I maintain feuristic, a GPL-3.0-only custom firmware for the Trezor Safe 3. It is a firmware project for existing hardware, built on the published trezor-firmware core/v2.12.5 sources with an exported patch series.

The device is repurposed from a cryptocurrency wallet into a USB authenticator and smart card. Implemented functions include FIDO2/WebAuthn, OpenPGP Card, PIV, TOTP/HOTP and AES-GCM. The existing screen and buttons provide configuration and operation confirmations in English or French.

The repository includes build instructions, protocol references, a threat model and downloadable development images for the two Safe 3 revisions, T2B1 and T3B1. Upstream components retain their own licences and notices. This is not a new board design or an open-hardware certification claim.

An initial physical T2B1/macOS campaign checked the main workflows and identity persistence after updates. T3B1 builds and emulator checks exist, but physical qualification remains pending.

The trade-off is substantial: installing erases the wallet and permanently removes original manufacturer attestation. The device keeps displaying the third-party firmware warning. This is unaudited development software, intended for disposable identities on spare hardware, and is independent of Trezor/SatoshiLabs.

Source and upstream notices · Architecture

The aim of sharing the implementation is to make this particular hardware-reuse experiment inspectable and reproducible.