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Motivation

The short version

Commercial security keys are excellent — and closed. The firmware is a black box, the capacity limits are product-segmentation choices, and when a key dies or a vendor discontinues a line, your enrolled identity dies with it. RS-Key exists to see how far an open, auditable, memory-safe implementation can get on a $5 board.

But the honest long version is a story about how one open-source project first amazed me, and then demonstrated — very concretely — what trust in a security project actually rests on.

The story

In the spring of 2025 I came across pico-fido, a firmware that turns a Raspberry Pi Pico into a FIDO2 key. A five-dollar board passed for a YubiKey, and the ecosystem tooling — browsers, ssh-keygen -t ed25519-sk, ykman — worked with it like with the real thing. Next to it lived pico-openpgp, and together they looked like a small miracle: a complete security key you assemble yourself and can read down to the last byte.

I was hooked and got involved right away. WebAuthn was broken in Firefox on Linux — Chromium worked, Firefox silently refused. I dug in with RUST_LOG=authenticator=debug and traced it down: Firefox’s strict CTAP2 parser was rejecting the device’s responses over garbage zero bytes trailing the CBOR payload (pico-fido#129). The fix was accepted, everything worked, and for the next year the key was simply part of my daily life.

The turn

On October 26, 2025, this commit landed: “Update license models and add ENTERPRISE.md”.

Point by point, without emotion:

  • The project split into a “Community Edition” and a proprietary “Enterprise Edition”, priced on request.
  • The list of paid enterprise options includes post-quantum cryptography support. Protection from a quantum adversary became a premium feature.
  • The combined firmware, pico-fido2 (FIDO + OpenPGP), moved into a repository consisting of three markdown files. There is no source code. Releases v7.0 and v7.2 exist — with zero attached files. The README, meanwhile, lists “Open source” among the features, and its build instructions begin with git clone https://github.com/youruser/pico-fido2 — an address with nothing behind it to clone.
  • There is exactly one way to get the firmware: through the companion app, under a per-device license — €29.49 for a single key, €49.49 for “Primary + Backup”. A firmware license for a five-dollar board, priced in the range of an entry-level commercial key (which at least ships with a secure element and audits behind it).

I am not arguing the maintainer has no right to earn money — he does; it is his code and his time. But a security key is a special case. The only thing separating a DIY key from a no-name dongle off AliExpress is that you can read the firmware down to the last byte. A binary-only security-key firmware is a “trust me” from a single person: no source, no audit, no guarantees — exactly the thing this project had been an escape from. That day I understood the project was over for me, and that I would have to write the replacement myself.

The principle

The irony is that Raspberry Pi themselves champion the opposite approach for the RP2350: security through transparency — open hacking challenges against their own chip, public write-ups of the attacks that succeeded, and a second round on fixed silicon. TROPIC01 does the same at the secure-element level: an open, auditable architecture instead of an NDA. That is the right side of this story, and RS-Key intends to stay on it.

What RS-Key does differently

  • AGPL-3.0-only, irreversibly. RS-Key is a derivative work of the AGPL-licensed pico-keys (see NOTICE), so the “relicense it proprietary” trick is legally impossible here — for anyone, me included. There is no CLA; contributors keep their copyright. That is not a promise of good behaviour; it is how the licensing is built.
  • Post-quantum in the open tree. ML-DSA-44 credentials work today, for free, with the source in front of you.
  • The “enterprise” features live in the public tree. Attestation, secure boot, backup, audit — the things usually kept behind a paywall land in the open repository.
  • Transparency as artifacts, not as a slogan. Every external-facing parser has a fuzz target, every unsafe is documented and justified, and the threat model was written down before anyone is asked to trust the key with something real.
  • Accessibility. A Trezor or a Nitrokey is hard and expensive to get in Russia. An RP2350 board is 500 rubles and a friend with a 3D printer.

And yes — this is still a love letter to writing real systems software in Rust on a ten-dollar board. Only now it comes with a moral: the openness of a security project is tested not by years of honest work, but by a single commit. RS-Key is built so that the relicensing in that commit cannot happen here.