How to Verify a Rust Coinflip Round in 30 Seconds
Verifying any coinflip outcome takes about 30 seconds using the revealed round inputs.
Step 1: find the round
Account → History → Coinflip → click the specific round. Each entry shows the server seed (revealed after the round), the client seed (yours or auto-generated), the nonce (per-game monotonic counter), and the actual outcome.
Note the values. You'll plug them into the verifier in a second.
The point isn't that you'll verify every round. The point is that any round you're suspicious about, you can verify in under a minute.
Step 2: hit verify
The Verify button on each round opens the inline verifier with the three inputs pre-filled. Click Run verification.
The verifier computes HMAC-SHA256(serverSeed, "${clientSeed}:${nonce}" + game salt), reduces the result to a 0/1 outcome, compares to the stored result. Match means the round was fair. Mismatch is a critical incident — we've never had one.
Step 3: check the inputs
The verifier needs the revealed server seed, original server-seed hash, client seed, nonce, RNG version, and game type. Those are the values that bind the completed round.
Compare the verifier result to the round's displayed outcome. If the re-derivation matches the recorded outcome, the commitment and reveal line up.
Why this works
HMAC-SHA256 is deterministic. Identical inputs always produce identical outputs. The server commits SHA-256(seed) before the round, reveals the raw seed after. A different seed would produce a different hash, breaking the commitment.
Because the outcome is deterministic, the same published inputs must always reproduce the same result. A mismatch is not a normal support issue; it is an incident.
Frequently asked questions
- What if the verifier disagrees with the round outcome?
- Critical incident — email contact@rustsnowball.com with the round ID immediately. We treat verifier mismatches as production-down.
- Does the verifier work for all games?
- Yes. The verifier page supports all public game types and their game-specific inputs.
- What's the rngVersion parameter?
- v2 is the current domain-separated format. v1 is legacy for rounds before late 2026. The history page shows which version each round used.
- Can I verify someone else's rounds?
- Yes. All rounds publish seeds after settlement. You don't need to be the player to verify.