Older blog entries for LaForge (starting at number 295)

Returning from TelcoSecDay 2017 / General Musings

I'm just on my way back from the Telecom Security Day 2017 <https://www.troopers.de/troopers17/telco-sec-day/>, which is an invitation-only event about telecom security issues hosted by ERNW back-to-back with their Troopers 2017 <https://www.troopers.de/troopers17/> conference.

I've been presenting at TelcoSecDay in previous years and hence was again invited to join (as attendee). The event has really gained quite some traction. Where early on you could find lots of IT security / hacker crowds, the number of participants from the operator (and to smaller extent also equipment maker) industry has been growing.

The quality of talks was great, and I enjoyed meeting various familiar faces. It's just a pity that it's only a single day - plus I had to head back to Berlin still today so I had to skip the dinner + social event.

When attending events like this, and seeing the interesting hacks that people are working on, it pains me a bit that I haven't really been doing much security work in recent years. netfilter/iptables was at least somewhat security related. My work on OpenPCD / librfid was clearly RFID security oriented, as was the work on airprobe, OsmocomTETRA, or even the EasyCard payment system hack

I have the same feeling when attending Linux kernel development related events. I have very fond memories of working in both fields, and it was a lot of fun. Also, to be honest, I believe that the work in Linux kernel land and the general IT security research was/is appreciated much more than the endless months and years I'm now spending my time with improving and extending the Osmocom cellular infrastructure stack.

Beyond the appreciation, it's also the fact that both the IT security and the Linux kernel communities are much larger. There are more people to learn from and learn with, to engage in discussions and ping-pong ideas. In Osmocom, the community is too small (and I have the feeling, it's actually shrinking), and in many areas it rather seems like I am the "ultimate resource" to ask, whether about 3GPP specs or about Osmocom code structure. What I'm missing is the feeling of being part of a bigger community. So in essence, my current role in the "Open Source Cellular" corner can be a very lonely one.

But hey, I don't want to sound more depressed than I am, this was supposed to be a post about TelcoSecDay. It just happens that attending IT Security and/or Linux Kernel events makes me somewhat gloomy for the above-mentioned reasons.

Meanwhile, if you have some interesting projcets/ideas at the border between cellular protocols/systems and security, I'd of course love to hear if there's some way to get my hands dirty in that area again :)

Syndicated 2017-03-21 17:00:00 from LaForge's home page

Gory details of USIM authentication sequence numbers

I always though I understood UMTS AKA (authentication and key agreement), including the re-synchronization procedure. It's been years since I wrote tools like osmo-sim-auth which you can use to perform UMTS AKA with a SIM card inserted into a PC reader, i.e. simulate what happens between the AUC (authentication center) in a network and the USIM card.

However, it is only now as the sysmocom team works on 3G support of the dedicated OsmoHLR (outside of OsmoNITB!), that I seem to understand all the nasty little details.

I always thought for re-synchronization it is sufficient to simply increment the SQN (sequence number). It turns out, it isn't as there is a MSB-portion called SEQ and a lower-bit portion called IND, used for some fancy array indexing scheme of buckets of highest-used-SEQ within that IND bucket.

If you're interested in all the dirty details and associated spec references (the always hide the important parts in some Annex) see the discussion between Neels and me in Osmocom redmine issue 1965.

Syndicated 2017-03-07 23:00:00 from LaForge's home page

GTA04 project halts GTA04A5 due to OMAP3 PoP soldering issues

For those of you who don't know what the tinkerphones/OpenPhoenux GTA04 is: It is a 100% community-backed open hardware project creating updated mainboards that can be used to upgrade Openmoko phones. They fit into the same enclosure and can use the same display/speaker/microphone.

What the GTA04 guys have been doing for many years is close to a miracle anyway: Trying to build a modern-day smartphone in low quantities, using off-the-shelf components available in those low quantities, and without a large company with its associated financial backing.

Smartphones are complex because they are highly integrated devices. A seemingly unlimited amount of components is squeezed in the tiniest form-factors. This leads to complex circuit boards with many layers that take a lot of effort to design, and are expensive to build in low quantities. The fine-pitch components mandated by the integration density is another issue.

Building the original GTA01 (Neo1937) and GTA02 (FreeRunner) devices at Openmoko, Inc. must seem like a piece of cake compared to what the GTA04 guys are up to. We had a team of engineers that were familiar at last with feature phone design before, and we had the backing of a consumer electronics company with all its manufacturing resources and expertise.

Nevertheless, a small group of people around Dr. Nikolaus Schaller has been pushing the limits of what you can do in a pure community project, and the have my utmost respect. Well done!

Unfortunately, there are bad news. Manufacturing of their latest generation of phones (GTA04A5) has been stopped due to massive soldering problems with the TI OMAP3 package-on-package (PoP). Those PoPs are basically "RAM chip soldered onto the CPU, and the stack of both soldered to the PCB". This is used to save PCB footprint and to avoid having to route tons of extra (sensitive, matched) traces between the SDRAM and the CPU.

According to the mailing list posts, it seems to be incredibly difficult to solder the PoP stack due to the way TI has designed the packaging of the DM3730. If you want more gory details, see this post and yet another post.

It is very sad to see that what appears to be bad design choices at TI are going to bring the GTA04 project to a halt. The financial hit by having only 33% yield is already more than the small community can take, let alone unused parts that are now in stock or even thinking about further experiments related to the manufacturability of those chips.

If there's anyone with hands-on manufacturing experience on the DM3730 (or similar) TI PoP reading this: Please reach out to the GTA04 guys and see if there's anything that can be done to help them.

Syndicated 2017-03-05 23:00:00 from LaForge's home page

Manual testing of Linux Kernel GTP module

In May 2016 we got the GTP-U tunnel encapsulation/decapsulation module developed by Pablo Neira, Andreas Schultz and myself merged into the 4.8.0 mainline kernel.

During the second half of 2016, the code basically stayed untouched. In early 2017, several patch series of (at least) three authors have been published on the netdev mailing list for review and merge.

This poses the very valid question on how do we test those (sometimes quite intrusive) changes. Setting up a complete cellular network with either GPRS/EGPRS or even UMTS/HSPA is possible using OsmoSGSN and related Osmocom components. But it's of course a luxury that not many Linux kernel networking hackers have, as it involves the availability of a supported GSM BTS or UMTS hNodeB. And even if that is available, there's still the issue of having a spectrum license, or a wired setup with coaxial cable.

So as part of the recent discussions on netdev, I tested and described a minimal test setup using libgtpnl, OpenGGSN and sgsnemu.

This setup will start a mobile station + SGSN emulator inside a Linux network namespace, which talks GTP-C to OpenGGSN on the host, as well as GTP-U to the Linux kernel GTP-U implementation.

In case you're interested, feel free to check the following wiki page: https://osmocom.org/projects/linux-kernel-gtp-u/wiki/Basic_Testing

This is of course just for manual testing, and for functional (not performance) testing only. It would be great if somebody would pick up on my recent mail containing some suggestions about an automatic regression testing setup for the kernel GTP-U code. I have way too many spare-time projects in desperate need of some attention to work on this myself. And unfortunately, none of the telecom operators (who are the ones benefiting most from a Free Software accelerated GTP-U implementation) seems to be interested in at least co-funding or otherwise contributing to this effort :/

Syndicated 2017-02-23 23:00:00 from LaForge's home page

Cellular re-broadcast over satellite

I've recently attended a seminar that (among other topics) also covered RF interference hunting. The speaker was talking about various real-world cases of RF interference and illustrating them in detail.

Of course everyone who has any interest in RF or cellular will know about fundamental issues of radio frequency interference. To the biggest part, you have

  • cells of the same operator interfering with each other due to too frequent frequency re-use, adjacent channel interference, etc.
  • cells of different operators interfering with each other due to intermodulation products and the like
  • cells interfering with cable TV, terrestrial TV
  • DECT interfering with cells
  • cells or microwave links interfering with SAT-TV reception
  • all types of general EMC problems

But what the speaker of this seminar covered was actually a cellular base-station being re-broadcast all over Europe via a commercial satellite (!).

It is a well-known fact that most satellites in the sky are basically just "bent pipes", i.e. they consist of a RF receiver on one frequency, a mixer to shift the frequency, and a power amplifier. So basically whatever is sent up on one frequency to the satellite gets re-transmitted back down to earth on another frequency. This is abused by "satellite hijacking" or "transponder hijacking" and has been covered for decades in various publications.

Ok, but how does cellular relate to this? Well, apparently some people are running VSAT terminals (bi-directional satellite terminals) with improperly shielded or broken cables/connectors. In that case, the RF emitted from a nearby cellular base station leaks into that cable, and will get amplified + up-converted by the block up-converter of that VSAT terminal.

The bent-pipe satellite subsequently picks this signal up and re-transmits it all over its coverage area!

I've tried to find some public documents about this, an there's surprisingly little public information about this phenomenon.

However, I could find a slide set from SES, presented at a Satellite Interference Reduction Group: Identifying Rebroadcast (GSM)

It describes a surprisingly manual and low-tech approach at hunting down the source of the interference by using an old nokia net-monitor phone to display the MCC/MNC/LAC/CID of the cell. Even in 2011 there were already open source projects such as airprobe that could have done the job based on sampled IF data. And I'm not even starting to consider proprietary tools.

It should be relatively simple to have a SDR that you can tune to a given satellite transponder, and which then would look for any GSM/UMTS/LTE carrier within its spectrum and dump their identities in a fully automatic way.

But then, maybe it really doesn't happen all that often after all to rectify such a development...

Syndicated 2017-02-15 23:00:00 from LaForge's home page

Towards a real SIGTRAN/SS7 stack in libosmo-sigtran

In the good old days ever since the late 1980ies - and a surprising amount even still today - telecom signaling traffic is still carried over circuit-switched SS7 with its TDM lines as physical layer, and not an IP/Ethernet based transport.

When Holger first created OsmoBSC, the BSC-only version of OpenBSC some 7-8 years ago, he needed to implement a minimal subset of SCCP wrapped in TCP called SCCP Lite. This was due to the simple fact that the MSC to which it should operate implemented this non-standard protocol stacking that was developed + deployed before the IETF SIGTRAN WG specified M3UA or SUA came around. But even after those were specified in 2004, the 3GPP didn't specify how to carry A over IP in a standard way until the end of 2008, when a first A interface over IP study was released.

As time passese, more modern MSCs of course still implement classic circuit-switched SS7, but appear to have dropped SCCPlite in favor of real AoIP as specified by 3GPP meanwhile. So it's time to add this to the osmocom universe and OsmoBSC.

A couple of years ago (2010-2013) implemented both classic SS7 (MTP2/MTP3/SCCP) as well as SIGTRAN stackings (M2PA/M2UA/M3UA/SUA in Erlang. The result has been used in some production deployments, but only with a relatively limited feature set. Unfortunately, this code has nto received any contributions in the time since, and I have to say that as an open source community project, it has failed. Also, while Erlang might be fine for core network equipment, running it on a BSC really is overkill. Keep in miond that we often run OpenBSC on really small ARM926EJS based embedded systems, much more resource constrained than any single smartphone during the late decade.

In the meantime (2015/2016) we also implemented some minimal SUA support for interfacing with UMTS femto/small cells via Iuh (see OsmoHNBGW).

So in order to proceed to implement the required SCCP-over-M3UA-over-SCTP stacking, I originally thought well, take Holgers old SCCP code, remove it from the IPA multiplex below, stack it on top of a new M3UA codebase that is copied partially from SUA.

However, this falls short of the goals in several ways:

  • The application shouldn't care whether it runs on top of SUA or SCCP, it should use a unified interface towards the SCCP Provider. OsmoHNBGW and the SUA code already introduce such an interface baed on the SCCP-User-SAP implemented using Osmocom primitives (osmo_prim). However, the old OsmoBSC/SCCPlite code doesn't have such abstraction.
  • The code should be modular and reusable for other SIGTRAN stackings as required in the future

So I found myself sketching out what needs to be done and I ended up pretty much with a re-implementation of large parts. Not quite fun, but definitely worth it.

The strategy is:

And then finally stack all those bits on top of each other, rendering a fairly clean and modern implementation that can be used with the IuCS of the virtually unmodified OsmmoHNBGW, OsmoCSCN and OsmoSGSN for testing.

Next steps in the direction of the AoIP are:

  • Implementation of the MTP-SAP based on the IPA transport
  • Binding the new SCCP code on top of that
  • Converting OsmoBSC code base to use the SCCP-User-SAP for its signaling connection

From that point onwards, OsmoBSC doesn't care anymore whether it transports the BSSAP/BSSMAP messages of the A interface over SCCP/IPA/TCP/IP (SCCPlite) SCCP/M3UA/SCTP/IP (3GPP AoIP), or even something like SUA/SCTP/IP.

However, the 3GPP AoIP specs (unlike SCCPlite) actually modify the BSSAP/BSSMAP payload. Rather than using Circuit Identifier Codes and then mapping the CICs to UDP ports based on some secret conventions, they actually encapsulate the IP address and UDP port information for the RTP streams. This is of course the cleaner and more flexible approach, but it means we'll have to do some further changes inside the actual BSC code to accommodate this.

Syndicated 2017-02-12 23:00:00 from LaForge's home page

Testing (not only) telecom protocols

When implementing any kind of communication protocol, one always dreams of some existing test suite that one can simply run against the implementation to check if it performs correct in at least those use cases that matter to the given application.

Of course in the real world, there rarely are protocols where this is true. If test specifications exist at all, they are often just very abstract texts for human consumption that you as the reader should implement yourself.

For some (by far not all) of the protocols found in cellular networks, every so often I have seen some formal/abstract machine-parseable test specifications. Sometimes it was TTCN-2, and sometimes TTCN-3.

If you haven't heard about TTCN-3, it is basically a way to create functional tests in an abstract description (textual + graphical), and then compile that into an actual executable tests suite that you can run against the implementation under test.

However, when I last did some research into this several years ago, I couldn't find any Free / Open Source tools to actually use those formally specified test suites. This is not a big surprise, as even much more fundamental tools for many telecom protocols are missing, such as good/complete ASN.1 compilers, or even CSN.1 compilers.

To my big surprise I now discovered that Ericsson had released their (formerly internal) TITAN TTCN3 Toolset as Free / Open Source Software under EPL 1.0. The project is even part of the Eclipse Foundation. Now I'm certainly not a friend of Java or Eclipse by all means, but well, for running tests I'd certainly not complain.

The project also doesn't seem like it was a one-time code-drop but seems very active with many repositories on gitub. For example for the core module, titan.core shows plenty of activity on an almost daily basis. Also, binary releases for a variety of distributions are made available. They even have a video showing the installation ;)

If you're curious about TTCN-3 and TITAN, Ericsson also have made available a great 200+ pages slide set about TTCN-3 and TITAN.

I haven't yet had time to play with it, but it definitely is rather high on my TODO list to try.

ETSI provides a couple of test suites in TTCN-3 for protocols like DIAMETER, GTP2-C, DMR, IPv6, S1AP, LTE-NAS, 6LoWPAN, SIP, and others at http://forge.etsi.org/websvn/ (It's also the first time I've seen that ETSI has a SVN server. Everyone else is using git these days, but yes, revision control systems rather than periodic ZIP files is definitely a big progress. They should do that for their reference codecs and ASN.1 files, too.

I'm not sure once I'll get around to it. Sadly, there is no TTCN-3 for SCCP, SUA, M3UA or any SIGTRAN related stuff, otherwise I would want to try it right away. But it definitely seems like a very interesting technology (and tool).

Syndicated 2017-02-11 23:00:00 from LaForge's home page

FOSDEM 2017

Last weekend I had the pleasure of attending FOSDEM 2017. For many years, it is probably the most exciting event exclusively on Free Software to attend every year.

My personal highlights (next to meeting plenty of old and new friends) in terms of the talks were:

I was attending but not so excited by Georg Greve's OpenPOWER talk. It was a great talk, and it is an important topic, but the engineer in me would have hoped for some actual beefy technical stuff. But well, I was just not the right audience. I had heard about OpenPOWER quite some time ago and have been following it from a distance.

The LoRaWAN talk couldn't have been any less technical, despite stating technical, political and cultural in the topic. But then, well, just recently 33C3 had the most exciting LoRa PHY Reverse Engineering Talk by Matt Knight.

Other talks whose recordings I still want to watch one of these days:

Syndicated 2017-02-10 23:00:00 from LaForge's home page

Osmocom Conference 2017 on April 21st

I'm very happy that in 2017, we will have the first ever technical conference on the Osmocom cellular infrastructure projects.

For many years, we have had a small, invitation only event by Osmocom developers for Osmocom developers called OsmoDevCon. This was fine for the early years of Osmocom, but during the last few years it became apparent that we also need a public event for our many users. Those range from commercial cellular operators to community based efforts like Rhizomatica, and of course include the many research/lab type users with whom we started.

So now we'll have the public OsmoCon on April 21st, back-to-back with the invitation-only OsmoDevcon from April 22nd through 23rd.

I'm hoping we can bring together a representative sample of our user base at OsmoCon 2017 in April. Looking forward to meet you all. I hope you're also curious to hear more from other users, and of course the development team.

Regards,
Harald

Syndicated 2017-01-31 23:00:00 from LaForge's home page

Autodesk: How to lose loyal EAGLE customers

A few days ago, Autodesk has announecd that the popular EAGLE electronics design automation (EDA) software is moving to a subscription based model.

When previously you paid once for a license and could use that version/license as long as you wanted, there now is a monthly subscription fee. Once you stop paying, you loose the right to use the software. Welcome to the brave new world.

I have remotely observed this subscription model as a general trend in the proprietary software universe. So far it hasn't affected me at all, as the only two proprietary applications I use on a regular basis during the last decade are IDA and EAGLE.

I already have ethical issues with using non-free software, but those two cases have been the exceptions, in order to get to the productivity required by the job. While I can somehow convince my consciousness in those two cases that it's OK - using software under a subscription model is completely out of the question, period. Not only would I end up paying for the rest of my professional career in order to be able to open and maintain old design files, but I would also have to accept software that "calls home" and has "remote kill" features. This is clearly not something I would ever want to use on any of my computers. Also, I don't want software to be associated with any account, and it's not the bloody business of the software maker to know when and where I use my software.

For me - and I hope for many, many other EAGLE users - this move is utterly unacceptable and certainly marks the end of any business between the EAGLE makers and myself and/or my companies. I will happily use my current "old-style" EAGLE 7.x licenses for the near future, and theS see what kind of improvements I would need to contribute to KiCAD or other FOSS EDA software in order to eventually migrate to those.

As expected, this doesn't only upset me, but many other customers, some of whom have been loyal to using EAGLE for many years if not decades, back to the DOS version. This is reflected by some media reports (like this one at hackaday or user posts at element14.com or eaglecentral.ca who are similarly critical of this move.

Rest in Peace, EAGLE. I hope Autodesk gets what they deserve: A new influx of migrations away from EAGLE into the direction of Open Source EDA software like KiCAD.

In fact, the more I think about it, I'm actually very much inclined to work on good FOSS migration tools / converters - not only for my own use, but to help more people move away from EAGLE. It's not that I don't have enough projects at my hand already, but at least I'm motivated to do something about this betrayal by Autodesk. Let's see what (if any) will come out of this.

So let's see it that way: What Autodesk is doing is raising the level off pain of using EAGLE so high that more people will use and contribute FOSS EDA software. And that is actually a good thing!

Syndicated 2017-01-22 23:00:00 from LaForge's home page

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