His first steps were to search for the frequency which he found active at 390 MHz. He then moved on to analyzing the signal with Inspectrum, discovering the OOK modulation, then working his way towards the binary control strings. One thing that helped with his reverse engineering was the use of the 9-bit DIP switches on the remote that configure the security code that opens up a specific door as this allowed him to control the transmitted bits, and determine which bits were used for the security code. With this and a bit of GNU Radio code he was able to recreate the signal and transmit it with his HackRF.
Finally Maxwell wanted to see how vulnerable this door is to a brute force attack that simply transmits every possible security code. Through some calculations, he discovered that brute forcing every possible security code in the 9-bit search space would only take 104 minutes to open any garage using this opener.
Over on YouTube user kwon lee has uploaded a video demonstrating a replay attack against a parking barrier arm. The tools he uses are a HackRF and Portapack running the Havok firmware. A replay attack involves recording a control signal with the HackRF+Portapack, and then replaying it later with the transmit function of the HackRF. If no wireless security mechanism like rolling-codes are used, simply replaying the signal will result in the transmission being accepted by the controller receiver.
As he has access to the remote control he records the transmission that is sent when the open button is pressed on the remote. Later once outside he shows how transmitting with the HackRF+Portapack results in the barrier arm opening.
This reminds us of a previous post where we noted how a HackRF was used to jam a garage door keyfob to prevent people from leaving in the TV show "Mr. Robot".
Tesla vehicles have a feature where they can copy and mimic a garage door remote via a built in transmitter on the car itself. This frees you from having to carry around a garage door key fob, and you can simply open your garage door by pressing a button on the car's LCD screen.
However, some people have reportedly been having a little trouble with this feature as in some cases the garage door would begin opening, and then suddenly stop opening as if the keyfob button had been pressed twice.
Over on YouTube CWNE88 decided to investigate this problem using his HackRF and GNU Radio. From a simple waterfall he was able to determine that the Tesla actually transmits the mimic'd garage door signal for a full two seconds.
As a keypress from the original keyfob would typically result in a much shorter transmission, CWNE88 believes that the long two second transmission could in some cases be seen as two transmissions by the garage door, resulting in an open, and then close command being detected.