RFID tags offer us a lot of convenience by speeding up financial transactions and simplifying authentication. However, these conveniences come with a cost: since the tags can be read remotely without the owner’s knowledge, they introduce significant risks to both personal privacy and data security. For this reason, security-minded individuals commonly use measures that block RFID readers from snagging their data without their consent.
In a recent project, hardware hacker and security enthusiast CiferTech designed a pocket-sized device that confuses and blocks nearby RFID readers. For the curious — and for experimentation — this device can also probe, stress-test, and audit RFID and NFC systems.
The prototype (📷: CiferTech)
The device is a rebuilt and significantly upgraded version of an earlier project called “NullTag.” Rather than relying on off-the-shelf modules, the new design features a custom three-board architecture intended to maximize performance and flexibility while maintaining a compact handheld form factor.
The main board is powered by an ESP32-S3 microcontroller, chosen for its processing speed and ability to keep the device’s graphical interface smooth and responsive. A full-color TFT display driven by the ST7789 controller replaces the tiny monochrome OLED found in previous builds, providing a cleaner interface and making it easier to navigate menus and view tag data. A simple three-way switch serves as the primary input for selecting modes and navigating through the device’s features.
Handling the RFID logic itself is a dedicated controller board built around the PN532 chip. Instead of using the popular pre-made PN532 breakout boards commonly found in hobby projects, CiferTech designed a custom PCB containing the chip and its required analog support circuitry. The controller communicates with the ESP32-S3 over an SPI interface.
Another look at the device (📷: CiferTech)
Completing the stack is a third board devoted entirely to the antenna. This custom 13.56 MHz PCB trace antenna is physically separated from the digital electronics to reduce electromagnetic interference. That design decision reflects one of the most challenging aspects of RFID hardware: tuning the RF front end so that the antenna produces a stable field capable of reading tags reliably.
Once operational, the device offers a range of tools for examining RFID systems. It can clone compatible tags, dump raw memory data for analysis, and translate the cryptic “access bytes” that determine how a card can be read or written.
More aggressive modes allow the device to stress-test tags with rapid authentication cycles or emulate unusual tag responses such as timeouts and errors. These capabilities can reveal how commercial readers react to unexpected conditions, making the tool useful for auditing the resilience of RFID-based security systems.
If you want to improve your digital security, be sure to give the video below a close watch.
