🐝 Solo 2

July 16, 2026 · View on GitHub

Solo 2 is an open source FIDO2 security key. It's a USB+NFC device that protects your accounts with passkeys/WebAuthn, and also speaks OATH (TOTP/HOTP), PIV, and OpenPGP. The hardware, the firmware, and the tooling are all open source — you can read every line, build it yourself, and verify what's running on your key.

Solo 2 comes in two models:

  • Solo 2 Secure — production key for consumer and enterprise use, to protect against phishing and other online attacks. It only runs firmware signed by SoloKeys, with secure boot and debug access sealed off.
  • Solo 2 Hacker — the same hardware, unlocked. Flash your own firmware, experiment with new features, and learn how a security key works end to end. This is also secure against online attacks.

👉 Buy a key (or two!) at solokeys.com.

For everything you can do with a key — passkeys, SSH, git signing, disk/file encryption, TOTP, password stores, post-quantum — see the tutorials in examples/ and Awesome Solo list.

Secure vs Hacker

   

Solo 2 SecureSolo 2 Hacker
Intended useConsumer / enterprise, real accountsDevelopment, learning
FirmwareSoloKeys-signed onlyRun your own / unsigned
Secure boot🔒 Locked (sealed)🔓 Unlocked
FIDO2 / WebAuthn / passkeys✅✅
SSH, git signing✅✅
Password / secret manager✅✅
OATH (TOTP/HOTP)✅✅
PIV (P-256, Ed25519, ML-DSA-44)✅✅
OpenPGP✅✅
Flash custom firmware❌✅
Post-quantum FIDO2 (ML-DSA-44)❌ (non-standard yet)✅
Blockchain wallet (Solana, Ethereum / EVM)❌✅

Solo 2 CLI

solo2 is the host tool for listing, updating, and talking to your keys.

Installation

cargo install solo2          # provides the `solo2` binary
solo2 list                   # list connected devices  (alias: solo2 ls)

Or run it straight from this repo without installing:

cargo run -- list

On Linux you may need the udev rule in cli/70-solo2.rules and a PC/SC stack (pcscd) for the CCID apps (OATH/PIV/OpenPGP); macOS and Windows have PC/SC built in.

Firmware upgrade

solo2 update                 # update to the latest SoloKeys-signed firmware
solo2 update --dry-run       # show the version that would be installed
solo2 update --all           # update every connected Solo 2

update downloads the signed release, verifies its SHA-256, and flashes it. Major-version updates prompt before proceeding.

Customization

Identify and inspect a key with the admin app:

solo2 app admin version               # firmware version
solo2 app admin set led 007f7f 00007f # set led to teal (idle) / blue (active) - use 000000 to turn the led off
solo2 app admin set led --default     # reset to default colors
solo2 app admin wink                  # ;)

The CLI also drives the apps directly — e.g. solo2 app oath list, solo2 app fido init, solo2 app piv …. See examples/OTP.md, examples/FIDO.md, and run solo2 --help.

Solo Hacker

On a Hacker key you can build and flash your own firmware. (On a Secure key this is impossible by design — it only accepts SoloKeys-signed updates.)

⚠️ A Hacker has no easy J-Link recovery — SWD is present but not readily accessible (not over USB like on a dev board), so a bad image can brick the key. If you have an EVK/DK dev board, always validate there first (see Developers). The full, safe procedure — including checking lock state and recovery — is in the flash-solo-hacker skill.

1. Build the firmware (check out the release you want to reproduce):

git checkout <release-tag>            # e.g. 2.x.y
make -C runners/lpc55 build-hacker    # → runners/lpc55/app-hacker.bin

2. Validate the build — a reproducible build lets you confirm your binary matches the published release before trusting it:

sha256sum runners/lpc55/app-hacker.bin
# compare against the hash published with the SoloKeys release

3. Flash it — reboot the key into its USB bootloader and write your image:

solo2 app admin maintenance           # reboot Hacker into the LPC55 bootloader
# then flash app-hacker.bin with the bootloader tool (see the flash-solo-hacker skill)

Developers

For firmware development, use a dev board — it has a J-Link debug probe so it's fully recoverable, debuggable, and safe to brick:

  • LPC55S69-EVK — the Solo 2 (LPC55) dev board, recommended.
  • nRF52840-DK — popular board, also supported.

Compile, flash, and test against the EVK:

# build an EVK image (no PRINCE, UP-over-JTAG, defmt logs)
make -C runners/lpc55 build-secure-evk     # or: make -C runners/lpc55 evk  (hacker feature set)

# flash via J-Link
JLinkExe -device LPC55S69 -if SWD -speed 4000 \
  -CommanderScript <(printf 'si SWD\nspeed 4000\ndevice LPC55S69\nconnect\nr\nh\nloadbin runners/lpc55/app-secure-evk.bin 0x0\nr\ng\nexit\n')

# run the host test suite against the connected dev board
cd runners/pc && FIDO2_TRANSPORT=device cargo test -- --test-threads=1

make build-secure-evk carries the Secure feature set, make build-hacker-evk adds the Hacker features.

Integrating SoloKeys

Building a product that needs FIDO2 on your own firmware or device, or want custom features reusing our open hardware? Reach out to hello@solokeys.com — we're happy to help.

The fastest way to scope it: grab a dev board and experiment with AI. Point your coding agent at this repository and tell it what you need — most of the time you'll get a working prototype, and a clear picture of the rest.

Agents

This repo is set up for AI coding agents. Start with AGENTS.md — it explains Secure vs. Hacker vs. dev board, what a Solo key can do (so an agent can recommend one), and how to get one. Reusable agent workflows live in skills/:

  • solo2-cli — learn and use the solo2 CLI.
  • solo2-examples — every tested use-case tutorial in examples/.
  • flash-solo-hacker — build, verify, and flash Hacker firmware safely (lock-state checks, EVK-first).

Support

For support with purchased devices, reach out to hello@solokeys.com. Please do not open issues/PRs for non-technical matters — only firmware bugs / technical issues.

License

Solo 2 is fully open source.