Shmoocon: Delightful Doppler Direction Finding With Software Defined Radio

When it comes to finding what direction a radio signal is coming from, the best and cheapest way to accomplish the task is usually a Yagi and getting dizzy. There are other methods, and at Shmoocon this last weekend, [Michael Ossmann] and [Schuyler St. Leger] demonstrated pseudo-doppler direction finding using cheap, off-the-shelf software defined radio hardware.

The hardware for this build is, of course, the HackRF, but this pseudo-doppler requires antenna switching. That means length-matched antennas, and switching antennas without interrupts or other CPU delays. This required an add-on board for the HackRF dubbed the Opera Cake. This board is effectively an eight-input antenna switcher using the state configurable timer found in the LPC43xx found on the HackRF.

The key technique for pseudo-doppler is basically switching between an array of antennas mounted in a circle. By switching through these antennas very, very quickly — on the order of hundreds of thousands of times per second — you can measure the Doppler shift of a transmitter.

However, teasing out a distinct signal from a bunch of antennas virtually whizzing about isn’t exactly easy. If you look at what the HackRF an Opera Cake receive on a waterfall display, you’ll find a big peak around where you expect, and copies of that signal trailing off, separated by whatever your antenna switching frequency is. This was initially a problem for [Schuyler] and [Ossmann]’s experiments. Spinning the antennas at 20 kHz meant there was only 20 kHz difference in these copies, resulting in a mess that can’t be decoded. The solution was to virtually spin these antennas much faster, resulting in more separation, and a clean signal.

There are significant challenges when it comes to finding the direction of modern radio targets. Internet of Things things sometimes have very short packet duration, modulation interferes with antenna rotation, and packet detection must maintain the phase. That said, is this technique actually able to find the direction of IoT garbage devices? Yes, the demo on stage was simply finding the direction of one of the wireless microphones for the talk. It mostly worked, but the guys have some ideas for the future that would make this technique work a little better. They’re going to try phase demodulation instead of only frequency-based demodulation. They’re also going to try asymmetric antenna arrays and pseudorandom antenna switching. With any luck, this is going to become an easy and cheap way to do pseudo-doppler direction finding, all enabled by a few dollars in hardware and a laser-cut jig to hold a few antennas.

Hackaday Links: January 7, 2018

Whelp, Spectre and Meltdown are the tech news du jour right now, and everyone is wondering: what is the effect of this problem on real hardware in real server rooms? Epic Games patched their machines and found something shocking. The CPU utilization for one of their online services increased about 100%. We don’t know what this server is doing, or what this process is, but the Spectre and Meltdown patches will increase CPU load depending on the actual code running. This is bad for Epic — they now have to buy an entirely new server farm. This is doubly bad for Intel, and there is speculation of a class action suit floating around the darker corners of the Interwebs.

It is with a heavy heart that I must report the passing of John Young, the only person to have commanded four different classes of spacecraft (five if you include the lunar rover), including the first launch of the Space Shuttle. He was, simply, the most badass astronaut to ever live. Need proof of that? His heart rate during the launch of a Saturn V was seventy.

By the time this post is published, you’ll have less than twenty-four hours to submit your project to the Coin Cell Challenge. Get to it!

A short reminder that Shmoocon is a mere two weeks away. What is Shmoocon? A totally chill cyber/sec/hacker con at the Washington D.C. Hilton (yes, where Reagan was shot). We’ll be there, and we’re looking for some like-minded Hackaday peeps to chill out with. Want a meetup? Reply in the comments.

A few years ago, the ESP8266 appeared out of the blue in a few Chinese reseller’s web shops, and everything has been gravy since. Now there’s a new magic do-everything chip appearing on AliExpress and Taobao. It’s the RDA5981, a chip with an ARM Cortex M4 core, 32Mbit of Flash, 192k or user RAM, b/g/n WiFi, I2S, and enough peripherals to be useful. Given the support for a MIC, line in, MP3, WAV, WMA and AAC, it appears this is an all-in-one chip designed for Bluetooth speakers or some other audio application. You can find modules on Alibaba and a few breakout boards on Taobao.

According to my sources (the press releases that somehow slipped through the ‘CES’ filter on my email), the world’s fastest, smallest, biggest, least expensive, and newest drone is set to be unveiled at CES in Vegas this week.

Shmoocon 2017: Dig Out Your Old Brick Phone

The 90s were a wonderful time for portable communications devices. Cell phones had mass, real buttons, and thick batteries – everything you want in next year’s flagship phone. Unfortunately, Zach Morris’ phone hasn’t been able to find a tower for the last decade, but that doesn’t mean these phones are dead. This weekend at Shmoocon, [Brandon Creighton] brought these phones back to life. The Motorola DynaTAC lives again.

[Brandon] has a history of building ad-hoc cell phone networks. A few years ago, he was part of Ninja Tel, the group that set up their own cell phone network at DEF CON. That was a GSM network, and brickphones are so much cooler, so for the last few months he’s set his sights on building out a 1G network. All the code is up on GitHub, and the hardware requirements for building a 1G tower are pretty light; you can roll your own 1G network for about $400.

The first step in building a 1G network, properly referred to as an AMPS network, is simply reading the documentation. The entire spec is only 136 pages, it’s simple enough for a single person to wrap their head around, and the concept of a ‘call’ really doesn’t exist. AMPS looks more like a trunking system, and the voice channels are just FM. All of this info was translated into GNU Radio blocks, and [Brandon] could place a call to an old Motorola flip phone.

As far as hardware is concerned, AMPS is pretty lightweight when compared to the capabilities of modern SDR hardware. The live demo setup used an Ettus Research USRP N210, but this is overkill. These phones operate around 824-849 MHz with minimal bandwidth, so a base station could easily be assembled from a single HackRF and an RTL-SDR dongle.

Yes, the phones are old, but there is one great bonus concerning AMPS. Nobody is really using these frequencies anymore in the US. That’s not to say building your own unlicensed 1G tower in the US is legally permissible, but if nobody reports you, you can probably get away with it.

Shmoocon 2017: A Simple Tool For Reverse Engineering RF

Anyone can hack a radio, but that doesn’t mean it’s easy: there’s a lot of mechanics that go into formatting a signal before you can decode the ones and zeros.

At his Shmoocon talk, [Paul Clark] introduced a great new tool for RF Reverse Engineering. It’s called WaveConverter, and it is possibly the single most interesting tool we’ve seen in radio in a long time.

If you wanted to hack an RF system — read the data from a tire pressure monitor, a car’s key fob, a garage door opener, or a signal from a home security system’s sensor — you’ll be doing the same thing for each attack. The first is to capture the signal, probably with a software defined radio. Take this data into GNU Radio, and you’ll have to figure out the modulation, the framing, the encoding, extract the data, and finally figure out what the ones and zeros mean. Only that last part, figuring out what the ones and zeros actually do, is the real hack. Everything before that is just a highly advanced form of data entry and manipulation.

[Paul]’s WaveConverter is the tool built for this data manipulation. Take WaveConverter, input an IQ file of the relevant radio sample you’d like to reverse engineer, and you have all the tools to turn a radio signal into ones and zeros at your disposal. Everything from determining the preamble of a signal, figuring out the encoding, to determining CRC checksums is right there.

All of this is great for reverse engineering a single radio protocol, but it gets even better. Once you’re able to decode a signal in WaveConverter, it’s set up to decode every other signal from that device. You can save your settings, too, which means this might be the beginnings of an open source library of protocol analyzers. If someone on the Internet has already decoded the signals from the keyfob of a 1995 Ford Taurus, they could share those settings to allow you to decode the same keyfob. This is the very beginnings of something very, very cool.

The Github repo for WaveConverter includes a few sample IQ files, and you can try it out for yourself right now. [Paul] admits there are a few problems with the app, but most of those are UI changes he has in mind. If you know your way around programming GUIs, [Paul] would appreciate your input.

Shmoocon 2017: So You Want To Hack RF

Far too much stuff is wireless these days. Home security systems have dozens of radios for door and window sensors, thermostats aren’t just a wire to the furnace anymore, and we are annoyed when we can’t start our cars from across a parking lot. This is a golden era for anyone who wants to hack RF. This year at Shmoocon, [Marc Newlin] and [Matt Knight] of Bastille Networks gave an overview of how to get into hacking RF. These are guys who know a few things about hacking RF; [Marc] is responsible for MouseJack and KeySniffer, and [Matt] reverse engineered the LoRa PHY.

In their talk, [Marc] and [Matt] outlined five steps to reverse engineering any RF signal. First, characterize the channel. Determine the modulation. Determine the symbol rate. Synchronize a receiver against the data. Finally, extract the symbols, or get the ones and zeros out of the analog soup.

From [Marc] and [Matt]’s experience, most of this process doesn’t require a radio, software or otherwise. Open source intelligence or information from regulatory databases can be a treasure trove of information regarding the operating frequency of the device, the modulation, and even the bit rate. The pertinent example from the talk was the FCC ID for a Z-wave module. A simple search revealed the frequency of the device. Since the stated symbol rate was twice the stated data rate, the device obviously used Manchester encoding. These sorts of insights become obvious once you know what you’re looking for.

In their demo, [Marc] and [Matt] went through the entire process of firing up GNU Radio, running a Z-wave decoder and receiving Z-wave frames. All of this was done with a minimum of hardware and required zero understanding of what radio actually is, imaginary numbers, or anything else a ham license will hopefully teach you. It’s a great introduction to RF hacking, and shows anyone how to do it.

Shmoocon 2017: On Not Reverse Engineering Through Emulation

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.

tyteraNow 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.

Bring Your Palm VII To ShmooCon This Weekend

We’re not even halfway through January, and already the conference season is upon us. This weekend, Hackaday will be attending Shmoocon at the Hilton in Washington, DC. I’ll be there getting the full report on Russian hackers, reverse engineering, and what the beltway looks like with an ice storm during morning rush hour.

What’s in store for Shmoocon attendees? The schedule looks really cool with talks on something like inline assembly in Python, tools for RF reverse engineering, manufacturing and selling a U2F token, emulating ARM firmware, and so much more. Want to attend Shmoocon? Too bad! Tickets sold out in less than 10 seconds, and we’re totally not going to talk about the BOTS Act at all. If you’re clever you can still pick up a barcode on Craigslist for $300-400, but I wouldn’t recommend that.

As we did last year, Hackaday is going to have a lobbycon with Dunkin Saturday morning at 08:30, although which lobby is still up in the air. Check out the Hackaday Twitter for a few real-time updates. This is a bring-a-hack event, and I’ll be showing off how to add 18dBi of gain to a standard ESP8266 module. Show off what you’re working on and get a donut.