HOW TO VERIFY PROVABLY FAIR CRASH
Verify Your Last Crash Round Right Now
Grab your server seed, client seed, and nonce from your casino's fairness page and paste them into our verifier. It reproduces the exact crash-point formula in your browser — completely free, no sign-up required.
Open Provably Fair VerifierThe Three Seeds and What Crash Verification Proves
Every provably fair Crash round is built from three inputs. The server seed is a random string the casino generates and keeps secret during play — but it commits to it in advance by publishing its SHA-256 hash, like a sealed envelope. The client seed is yours; you can set it to any value, which guarantees the casino could not have pre-computed the bust points just for you. The nonce is a counter that increases by one with every round on that seed pair.
For Crash specifically, verification proves one thing precisely: the bust multiplier was fixed before the round began, and was not lowered the moment you placed a large bet. Because the server seed hash was published in advance and you chose the client seed, neither side can change where the round crashes. After you rotate (retire) the seed pair, the casino reveals the unhashed server seed and you can recompute every multiplier. For the general mechanics across all games, see our complete guide to verifying provably fair results.
How the Hash Becomes a Multiplier: The Real Formula
There are two crash formulas in common use, and it matters which one your casino uses. This guide covers the Stake-compatible model, as implemented in the widely used open-source reference verifier lucasholder/fair (explicitly built to match Stake's output). Here are the steps:
- 1Build the HMAC. The server seed is the HMAC key; the message is
clientSeed:nonce. ComputingHMAC_SHA256(serverSeed, "clientSeed:nonce")produces a 32-byte hash (64 hex characters). - 2Read the first 4 bytes as an integer. Take the first 8 hex characters and read them as a big-endian 32-bit unsigned integer, giving a whole number
intfrom 0 to 4,294,967,295 (that is 2³² − 1). - 3Apply the crash formula.
crashPoint = max(1, (2³² / (int + 1)) × 0.99), then floor to two decimals. The × 0.99 is the 1% house edge; the max(1, …) guarantees the result is never below 1.00x.
The instant 1.00x — how the house edge bites. When int is very large, 2³² / (int + 1) drops below 1, and after the × 0.99 the value is ≤ 1. The max(1, …) then pins the round to exactly 1.00x — an instant bust. This happens for the top ~1% of integer values, so about 1 in 100 rounds busts immediately. It is fully determined by the hash, not chosen live by the casino. (Note: the classic Bustabit formula instead reads 52 bits and forces 1.00x when the value is divisible by a constant — a different mechanism for the same purpose.)
Skip the Maths — Let the Tool Do It
You do not have to compute HMACs by hand. Paste your seeds and nonce into our verifier and it reproduces the crash-point formula above instantly, in your browser, with nothing sent to a server.
Launch the Verifier ToolWorked Example You Can Reproduce
Let us derive a real multiplier from real inputs. These are genuine values computed with HMAC-SHA256 — paste them into any HMAC tool (or our verifier) and you will get the identical hash.
| Input | Value |
|---|---|
| Server seed | serverSeed123 |
| Client seed | clientSeed456 |
| Nonce | 7 |
- 1Compute the HMAC.
HMAC_SHA256("serverSeed123", "clientSeed456:7")=2582e59bd17a0f39282f13349ff7b3f803c57fa6a22315403869a9c6da6de5bc - 2Read the first 8 hex characters as an integer.
2582e59bin decimal is 629,335,451. - 3Apply the formula. (2³² / (629,335,451 + 1)) × 0.99 = (4,294,967,296 / 629,335,452) × 0.99 = 6.8246 × 0.99 = 6.756. Since that is above 1, max(1, …) keeps it, and flooring to two decimals gives 6.75x.
Result: these seeds at nonce 7 crash at 6.75x — every single time, on any machine. If the casino had busted you earlier than 6.75x on these exact inputs, the verification would fail and you would know the round had been altered. That reproducibility is the entire point.
Where to Find Your Crash Seeds
Before you can verify, you need the unhashed server seed, which the casino only reveals once you rotate (retire) the seed pair. Here is where to look on the main provably fair platforms:
| Casino | How to Find Your Seeds |
|---|---|
| Stake | Profile icon → Settings → Fairness. Note your active client seed and the next server seed hash, then click Rotate / New Seed to reveal the previous unhashed server seed. The Crash bet detail shows the nonce. |
| Roobet | Open your Game History, click the Crash bet, then Fairness / Reveal Seeds. The server seed is shown after the pair is rotated, alongside the client seed and nonce. |
| BC.Game | Avatar → Profile → Fairness. View the current seed pair, then rotate to unhash the old server seed. Open Game History for the per-round nonce. |
What This Proves — and What It Does Not
Provably fair verification is powerful, but it is precise about what it guarantees. Be clear on both sides:
- ✓It proves the crash point was not altered after your bet. The multiplier was committed by the server seed hash before the round, so the casino could not lower it to bust you early.
- ✓It proves the casino used the seeds it claimed. A matching multiplier confirms the published server seed really does hash to the committed value and produces the crash point you saw.
- ✗It does NOT remove the house edge. The × 0.99 factor and the ~1% instant busts are baked into the formula itself. A fair crash point and a long-term mathematical edge for the casino coexist — verification confirms fairness, not profitability.
- ✗It does NOT guarantee you get paid. Provably fair maths says nothing about whether a casino will process your withdrawal or treat you fairly elsewhere. For that, choose a licensed, reputable operator — see our best provably fair casinos.
Key Takeaways
Provably fair Crash (Stake model) derives the multiplier from HMAC-SHA256(serverSeed, clientSeed:nonce): the first 4 bytes become a 32-bit integer, then crashPoint = max(1, (2³² / (int + 1)) × 0.99). The × 0.99 and the resulting ~1% instant-1.00x busts are the house edge. Our worked example (serverSeed123 / clientSeed456 / nonce 7) crashes at 6.75x, reproducibly. Check your own rounds with our Provably Fair Verifier.
Frequently Asked Questions
max(1, (2³² / (int + 1)) × 0.99), rounded down to two decimals. The 0.99 factor is the 1% house edge. The same seeds always reproduce the same multiplier, so you can verify any round after the seed is revealed with our verifier tool.(2³² / (int + 1)) × 0.99 works out to 1.0 or less, the max(1, ...) clamp pins the result at exactly 1.00x. That happens for roughly the top 1% of integer values, so about 1 in 100 rounds crashes immediately. It is fully determined by the hash, not chosen by the casino in the moment.max(1, ...) clamp produce the instant-1.00x cases. Both are verifiable; this guide uses the Stake-compatible formula from the open-source lucasholder/fair reference.