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docs(wiki): ATECC608 is upcoming — retag ledger signing to the on-host reality

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No secure element is on-site: event signing runs on the software HMAC
(EVENT_SIGNING_KEY, an env var on the host disk), so the ledger is
tamper-EVIDENT but forgeable by anyone who owns the host. Several pages
overstated it as present-tense "ATECC608-signed / unforgeable"; correct them.

- NEW concepts/hardware-signer-options.md: four options for a non-extractable
  signing key (USB HSM / YubiKey / reuse the TPM / plain-dongle trap) + the
  recommendation (TPM interim → USB-HSM target; ATECC608 stays for the embedded
  ESP32, wrong part for a PC host).
- entities/atecc608.md: UPCOMING-not-present status banner + PC-vs-embedded.
- disk-os-hardening.md: fix the live-USB row (BIOS boot-order password is
  load-bearing, not Secure Boot — a signed live USB runs); add a physical-tamper
  chain (Dell 7070 CMOS-reset → live-USB → PCR-7 same-signer unseal) + accepted
  risks (that unseal, unsigned-initramfs evil-maid, operator-USB read TODO).
- open-questions #6 reframed; standing-decisions / overview / threat-model /
  index de-overstated; log query entry.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V
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Julian Çuni
2026-07-04 13:41:11 +02:00
parent 306d136a08
commit c142166972
9 changed files with 274 additions and 27 deletions
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wiki/decisions/standing-decisions.md
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@@ -25,9 +25,11 @@ The decisions treated as settled in the design notes. (See [[parking-system-arch
deny-by-default native surface that fits [[threat-model|the booth-operator threat model]]. The
shell stays **thin**: all privileged logic remains in [[fastify]]. One open dependency — the
appliance's WebKitGTK version (see [[open-questions]] #11).
- **Integrity:** append-only, hash-chained, [[atecc608]]-signed event log
([[append-only-event-chain]]); **[[reconciliation]] is the anti-fraud control**; encryption
protects only at-rest (see [[threat-model]]).
- **Integrity:** append-only, hash-chained, **software-signed** event log
([[append-only-event-chain]]) — hardware-backed signing (a non-extractable key in the
**[[tpm|TPM]]** or a **USB HSM**; the [[atecc608]] is [[open-questions|upcoming, not present]]) is
the target that makes it unforgeable by a host owner ([[hardware-signer-options]]). **[[reconciliation]]
is the anti-fraud control**; encryption protects only at-rest (see [[threat-model]]).
- **Access control:** the **[[dingtian-relay]]** relay+input controller, on an **isolated VLAN**
([[network-isolation]]). Chosen because its **inputs are decoupled from its relays**, enabling
host-in-the-loop ticket-first entry — the resolution to [[access-controller-button-flow]].