The key takeaways are that ASK modulation is simple, but prone to interference. FSK is less prone to interference, but requires more bandwidth. LoRa is good for receiver sensitivity and interference immunity, but comes at the expense of bandwidth efficiency. In addition LoRa modulation is patented, resulting in higher hardware costs.
Foo-Manroot first explains how easily capture and replay a signal with the HackRF. If the signal is simple without any security like rolling codes then a simple replay attack like this will allow the HackRF to control the device quite easily. In the next section he goes on to explain how to actually analyze and synthesize the packets yourself using Python and GNU Radio. Finally he also shows that a brute force attack can be applied once you know how to synthesize the signal. Brute forcing runs over every possible packet combination in a short time and this can be pretty fast for simple protocols like those used in wireless remote controls. His post also includes all the GNU Radio files required so it is easy for someone to replicate his work easily.
If you are interested in controlling simple OOK devices like a wireless powerplug with replay attacks then we have a tutorial for doing this with a simple RTL-SDR and Raspberry Pi running RpiTX which might be useful for those who don't have a HackRF.
Erhard E. has been experimenting with capturing, analyzing, reverse engineering and then transmitting new ASK/OOK signals with his RTL-SDR and Raspberry Pi running RPiTX. Erhard has written a very informative guide/tutorial (pdf) that explains how he did it for wireless doorbell and for remote control toy cars. RPiTX is software for the Raspberry Pi which allows it to transmit almost any signal via modulation of a GPIO pin. RPiTX related posts have been featured on this blog several times in the past.
First Erhard records a copy of the doorbell signal using his RTL-SDR and then views the waveform in Audacity. He then writes that you’ll need to find the waveform characteristics either manually using Audacity, or by using the rtl_433 decoder. In the tutorial he uses rtl_433 which automatically gives his the pulse width, gap width and pulse period.
Next in order to actually generate the signal using RPiTX he uses the waveform characteristics that he found out and manually creates a .ft hex file that describes the signal to be generated. Then using using the rpitx command, the .ft file can be transmitted.
Later in the tutorial he also shows how he performed the same reverse engineering process with a cheap RC car toy (forward/reverse commands only), which uses OOK encoding on the wireless controller.
Over on his YouTube channel user Gareth has uploaded a video that shows a full tutorial on quickly decoding an On Off Keyed (OOK) signal with a HackRF (or RTL-SDR) and the Inspectrum software. Once decoded he then shows how to use a Yardstick One to duplicate the signal.
Inspectrum is a Linux based program that allows you to easily determine various parameters of a digital modulated signal by positioning an overlay over the waveform of a signal recorded with an SDR. Basically Gareth’s process is to first extract signal level values using Inspectrum, then secondly use a simple Python program to turn these values into binary bits, which gives him the data packet. He is then finally able to write another quick Python program to interface with the Yardstick One and retransmit the string.
The Yardstick One is a multipurpose radio (not a SDR) for transmitting modulated signals like OOK.
My quickest and easiest method for OOK signal decoding & replication in 2016
By first looking at the old FCC label on the keypad, Veghead discovered that the device transmitted between 319 MHz and 340 MHz. He then used his RTL-SDR dongle to take a recording of the transmitted signals, before opening them up in Audacity – a free audio processing program.
By analyzing the waveform in Audacity, Veghead discovered that the alarm panel uses simple ON-OFF Keying (OOK) modulation. Although the frequency of the signal drifted a lot (probably due to aged components), he was able to write a decoder that he called cletus which converts the recorded complex I/Q signal into a real signal and then uses a state machine to turn the waveform into 1’s and 0’s. Finally the program then outputs the correct button that was pressed to the terminal.
Wireless wall outlets are electrical outlets that can be turned on or off by a wireless remote. Fabien is an experimenter who was looking for a way to control the power of his home devices from a remote location using HTTP. He thought of building his own from scratch, but quickly realized that the device would need to be certified for insurance purposes. Instead he bought a cheap commercially made certified wireless wall outlet and reverse engineered the protocol using an RTL-SDR.
To do that he used the existing OOK-Decoder software available on GitHub. From the analysis provided by OOK-Decoder, Fabien was able to successfully reimplement the transmission using an AVR microcontroller and 433 MHz transceiver circuit from Sparkfun.