Most modern vehicles use some form of rolling code security on their wireless keyfobs to prevent unauthorized replay attacks. When the car owner presses a button on the keyfob, a unique rolling code is sent to the car. If it matches one of the codes currently stored in the car, the car will unlock and then invalidate that code so it can never be used again, thus preventing a replay attack. On the next press the keyfob sends a new code. In most designs when a code is used up, a new code is added to the list of valid codes via a random number generator based on a secure algorithm only known (presumably) to the engineers.
Essentially Tom found that instead of producing a randomly generated rolling code, the Subaru keyfob simply increments the rolling code number each time. This allows an attacker to perform a second key press simply recording an initial real key press, decoding the packet, increasing the decoded rolling code by one, then re-transmitting. It also means that the attacker could continually raise the rolling code value on the car himself, which would eventually make the real keyfob useless as the codes on the keyfob would be outdated and no longer match the same number range as the car.
The entire exploit was found on a super low budget. Tom used only an RTL-SDR and Raspberry Pi. The receive is obviously handled by the RTL-SDR, but the transmit side is handled by RPiTX which is software that allows the Raspberry Pi to transmit RF signals directly from a GPIO pin without the need for any additional transmitting hardware. Tom writes that the exploit probably affects the 2006 Subaru Baja, 2005 - 2010 Subaru Forester, 2004 - 2011 Subaru Impreza, 2005 - 2010 Subaru Legacy and the 2005 - 2010 Subaru Outback. Tom also writes that various dealers and spokes people have contacted him stating that the exploit probably only affects US models. If you have one of the affected models and are worried the only way to stay safe is to simply not use wireless entry on the keyfob, at least until/if Subaru fixes the issue with a recall. Although so far no statement from Subaru has been released.
Tom has also uploaded a demonstration video to YouTube which is shown below.
The PandwaRF (formerly known as GollumRF) is an RF analysis transceiver tool that can be very useful for investigating ISM band devices that communicate with digitally modulated RF signals. It can be used for applications such as performing replay attacks, brute force attacks, and other analysis. The RX/TX frequency range of the device is from 300 – 928 MHz, with a transmit power of up to +10 dBm.
The PandwaRF is based on the CC1111 chip which is the same chip used in devices like the Yard Stick One from Great Scott Gadgets (creators of the HackRF). Compared to the YS1 the PandwaRF is essentially the same, but designed to be much more portable, with a built in battery and an Android app that you connect to via Bluetooth. This makes it very useful for taking out in the field as no laptop is required to use it, just a phone or tablet. The PandwaRF can be used just like a YardstickOne when plugged into a PC however.
We should also clarify that CC1111 based devices like the PandwaRF and YS1 are not classed as SDRs. Rather they are RF transceiver chips that can demodulate, decode and transmit a fixed set of digital modulation schemes, such as OOK/ASK, 2-FSK, 4-FSK, GFSK, and MSK. While these devices are not able to receive or transmit any arbitrary signal like an SDR, they make reverse engineering, analysis, replay attacks, brute force attacks etc much simpler for common modulation schemes compared to using an SDR for the same purpose.
Early on in the year PandwaRF sent us a sample of their device for review. Unfortunately during that time their Android software was extremely buggy and we were simply unable to use the device properly. Others reported similar troubles on forums and blog comments. However fast forward to today and it now seems that the Android software is stable and functioning properly.
We first tested the PandwaRF on a simple task which was a replay attack. The goal was to record the signal of a cheap wireless RF alarm, and see if we could replay it back. The wireless alarm is controlled with a keyfob.
First we used the Spectrum Analyzer tool in the PandwaRF app to try and get the frequency of the keyfob. The Spectrum Analyzer tool allows you to see about 1.2 MHz of bandwidth. We assumed the signal would be around 433 MHz. After pressing the button a few times the peak showed up at about 433.9 MHz on the spectrum analyzer. The refresh rate of the spectrum analyzer is quite low, so if the signal is not continuous it’s possible to miss the signal, which is we why we had to try several presses before the signal showed. A standard SDR like an RTL-SDR might be better for this initial frequency searching. We confirmed the frequency to be at 433.893 MHz on an RTL-SDR blog V3.
Next we switched to the RX/TX tool. Here you can enter the frequency of interest and set the expected modulation. We know that this device is ASK/OOK modulated, so we chose this setting. You also need to set the data rate. If you don’t know this value then the app has a data rate measuring tool. So we just pressed on the Measure button, and then pressed a button on the remote until it converged to a data rate of 5,121.
Next you need to set the ‘desired payload’. This is how many bytes long the packet is and determines how long the capture is. As we were unsure we simply set it to 250 bytes to ensure that a longer capture was taken. The PandwaRF will keep on receiving until it receives the desired payload of 250 bytes or is stopped manually. Setting it longer allows us to capture a longer signal, and ensure that the replayed signal is received. For this alarm device it is okay if the same signal is played multiple times in a short time frame.
The final setting is the RX Frame length. This determines how many bytes will be captured before transferring the data to Android. So for example, if you set the desired payload to 100 Bytes, and the RX Frame length to 52 bytes, then in total you will capture 104 Bytes of data. The PandwaRF can only transfer in 14, 33, 52, 71 or 90 bytes, so select one that is closest to a multiple of your desired payload.
Finally we pressed on ‘Sniff’ and pressed the ‘bell’ button on the remote. The PandwaRF detected the signal and recorded the data. Now pressing Xmit replays the signal successfully causing the alarm bell to sound.
Brute Force Attack
The PandwaRF can also be used as a brute forcing tool. With cheap alarms the alarm code is relatively short, so can be brute forced in a matter of minutes. The PandwaRF already had a preset mode for our cheap Forecum door alarm, so we simply selected this mode and started the brute force. It gave an estimated brute force time of 28 minutes, which is the time it takes to run through every possible alarm code.
The PandwaRF app currently supports the Idk and PT2262 chipsets, as well as some models of DIO, Extel and Forecum house alarms. If the device that you want to brute force is not yet in their database, then you’ll probably need to do some analysis first on the PC with an SDR. Software like Universal Radio Hacker and DSpectrumGUI are good tools for this. Once you know the structure of the data, then you can program PandwaRF to perform the brute force attack.
Note that their newer ‘PandwaRF Rogue’ product is supposed to be significantly faster at brute forcing. For example the Android software gives us a estimated duration of 28 minutes with the standard PandwaRF, and only 3 minutes with the Rogue.
The Rogue is also able to brute force 32 bit codewords with zero delay in between transmissions. The standard PandwaRF has a minimum delay of 100 ms which can really slow things down. It also allows for function mask bit skipping, enable more brute force patterns and can split the brute force attempt into several steps. Also as we’ve seen from their videos the Rogue has more pre-set commercial devices built into its app.
So if brute forcing is your main use for the PandwaRF then it seems to make sense to get the Rogue. Unfortunately the Rogue is significantly more costly, coming in at 990 euros, vs 145 euros for the standard PandwaRF. Of course you could still use the standard PandwaRF on a PC with tools like rfcat to perform a faster brute force attack as well, just like you would with a YardstickOne.
The code runs on the Android device and not on the PandwaRF, so each RF command generates a bluetooth transfer which can be quite slow. They write this is why they have created a specific brute force implementation in the app, so that they can run their native brute force code on the PandwaRF itself, which is must faster than transferring the RF command for every brute force step.
Overall the PandwaRF is a very handy tool for doing replay and brute force attacks while in the field. It can also be converted back into a PC based CC1111 device, like a Yardstick One simply by plugging it into a computer with a USB cable so you’re not missing out on that functionality either.
Compared to the Yardstick One the cost is a bit more, with the Yardstick One costing $99 USD at most outlets, and the PandwaRF costing 145 Euros (~$173 USD). So it is probably only really worth it if you are doing field testing.
That said, now that the PandwaRF software seems stable it is an excellent tool for investigating wireless devices in a simpler way compared to with an SDR. An SDR is still much more powerful, but tools like this simplify the process significantly. The best set of tools for reverse engineering would be a SDR combined with a device like this.
In the future it looks like they plan to implement new features such as De Bruijn (OpenSesame) attack’s and rolling code attacks and we look forward to testing those out.
Over on his YouTube channel Tysonpower (aka Manuel) has uploaded a video showing how he was able to use his PlutoSDR to perform some simple replay attacks that open his garage and car doors. To do this he records the signal from the wireless keyfobs with the PlutoSDR, and then uses a GNU Radio program to replay that signal again at a later time. From the tests he concludes that the PlutoSDR can be a great cheaper alternative to a HackRF, with the PlutoSDR coming in at $100 vs $300 for the HackRF.
To get around the rolling code security on his car he records the keyfob with the PlutoSDR while it’s out of the wireless range of his car, so that the rolling code will not be invalidated. Then later closer to the car the PlutoSDR is used to replay the car keyfob signal which opens the door.
Note that Tysonpower’s video is narrated in German, but English subtitles are available through the YouTube interface.
Over on YouTube user Keld Norman has uploaded a video showing how he uses an RTL-SDR with gr-gsm and a Python script to create a simple IMSI catcher. IMSI stands for International mobile subscriber identity and is a unique number that identifies a cell phone SIM card in GSM (2G) mobile phone systems. For security IMSI numbers are usually only transmitted when a connection to a new cell tower is made. More advanced IMSI-catchers used by governmental agencies use a fake cell tower signal to force the IMSI to always be revealed. This way they can track the location of mobile phones as well as other data like who or when you are calling.
In the video Keld uses a Python script called IMSI-Catcher. This script displays the detected IMSI numbers, country, and mobile carrier on a text display. The video description shows how to install GR-GSM and the IMSI-Catcher script on Ubuntu.
With an RTL-SDR dongle, Raspberry Pi, piece of wire and literally no other hardware it is possible to perform replay attacks on simple digital signals like those used in 433 MHz ISM band devices. This can be used for example to control wireless home automation devices like alarms and switches.
In this tutorial we will show you how to perform a simple capture and replay using an RTL-SDR and RPiTX. With this method there is no need to analyze the signal, extract the data and replay using a 433 MHz transmitter. RPiTX can replay the recorded signal directly without further reverse engineering just like if you were using a TX capable SDR like a HackRF to record and TX an IQ file.
Note that we’ve only tested this replay attack with simple OOK 433 MHz devices. Devices with more complex modulation schemes may not work with this method. But the vast majority of 433 MHz ISM band devices are using simple modulation schemes that will work. Also replay attacks will not work on things like car keys, and most garage door openers as those have rolling code security.
A video demo is shown below:
RPiTX is open source software which allows you to turn your Raspberry Pi into a general purpose transmitter for any frequency between 5 kHz to 500 MHz. It works by using square waves to modulate a signal on the GPIO pins of the Pi. If controlled in just the right way, FM/AM/SSB or other modulations can be created. By attaching a simple wire antenna to the GPIO pin these signals become RF signals transmitted into the air.
Of course this creates an extremely noisy output which has a significant number of harmonics. So to be legal and safe you must always use bandpass filtering. Harmonics could interfere with important life critical systems (e.g. police/EMS radio, aircraft transponders etc).
For testing, a short wire antenna shouldn’t radiate much further than a few meters past the room you’re in, so in this case you should be fine without a filter. But if you ever connect up to an outdoor antenna or amplify the signal then you absolutely must use adequate filtering, or you could find yourself in huge trouble with the law. Currently there are no commercially made 433 MHz filters for RPiTX available that we know of, so you would need to make your own. Also remember that you are still only allowed to transmit in bands that you are licensed to which for most people will be the ISM bands.
Back in May of this year the DailyMail ran an article discussing how the HackRF by Great Scott Gadgets could be used to break into cars. The DailyMail is a British tabloid magazine well known for its low credibility and alarmist articles. This week they ran a new article about Great Scott Gadgets other product, the Yard Stick One. In the article they discuss how the £109 Yard Stick One tool can be used to disable wireless burglar alarms. The YARD Stick One is not an SDR, but rather a computer controlled radio which can be used to transmit and receive wireless digital signals below 1 GHz. It is useful for wireless security research and reverse engineering digital signals in a way that is a bit easier than with using an SDR like the HackRF.
In the experiment performed in the article they use the YARD Stick one to jam a wireless home alarm for a few seconds allowing entry to the property without setting off the alarm. All in all the article is a good advert for the YARD Stick One, and does do a decent job at drawing attention to the lack of security provided by many wireless security devices.
These days it’s quite easy to share your ADS-B reception on the internet with giant worldwide aggregation sites like flightaware.com and flightradar24.com. These sites aggregate received ADS-B plane location data received by RTL-SDR users from all around the world and display it all together on a web based map.
However, what if you don’t want to share your data on these sites but still want to share it over the internet with friends or others without directly revealing your IP address? Some of the team at beame.io have uploaded a post that shows how to use their beame.io service to securely share your ADS-B reception over the internet. Beame.io appears to be a service that can be used to expose local network applications to the internet via secure HTTPS tunneling. Essentially this can allow someone to connect to a service on your PC (e.g. ADS-B mapping), without you revealing your public IP address and therefore exposing your PC to hacking.
On their post they show how to set up the RTL-SDR compatible dump1090 ADS-B decoder on a Raspberry Pi, and then connect it to their beame-instal-ssl service.
It’s been known for a while now that it is possible to break into cars using simple wireless attacks that involve jamming of the car keyfob frequency. Sammy Kamkars “rolljam” is one such example that can be built with a cheap Arduino and RF transceiver chip. One way to secure yourself against wireless attacks like this is to run a jammer detector.
A jammer detector is quite simple in theory – just continuously measure the signal strength at the car keyfob frequency and notify the user if a strong continuous signal is detected. Over on his blog author mikeh69 has posted about his work in creating a wireless jammer detector out of a Raspberry Pi and RTL-SDR dongle. He uses a Python script and some C code that he developed to create a tool that displays the signal strength on an onscreen bar graph and also conveys signal strength information via audio tones. He writes that with a pair of earphones and battery pack you can use the system while walking around searching for the source of a jammer.
Mikeh69’s post goes into further detail about installing the software and required dependencies. He also writes that in the future he wants to experiment with creating large area surveys by logging signal strength data against GPS locations to generate a heatmap. If you are interested in that idea, then it is similar to Tim Haven’s driveby noise detector system which also used RTL-SDR dongles, or the heatmap feature in RTLSDR Scanner.