Cryptohack Badge Hacking

The talk, given by members of the Cryptocurrency Village, explains how a challenge badge was built to work like a hardware wallet at a fraction of the usual price. The companion app holds no secrets and only relays requests. The badge keeps the seed, signs transactions on the device, and shows the destination address on its own screen so a compromised app cannot swap it unnoticed. The design includes a dedicated approve button wired straight to the microcontroller, custom display drawing code, and end-to-end encryption over USB or Bluetooth, with a secure element handling key material.

The second half turns to the case where an attacker physically holds the badge. The speaker, who described himself as still learning, lists six broad hardware attack classes: flash dumping, fault injection, side-channel analysis, debug port access, secure element attacks, and counterfeit swaps. Fault injection gets the most detail, since the ESP32-C3 microcontroller is not hardened against glitching. Keeping the seed inside the secure element means a flash dump yields only ciphertext and nonces, not anything spendable.

In the question period, the speakers covered provisioning. A one-time setup flow loads the seed into the secure element and burns eFuses so the provisioning firmware cannot be reflashed. Firmware releases are signed by the organizers, and most of the code is open source, though the secure element driver is under NDA and closed. The session closed with an invitation to try the village's hands-on CTF badges.