Winning The Interface War: Extracting Information From Electronic Devices With The SEC Xtractor

To overcome all of these problems, we decided to create a tool that provides connections to be wired with simple connection wires and ZIF sockets. That way, people that are able to read a simple circuit, can dump out every kind of memory chip without soldering (it must be removed from the target though). The tool, which was later named “SEC Xtractor”, started as a simple memory extraction and UART interface project.

Choosing the FT2232HQ chip that comes with the FT2232 mini-module was thoroughly-considered and the most natural choice. The very first prototype for dumping memory chips was born!

A new era

During the development of the SEC Xtractor platform, countless hours were spent browsing and shopping online for fitting adapters and parts that could be used for the prototype. A PCB was routed after successfully reading the first binaries from unsoldered memory chips. It only contained the FT2232 mini-module, which was considered the most useful tool to support voltage switching between 3.3V and 5.5V out of the box. The parallel header rows were connected with jumper wires according to the memory chip alignment.

This simple PCB unleashed the power of the mini-module, which was handy for nearly every project that had to do with embedded device pentesting. One project that came in was testing a medical device that had a NOR flash memory chip that contained the whole firmware. We used an extension PCB with a microcontroller that was easy to program to read out the content via the UART interface. It was a minimalist solution.

The biggest challenge that had to be mastered every time a hardware security assessment or research project was done, was to attach the wires. Not only did they look messy, but the connections were so unstable – that a simple touch during the reading would be fatal! Furthermore, a bit more expertise was necessary to perform this. The overall objective set by the SEC Xtractor solution was to have better flexibility for non-hardware experts that would just dump the firmware and keep on pentesting.

When all these PCBs were developed, another tool, called Hardsploit, came up.We soon uncovered it was a large breakout board with an FPGA. There was no doubt that a software engineer would have trouble modifying it easily because it looked to be too complex and not entirely open-source. The best choice would be something simple, a little more powerful than a small 8-bit microcontroller, programmable in C, but not too complex. In an ideal world, with ready to use adapters for different memory chips to overcome the need of wiring.

SEC Xtractor Version 1.0 – The First Generation

The extension board was equipped with an ATXmega128A1U controller an easy to program 8-bit microcontroller without a big framework of header files and a jungle of functions. It made sense to keep it and combine it with the FT2232 mini-module :) . To extend the range of target electronics, universal level shifters (TXS0108E-Q1) were added to all IOs. This includes the FT2232 and ATXmega128A1U pins.

To avoid the chaos of wires as seen in the picture above, we designed a pin header where NAND and NOR memory chips could be mounted. This pin header can be spotted on the picture in the left bottom corner. Because of the number of pins, adding a microcontroller sounded like a hacky solution at first, but after adding some functions from JTAGenum and other custom functions, the ATXmega became more and more useful for different purposes.

Worst case scenario, a wrong voltage level can destroy the target device and delay or thwart the whole security assessment. Therefore, three seven-segment displays were added to ensure the right voltage was constantly used for the right IOs. This two-sided layout can easily be reproduced, even for DIY etching, and comes with through-hole resistors that can be changed when other values are needed (e.g. to change the voltage limits of the adjustable power supply). This deliberate fact enables makers and hackers to use the hardware of the SEC Xtractor for tailored applications.

The first real application, that was initially programmed for the simple ATXmega breakout board on the previous picture, was the shell. It can be reached with 4M Baud via the first serial to the USB interface of the FT2232 mini-module. This was the highest (official) available frequency in the datasheet of the ATXmega but overclocking, which results in faster memory dumps, could increase it.

One noticeable fact is that the level shifters were used out of spec since the first hardware version. They are designed to operate on their A port between 1.4V and 3.6V and on their B port between 1.65V and 5.5V. Furthermore, the power supply of the A port must be less or equal to the B port, otherwise the level shifter will not work. Because of the additional ESD input protection and the higher voltage range, port B was chosen as interface to the world and port A as interface to the microcontroller. This usually means that voltages below the internal microcontroller power supply could not be used. But after experimenting different options we discovered that levels could also be shifted from the A port (with 3.3V) to the B port (with 2.1V). Conclusion, we invalidated the rule in the datasheet.

All these edge-cases were conducted with a lot of equipment during the many years  it took to develop the SEC Xtractor hardware. Our best friend during that time was an oscilloscope and a counter implementation on the SEC Xtractor (see figure below).

Past Targets

The tool was tested at the end of 2016 for all kinds of projects and was first mentioned during a blogpost in 2017. JTAG brute-forcing was tested with the old and new hardware to verify its correct operation. With the help of the SEC Xtractor, we then created an advisory regarding an oscilloscope. The UART port (Tx Rx GND) of the following picture was used to connect to the device and dump running processes and the firmware.

We mainly used the SEC Xtractor during a longer hardware security research project, conducted in 2018 and first presented it during Black Hat Asia in 2019. The outcome was a reverse engineered JTAG interface, dumped NOR flash memory and the ability to reprogram an industrial PLC from Siemens. The (red) next version of SEC Xtractor, namely version 1.20, was used for this project. Its internal power supply was decreased to 2.7V so that the level shifters could reach the 1.8V limit needed for the low voltage memory chips and microprocessors.

SEC Xtractor Version 1.31 – Black Edition

Version 1.31 comes with improvements like a boot button and additional labels three years after the initial hardware version. An open-source bootloader was used to program the device via USB. No external programmer is needed to reflash the ATXmega microcontroller. The black color for the main PCB and the NAND/NOR adapters were chosen because the launch was made during Black Hat Europe 2019 Arsenal.

This project is now live and contributions are encouraged! New designs with other microcontrollers were discussed internally and can be implemented thanks to the separated hardware abstraction layer in the firmware. The refactoring and fine-tuning of the shell and the overall structure, which makes separation possible, was done by Wolfgang Ettlinger. The UART scanner, another important part, was re-implemented by Steffen Robertz. He also restructured and extended the NAND/NOR chip functions.

One textbook use-case is NAND flash reading. A photo shows the assembly of typical memory chips inside the adapters: