 31st 2011 the first commit for openLTE had been uploaded and for the very first time, there was an open-source implementation of the LTE stack aiming to go beyond the PHY layer. Just a couple of years later, by 2013/2014, after outstanding progress in the development of openLTE, I was in the lab able to test LTE IMSI-catching, taking advantage of unprotected AttachReject messages and tracking devices via mapping MSISDN (i.e. phone numbers) to TMSI to C-RNTI.

During those years, other implementations of the LTE stack became available, though I stuck with openLTE until srsLTE reached a significant level of maturity. Currently srsLTE is by far the best and most widely used – both in academia and industry – tool for LTE security research. srsLTE has been my tool of choice since my career change in Fall 2015, after which I used it to rewrite my IMSI catchers, protocol exploits, and RNTI-based techniques for my January 2016 ShmooCon talk.

Around that time, I wrote an article predicting that the combination of a) low-cost software-radios, b) mature and very stable open-source implementations of the LTE protocol stack, and c) an army of bright, smart and talented grad students, could only have one possible outcome. I predicted – not taking much credit for that prediction, as it was quite clear that it would happen anyways – that within the following few years there would be a number of new academic research labs working in cellular network security projects, and a large number of new exploits identified in cellular networks released in papers at top security conferences.

It has been 3 years since I published that article and, indeed, researchers have found numerous flaws in the LTE protocol by applying formal verification techniques to the LTE standards, hijacked DNS requests and responses at LTE’s layer 2, exploited flaws in the Self Organizing Network protocols of LTE, and tracked devices via their GUTI, to name just a few.

Most of the vulnerabilities identified by researchers so far primarily affect subscribers and mobile devices. However, the latest addition to the srsLTE toolset, srsUE, is already changing the cellular security research landscape. srsUE is an open-source implementation of the UE (User Equipment) LTE stack. As such, it facilitates the same type of security research against the network infrastructure, as opposed to just mobile devices. In other words, it is now possible to fuzz cellular protocols in the uplink against the network infrastructure and, for example, send arbitrary messages to an MME (Mobility Management Entity, one of the core parts of an LTE network).

It is worth noting that some teams in academia have already started experimenting with uplink LTE protocol fuzzing. Recent results indicate the feasibility of crashing network equipment. In addition, an academic research team published an excellent paper identifying a number of previously unknown protocol exploits in LTE that are being assigned CVEs and addressed by the OEMs and operators.

In parallel, the industry is in the midst of the 5G marketing frenzy. 5G is introduced as a panacea to everything that needed to be addressed in previous mobile generations: a revolutionary technology that will empower exciting new applications such as smart vehicles, critical control of remote devices, virtual reality, etc. In that context, the industry has been raving about the security of 5G and its resilience to cyber-attacks. However, a number of recent studies and publications indicate that the marketing statements about 5G security are actually inaccurate and things are not much different than in LTE.

The security research landscape has changed drastically when it comes to cellular network security. The GSM (Global Standard for Mobile communications) standards were drafted in the late 80s and no major vulnerabilities were publicly released until the Barkan attacks against A5/1 and Karsten Nohl’s presentation at the Chaos Communication Congress in 2010. It took over 10 years from GSM to be standardized and deployed to the first security issues being identified. Similarly, the LTE standards were finalized sometime between 2007 and 2008, and operators started deploying LTE networks sometime around 2011. It only took a few years, though, for security researchers to identify and release exploits in late 2015, including the excellent work from an academic team in TU Berlin and the results I myself released at ShmooCon.

This trend of identifying protocol vulnerabilities sooner and sooner after the inception of a new mobile generation also applies for 5G. The first release of the 5G specifications was published in March 2018. Just a bit over a year later, the research community has identified protocol vulnerabilities in the 5G-AKA (Authentication and Key Agreement) and privacy breaches in 5G. It is worth highlighting here that 5G mobile networks are not even deployed commercially yet, though over the last year there has been half a dozen papers published highlighting critical vulnerabilities in the technology that is supposed to drive mobile systems and innovation for the next 10 years. More importantly, a recent study highlights the fact that 5G protocols are still vulnerable to the great majority of exploits existing in LTE as they carry over the main root cause of threats against LTE.

The greatest common divisor of most vulnerabilities identified in LTE over the last 5 years is what the research world refers to as pre-authentication messages. Unlike other layer 2 protocols, cellular networks rely on an implicit reciprocal trust between Alice and Bob prior to executing the authentication cryptographic handshake. In other words, a UE blindly trusts any base station that appears to be legitimate and the base station blindly trusts anything that looks like a commercial UE even before they have mutually authenticated. Needless to say, it is trivial to configure a rogue base station or rogue UE to look like a real one.

Security threats spawn from the fact that, by spoofing or intercepting such pre-authentication messages, an adversary can turn a smartphone or mobile IoT device into a connectionless brick or silently downgrade any UE to an insecure connection over GSM. IMSI catchers, commonly referred to as Stingrays or cell site simulators, are actually possible in LTE because of the exact same reason. The message that instructs a UE to disclose its IMSI in the clear is a pre-authentication message that can be trivially spoofed and directed to all UEs in a geographical region. Note that this is possible by literally just adding a couple extra lines of code to srsLTE. Spoofing presidential emergency alert messages is also possible because many messages in LTE cannot be properly identified and attributed.

Stingrays have been for years the security threat in cellular networks that attracts the most attention from the media, especially since the discovery last year of evidence of numerous Stingrays in the Washington DC area. This might be the motivation behind the proposal in 5G for a solution to prevent IMSI catchers. This specific solution, if implemented, would indeed prevent certain IMSI catcher style attacks in 5G. As such, it has been the cornerstone of the industry’s elevator pitch praising 5G security. Unfortunately, this security feature in 5G appears to be defined, as many others, as optional, leaving it up to the operator whether to implement it or not. The history of previous generations indicates that optional features rarely get fully implemented. This is one of the reasons why the implementations of the same cellular protocols end up being dramatically different from operator to operator.

After years of cellular security research, many scientific publications at top security conferences, and numerous exploits and vulnerabilities, all with one single clear root cause, it is interesting that the industry and standardization bodies have not yet tackled the pre-authentication message challenge. After all, there are mature and widely deployed technologies in the Internet that allow endpoints to validate the identity of a server before needing to perform a cryptographic handshake. TLS (Transport Layer Security) and its deprecated predecessor, SSL (Secure Sockets Layer), are perhaps the best-known examples. These technologies have made possible the rise of eCommerce and other modern applications, providing the necessary tools to authenticate communication endpoints prior to any handshake by means of digital certificates.

A number of security researchers, myself included, have been advocating for the application of digital certificates or related technologies to cellular networks for years. An excellent recent paper implements a proof of concept of the application of X.509 certificates in cellular networks, presenting very promising results. This is the first time, to the best of my knowledge, that such a study is published.

Leveraging digital certificates in cellular networks would require architectural changes from the ground up at a very large scale and, unfortunately, this is unlikely to occur. There is little incentive in the industry to make large changes to a security architecture that has remained rather unchanged for many years.

The cellular industry and the technology behind it are tightly driven and regulated by the 3GPP (3rd Generation Partnership Project) standards, which could and should be the driving force behind such a paradigm change in how security and trust are established in cellular networks. However, the strongest forces sitting around the table at standardization meetings are the cellular industry itself, both telcos and OEMs, which seems like a clear conflict of interest. As a result, the outlook of the state of affairs in mobile network security is not likely to change in the short term.

It took over 10 years for researchers to find security flaws in the GSM protocol, just a few years for the first protocol exploits to be identified in LTE and, in the case of 5G, researchers are already highlighting vulnerabilities before the technology is deployed and available for consumers. Despite the challenges and lack of incentives for the industry, this might finally be the time to start addressing security weaknesses inherent to cellular protocols since their very inception. Until that happens, though, I look forward to excellent cellular security research from bright grad students and hackers alike, and to reading future papers they publish.

The first version of the LTE specifications (3GPP Release 8) was published in 2007. For obvious reasons, I am unaware of the state of R&D in LTE security in 3-letter agencies. In the research community, though, the first public disclosure of protocol exploits against LTE did not occur until early 2016 with the work of the team of Prof. Jean-Pierre Seifert at TU Berlin [1] and myself [2].

Back in May of that same year I wrote an article discussing the main reasons why it took 9 years for us security researchers to start finding vulnerabilities in LTE protocols and testing them. The lack of maturity of software-defined radio hardware and, mostly, the lack of open-source low-cost software implementations of the LTE protocol stack. However, as I stated in that article, when the first commit of openLTE was pushed in 2012 things started to change. And then, a couple of years later, srsLTE was available as well. Back in 2016 I anticipated to see a wave of excellent security research in LTE, which would uncover all sorts of vulnerabilities.

As I expected, over the last 3 years, some academic research teams have crafted excellent research and published groundbreaking papers disclosing new vulnerabilities of the LTE protocols (e.g. [3,4,5]). And now, with the availability of srsUE, the possibilities are endless in terms of exploring the security of LTE against the operator’s infrastructure. I am myself collaborating with two teams in academia in what I call LTE protocol fuzzing using srsUE, and there has been already some very interesting findings of potential exploits in the uplink [6].

How do things look like in 5G? Quite different, actually. The first release of the 5G specifications (3GPP Release 15) was published in December 2017, and the first security specifications document was published in March 2018 [7]. However, this time the research community is not waiting to start working and identifying potential protocol vulnerabilities. Despite the lack of open-source implementations of the 5G protocols and tools to facilitate this work, security researchers are not giving any headstart to 3GPP this time. In fact, ever since the publication of the 5G security specifications, these very interesting papers have been published:

It is interesting to note that the first paper above was released in February 2018, before the actual 5G security specifications. Those researchers did their work with the drafts that 3GPP often releases before an official specification release is closed. It is pretty clear that this time the research community is ready and prepared to analyze the proposed security specifications of 5G and an insecure protocol will not slip again and end up being deployed in the field (hopefully). Note that, by the time [1] and [2] identified the first known protocol exploits on LTE, LTE networks were widely deployed already and being used by hundreds of millions of people all over the world.

The current 5G specifications are not optimal yet. Despite a technique to tackle IMSI catchers, it is yet to be seen if a rogue base station of malicious application could easily trigger a mobile device to perform one of the few things that would result in a device disclosing its IMSI in the clear (transmit its SUPI not concealed, using 5G jargon). Also, there is yet no clear way in 5G to tackle the challenge of pre-authentication messages, which are the root cause of most protocol exploits in LTE. Moreover, some of the aforementioned papers and research reports have identified potential vulnerabilities in the Authentication and Key Agreement protocol in 5G. And the media is already picking up on these papers and making noise about them.

There is still work to be done and things to polish in 5G security, but this time it will not take years to identify security problems and start fixing them. The research community, academia, industry and standardization bodies will hopefully start working together with the goal of designing a 5G security architecture that will substantially raise the bar with respect to previous generations.

By the way, I recently found out of an actual software implementation of the 5G core based on 3GPP Release 15. This s great news and will fuel so much more research in this field. The two university teams I collaborate with and myself will start using this tool for our research. Looking forward to it.

Ps. By the way, students with a strong background in math, signal processing, communication systems, Python and C++, both academic groups are looking for PhD students and postdocs. Ping me if you are interested!

[1] A. Shaik, R. Borgaonkar, N. Asokan, V. Niemi, and J.-P. Seifert, “Practical attacks against privacy and availability in 4G/LTE mobile communication systems,” in Proceedings of the 23rd Annual Network and Distributed System Security Symposium (NDSS 2016), 2016.

[2] Jover, R.P., 2016. LTE security and protocol exploits. Shmoocon 2016.

[3] Hussain, S.R., Chowdhury, O., Mehnaz, S. and Bertino, E., 2018, February. LTEInspector: A Systematic Approach for Adversarial Testing of 4G LTE. In Symposium on Network and Distributed Systems Security (NDSS) (pp. 18-21).

[4] Shaik, A., Borgaonkar, R., Park, S. and Seifert, J.P., 2018, June. On the Impact of Rogue Base Stations in 4G/LTE Self Organizing Networks. In Proceedings of the 11th ACM Conference on Security & Privacy in Wireless and Mobile Networks (pp. 75-86). ACM.

[5] Rupprecht, D., Kohls, K., Holz, T. and Pöpper, C., Breaking LTE on Layer Two. In Breaking LTE on Layer Two (p. 0). IEEE.

[6] Raza, Muhammad Taqi, Fatima Muhammad Anwar, and Songwu Lu. “Exposing LTE Security Weaknesses at Protocol Inter-Layer, and Inter-Radio Interactions.” In International Conference on Security and Privacy in Communication Systems, pp. 312-338. Springer, Cham, 2017.

[7] 3GPP TS 33.501 V15.0.0 (2018-03).


Edited on 12/26/2018: Adding yet more papers and studies finding issues in the 5G security specifications.

We recently released a pre-print of our paper analyzing the 5G security specifications. The idea of releasing the pre-print while the paper is under submission was to get it out there soon and start collecting feedback in parallel to the actual review. There are a couple of things we want to clarify in the published version. The editorial process for this paper is taking longer than anticipated, so I thought I could make a quick update as sneak peak.

A few folks have pinged us with some questions and really good constructive feedback about the paper. Some questions were related to the main two concepts we will be clarifying in the final version.

  1.  The IMSI (SUPI in the context of 5G – I have been working in LTE security for many years and I am too used to saying IMSI, so I might wrongly refer to the IMSI here when I mean SUPI…) will be concealed using the public key of the home network, which does indeed imply that a SIM card only requires to have one single public key stored in order to conceal the SUPI into the SUCI.The SUPI will still be transmitted in the clear if there is no public key for the home network provisioned or in the case of an unauthenticated emergency call. It is not clear yet whether a rogue 5G base station could trick a device to issue such an unauthenticated call. Also, similarly to a recovery from a network outage in LTE, 5G might (should?) support a similar procedure for 5G. It is not clear yet either how the operator will indicate a UE/USIM that it needs to rotate the secret key (maybe it has been compromised, maybe it is time to rotate it… because they plan to rotate them, right???). In that scenario, implicitly, the operator will need to require the UE to authenticate in a manner that will not allow the SUPI to be concealed. To make things more complex, key management and rotation and what to do in these cases is left outside of the specifications.
  2. The 5G security specifications never explicitly state that a USIM will require to have a public key for every operator from every country. That is, however, an implicit requirement for the secure implementation of the protocol and to tackle the known LTE exploits (e.g. Attach Reject to DoS the device or downgrade it to GSM). Most of the protocol exploits discovered in LTE exploit one or multiple pre-authentication PHY, RRC or NAS messages before the handshake. An IMSI catcher returns an Attach Reject “I don’t know your TMSI/GUTI, send me your IMSI” message, a DoS-device replies with an AttachReject EMM Cause Code (for example) 0x03 Illegal UE and the device stops trying to connect until the timer T3245 expires (24h to 48h). A sophisticated Stingray replies with AttachReject EMM Cause Code 0x07 EPS Services Not Allowed and downgrades the UE to GSM to Man in the Middle the connection.Note that, in the case of IMSI/SUPI catching, 5G is *not* preventing the pre-authentication message to be exploited. In 5G, when an adversary sends an AttachReject “I don’t know your TMSI/GUTI send me your SUPI”, the UE replies with the SUPI, but this identifier is concealed. So the adversary catches the identifier, tough she/he cannot decrypt it. All the other exploits that leverage pre-authentication messages, and any other one that has not been identified yet, could still potentially be possible in 5G unless pre-authentication messages can be cryptographically authenticated by the UE. If mobile users never roamed to other networks or countries, having the public key of the home network would suffice. But, factoring roaming into the equation, the only way a UE could possibly cryptographically authenticate PHY, RRC and NAS pre-authentication messages is if the UE had a public key for every single operator from every single country. Otherwise, if I am missing a public key from an operator from say, Spain, I just need to set up my rogue 5G base station to broadcast, for example, MCC=214 MNC=07 (for Movistar) and the UE will implicitly trust every single PHY, RRC and NAS message that comes before the NAS authentication process.

    An alternative could be to have NAS messages from roaming UEs always routed back to/from the home operator in the home country. This would likely be an overload nightmare for Diameter networks and the mobile core networks. And, actually, probably this is something that could be exploited as a DDoS attack against mobile operators by having an army of fake software-radio based UEs initiating connections from different locations claiming to be USIM’s from all over the world. There might be other potential solutions to this problem, and I know of a couple research groups in academia doing excellent work to tackle this challenge.

Long story short, IMSI catching trickier in 5G but still not clear if fully prevented, and the requirement for a public key from all operators and countries is not an explicit requirement in the specifications but an implicit requirement if 5G is to tackle protocol exploits leveraging pre-authentication messages.

We will update the document on arXiv soon with these clarifications. Thank you very much again to everyone who has sent us feedback on the paper. We really appreciate it!

Ps. Good game by Barcelona last night despite having Messi out! 😀

EDIT: Just to clarify further. The public key of the home network at the USIM is intended only to conceal the SUPI. We are not trying to imply that this key is intended to apply to pre-authentication PHY/RRC/NAS messages. If this public/private key scheme was to be used to protect pre-authentication messages, though, then there would be an implicit requirement of having public keys for all operators.

Yesterday Google Scholar sent me another alert about a new paper. I must say that Google Scholar is becoming my number 1 source to stay up to date about research in mobile security.

The paper, “Formal analysis of 5G authentication“, is a pre-print released by  a team from ETH Zurich, University of Lorraine and University of Dundee. Similarly to a recent paper on LTE security (LTEInspector: A Systematic Approach for Adversarial Testing of 4G LTE), the authors translate the 3GPP protocol specifications into pseudo-code that can be formally verified and analyzed. In this case, the authors analyze the recently released 5G 3GPP specifications, with special focus on the authentication protocols. To do so, the authors use Tamarin, a protocol verification tool.

I strongly recommend reading the paper. As I expected, the authors found a few weaknesses on the protocol. The 5G AKA protocol appears to fail to meet several security goals that are explicitly required by the 3GPP specifications, as well as other critical security properties. The paper highlights weaknesses in the standard and suggests improvements and refinements. Such an interesting work and an excellent paper.

It is worth noting that a couple months ago I was invited to write an opinion article on 5G security and I got some criticism from 3GPP folks on it, claiming that 5G is secure and things have been improved very much. As I stated in my article (Are we there yet? The long path to securing 5G mobile communication networks), I still see a long way to go to fully secure mobile communication networks. And the new sophisticated security architecture and PKI infrastructure are very interesting, but based on the unrealistic assumption that each SIM will have a public key or certificate for all operators from all countries. I always acknowledge that it is very hard to achieve a secure mobile communications system and the only reason I work in proactively identifying security weaknesses is to keep raising awareness on this problem.

It makes me happy to see so much excellent work coming from academia in the area of mobile security. Excellent research topic for talented PhD students to work on. And it makes me even happier that, just a couple of months after being publicly released, there is security research analyzing the 5G specifications. I am myself currently involved in a research project on 5G security with a team from VATech under Prof. Jeffrey Reed and Prof. Vuk Marojevic. We are working on a new paper on 5G security that should be out sometime later this summer or early Fall. Stay tuned! For the ones of you who saw me speak at UC Irvine last May or at Hushcon East in NY in June, you already got a bit of a sneak peak.

Yesterday, Google Scholar sent me an alert of a paper I might be interested in. It turns out, I am indeed very interested in it. This is a paper already accepted, in its new rolling window review process, for the IEEE Security and Privacy symposium of 2019 (link for this year’s symposium): Breaking LTE on Layer 2.

There is no available pre-print yet, but there’s an abstract already:

Long Term Evolution (LTE) is the latest mobile communication standard and has a pivotal role in our information society: LTE combines performance goals with modern security mechanisms and serves casual use cases as well as critical infrastructure and public safety communications. Both scenarios are demanding towards a resilient and secure specification and implementation of LTE, as outages and open attack vectors potentially lead to severe risks. Previous work on LTE protocol security identified crucial attack vectors for both the physical (layer one) and network (layer three) layers. Data link layer (layer two) protocols, however, remain a blind spot in existing LTE security research. In this paper, we present a comprehensive layer two security analysis and identify three attack vectors. These attacks impair the confidentiality and/or privacy of LTE communication. More specifically, we first present a passive identity mapping attack that matches volatile radio identities to longer lasting network identities, enabling us to identify users within a cell and serving as a stepping stone for follow-up attacks. Second, we demonstrate how a passive attacker can abuse the resource allocation as a side channel to perform website fingerprinting that enables the attacker to learn the websites a user accessed. Finally, we present the A LTE R attack that exploits the fact that LTE user data is encrypted in counter mode (AES-CTR) but not integrity protected, which allows us to modify the message payload. As a proof-of-concept demonstration, we show how an active attacker can redirect DNS requests and then perform a DNS spoofing attack. As a result, the user is redirected to a malicious website. Our experimental analysis demonstrates the real-world applicability of all three attacks and emphasizes the threat of open attack vectors on LTE layer two protocols.

It is always great news to see excellent security research on LTE published that is based on open source implementations of the LTE stack. This is something I anticipated a few years ago. I am also very familiar with the work of this new paper’s authors. They have worked on some really interesting security research work on LTE and I have discussed some of their most recent papers in this blog.

This new paper is particularly exciting because it seems to build up on some of my work from a few years ago. Based on the abstract (“we first present a passive identity mapping attack that matches volatile radio identities to longer lasting network identities, enabling us to identify users within a cell and serving as a stepping stone for follow-up attacks), it sounds like they are implementing RNTI-based user tracking and using it for what sounds like a series of new really interesting attacks against LTE. I really look forward to reading the paper and learning more about the excellent work they did and the new protocol exploits they found.

Back in 2016 I presented at ShmooCon (slides and video) and published a paper discussing and implementing Denial of Service attacks against LTE, IMSI catchers on LTE and, relevant to this new paper, presenting and implementing in a real network for the first time a user location tracking attack leveraging the PHY layer id known as RNTI (Radio Network Temporary Identifier). For details, see slides 31 to 44 here and section V.F of my paper from 2016.

In a nutshell, the RNTI is an id derived and assigned in the RACH handshake in plain text (and thus can be easily captured with a simple LTE downlink sniffer such as AirScope from Software Radio Systems). It is included in plaintext in the header of every single PHY layer packet, which means that it is included in the plaintext in all uplink and downlink packets of a connection. As such, it can obviously allow to distinguish traffic flows from multiple users and track a given user, if one can map the RNTI to something else. As I implemented in my work a couple years ago, mapping the RNTI to the TMSI or even the MSISDN (the phone number of the user) is trivial. Once one maps an RNTI to a TMIS, then one can leverage paging messages to further expand the ability to track a user, as Kune showed in a really cool paper from a few years ago. I also recently read a paper that expands even further the ability of user tracking on LTE by using the GUTI.

A couple of years ago I also demo-ed at HackerHalted an implementation of an RNTI-based tracker running passively using a modified version of srsLTE and a USRP radio (see slides here).

The authors of “Breaking LTE on layer 2” seem to have implemented and tested the RNTI tracking techniques in their paper and used it as the stepping stone for new attacks that sound pretty cool and interesting, given what the abstract reads. Hopefully we don’t have to wait until IEEE S&P 2019 (May 2019) to learn more details on their new research. Knowing the excellent work that this authors have published in the recent years, I expect a very good paper that is likely to generate a lot of conversations and discussions. The more work in this area the better, as we need people talking about this and actively working in making mobile networks more secure. Really looking forward to reading their paper!

Related published work on user tracking and, specifically, RNTI tracking:

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

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

[3] Hong, Byeongdo, Sangwook Bae, and Yongdae Kim. “GUTI Reallocation Demystified: Cellular Location Tracking with Changing Temporary Identifier.” In Symposium on Network and Distributed System Security (NDSS). ISOC. 2018.

[4] Kune, Denis Foo, John Koelndorfer, Nicholas Hopper, and Yongdae Kim. “Location leaks on the GSM air interface.” ISOC NDSS (Feb 2012) (2012).

[5] Jover, Roger Piqueras. “Some key challenges in securing 5G wireless networks.” Electronic Comment Filing System, Jan(2017). [PDF]


UPDATE (06/28/2018) – The authors have released a web site describing their findings and, more importantly, including a pre-print of the paper. As I had guessed, this is indeed based on my RNTI tracking techniques. The authors leverage those techniques to fingerprint web traffic and, despite being encrypted, they can estimate who browses what websites. They test this with a bunch of top 50 Alexa sites. The other new attack, aLTEr, is very interesting. By exploiting the fact that certain layer 2 messages are encrypted but not integrity checked, they flip bits in the cipher text in a very smart way to modify the destination IP fr DNS queries, effectively redirecting any mobile device to, for example, a malicious domain when they believe they are browsing a legitimate service.

The paper seems to indicate that I did not test and implement RNTI tracking a couple of years ago, but I actually did. And also showed a demo at HackerHalted in Atlanta back in 2016. Regardless, this new paper is excellent, and worth a read. Check out the references, as they link to some of the working documents from GSMA and 3GPP  after receiving the authors’ disclosure about this protocol exploits. Interesting, though, that #GPP and GSMA seems to only be concerned about the aLTEr exploit and not really worried about the other one (see S3-181429 document from the 3GPP TSG SA WG3 Security Meeting #91).

(Originally posted as an article on LinkedIn)

The mobile and wireless communication industry is highly susceptible, as are most sectors in the information technology industry, to drowning in a sea of buzzwords. “5G” is a concept that has been thrown around frequently for the past 6 years or so to define a futuristic – and potentially hard to achieve – connectivity scenario in which speeds of 1Gbps are ubiquitous, sub-10ms latencies are the norm, and the network can take on 1,000 times more connected devices without any hiccups. This utopian connected world has always been promised to arrive in 2020, to coincide with the Tokyo Summer Olympics, with the first trials during the 2018 Winter Olympics.

While the buzz around 5G has spawned conferences, workshops, symposiums, industry consortiums, and tomes of scientific press, some great minds in both academia and industry have been working on actual technology which, unlike big stands at expos and conferences and flashy slide decks, will solve the 5G connectivity challenges. mmWave communications are the clear path towards being able to achieve gigabit rates ubiquitously in dense urban scenarios and, although radio signal propagation is very challenging at such high bands, massive MIMO (Multiple-Input Multiple-Output) and adaptive beamforming arrays are the promising technologies that will help close that gap.

While 5G has mostly been a buzzword attached to flashy presentations and keynotes during the last few years, this does not change the fact that there have been outstanding research and development advances in some of the key technology areas that will sustain the connectivity demands of the next decade. That is, things that will make the concept of 5G an actual reality. As a result of this excellent work, the first official release of the 3GPP standards for 5G communication systems was published in December 2017. The new proposed mobile communication system is known as New Radio (NR) and its Core Network (as opposed to the Radio Access Network) is known as 5G System (5G-S).

While the technology pillars for future 5G mobile systems were being developed, there has been a spike in excellent security research work in the general field of mobile communications, and LTE mobile networks more specifically. As I anticipated 2 years ago, open source platforms have provided the perfect tools for bright security researchers to work on outstanding research projects that have yielded the discovery of all sorts of implementation issues and communication protocol deficiencies in LTE mobile networks. In some cases, the technology press has picked up on some of the resulting scientific publications at top conferences, which has sent shockwaves throughout the mobile communications industry. Such great research has also driven security innovation and protocol improvements that are making mobile networks nothing but more secure and resilient.

For quite a few years, I have been among the advocates for piggybacking on the technology disruption of 5G to address the well-known and, in many cases, very concerning security and scalability issues in LTE mobile networks. Although the major breakthrough in 5G will be at the physical layer (PHY), we are long overdue on reconsidering the current circuit-switched architecture of core mobile networks and embracing a fully packet-switched architecture. Although the mobile core of LTE is already fully IP-based, the architecture of the network still heavily relies on circuits – known as bearers in 3GPP jargon – and complex state machines. Among many other reasons for embracing a packet-switched architecture, the goal of massive connectivity in 5G networks will never be achieved in current control plane signaling-constrained networks. This is especially true when the goal is achieving connectivity for 1,000 times more devices and the Internet of Things (IoT) is at our doorstep, waiting to enter the game. As a great point of reference for this massive challenge in mobile networks, I always like to refer my colleagues to the visionary paper by J Kim and Paul Henry.

In general, the disruption of 5G is indeed the perfect opportunity for major architectural changes in the core network, though this is a challenging goal. However, it would be a big loss if, at the very least, 5G was not used to address the minor, and narrower in scope, changes required to tackle concerning security exploits uncovered in LTE. By now, it is well understood that there are multiple ways an adversary could abuse the pre-authentication Radio Resource Control (RRC) and Non-Access Stratum (NAS) messages, both of which are neither authenticated nor encrypted. As such, LTE mobile networks and, more importantly, LTE smartphones and network equipment, are potentially vulnerable to certain privacy leaks and Denial of Service (DoS) attacks, as prototyped in the lab by several research projects over the last 5 years.

The first release of the NR and 5G-S standards (Release 15 of the 3GPP standards), with the initial specifications released in December 2017, makes a partial attempt at addressing such security issues. Interestingly, most of the security definitions have not been included in the specifications until the updated documents released in March 2018. There are some ongoing efforts in protecting the International Mobile Subscriber Identifier (IMSI) using Public Key Infrastructure (PKI), likely motivated due to the recent amount of press and media coverage on IMSI catchers, in addition to leveraging PKI to authenticate certain pre-authentication messages. However, it is still to be seen how certain challenges, such as how to authenticate or implement PKI with a subscriber roaming from another network – or even a foreign network – will be solved. There are also several edge cases in which null integrity and null ciphering are used, such as the initial registration procedure for emergency services (3GPP TS 24.501 V1.0.0 2018-03 – Plus, the fact that null ciphering and null integrity are supported (3GPP TS 24.501 V1.0.0 2018-03 – Table could potentially end up in insecure, unexpected protocol edge cases. Besides that, the sheer number of pre-authentication messages still exposes protocols to potential security exploits.

I recently collaborated with a highly-renowned mobile security research team from academia (Prof. Jeffrey H. Reed and Dr. Vuk Marojevic at Wireless @ Virginia Tech) in a security analysis of the NR standards. In the past, both that team and I had been involved in research on protocol-aware jamming and the underlying vulnerability of LTE mobile networks to adversarial RF jamming. The goal of this latest security analysis was to investigate the feasibility of protocol-aware jamming in the proposed PHY layer in NR. The outcome of the study will be presented in the 1st IEEE Workshop on 5G Wireless Security coming up this May in Kansas City, but the results are already available to the public in our paper.

Although the outcome of the security analysis is not encouraging, one must acknowledge that it would have been a massive achievement to simultaneously tackle the challenge of gigabit connectivity, mmWave combined with massive MIMO and, on top of that, security and resiliency. Things at the higher protocol layers still look rather challenging as well. Despite my forays into PHY layer security and protocol-aware jamming, most of my security research work over the last 8 years has focused on protocol-level exploits on various wireless technologies, with great focus on 3GPP’s LTE as defined starting on Release 8. As one of the few researchers who has uncovered numerous protocol exploits that would result in DoS of mobile devices and privacy leaks, I was, and still am, optimistic about the role of 5G disruption in enhancing the security of mobile networks. And leveraging PKI is definitely a step in the right direction.

Nevertheless, what we have seen so far in the NR and 5G-S standards is not a complete solution yet, despite attempts to address protocol exploits. In parallel, there is also a set of new pre-authentication messages and new fields and configurations in existing messages. One must acknowledge, though, that fully securing mobile communication networks is a massive challenge that will require collaboration among academia, industry and researchers.

As a security researcher, many of my colleagues and I see the emerging landscape of 5G as a blank canvas to experiment with the potential security impact of adversarial tampering, spoofing and intercepting of these pre-authentication messages in NR and 5G-S. And it is critical that the security research community and the mobile communications industry work together in identifying such potential exploits and, more importantly, their root causes, so the security of the upcoming 5G networks can be enhanced in short order. There is still time until 2020 to enhance mobile communication networks even further.

Although we could – and perhaps should – be much closer by now, there is still a very long way to go to fully secure mobile communication networks. The same applies to reaching a flexible and truly scalable mobile architecture capable of supporting the connectivity demands of the future. However, the very active community of mobile security researchers will hopefully take us to that stage.

Equipped with an army of software radios, mostly USRP B210s, and my new toolset based on srsLTE, I continue my work on protocol-fuzzing mobile and wireless network standards with the goal of contributing to the security of the communication systems used by billions on a regular basis. In my case, time is now slightly scarcer due to my recent fatherhood. But, I continue to work and follow closely the excellent work of the few other teams in this research field, where outstanding graduate students and researchers are paving the way towards secure and reliable mobile communication networks.

This time, I cannot predict whether there will be a large number of new security exploits identified and prototyped in NR and 5G-S networks in the near future or a spike in mobile security findings in this field, mainly because there are no available test-beds or open source implementations of the Release 15 stack. But, as long as the folks behind tools such as srsLTE keep up their great work, it will not take long for the right tools to be available for applied security research on 5G mobile systems. And when that day comes, it is game on!

Roger Piqueras Jover is a Security Architect in the Office of the CTO at Bloomberg, where he is actively engaged in mobile and wireless security research. He maintains a bibliography of his previously released and published work at his personal website:

About me:

Born in Barcelona, moved to Los Angeles, and 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.
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