Piezomagnetic Trick Shrinks 2.5 GHz Antennas

To a ham radio operator used to “short”-wave antennas with lengths listed in tens of meters, the tiny antennas used in the gigahertz bands barely even register. But if your goal is making radio electronics that’s small enough to swallow, an antenna of a few centimeters is too big. Physics determines plausible antenna sizes, and there’s no way around that, but a large group of researchers and engineers have found a way of side-stepping the problem: resonating a nano-antenna acoustically instead of electromagnetically.

Normal antennas are tuned to some extent to the frequency that you want to pick up. Since the wavelength of a 2.5 GHz electromagnetic wave in free space is 120 cm mm, most practical antennas need a wire in the 12-60 cm mm range to bounce signals back and forth. The trick in the paper is to use a special piezomagnetic material as the antenna. Incoming radio waves get quickly turned into acoustic waves — physical movement in the nano-crystals. Since these sound waves travel a lot slower than the speed of light, they resonate off the walls of the crystal over a much shorter distance. A piezoelectric film layer turns these vibrations back into electrical signals.

Ceramic chip antennas use a similar trick. There, electromagnetic waves are slowed down inside the high-permittivity ceramic. But chip antennas are just slowing down EM waves, whereas the research demonstrated here is converting the EM to sound waves, which travel many orders of magnitude slower. Nice trick.

Granted, significant material science derring-do makes this possible, and you’re not going to be fabricating your own nanoscale piezomagnetic antennas any time soon, but with everything but the antenna getting nano-ified, it’s exciting to think of a future where the antennas can be baked directly into the IC.

Thanks [Ostracus] for the tip in the comments of this post on antenna basics. Via [Science Magazine].

DIY Wireless Sprinkler System? Don’t Mind If I Do.

What to do once you have a sprinkler system installed on your property: buy a sprinkler control system or make your own? The latter, obviously.

[danaman] was determined to hack together a cheap, IoT-enabled system but it wasn’t easy — taking the better part of a year to get working. Instead of starting right from scratch, he used the open-source Sustainable Irrigation Platform(SIP) control software — a Python sprinkler scheduler with some features [danman] was looking for(eg: it won’t activate if there’s rain in the forecast). Since he wasn’t running it with a Raspberry Pi as recommended, [danman] wrote a Python plugin that runs on his home server as a daemon which listens to TCP port 20000 for connections and then updates the relevant relays. Ok, software done; on to the relay controller box!

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WiFi Deauthentication VS WiFi Jamming: What is the difference?

Terminology is something that gets us all mixed up at some point. [Seytonic] does a great job of explaining the difference between WiFi jammers and deauthenticators in the video embedded below. A lot of you will already know the difference however it is useful to point out the difference since so many people call deauth devices “WiFi Jammers”.

In their YouTube video they go on to explain that jammers basically throw out a load of noise on all WiFi channels making the frequencies unusable in a given distance from the jammer. Jammers are also normally quite expensive, mostly illegal, and thus hard to find unless of course you build your own.

WiFi deauthentication on the other hand works in a very different way. WiFi sends unencrypted packets of data called management frames. Because these are unencrypted, even if the network is using WPA2, malicious parties can send deauthentication commands which boot users off of an access point. There is hope though with 802.11w which encrypts management frames. It’s been around for a while however manufacturers don’t seem bothered and don’t implement it, even though it would improve the security of a WiFi device from these types of attacks.

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FLEX Pager Protocol in Depth

We love pager hacks. One of our earliest head-slappers was completely reverse-engineering a restaurant pager’s protocol, only to find out that it was industry-standard POCSAG. Doh!

[Corn] apparently scratches the same itch, but in the Netherlands where the FLEX protocol is more common. In addition to walking us through all of the details of the FLEX system, he bought a FLEX pager, gutted it, and soldered on an ATMega328 board and an ESP8266. The former does the FLEX decoding, and the latter posts whatever it hears on his local network.

These days, we’re sure that you could do the same thing with a Raspberry Pi and SDR, but we love the old-school approach of buying a pager and tapping into its signals. And it makes a better stand-alone device with a lot lower power budget. If you find yourself in possession of some old POCSAG pagers, you should check out [Corn]’s previous work: an OpenWRT router that sends pages.

Making a Cheap Radar Unit Awesome

[JBeale] squeezed every last drop of performance from a $5 Doppler radar module, and the secrets of that success are half hardware, half firmware, and all hack.

On the hardware side, the first prototype radar horn was made out of cardboard with aluminum foil taped around it. With the concept proven, [JBeale] made a second horn out of thin copper-clad sheets, but reports that the performance is just about the same. The other hardware hack was simply to tack a wire on the radar module’s analog output and add a simple op-amp gain stage, which extended the sensing range well beyond the ten feet or so that these things are usually used for.

With all that signal coming in, [JBeale] separates out the noise by taking an FFT of the Doppler frequency-shift signal. Figuring that people walk around 2.2 miles per hour, [JBeale] focuses on the corresponding 70 Hz frequency bin and finds that the radar will detect people out to 80 feet. Wow!

This trick of taking an el-cheapo radar unit and amplifying the signal to do something useful isn’t new to Hackaday. [Mathieu] did it with the very same HB-100 unit way back in 2013, and then again with a more modern CDM324 model. But [JBeale]’s hacked horn and clever backend processing push out the limits of what you can expect to do with these cheap units. Kudos.

[via PJRC]

Quick Robin! The Bat Keychain!

We don’t know if Batman has a keychain for the keys to the Bat mobile, the Bat copter, and all his other vehicles. But we are guessing if he did, it didn’t look like the one [krishnan793] picked up cheap. It had a little button that lit up some LEDs and played a little tune. [Krishnan] thought he could do better with an ESP8266. After chopping up some headphones and adding a LiPo battery, he wound up with an improved key chain you can see in the video below. The first video is the before video. The second is after the modification. Sure, it is only a small improvement on LEDs and a simple tune, but now it is hackable to do more interesting things if you want to take the trouble to do so.

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“Borrow” Payment Cards with NFC Proxy Hardware

Contactless payments are growing in popularity. Often the term will bring to mind the ability to pay by holding your phone over a reader, but the system can also use NFC tags embedded in credit cards, ID card, passports, and the like. NFC is a reasonably secure method of validating payments as it employs encryption and the functional distance between client and reader is in the tens of centimeters, and often much less. [Haoqi Shan] and the Unicorn team have reduced the security of the distance component by using a hardware proxy to relay NFC interactions over longer distances.

The talk, give on Sunday at DEF CON, outlined some incredibly simple hardware: an NFC antenna connected to a PN7462AU, an NRF24L01 wireless transceiver, and some power regulation. The exploit works by using a pair of these hardware modules. A master interfaces with the NFC reader, and a slave reads the card. The scenario goes something like this: a victim NFC card is placed near the slave hardware. The master hardware is placed over a payment kiosk as if making a normal payment. As the payment kiosk reader begins the process to read an NFC card, all of the communications between it and the actual card are forwarded over the 24L01 wireless connection.

The demo video during the talk showed a fast-food purchase made on the Apple Pay network while the card was still at a table out in the dining area (resting on the slave hardware module). The card used was a QuickPass contactless payment card from China UnionPay. According to a 2016 press release from the company, over two billion of these cards had been issued at the time. With that kind of adoption rate there is a huge incentive to find and patch any vulnerabilities in the system.

The hardware components in this build aren’t really anything special. We’ve seen these Nordic wireless modules used in numerous projects over they years, and the NXP chip is just NFC build around an ARM core. The leaps that tie this together are the speed-ups to make it work. NFC has tight timing and a delay between the master and slave would invalidate the handshake and subsequent interactions. The Unicorn team found some speedups by ensuring the chip was waking from suspend mode (150 µS) and not a deeper sleep. Furthermore, [Haoqi] mentioned they are only transmitting “I/S/R Block Data” and not the entirety of the interaction to save on time transmitting over the 24L01 wireless link. He didn’t expand on that so if you have details about what those blocks actually consist of please let us know in the comments below.

To the card reader, the emulated payment card is valid and the payment goes through. But one caveat to the system is that [Haoqi] was unable to alter the UID of the emulator — it doesn’t spoof the UID of the payment card being exploited. Current readers don’t check the UID and this could be one possible defense against this exploit. But to be honest, since you need close physical proximity of the master to the reader and the slave to the payment card simultaneously, we don’t see mayhem in the future. It’s more likely that we’ll see hacker cred when someone builds a long-range link that lets you leave your NFC cards at home and take one emulator with you for wireless door access or contactless payments in a single device. If you want to get working on this, check out the talk slides for program flow and some sourcecode hints.