Tagged: reverse engineering

Reviewing the PandwaRF: CC1111 Based Transceiver for RF Security Analysis

The PandwaRF

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.

Replay Attack

PandwaRF Spectrum Analyzer Tool
PandwaRF Spectrum Analyzer Tool

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.

PandwaRF RX/TX Replay Attack Screen
PandwaRF RX/TX Replay Attack Screen

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.

Replayed and Original Signal received with an RTL-SDR
Replayed and Original Signal received with an RTL-SDR

Brute Force Attack

Brute force settings
Brute force settings

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.

More advanced brute force settings
More advanced brute force settings

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.

PandwaRF Brute Force attack as seen by an RTL-SDR
PandwaRF Brute Force attack as seen by an RTL-SDR


Javascript in PandwaRF

If you need more powerful analysis or TX capabilities, then the PandwaRF can be controlled in Javascript code. For example, you might have already reverse engineered a device, and simply require the PandwaRF to transmit the correct code to replace a remote control. You could also create a jammer with this.

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.

If you want more information about the PandwaRF you can visit their site, or check out their Wiki, or have a look at the demo videos on their YouTube page.

Disclaimer: The PandwaRF was provided to us for free in exchange for an honest review.

YouTube Talk: Introduction to DSpectrum for Reverse Engineering Signals

Over on YouTube a talk from the author of DSpectrum has been uploaded from his talk during the 13th Cyberspectrum Melbourne meetup. In his talk he goes through the full process of reverse engineering a wireless alarm system in DSpectrumGUI. DSpectrum is a reverse engineering tool that aims to make it trivial to demodulate digital RF transmissions using data captured from SDRs like an RTL-SDR or HackRF.

In the video he shows how to create a project, import a capture and create an overlay on Inspectrum and bring the waveform back into DSpectrum. DSpectrum was then able to automatically detect that the encoding used was PWM and convert it into a bit string. Then by importing multiple captures from various buttons on the alarm he shows how easy it is to see the differences in the bit strings from within DSpectrum. From these differences he uses DSpectrum to help identify what the function of each byte of the bitstring is. Finally he shows how to perform a replay attack with RFcat or similar hardware using the data gathered.

This is a really good talk to watch if you’re interested in getting started with reverse engineering simple digital signals, like those from ISM band devices.

Signal Reverse Engineering Tool DSpectrum Upgraded to DSpectrumGUI

DSpectrum is a reverse engineering tool that aims to make it trivial to demodulate digital RF transmissions. It is built on top of the Inspectrum tool which makes it easy to visualize and manually turn a captured digital RF waveform into a string of bits for later analysis by providing a draggable visual overlay that helps with determining various digital signal properties. DSpectrum added features to Inspectrum like automatically converting the waveform into a binary string with thresholding. RF .wav files for these tools can be captured by any capable radio, such as an RTL-SDR or HackRF.

DSpectrum has recently been depreciated in favor of the new DSpectrumGUI which builds on the success of DSpectrum by providing a full interactive GUI that helps with the reverse engineering workflow. Some interesting new features include things like automatic analysis of the binary to determine the modulation and encoding types, the ability to submit/download reverse engineering worksheet templates to/from the community and binary generation for transmitting with a RFCat.

A similar tool is Universal Radio Hacker.


Reverse Engineering and Controlling an RC Toy Tank with a HackRF and GNU Radio

Last year during a Russian wireless ‘capture the flag’ (CTF) competition one of the goals was to reverse engineer a remote controlled toy tank, and then to control it with a HackRF. One of the Russian CTF teams has posted a thorough write up on the reverse engineering process that was used on the toy tank (the link is in Russian, but Google Translate works okay).

The write up first shows the reception of the signal from the wireless controller, and then moves on to show how to receive it in GNU Radio and obtain a time domain graph of the digital signal. From the pulses it is simple to visually work out the binary string. Next an instruction decoder is created in GNU Radio which automatically obtains the binary string from the signal directly. Then once the codes for back, forward, left and right were obtained it was possible to write another GNU Radio program to transmit these codes to the RC toy tank from the HackRF.

HackRF used to control an RC toy tank
HackRF used to control an RC toy tank

Reverse Engineering Linear DX Wireless Door Locks

Employees at the network data security company Duo recently had their interest piqued when they discovered that their office’s keycard based door system had a wireless remote which was used by reception to unlock and lock the door. The device was a DX model magnetic lock created by Linear.

After noting down the FCC ID printed on the device, they determined that the operating frequency was 315 MHz. They discovered from the documentation that each wireless DX device is encoded with a unique code that is precoded at the factory. Only remotes with the correct code programmed in can open the door.

The first attack they tried was a simple replay attack. They used a HackRF to record the signal, and then play it back again. This worked perfectly first time.

Next they decided to take this further and reverse engineer the protocol and see if a brute force attack could be applied. By doing some logic analysis on the circuit, they were able to figure out how to iterate over the entire key space. It turns out that the lock can be brute forced in at most 14.5 hours, or 7.25 hours on average.

The Linear DX Wireless Door Lock
The Linear DX Wireless Door Lock

Reverse Engineering Signals with the Universal Radio Hacker Software

Thanks to RTL-SDR.com reader M Kizan who notified us about a Python based digital signal reverse engineering software program called ‘Universal Radio Hacker’ which is developed by Johannes Pohl. The software supports hardware interfaces for SDRs such as the RTL-SDR and HackRF and can be run on Windows, MacOS and Linux.

The Universal Radio Hacker is a software for investigating unknown wireless protocols. Features include

  • hardware interfaces for common Software Defined Radios
  • easy demodulation of signals
  • assigning participants to keep overview of your data
  • customizable decodings to crack even sophisticated
  • encodings like CC1101 data whitening
  • assign labels to reveal the logic of the protocol
  • fuzzing component to find security leaks
  • modulation support to inject the data back into the system

Inspectrum and Waveconverter are two similar programs for analyzing digital signals, however Universal Radio Hacker seems to be the most advanced.

Johannes has also uploaded four tutorial videos to YouTube which show the software in action. In the videos he uses Universal Radio Hacker to reverse engineer a wirelessly controlled power socket, and then in the last video he uses the software to transmit the reverse engineered signals via a HackRF.

Reverse Engineering Honeywell 345 MHz Home Automation Sensors with an RTL-SDR

OpenHAB is an open source home automation software program which is designed to interface and manage all the various sensors and systems in an automated house. One problem however, is that many wireless sensors and actuators utilize a proprietary communications protocol that is not supported by OpenHAB.

In his home, Dan Englender had several Honeywell 5800 series 345 MHz wireless security door sensors, all of which interface using a proprietary protocol that is not yet implemented in OpenHAB. In order to get around this, Dan decided to reverse engineer the protocol and implement a decoder into OpenHAB himself. 

Dan’s four part write up covers the RF capture & demodulation, protocol reverse engineering and implementation into OpenHAB. First he looked up the frequency and bandwidth of the signal via the FCC filing information on fcc.io. Then he captured some packets from a door sensor using his RTL-SDR and GNU Radio, and then wrote a short Python program to decode the protocol and transmit the door open/closed information to OpenHAB. In the future he hopes to optimize the decoder so that it can comfortably run on a Raspberry Pi as the GNU Radio script uses quite a bit of computing power.

The final project is called decode345 and the code is available over on his GitHub.

Honeywell 345 MHz Door Sensor
Honeywell 345 MHz Door Sensor
Custom Door Sensor Status in OpenHAB
Custom Door Sensor Status in OpenHAB
[Also seen on Hackaday]


Hacking a Danfoss Wireless Thermostat with an RTL-SDR

Over on his blog Andy writes how he wanted a smart way to control his central heating system with a Raspberry Pi and Arduino microcontroller. He discovered that if he could reverse engineer his existing wireless thermostat then he would have an easy way to control the boiler in his house and with that a smart controller could be made. By reverse engineering the thermostat he also avoids the need to rig up his own control system.

The existing thermostat wireless receiver is a Danfoss RX2. In order to reverse engineer the protocol Andy opened up an older that one he had and saw that it used an Infineon TDA5210 RF receiver chip. Armed with this part number he was able to look up the datasheet and determine the operating frequency. Then by using an RTL-SDR he captured some packets while pressing buttons on the thermostat transmitter and piped the audio file into audacity, where he was able to clearly see the digital waveform.

Andy then wrote a Python program using the ‘wave’ library, which allowed him to easily read binary values for a .wav file. With his code he was able to extract the data from the signal and determine the preamble, sync word, thermostat ID and the instruction code (on/off/learn).

In a future post Andy hopes to show us how he’ll use an RF69 module with an Arduino to actually control the thermostat using the reverse engineered packet knowledge.

Danfoss Wireless Thermostat and a Received Binary Waveform in Audacity
Danfoss Wireless Thermostat and a Received Binary Waveform in Audacity