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nixtropic

Open-source firmware that turns the Tropic Square TS1302 USB devkit into a FIDO2 and OpenPGP security key, with keys held in the TROPIC01 secure element.

The TROPIC01 is an open-architecture secure element. nixtropic runs on the board's STM32U535 microcontroller, speaks the two standard security-key protocols over USB, and keeps the keys inside the chip. It is built reproducibly with Nix and tested against a simulated chip, with planted bugs, and on real hardware.

Development release — not a production security key

v0.3 uses Tropic Square's public development pairing key: anyone holding the dongle can make it sign. It fixes the known host-side attack paths of v0.2 and stores no readable secrets on the chip; it does not defend against physical attacks. Read the security model before you rely on it.

  • FIDO2 / WebAuthn

    Passkeys and security-key logins. EdDSA and ES256 keys generated and used inside TROPIC01; PIN, alwaysUv, credential management.

  • OpenPGP card

    gpg signing, decryption and SSH through gpg-agent. Ed25519 keys inside TROPIC01; the X25519 decryption key sealed under your PIN.

  • Chip-enforced PIN limits

    Every guess consumes MAC-and-Destroy state on the chip that only the right PIN restores. No PIN hash is stored anywhere.

  • Fault-tolerant state

    Settings and PINs are mirrored and read back. One power cut, lost reply or damaged slot never grants access or undoes a completed change (limits).

  • User presence

    Button SW1 and the LED confirm every FIDO2 registration and login, and by default every OpenPGP signature, decryption and SSH login.

  • Reproducible

    Every input pinned. nix build produces the same firmware from the same commit; nix run flashes it.

Get started

  • Flashing

    Check the chip firmware, enter DFU mode, flash with or without Nix.

  • Linux setup

    pcscd, scdaemon, udev rules and the libccid patch; a NixOS module does it all.

  • Windows

    The OpenPGP card with Gpg4win and Kleopatra; FIDO2 status.

  • Card setup

    PINs, touch policy, key generation, resets.

  • Recovery

    What each kind of reset changes, and how to get back.

Under the hood

Architecture · Hardware · Design decisions · Security model · Testing · Status · Roadmap