gnuradio – Factoria Labs

Arsenal Labs at Black Hat 2022

Hello Factoria Labs readers! As you may know, Black Hat USA happened earlier this month in Las Vegas. As well as teaching an in-person SDR class, I was also honored to present a hands-on project at the Arsenal Labs – we had a great turnout, as you can see from the picture.

My project was an end-to-end, RF reversal of a simple garage door protocol. Although the signal produced by the garage door remote was not terribly complicated, the project provided a full view of the reversing process, including:

scanning for the remote’s signal
capturing the signal to disk
tuning and demodulating to produce a digital baseband waveform
identifying the framing and encoding of the baseband waveform and then extracting the bits
building a simple transmitter to implement the reversed protocol
building a more complex transmitter to implement brute force attacks

If you caught my presentation and wanted to look at starter and solution projects, it’s all at:

https://github.com/paulgclark/garage_door

I’ve also included a PDF of the printed handout we had for Arsenal attendees.

If you’re curious, the garage door remote used in the lab was this model:

https://www.amazon.com/dp/B08RSDQKM9

Thanks for reading!

Updated gnuradio Install Instructions

As some of you have noted, the installation instructions for gnuradio and HackRF contained in our Field Expedient SDR series no longer work. To remedy this I’ve created a set of installation scripts that automate nearly all of the steps required, updated for newer versions of gnuradio/uhd/osmosdr and supporting the Ubuntu 18.04 LTS.

The scripts install from specific releases and commits of the source code, so they should be much more stable than previous iterations of the instructions.

TLDR

On an Ubuntu 18.04 installation perform the following:

Open a new terminal (Ctl+Alt+t) and type:
sudo apt -y install git mkdir -p install cd install git clone https://github.com/paulgclark/grc-install cd grc-install/install_scripts sudo ./grc_from_source.sh
(This will install both gnuradio and the UHD drivers. It will take between 0.5 to 1.5 hours.)
Open a new terminal and type:
cd install/grc-install/install_scripts
./hackrf_from_source.sh
(This will install the hackrf tools and the osmocom blocks. It will take only a few minutes.)
Open a third terminal and start gnuradio companion with:
gnuradio-companion
Depending on the hardware you have available, you can open the following flowgraphs inside gnuradio-companion to test your setup:
~/install/grc-install/grc/hackrf-test/fm_receiver_hardware.grc ~/install/grc-install/grc/uhd-test/fm_receiver_hardware.grc

Installing gnuradio 3.8

By default the gnuradio install script installs version 3.7.13.5, the latest release before 3.8. If you want to try out the new version, simply type:
sudo ./grc_from_source.sh 3.8

Note that the osmocom team hasn’t yet updated the blocks used for interfacing with the HackRF such that they work with version 3.8 of gnuradio. I’ve instead used Igor Freire‘s fork of their repository (actually, it’s his fork of Mickey Vänskä‘s fork of the osmocom repo). Thanks to both Igor and Mickey!

Installation Scheme

One of the big benefits of the PyBOMBS scheme we originally used in the book was the fact that it installs everything to a target directory under your home directory, rather than doing a global install to root-owned directories. The environment is then loaded with a simple call to a setup_env.sh script generated by the install process (which is automatically added to your ~/.bashrc).

This means if something goes wrong, you can just rm -r the target directory and delete a single line from your .bashrc file. You can then start over without worrying about the previous install polluting your environment.

I’ve preserved this scheme in the new scripts as well. By default the scripts will use the following directory for the target:
~/install/sdr

If you want to use a different target, simply run the script with the new target directory as the second argument. If installing 3.7 this would be:
sudo ./grc_from_source.sh 3.7 ~/install2

For 3.8, it would be
sudo ./grc_from_source.sh 3.8 ~/install2

This installation flow also allows you to easily keep multiple versions of gnuradio on disk. You simply install 3.7 to one target directory and 3.8 to another. You then enable the setup_env.sh file corresponding to the one you want to use at any given moment.

Conclusion

I’ve tested these scripts on numerous laptops and believe I’ve worked out all the issues with both Ettus and HackRF hardware. If you do have an issue, please let me know on GitHub or via email.

Learn SDR with us at Black Hat Vegas!

I believe it takes 4 days to learn the basics of software defined radio, even if you’ve never done a single radio-related thing in your life. Less than a week.

If you lay that solid foundation in SDR and gnuradio, you’ll be far more effective in your future endeavors, whether that’s:

scanning for and intercepting signals
reverse engineering transmissions
building your own programmable RF systems for exfiltration

Join us this August at Black Hat to get started with SDR. We have a two-day introductory class that’s perfect for beginners. You don’t need to know a thing, and you don’t need to bring a thing. You’ll use our laptops and SDR hardware. No pre-class installation homework, just show up and sit down. You’ll learn the basics of gnuradio, RF theory and SDR operation – which will enable you to build analog transmitters and receivers.

You can then move on to our Intermediate Digital SDR class, where we’ll work through all the stuff you need to build digital radios:

OOK, FSK, GFSK and PSK modulation
handling preambles, payload encodings and CRCs
clock synchronization!
and much more

If you’ve already spent some time with SDR and know the basics of gnuradio, you can jump straight to the intermediate class. Feel free to contact us if you have any questions about this. We can also chat about our advanced classes in reverse engineering or gnuradio application development.

Hope to see you in Vegas!

Presentation at Wild West Hackinfest 2018

Yesterday, I had the privilege of giving a talk about a project I’d been working on to the Wild West Hackinfest in Deadwood, SD. Over the last year or two I’d been wanting to build a clean radio communication system using SDR and gnuradio. There were a number of not-so-obvious things I’d learned over the years, and I thought releasing some code that implemented such a system could help out folks that may have been struggling with some of the same things that I did.

The project I settled on was an RF exfiltration system, with a host laptop sending commands to a headless Raspberry Pi 3 B+. The twist, however, was that each time the host requested data, it also told the xfil box how to send the data: what frequency, modulation scheme, preamble, etc. The goal was to be able to communicate in a manner that was as flexible as possible, even capable of changing the RF parameters with each transmission.

The code is still at “proof-of-concept maturity” but it should help you see how to get digital payloads from external Python code into a flowgraph (on transmit) and vice versa (on receive). You can see it all here:

http://github.com/paulgclark/exfil

I’m incredibly grateful to John Strand and all the folks who made the conference happen. It’s an awesome event with great people both running and attending. If you haven’t been, you should definitely go in 2019.

PS There was a camera running, so I’ll provide an update post when the video is posted.

New GRC Block for Reversing Simple Protocols

Hello SDR fans. A long-standing wish of mine is to have a grc block that detects a preamble on an incoming byte stream and tags it with a fixed length. There has been a block in grc for a long time called the Correlate Access Code – Tag Stream (kind of a mouthful, I know) which almost does this but not quite. This original block scans the 32 samples after the preamble and tries to extract a frame length field, which it will then use for the tag value. That function is kind of neat if you’re building your own transmitter/receiver pair, but it doesn’t help when you’ve got a mystery signal on your hands that won’t have that header in place.

So for a while a worked around the issue. On short projects, I’d use the now-deprecated Correlate Access Code block, dump the data to a file and whip up a quick Python script to handle things (you can see some examples of this in Volume 3 of our book series). For more complex situations, I employ WaveConverter, which I built to extract and analyze large amount of payload data. Despite these options, I always wanted a simple grc-only method of quickly looking at payload data.

All of which brings me to the block I built, Correlate Access Code – Tagged Stream – Fixed Length (yeah, I didn’t really reduce the mouthful any). I simply created a new module and block with the gr_modtool utility and copied over the *.cc, *.h and *.xml files from the original block. I then cut out the header parsing and added a property for you to set the Packet Length. After a bit of debug and cleanup, I had a useable block, which you can grab from:

https://github.com/paulgclark/gr-reveng

The example flowgraph below shows how easy it is to use:

The new block allows you to detect the preamble and tag it such that the subsequent Tagged Stream to PDU block can convert the payload (and only the payload) to a Message PDU, which you can then print out with a Message Debug sink. The PDUs simply appear in the console window as you run your flowgraph.(I’m using the print input of the Message Debug block because I have ASCII data, but if you have binary data, you should use the print_pdu input instead.)

Note that you can also dump the message PDUs to a File Sink, which gives you a nice file containing only payload data, none of the preamble or inter-frame dead air. A couple lines of Python can read this file and extract each payload into a list, from which you can do all sorts of fun stuff.

Getting Started with SDR on Black Hills InfoSec Webcast

I’ll be on the Black Hills InfoSec webcast tomorrow talking about all the things you need to know to get started with SDR. You can register for the webcast at the link below:

https://register.gotowebinar.com/register/3587817882602530306

Please bring your questions on SDR hardware, software, installation issues or anything else you can think of. See you there!

Installing gnuradio with Lime, HackRF and UHD support

The LimeSDR Mini is a great combination of things: affordable, full-duplex and incredibly configurable. Until recently, though, it wasn’t the easiest thing to get running. Scanning the forums at MyriadRF (the folks who make the Lime products) shows that a number of people have been able to get the Mini working but also that a number have not had so much success.

I was a pre-production supporter of the CrowdSupply campaign and had my LimeSDR Mini delivered in March. At first it was rough going, but after numerous attempts, I’ve been able to get a repeatable installation flow that works on Ubuntu 16.04 and supports UHD and HackRF hardware as well (it may support BladeRF, but I don’t have the hardware to test it).

You can grab the install script from my GitHub at:
https://github.com/paulgclark/grc-install

The git bundle also contains a number of simple grc files to validate your installation versus each of the three hardware platforms. After installation, my advice is that you test things with:
./grc/audio_tone.grc
./grc/lime-test/fm_receiver_hardware_lime.grc
(make sure to tune to one of your local stations)

Next, if you’ve got a second SDR (and computer) you can use the GFSK transmit and receive flowgraphs to send simple digital data back and forth between them. You should be able to send and receive from any combination of the three SDR platforms, though you will likely need to adjust the squelch levels depending on the physical distance between your SDRs. If a HackRF is involved, you’ll also need to fine tune the receiver flowgraph to compensate for their frequency error.

One thing to note about this install flow: you get version 3.7.10 of gnuradio-companion, not the latest as you’d get with a PyBOMBS installation.

Hope this helps!

Addendum: This flow will work for Ubuntu 18.04, but you’ll need to go into the install script and tweak one line per the commented instructions. You’ll also need to adjust the device args for the hackrf transmit flowgraphs to “driver=hackrf,soapy=0” (but do NOT type a space between the comma and “soapy”). A bonus to using 18.04 is that you’ll get a slightly newer version of gnuradio companion (3.7.11).

Updated gnuradio Install Instructions

We’ve gotten some feedback recently from a number of our readers that the gnuradio installation process documented in our books (and on our books’ web site) has a few glitches. We knew that we’d need to update the instructions at some point, and the time had definitely come. If you’re planning on installing gnuradio any time soon, please see our updated instructions pdf.