Identify Your Devices by Their Unintentional Radiation

RFID was supposed to revolutionize asset tracking, replacing the barcode everywhere. Or at least that was the prediction once tags got under five cents apiece. They still cost seven to fifteen cents, even in bulk, and the barcode is still sitting pretty. [Chouchang (Jack) Yang] and [Alanson Sample] of Disney Research hope to change that.

Instead of tagging every electronic device, they use whatever electromagnetic emissions the device currently produces when it’s powered up. What’s surprising is not that they can tell an iPhone from a toy lightsaber, but that they can tell the toy lightsabers apart. But apparently there’s enough manufacturing and tolerance differences from piece to piece that they appear unique most of the time.

The paper (PDF) goes through the details and procedure. The coolest bit? The sensor they use is an RTL-SDR unit with the radio-mixer front end removed and replaced with a simple transformer. This lets them feed baseband (tuning from 0 to 28.8 MHz) straight into the DAC ADC and on to the computer which does the heavy math. Sawing off the frontend of a TV tuner is a hack, for those of you out there with empty bingo cards.

If you like statistics, you’ll want to read the paper for details about how they exactly do the classification of objects, but the overview is that they first start by figuring out what type of device they’re “hearing” and then focusing on which particular one it is. The measure that they use ends up being essentially a normalized correlation.

While we’re not sure how well this will scale to thousands of devices, they get remarkably good results (around 95%) for picking one device out of five. The method won’t be robust to overclocking or underclocking of the device’s CPU, so we’re concerned about temperature and battery-voltage effects. But it’s a novel idea, and one that’s ripe for the hacker-rebuild. And for the price of an RTL-SDR, and with no additional per-tag outlay as with an RFID system, it’s pretty neat.

Thanks [Static] for the tip! Via Engadget.

Which Wireless Tech is Right For You?

It seems these days all the electronics projects are wireless in some form. Whether you choose WiFi, Bluetooth Classic, Bluetooth Low Energy, ZigBee, Z-Wave, Thread, NFC, RFID, Cell, IR, or even semaphore or carrier pigeon depends a lot on the constraints of your project. There are a lot of variables to consider, so here is a guide to help you navigate the choices and come to a conclusion about which to use in your project.

We can really quickly reduce options down to the appropriate tech with just a few questions.

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WISP Needs No Battery Or Cable

One of the problems with the Internet of Things, or any embedded device, is how to get power. Batteries are better than ever and circuits are low power. But you still have to eventually replace or recharge a battery. Not everything can plug into a wall, and fuel cells need consumables.

University of Washington researchers are turning to a harvesting approach. Their open source WISP board has a sensor and a CPU that draws power from an RFID reader. To save power during communication, the device backscatters incoming radio waves, which means it doesn’t consume a lot of its own power during transmissions.

The big  news is that TU Delft has contributed code to allow WISP to reprogram wirelessly. You can see a video about the innovation below. The source code is on GitHub. Previously, a WISP had to connect to a PC to receive a new software load.

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RFID Lock Keeps Your Bike Safe

What do you do with an RFID chip implanted in your body? If you are [gmendez3], you build a bike lock that responds to your chip. The prototype uses MDF to create a rear wheel immobilizer. However, [gmendez3] plans on building a version using aluminum.

For the electronics, of course, there’s an Arduino. There’s also an RC522 RFID reader. We couldn’t help but think of the Keyduino for this application. When the system is locked, the Arduino drives a servo to engage the immobilizer. To free your rear wheel, simply read your implanted chip. The Arduino then commands the servo to disengage the immobilizer. You can see the system in operation in the video below.

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CarontePass: Open Access Control For Your Hackerspace

A problem faced by all collaborative working spaces as they grow is that of access control. How can you give your membership secure access to the space without the cost and inconvenience of having a keyholder on site at all times.

[Torehc] is working on solving this problem with his CarontePass RFID access system, at the Kreitek Makerspace (Spanish, Google Translate link) in Tenerife, Canary Islands.

Each door has a client with RFID readers, either a Raspberry Pi or an ESP8266, which  connects via WiFi to a Raspberry Pi 2 server running a Django-based REST API. This server has access to a database of paid-up members and their RFID keys, so can issue the command to the client to unlock the door. The system also supports the Telegram messaging service, and so can be queried as to whether the space is open and how many members are in at a particular time.

All the project’s resources are available on its GitHub repository, and there is a project blog (Spanish, Google Translate link) with more details.

This is a project that is still in active development, and [Torehc] admits that its security needs more work so is busy implementing HTTPS and better access security. As far as we can see through the fog of machine translation at the moment it relies on the security of its own encrypted WiFi network, so we’d be inclined to agree with him.

This isn’t the first hackerspace access system we’ve featured here. The MakerBarn in Texas has one using the Particle Photon, while the Lansing Makers Network in Michigan have an ingenious mechanism for their door, and the Nesit hackerspace in Connecticut has a very fancy system with video feedback. How does your space solve this problem?

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Passive WiFi On Microwatts

A lot of you use WiFi for your Internet of Things devices, but that pretty much rules out a battery-powered deployment because WiFi devices use a lot of juice. Until now. Researchers at the University of Washington have developed a passive WiFi implementation that uses only microwatts per device.

Working essentially like backscatter RFID tags do, each node has a WiFi antenna that can be switched to either reflect or absorb 2.4 GHz radiation. Your cell phone, or any other WiFi device, responds to this backscattered signal. All that’s missing is a nice steady signal to reflect.

passive_wifi-shot0008A single, plugged-in unit provides this carrier wave for multiple WiFi sensor nodes. And here’s the very clever part of the research: to keep the carrier from overwhelming the tiny modulated signal that’s coming from the devices, the plugged-in unit transmits off the desired frequency and the battery-powered units modulate that at just the right difference frequency so that the resulting (mixed) frequency is in the desired WiFi band.

If you’re a radio freak, you’ll recognize the WiFi node’s action being just like a frequency mixer. That’s what the researchers (slightly mysteriously) refer to as the splitting of the analog transmission stage from the digital. The plugged-in unit transmits the carrier, and the low-power nodes do the mixing. It’s like a traditional radio transmitter, but distributed. Very cool.

There’s a bunch more details to making this system work with consumer WiFi, as you’d imagine. The powered stations are responsible for insuring that there’s no collision, for instance. All of these details are very nicely explained in this paper (PDF). If you’re interested in doing something similar, you absolutely need to give it a read. This idea will surely work at lower frequencies, and we’re trying to think of a reason to use this distributed transmitter idea for our own purposes.

And in case you think that all of this RFID stuff is “not a hack”, we’ll remind you that (near-field) RFID tags have been made with just an ATtiny or with discrete logic chips. The remotely-powered backscatter idea expands the universe of applications.

Thanks [Ivan] for the tip!

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GuardBunny Active RFID Protection Going Open Hardware

There are two sides to every coin. Instead of swiping or using a chip reader with your credit card, some companies offer wireless cards that you hold up to a reader for just an instant. How convenient for you and for anyone who might what to read that data for their own use. The same goes for RFID enabled passports, and the now ubiquitous keycards used for door access at businesses and hotels. I’m sure you can opt-out of one of these credit cards, but Gerald in human resources isn’t going to issue you a metal key — you’re stuck hauling around that RFID card.

It is unlikely that someone surreptitiously reading your card will unlock your secrets. The contactless credit cards and the keylock cards are actually calculating a response based on a stored key pair. But you absolutely could be tracked by the unique IDs in your cards. Are you being logged when passing by an open reader? And other devices, like public transit cards, may have more information stored on them that could be harvested. It’s not entirely paranoid to want to silence these signals when you’re not using them.

One solution is to all of this is to protect your wallet from would-be RFID pirates. At this point all I’m sure everyone is thinking of a tin-foil card case. Sure, that might work unless the malicious reader is very powerful. But there’s a much more interesting way to protect against this: active RFID scrambling with a project called GuardBunny. It’s a card that you place next to whatever you want to protect. It’s not really RFID — I’ll get that in a moment — but is activated the same way and spews erroneous bits back at any card reader. Kristin Paget has been working on GuardBunny for several years now. As of late she’s had less time for active development, but is doing a great thing by letting version 1 out into the world for others to hack on. In her talk at Shmoocon 2016 she walked through the design, demonstrated its functionality, and shared some suggestions for further improvement.

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