julian
a20400c2c5
Creating a priced subscription wrote only the mutable `subscriptions`
master row and appended NOTHING to the signed ledger — so the cash an
operator collected showed in the live feed, drawer, and shift Z-report
nowhere, leaving no signed trace. A booth operator could sell
subscriptions and pocket the money untraceably — the exact
operator-as-adversary path the append-only signed ledger exists to close.
Found live: 3 priced subscriptions (27,000 ALL) had zero payment events.
Selling a priced subscription now appends a signed `payment` event at
create time: amount = priceMinor x months (full multi-month prepay),
operator-chosen tender (cash->drawer / card->bank), payload
{ subscriptionSale: true, permitId, operator, months }. Folds into the
shift Z-report/drawer with no new summing logic; the feed badges it
"subscription sale" and resolves the holder name. The create response
returns the recorded { sale }; subscriptionRoutes now takes the EventLog
and ShiftService.
Not hard-gated on an open shift (a sale can happen outside the booth money
path) — it warns instead. The 3 historical off-book sales are not
back-fillable (append-only forbids forging dated events) — reconcile via
cash_movement or a Z-report note.
Verified against a copy of the live DB with the real signing modules:
signed payment appended, hash-chain still verifies, lands in shift cash
totals. Build + lint 12/12.
Wiki: subscription "Collecting the fee" deferred -> BUILT (+ the off-book
hole and why); shift sale-folds-in; threat-model worked example
("store the price != account for the sale").
Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V
55 lines
3.1 KiB
Markdown
55 lines
3.1 KiB
Markdown
---
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type: concept
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tags: [parking, security, foundational]
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sources: [parking-system-architecture]
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updated: 2026-06-20
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---
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# Threat Model
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The **second foundational force** (with [[offline-first]]). The central insight is a
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**reframing of who the adversary is**. (See [[parking-system-architecture]] §3.)
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## The key reframing
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Early thinking focused on protecting the database **at rest** — SQLCipher, LUKS, BitLocker,
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TPM-sealed keys. All of that defends against **an outsider who steals the machine or boots from
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external media**.
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That is the **wrong primary threat**. The most likely adversary is the **legitimate operator at
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the booth**. While the app runs, the database is decrypted in memory and the operator has full
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authorised access *through the app*. Encryption does nothing against the classic parking fraud:
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**take the cash, then void/delete the entry/exit record so the books balance.**
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## Consequences
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The controls that actually address insider/operator fraud are different in kind:
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- **[[append-only-event-chain]]** — events appended, never edited/deleted; a "void" is itself a
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recorded event, hash-chained, and **[[atecc608]]-signed** (unforgeable).
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- **[[reconciliation]]** against an authority the operator can't alter — *this is what remote
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sync really is*: a fraud-control mechanism, not just a backup.
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- **[[disk-os-hardening]]** still worthwhile (defeats boot-from-USB) but **not the main event**;
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with LUKS in place, SQLCipher is optional defence-in-depth.
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The same reframing recurs at the device layer: the [[uhppote-controller]]'s real problem is
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unauthenticated commands ([[uhppote-udp-protocol]]), addressed by detection
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([[event-log-ingestion]]) or prevention ([[esp32-custom-controller]]).
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> **Worked example — "store the price" ≠ "account for the sale" (found + fixed 2026-06-20).** Every
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> money-taking action must append a signed `payment` event, or it is invisible to
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> [[reconciliation]]. A concrete miss: selling a [[subscription]] wrote only the mutable
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> `subscriptions` master row (the agreed *price*) and **appended nothing to the ledger**, so the cash
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> the operator collected showed up in the feed/drawer/Z-report **nowhere** — a clean off-book channel
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> (three real sales, 27,000 ALL, untraceable). The fix is the textbook control: append a signed
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> `payment` (`subscriptionSale: true`) at sale time so it folds into the [[shift]] like any taking.
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> **The lesson generalises:** whenever a feature records *an amount* in a mutable table, ask "where is
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> the signed event that says money changed hands?" — a price in master data is not an accountable
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> transaction. See [[subscription]] "Collecting the fee".
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> **Direction shift:** the system is heading toward **fully unmanned operation** — no operator, no
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> booth ([[autonomous-direction]]). That removes the booth-operator as the *primary* adversary, but
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> swaps in **unattended-machine threats** (tailgating, plate spoofing, physical tampering, forced
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> entry). The append-only signed log + reconciliation controls carry over; the emphasis moves from
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> "catch the cashier" to "trust the automated record and detect tampering."
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