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
58 lines
3.4 KiB
Markdown
58 lines
3.4 KiB
Markdown
---
|
|
type: concept
|
|
tags: [parking, security, foundational]
|
|
sources: [parking-system-architecture]
|
|
updated: 2026-06-20
|
|
---
|
|
|
|
# Threat Model
|
|
|
|
The **second foundational force** (with [[offline-first]]). The central insight is a
|
|
**reframing of who the adversary is**. (See [[parking-system-architecture]] §3.)
|
|
|
|
## The key reframing
|
|
|
|
Early thinking focused on protecting the database **at rest** — SQLCipher, LUKS, BitLocker,
|
|
[[tpm|TPM-sealed keys]]. All of that defends against **an outsider who steals the machine or boots
|
|
from external media**.
|
|
|
|
That is the **wrong primary threat**. The most likely adversary is the **legitimate operator at
|
|
the booth**. While the app runs, the database is decrypted in memory and the operator has full
|
|
authorised access *through the app*. Encryption does nothing against the classic parking fraud:
|
|
**take the cash, then void/delete the entry/exit record so the books balance.**
|
|
|
|
## Consequences
|
|
|
|
The controls that actually address insider/operator fraud are different in kind:
|
|
|
|
- **[[append-only-event-chain]]** — events appended, never edited/deleted; a "void" is itself a
|
|
recorded event, hash-chained, and signed. ⚠ Signing is **software today** (key on the host disk) →
|
|
tamper-*evident* but forgeable by a host owner; a non-extractable **hardware signer**
|
|
([[hardware-signer-options]]; [[atecc608]] upcoming) is what makes it truly *unforgeable*. Which is
|
|
why the load-bearing insider control is reconciliation, next.
|
|
- **[[reconciliation]]** against an authority the operator can't alter — *this is what remote
|
|
sync really is*: a fraud-control mechanism, not just a backup.
|
|
- **[[disk-os-hardening]]** still worthwhile (defeats boot-from-USB) but **not the main event**;
|
|
with LUKS in place, SQLCipher is optional defence-in-depth.
|
|
|
|
The same reframing recurs at the device layer: the [[uhppote-controller]]'s real problem is
|
|
unauthenticated commands ([[uhppote-udp-protocol]]), addressed by detection
|
|
([[event-log-ingestion]]) or prevention ([[esp32-custom-controller]]).
|
|
|
|
> **Worked example — "store the price" ≠ "account for the sale" (found + fixed 2026-06-20).** Every
|
|
> money-taking action must append a signed `payment` event, or it is invisible to
|
|
> [[reconciliation]]. A concrete miss: selling a [[subscription]] wrote only the mutable
|
|
> `subscriptions` master row (the agreed *price*) and **appended nothing to the ledger**, so the cash
|
|
> the operator collected showed up in the feed/drawer/Z-report **nowhere** — a clean off-book channel
|
|
> (three real sales, 27,000 ALL, untraceable). The fix is the textbook control: append a signed
|
|
> `payment` (`subscriptionSale: true`) at sale time so it folds into the [[shift]] like any taking.
|
|
> **The lesson generalises:** whenever a feature records *an amount* in a mutable table, ask "where is
|
|
> the signed event that says money changed hands?" — a price in master data is not an accountable
|
|
> transaction. See [[subscription]] "Collecting the fee".
|
|
|
|
> **Direction shift:** the system is heading toward **fully unmanned operation** — no operator, no
|
|
> booth ([[autonomous-direction]]). That removes the booth-operator as the *primary* adversary, but
|
|
> swaps in **unattended-machine threats** (tailgating, plate spoofing, physical tampering, forced
|
|
> entry). The append-only signed log + reconciliation controls carry over; the emphasis moves from
|
|
> "catch the cashier" to "trust the automated record and detect tampering."
|