01 — Problem
Making draw results verifiable
LuckyDraw lets players create accounts, buy tickets and view their participation history. An administration interface manages campaigns, results and statistics. The draw engine uses a commit-reveal mechanism so players can verify the result.
02 — Constraints
Verifying draws and representing amounts
Players need to be able to verify the result using information published by the engine. Monetary amounts are stored as integer cents to avoid errors from floating-point calculations.
03 — Approach
Commit, reveal, verify
Front-endA player area and an admin back-office for campaigns.
Back-endA draw engine that publishes a hash before the draw and reveals the seed afterwards.
DatabaseCampaigns, tickets, entries and transactions.
- Commit-reveal mechanism that lets players recalculate and verify the result
- Configurable campaigns (rules, schedule, prizes)
- Ticket purchase and participation history
- Back-office: results, transactions, analytics, exports
04 — Result
Verification covered by tests
Tests cover seed verification, rejection of a second draw and the representation of monetary amounts.
- Seed committed as a SHA-256 hash published before the draw, revealed after: a genuine draw is validated, a tampered seed is rejected
- Immutable draws: a second draw on the same lottery is refused
- Amounts stored as integer cents, with no floating-point arithmetic
- 45 automated tests (43 unit and integration, 2 end-to-end journeys); lint, type checks, tests and build required to pass in CI
Source access
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