Hackaday

Right now, I’m at Shmoocon, and it’s living up to all expectations. That’s a tall order — last year, the breakout talk was from [Travis Goodspeed] on his efforts to reverse engineer the firmware for a cheap Chinese radio. Four people in the room for that talk last year bought the radio on Amazon, and now there’s a legitimate open source project dedicated to building firmware and tools to support this radio.

Now that [Travis] has a few compatriots working on firmware for this radio, he has the same challenges as any other team. The project needs unit tests, and this isn’t easy to do when all the code is locked up inside a radio. Instead of setting up an entire development platform based around a cheap radio, [Travis] came up with a toolchain that’s unlike anything I’ve ever seen. Instead of reverse engineering the firmware for this radio, he’s simply emulating the ARM firmware on the desktop. Development is quick and easy, and he has the live demos to prove it.

The heart of the Tytera radio in question is an STM32F405. This is a pretty common part, and thanks to [Travis]’ work last year, he has all the firmware that ships on this radio. This doesn’t mean he has access to all the radio’s capabilities, though; there’s a black box in the code somewhere that translates .wav files to radio packets and back again. Open sourcing this would usually mean reverse engineering, but [Travis] had a better idea.

Instead of reverse engineering the entire radio, [Travis] is using QEMU to emulate an ARM microcontroller on his desktop, run the relevant code, and completely ignore any actual reverse engineering. Since this radio is already jailbroken and the community has a pretty good idea of where all the functions and subroutines are in the firmware, the most difficult part of pulling this trick off is setting up QEMU.

As a proof of concept, [Travis] downloaded raw AMBE packets from the radio to his laptop. These were then sent through the emulated radio, producing raw audio that was then converted into a .wav file. Effectively, a black box in this radio was emulated, which means [Travis] doesn’t need to know how the black box works.

All the code for this weird emulation / unit test, as well as everything the community has released for this radio is available on the GitHub. A lot of work has gone into the jailbreaking, reverse engineering, and emulation efforts here, making this radio somewhat ironically one of the most open radios you can buy.

Every once in a great while, a piece of radio gear catches the attention of a prolific hardware guru and is reverse engineered. A few years ago, it was the RTL-SDR, and since then, software defined radios became the next big thing. Last weekend at Shmoocon, [Travis Goodspeed] presented his reverse engineering of the Tytera MD380 digital handheld radio. The hack has since been published in PoC||GTFO 0x10 (56MB PDF, mirrored) with all the gory details that turn a $140 radio into the first hardware scanner for digital mobile radio.

The Tytera MD380 is a fairly basic radio with two main chips: an STM32F405 with a megabyte of Flash and 192k of RAM, and an HR C5000 baseband. The STM32 has both JTAG and a ROM bootloader, but both of these are protected by the Readout Device Protection (RDP). Getting around the RDP is the very definition of a jailbreak, and thanks to a few forgetful or lazy Chinese engineers, it is most certainly possible.

The STM32 in the radio implements a USB Device Firmware Upgrade (DFU), probably because of some example code from ST. Dumping the memory from the standard DFU protocol just repeated the same binary string, but with a little bit of coaxing and investigating the terrible Windows-only official client application, [Travis] was able to find non-standard DFU commands, write a custom DFU client, and read and write the ‘codeplug’, an SPI Flash chip that stores radio settings, frequencies, and talk groups.

Further efforts to dump all the firmware on the radio were a success, and with that began the actual reverse engineering of the radio. It runs an ARM port of MicroC/OS-II, a real-time embedded operating system. This OS is very well documented, with slightly more effort new functions and patches can be written.

In Digital Mobile Radio, audio is sent through either a public talk group or a private contact. The radio is usually set to only one talk group, and so it’s not really possible to listen in on other talk groups without changing settings. A patch for promiscuous mode – a mode that puts all talk groups through the speaker – is just setting one JNE in the firmware to a NOP.

The Tytera MD-830 ships with a terrible Windows app used for programming the radio — The Tytera MD-380 ships with a terrible Windows app used for programming the radio

With the help of [DD4CR] and [W7PCH], the entire radio has been reverse engineered with rewritten firmware that works with the official tools, the first attempts of scratch-built firmware built around FreeRTOS, and the beginnings of a very active development community for a $140 radio. [Travis] is looking for people who can add support for P25, D-Star, System Fusion, a proper scanner, or the ability to send and receive DMR frames over USB. All these things are possible, making this one of the most exciting radio hacks in recent memory.

Before [Travis] presented this hack at the Shmoocon fire talks, intuition guided me to look up this radio on Amazon. It was $140 with Prime, and the top vendor had 18 in stock. Immediately after the talk – 20 minutes later – the same vendor had 14 in stock. [Travis] sold four radios to members of the audience, and there weren’t that many people in attendance. Two hours later, the same vendor had four in stock. If you’re looking for the best hardware hack of the con, this is the one.