An NFC Antenna Ring With A Chip As Its Jewel

Contactless payment by means of NFC-enabled bank cards has made our everyday transactions far more convenient over the last decade, but there still remains the tedious task of finding the card and waving it over the reader. Maybe embedded chips are a step too far for many of us, but how about a bank card in a wearable such as a ring? [Jonathan Limén] shows us how, by taking the NFC chip module from a bank card and mounting it on a ring with a wire coil antenna embedded within it.

The chip in a bank card comes mounted on a small thin PCB with contacts on one side and a coil on the other that serves as its antenna. It’s not sensitive enough to work reliably with most card readers, so the card incorporates a separate printed circuit layer that forms a large-sized tuned circuit which couples to the chip antenna. After taking us through the removal of the chip from the card with some acetone, he proceeds to create a replacement for the card antenna by winding a wire coil round the ring. This becomes a trial-and-error process, but in the end, the result is a working NFC payment ring.

We quite like this idea, but would be tempted to both take away some of the trial and error with a vector network analyzer, and run a couple of turns of the wire as a closer coupling coil for the chip. This is a subject we’ve looked at before here at Hackaday, and we wouldn’t mind having another go at it.

Flipper Zero tool reading bank card, displaying data on LCD

What’s On Your Bank Card? Hacker Tool Teaches All About NFC And RFID

The Flipper Zero is a multipurpose hacker tool that aims to make the world of hardware hacking more accessible with a slick design, wide array of capabilities, and a fantastic looking UI. They are struggling with manufacturing delays like everyone else right now, but there’s a silver lining: the team’s updates are genuinely informative and in-depth. The latest update is all about RFID and NFC, and how the Flipper Zero can interact with a variety of contactless protocols.

Drawing of Flipper Zero and a variety of RFID tags
Popular 125 kHz protocols: EM-Marin, HID Prox II, and Indala

Contactless tags are broadly separated into low-frequency (125 kHz) and high-frequency tags (13.56 MHz), and it’s not really possible to identify which is which just by looking at the outside. Flipper Zero can interface with both, but the update at the link above goes into considerable detail about how these tags are used in the real world, and what they look like from both the outside and inside.

For example, 125 kHz tags have an antenna made from many turns of very fine wire, with no visible space between the loops. High-frequency tags on the other hand will have antennas with fewer loops, and visible space between them. To tell them apart, a bright light is often enough to see the antenna structure through thin plastic.

Low-frequency tags are “dumb” and incapable of encryption or two-way communication, but what about high-frequency (often referred to as NFC) like bank cards and applications like Apple Pay? One thing demonstrated is that mobile payment methods offer up considerably less information on demand than a physical bank or credit card. With a physical contactless card it’s possible to read the full card number, expiry date, and in some cases the name as well as recent transactions. Mobile payment systems (like Apple or Google Pay) don’t do that.

Like many others, we’re looking forward to it becoming available, sadly there is just no getting around component shortages that seem to be affecting everyone.

“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.

ShmooCon 2009: Chris Paget’s RFID Cloning Talk

When we first saw [Chris Paget]’s cloning video, our reaction was pretty ‘meh’. We’d seen RFID cloning before and the Mifare crack was probably the last time RFID was actually interesting. His ShmooCon presentation, embedded above, caught us completely off-guard. It’s very informative; we highly recommend it.

The hardest part about selling this talk is that it has to use two overloaded words: ‘RFID’ and ‘passport’. The Passport Card, which is part the the Western Hemisphere Travel Initiative (WHTI), is not like the passport book that you’re familiar with. It has the form factor of a driver’s license and can only be used for land and sea travel between the USA, Canada, the Caribbean region, Bermuda, and Mexico. They’ve only started issuing them this year.

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