julian
c142166972
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
45 lines
2.7 KiB
Markdown
45 lines
2.7 KiB
Markdown
---
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type: entity
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tags: [parking, hardware, security, crypto]
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sources: [parking-system-architecture]
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updated: 2026-07-02
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---
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# ATECC608 (secure element)
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An inexpensive **secure element** holding a signing key that **cannot be extracted, even by
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someone who owns the machine**. The design's intended keystone of ledger integrity. (See
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[[parking-system-architecture]] §3, §7.)
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> **⚠ STATUS — UPCOMING, NOT PRESENT (2026-07-02).** No ATECC608 (nor any secure element) is on
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> the booth today. Event signing runs on the **software `SoftwareSigner`** (HMAC-SHA256, key in
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> `EVENT_SIGNING_KEY`, an env var on the host disk). Consequence: the [[append-only-event-chain]]
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> is tamper-**evident** but **not** unforgeable by an adversary who owns the host — they can read
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> the key and re-sign a doctored chain ([[disk-os-hardening]] physical-tamper chain). Do not describe
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> the ledger as "hardware-signed / unforgeable" in present tense. This is the still-open
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> [[open-questions|open-question #6]].
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Two distinct **intended** uses:
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1. **Host-side event signing.** The design has each event in the [[append-only-event-chain]] signed
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by a non-extractable key so the hash chain is **unforgeable** rather than merely self-consistent.
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**Caveat:** the ATECC608 is an external I²C part native to embedded boards, **not a PC component** —
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on the PC-based booth appliance the realistic non-extractable host signer is the **[[tpm|TPM 2.0]]**
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already on the machine, or a **USB HSM** (Nitrokey HSM 2 / SmartCard-HSM). See
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[[hardware-signer-options]] for the full menu + the TPM-interim → USB-HSM-target recommendation.
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2. **Custom controller command authentication.** On the (deferred) [[esp32-custom-controller]], it
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would hold the key(s) for [[challenge-response-auth]] — generated on-chip, non-extractable, so
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popping the cabinet and dumping flash yields nothing usable. This use is **deferred** (access
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control is the [[dingtian-relay]] behind [[network-isolation]]).
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Confirming a real secure-element signer on the host is [[open-questions]] #6. Listed (aspirationally)
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in the [[bom]]; treat as a future line item until procured.
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> **Platform caveat (2026-06-21):** the ATECC608 is **not a PC component** — it's an external I²C
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> secure element you add/solder, native to embedded boards (the [[esp32-custom-controller]]), not to
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> an off-the-shelf host PC. For a **PC-based appliance** the realistic host secure-element for the
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> non-extractable event-signing key is the **[[tpm|TPM 2.0]]** the machine likely already has; reserve
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> the ATECC608 for the embedded controller. Both give the same non-extractable property — see [[tpm]]
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> "TPM vs. ATECC608". So use #1 (host event signing) is **TPM on a PC, ATECC608 on embedded**; use #2
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> (controller command auth) stays ATECC608.
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