julian
7de5c74500
- open-questions #7: symmetric vs. asymmetric JWT signing key (from the commit security review). Prefer RS256/EdDSA so verifying hosts hold only a public key — mirrors the ATECC608 / challenge-response "public key only" property. Decide before multi-host/multi-lane deployment. - Mark esp32-custom-controller status: deferred per decision not to build device-level auth now; access control stays on UHPPOTE + network isolation (noted in open-questions #6). - local-jwt-auth: document hardened secret handling + 8h expiry and the asymmetric-key pointer. - Update index.md and append a log.md entry.
48 lines
2.2 KiB
Markdown
48 lines
2.2 KiB
Markdown
---
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type: entity
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tags: [parking, hardware, access-control, upgrade-path]
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sources: [parking-system-architecture]
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updated: 2026-06-15
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status: deferred
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---
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# Custom ESP32 Controller (prevention alternative)
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> **Status: deferred — not being implemented for now.** Access control stays on the
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> [[uhppote-controller]] behind [[network-isolation]] (tamper-*evident*). This page is kept as
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> the documented upgrade path; revisit only if prevention-grade device authentication becomes a
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> requirement. See [[open-questions]] #6.
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A small custom controller for **device-level authentication** — a control path that holds even
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against an attacker on the wire. The prevention-grade upgrade from the [[uhppote-controller]]
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(which is only tamper-*evident*). It moves the [[trust-boundary]] to the device. (See
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[[parking-system-architecture]] §7.)
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## Requirement reframed
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The threat is **forged or replayed commands**, not eavesdropping ("open lane 2" isn't secret).
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So the essential requirement is **authenticity + freshness (anti-replay)**; encryption is
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optional defence-in-depth. This is implemented as [[challenge-response-auth]].
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## Hardware
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- **Olimex ESP32-POE** (wired Ethernet + PoE, open-source hardware) or **ESP32-S3 + W5500**.
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- **[[atecc608]]** secure element holding the key(s), generated on-chip, non-extractable.
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- **Opto-isolated relay** between GPIO and the barrier operator's dry-contact open input.
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- Enable **ESP32 flash encryption + secure boot** regardless.
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- Transport: Ethernet (one network paradigm on the managed switch), or **RS-485** multidrop for
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long/noisy runs.
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## Safety — treat as seriously as the crypto
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Governed by [[fail-state-safety]]: **entry fails closed, exit fails open**, a **hardware manual
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override** (key switch) that works with the ESP32 dead, a watchdog with a safe default, and the
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barrier operator still owns physical safety ([[barrier-not-a-door]]).
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## Trade-offs
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You take on firmware reliability, EMC/surge protection (TVS diodes, isolation, grounding,
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Ethernet surge arrestor outdoors), and field maintenance. Mitigate by keeping firmware **tiny
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and auditable**: verify a signed fresh command, pulse a relay, watchdog + safe state, nothing
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more. All parking logic stays on the host.
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