Hackathon

Ledger Tap

An app that runs on Ledger hardware wallets, mainly the ones with NFC. The aim was to prove one thing: that a non-fungible piece of data could be handed from one device to another, and that the device handing it over no longer holds it afterwards. The use case is a bearer instrument — a bearer bond, for example — where ownership changes hands between two wallets rather than through a registry in the middle.

Team: Felix Voo & Rammy Kim
Devices: Flex, Stax, Apex P (Nano S unsupported)
Language: Rust, no_std
Repo: github.com/feeerix/app-tap
Status: Hackathon build — runs on device and in the Speculos emulator

On the device

These are the app's real screens — screenshots committed to the repository by its functional test suite, captured on the Flex.

Device screen showing the address 0xFD2095A37E72BE2CD575D18FE8F16E78C51EAFA3 with Confirm and Cancel options — Address verification, the first step of the flow

Device screen showing the transaction review: Amount CRAB 777, Destination 0xDE0B295669A9FD93D5F28D9EC85E40F4CB697BAE, Memo 'For u EthDev' — Review: amount, destination and memo, one page of three

Device screen titled 'Sign transaction to send CRAB' with a 'Hold to sign' instruction — The last page asks for a physical hold to sign

Device screen showing a tick and the text 'Transaction signed' — Confirmation, then back to the home screen

Under the hood

Rust (no_std)
Ledger device SDK 1.34
NBGL device UI
secp256k1 ECDSA
Keccak-256
BIP32 derivation
APDU command layer
Ragger + Speculos tests

Built at the hackathon

Two of us, in person across the two days of the event. The build covers address verification, chunked transaction delivery, on-device review, signing, status reporting and the protocol for the NFC link.