The drivers had no cryptographic identity at all. Every build minted a fresh
`CN=punktfunk-driver` cert (build-pf-vdisplay.ps1, build-gamepad-drivers.ps1), and
install.rs `trust_cert` adds whatever .cer it finds in the unpacked bundle to
machine Root AND TrustedPublisher. So the signature vouched for nothing an
attacker couldn't restage — replace the bundle, ship your own cert beside your own
driver, install proceeds identically. It was ceremony to make PnP install quietly.
Worse, it leaked. `trust_cert` runs once per driver (install.rs:102 and :155), so
every upgrade added TWO more self-signed root CAs under the same name, and nothing
ever removed them: uninstalling punktfunk left trust behind that the user had no
reason to keep granting.
So: both build scripts now take a stable cert via DRIVER_CERT_PFX_B64 (they already
read the env var — windows-host.yml just never passed it) and fail closed on a v*
tag, same rule as the host and MSIX packers. `driver uninstall` purges every
`CN=punktfunk-driver` cert from both stores, and `driver install` purges before
adding, so an upgrade also collects the historical pile instead of adding to it.
Purge-before-add lives ONLY on the pf-vdisplay install path, not the gamepad one.
The installer runs vdisplay first and gamepad second; purging in both would have
the gamepad leg delete the cert the vdisplay leg just added whenever the two
bundles carry different certs — which is exactly what canary's per-build fallback
produces. Purging by subject rather than thumbprint is deliberate too: it is what
lets one install clean up certs from builds that no longer exist anywhere, and it
needs no parsing of certutil's localized output (this module exists because
locale-parsed PowerShell broke the driver install on a German box).
This does NOT make the driver download authenticated — a self-signed leaf is its
own root, so the installer must trust it for the driver to install at all. What it
buys is a fingerprint we can publish out-of-band so a substituted driver is
detectable, an allowlistable publisher, continuity across releases, and no root
accumulation. Attestation signing remains the real fix; documented as such.
Documented the key-custody trade honestly in packaging/windows/README.md: a stable
key trusted as a machine root on every install is worth stealing in a way a
throwaway never was, with no revocation path. CI secret only.
⚠️ The secrets must exist before the next v* tag or the release will fail — that
is the guard working, and the generation runbook is in that README. The fingerprint
line there is a placeholder until the key is generated.
Verified: punktfunk-host compiles clean on the windows-amd64 runner with this
install.rs (exit 0, no warnings); both build scripts parse; cargo fmt clean.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
enricobuehlerandClaude Opus 5
a49858f194