diskless-workstation/docs/secure-boot-keys.md

# Secure Boot key generation & enrollment — diskless fleet

The fleet boots a **signed UKI directly via systemd-stub** (no shim, no GRUB), so
UEFI Secure Boot verifies the UKI against keys **you** enrol in firmware. This
doc generates the three Secure Boot keys (the "trio": **PK, KEK, db**), enrols
them, and wires the `db` key into the build.

> **Invariant #7:** signing keys never enter the build VM or this repo. The
> commands below produce key material that lives **offline / in an HSM**. Only the
> **db** key signs UKIs routinely, and the build receives it as a *path*
> (`sb_key`/`sb_cert`) on the CI/HSM host — never committed, never echoed in logs.
> Treat every `*.key` file here as secret; never check one into git.

## The trio — roles and where each lives

| Key | Role | Used by | Where it lives |
|---|---|---|---|
| **PK** (Platform Key) | Root of trust; controls who may update the KEK. Setting it locks Secure Boot into User Mode. | Firmware enrolment only | **Offline / HSM**, used once (and for KEK rotation) |
| **KEK** (Key Exchange Key) | Signs updates to `db`/`dbx`. | Firmware enrolment only | **Offline / HSM** |
| **db** (Signature Database) | Signs the bootable UKI. | **The fleet build** — `sb_key`/`sb_cert` ([../scripts/build-oci.sh](../scripts/build-oci.sh) → ukify/sbsign) | HSM/CI signing host |

Trust chain at enrolment: **PK signs KEK → KEK signs db → db signs the UKI.**

Only `db` is online (it signs every release; the UKI cmdline is immutable once
signed — invariant #6 — so re-signing is part of each build). PK and KEK are only
needed to rotate keys later, so they stay offline.

## Tooling

```bash
# Fedora / RHEL:   dnf install openssl efitools sbsigntools
# Debian / Ubuntu: apt install openssl efitools sbsigntool
```

## 1. Generate the three key/cert pairs

```bash
GUID=$(uuidgen); echo "$GUID" > GUID.txt    # owner GUID for the EFI variables

# Platform Key
openssl req -newkey rsa:2048 -nodes -keyout PK.key -new -x509 -sha256 -days 3650 \
  -subj "/CN=Fleet Platform Key/" -out PK.crt
# Key Exchange Key
openssl req -newkey rsa:2048 -nodes -keyout KEK.key -new -x509 -sha256 -days 3650 \
  -subj "/CN=Fleet KEK/" -out KEK.crt
# Signature DB key  <-- this pair becomes sb_key / sb_cert
openssl req -newkey rsa:2048 -nodes -keyout db.key -new -x509 -sha256 -days 3650 \
  -subj "/CN=Fleet db/" -out db.crt
```

`rsa:2048` is the maximally firmware-compatible size for the enrolled variables;
`4096` works on most modern UEFI but some implementations reject it for
PK/KEK/db. The PEM `db.key`/`db.crt` are exactly what sbsign/ukify consume.

## 2. Convert to signed EFI variable updates (`.auth`)

```bash
for v in PK KEK db; do cert-to-efi-sig-list -g "$GUID" $v.crt $v.esl; done

sign-efi-sig-list -g "$GUID" -k PK.key  -c PK.crt  PK  PK.esl  PK.auth   # PK self-signs
sign-efi-sig-list -g "$GUID" -k PK.key  -c PK.crt  KEK KEK.esl KEK.auth  # PK signs KEK
sign-efi-sig-list -g "$GUID" -k KEK.key -c KEK.crt db  db.esl  db.auth   # KEK signs db
```

## 3. Enrol into firmware

Put the firmware in **Setup Mode** first (clear the existing keys in the UEFI
setup screen). Then enrol **db and KEK before PK** — setting PK last is what flips
the firmware out of Setup Mode and turns Secure Boot on:

```bash
efi-updatevar -f db.auth  db
efi-updatevar -f KEK.auth KEK
efi-updatevar -f PK.auth  PK      # do this LAST
```

Alternatively, enrol the `.auth`/`.esl` files via the firmware's own
"enrol key from file" UI or `KeyTool.efi` — useful for headless fleet hardware
where this is scripted into provisioning.

> The fleet uses a UKI with **no shim and no Microsoft keys**, so no MOK is
> needed. If a host must also boot vendor-signed media, *add* your `db` alongside
> Microsoft's UEFI CA instead of clearing it.

### Manual enrollment on a fleet workstation (over SSH)

The build bakes the EFI management tools into the image (`efitools` +
`efivar`/`mokutil`/`efibootmgr`, installed in the main package provisioner), so
you can enrol keys **manually over SSH** on a booted workstation that is in Setup
Mode — handy for provisioning before the automated flow (TODO #10) exists. The
tools write to `efivarfs` (`/sys/firmware/efi/efivars`), not the read-only root,
so they work at runtime; they're RPM-installed so fapolicyd already trusts them.

```bash
# on the workstation (as the sudo admin):
mokutil --sb-state                      # check Secure Boot / Setup Mode
efi-readvar                             # dump current PK/KEK/db/dbx
# copy your PK.auth/KEK.auth/db.auth (or .esl) onto the host, then in Setup Mode:
sudo efi-updatevar -f db.auth  db
sudo efi-updatevar -f KEK.auth KEK
sudo efi-updatevar -f PK.auth  PK       # last — leaves Setup Mode
efi-readvar                             # read back + confirm fingerprints match
```

Only the **public** certs/`.esl`/`.auth` need to reach the workstation — never
copy `PK.key`/`KEK.key`/`db.key` onto a host.

## 4. Wire `db` into the build

```bash
packer build -var image_version=X.Y.Z \
  -var sb_key=/path/to/db.key \
  -var sb_cert=/path/to/db.crt \
  -var oci_image=<registry>/fleet-boot .
```

ukify signs `fleet-<ver>.efi` with `db`; the enrolled `db` cert lets firmware
verify it. Without these vars the build stays **unsigned** (lab-only, with the
loud warning). In CI, `sb_key`/`sb_cert` are secret paths on the HSM/signing host.

## Signing in CI (Gitea Actions)

`sb_key`/`sb_cert` **can** be Gitea repo secrets, with one wrinkle: ukify consumes
them as **file paths**, not values, and the signing post-processor runs
**shell-local on the runner** (not in the build VM — consistent with invariant
#7). So the job materializes the secrets to runner-temp files, passes the paths,
and shreds the key afterward. This is wired in
[../.gitea/workflows/gitea-main-ci.yaml](../.gitea/workflows/gitea-main-ci.yaml)
(steps: *Materialize Secure Boot signing material* → *packer build* → *Shred
Secure Boot signing key*). Set repo secrets **`SB_KEY`** (the `db` private key,
PEM) and **`SB_CERT`** (the `db` cert, PEM); leave them unset for an unsigned lab
build.

Caveats:
- **Only `db` belongs in CI.** PK and KEK never leave the offline/HSM store.
- `SB_CERT` is a public cert (not secret); kept as a secret only for convenience.
- A CI secret puts the private key **in plaintext on the runner FS** for the
  duration of the build — only as safe as the runner. Use a **trusted,
  ephemeral/self-hosted** runner, ensure secrets are **not exposed to fork/PR
  builds**, and rely on `RUNNER_TEMP` wipe + the shred step. Gitea masks secret
  values in logs, and `build-oci.sh` passes the *path* (not content) to ukify, so
  the key won't leak into logs.
- **Stronger (production target):** keep `db.key` in an **HSM/PKCS#11** token or
  KMS and sign *through* it, so the raw key never touches the runner disk. The
  CI-secret flow is a reasonable interim; the HSM flow is the invariant-#7 ideal
  (TODO #8).

## Key hygiene & lifecycle

- **PK.key and KEK.key go offline / into an HSM and stay there.** They are only
  needed to rotate keys; routine signing uses **db.key** only.
- **Production ideal:** keep `db.key` in an HSM/PKCS#11 token and have
  sbsign/ukify sign *through* it rather than reading a file from disk.
- **Validity:** `-days 3650` is 10 years; pick a rotation policy. Rotating `db`
  = sign new `db.esl` with KEK, push the `db` variable update, re-sign UKIs.
- **dbx** (the revocation list) is a fourth, optional variable — manage it to
  blacklist a compromised `db` cert.
- **Lab shortcut:** [`sbctl`](https://github.com/Foxboron/sbctl)
  (`sbctl create-keys` → `sbctl enroll-keys`) generates and enrols the whole trio
  and tracks signed files — convenient for a dev box, but it keeps keys as local
  files, so for the fleet's HSM/offline-PK model use the manual flow above for
  PK/KEK.

## Related

- Invariants #6 (UKI cmdline immutable once signed), #7 (keys never in repo/VM),
  #5 (roothash↔UKI hard gate) — [../CLAUDE.md](../CLAUDE.md).
- Signing is the production-posture step in [TODO.md](TODO.md) #8.
- FIPS is currently off and is to be revisited alongside signing/Secure Boot
  ([stig-deviations.md](stig-deviations.md) #5).