FIDO2 with a SoloKey

Works on: Secure + Hacker. Core FIDO2/WebAuthn.

Solo 2 is a FIDO2/CTAP2 authenticator. Credentials are ES256 (ECDSA P-256, alg -7) or EdDSA (Ed25519, alg -8); the hmac-secret extension provides a per-credential symmetric secret used by tools like age and LUKS.

Passkeys in the browser

Register/sign in at https://webauthn.io (or any FIDO2 site: GitHub, Google, …). Resident credential + PIN + touch = a passkey.

With the `solo2` CLI

cargo install solo2          # provides the `solo2` binary
solo2 ls                     # devices + firmware, e.g. "Solo 2 … (CTAP+PCSC, firmware 2:…)"
solo2 app fido init          # FIDO init response: major/minor, can_wink/can_cbor/can_msg
solo2 app fido wink          # blink the key to identify it

The CLI manages the device; credential create/assert is done by a FIDO2 client (browser, or the snippets below).

Programmatic: make a credential with each algorithm

With python-fido2. Touch the Solo at each make_credential.

import hashlib
from fido2.hid import CtapHidDevice
from fido2.ctap2 import Ctap2

ctap = Ctap2(next(CtapHidDevice.list_devices()))
print("algorithms:", [a["alg"] for a in ctap.get_info().algorithms])   # [-7, -8, -50]

rp   = {"id": "fido.demo", "name": "FIDO Demo"}
user = {"id": b"u1", "name": "u", "displayName": "u"}
cdh  = hashlib.sha256(b"demo").digest()

for alg in (-7, -8):          # ES256, EdDSA  -- touch for each
    att = ctap.make_credential(cdh, rp, user, [{"type": "public-key", "alg": alg}])
    print(f"alg {alg}: credential_id {len(att.auth_data.credential_data.credential_id)} bytes")

(-50 is ML-DSA-44, Hacker only — see POST_QUANTUM.md.)

hmac-secret

hmac-secret lets the host derive a stable 32-byte secret from the credential + a salt, computed on the key (HMAC-SHA256). It's how FIDO2 powers symmetric encryption without storing keys on the host.

Request it at credential creation, then evaluate it at assertion:

att = ctap.make_credential(cdh, rp, user, [{"type":"public-key","alg":-7}],
                           extensions={"hmac-secret": True})        # touch
# later, at get_assertion, supply a salt to get back the derived secret
# (the platform wraps the salt with a shared secret; see python-fido2's HmacSecret extension)

The easiest way to use hmac-secret is via age + age-plugin-fido2-hmac, which handles the salt/derivation for you.

CLI alternative

libfido2's tools also work: fido2-token -L (list), fido2-cred (make credential), fido2-assert (assert).

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