What Is Provably Fair? How Flush Originals Prove Every Round Is Honest

Written by Boris Beria, crypto casino specialist. Updated June 2026.

‍

Provably fair is a cryptographic system that lets you confirm every game result was generated honestly, before and after the round happens. You verify the math yourself, you do not trust a certificate. At Flush, the system applies to our in-house Originals games, not to third-party slots or live dealer titles.

If you have ever wondered whether a provably fair bitcoin casino actually delivers on the claim, this guide covers the mechanics in full: what the three inputs are, how HMAC turns them into a verifiable outcome, which Flush Originals use it, and how to run the check yourself in under three minutes.

Scope note: Provably fair at Flush applies to our in-house Flush Originals (Plinko, Dice, Crash, Mines, Keno, Wheel, Video Poker, and 11 more titles). Third-party slot games and live dealer titles use the providers' own certified RNGs, audited by independent labs including Gaming Laboratories International, iTech Labs, and eCOGRA. Verification of Flush Originals results happens inside each game.

‍

How Provably Fair Works: Server Seed, Client Seed, Nonce, and HMAC

Provably fair runs on three pieces of data and one hash function. Together they make every round mathematically verifiable by anyone with a calculator and an internet connection.

Server seed

Flush generates a long random string before your session starts. The system immediately hashes it using HMAC-SHA256 and shows you only the hash. The original seed stays locked until the session ends or you rotate seeds. The hash is the commitment: a one-way fingerprint that cannot be reversed but can be checked against the original seed once it is revealed.

Client seed

You set it. It can be any string up to 64 characters, and you can rotate it whenever you want from the Fairness menu inside the game. The client seed is your contribution to the randomness. The casino cannot predict what you will choose, which means it cannot pre-engineer results.

Nonce

A counter that increases by one with every bet, so the same pair of seeds produces a fresh outcome on each round. If nonces did not exist, two bets placed with the same seeds in the same session would produce identical results.

How the round resolves

When the round resolves, the function below produces a hex string:

HMAC_SHA256(serverSeed, clientSeed:nonce:hashIndex)

The game maps that hex string to an outcome using a documented per-game algorithm. At session end, or whenever you rotate seeds, the original server seed is revealed. You hash it yourself using SHA256 and confirm it matches the commitment you saw at the start.

Two consequences matter:

• The casino cannot pick a server seed after seeing your bet, because the hash was visible before the bet. Changing the seed changes the hash, and the new hash would not match.
• You cannot game the system by knowing the outcome in advance, because the server seed stays locked until the round closes.

‍

The three-step provably fair cycle. Every result is cryptographically locked before you bet and verifiable after.

The Five Components of Every Provably Fair Round

• Server seed: a random 64-character hex string generated by the casino before your session begins. Never revealed until after the round ends.
• Server seed hash: the SHA256 fingerprint shown to you before you play. This is the commitment.
• Client seed: your contribution to the randomness, up to 64 characters. You control it and can change it at any time.
• Nonce: a counter that increases by one with every bet. Ensures each result is unique even when the seeds stay the same.
• Result: generated by combining all three inputs through HMAC-SHA256. Reproducible by anyone with those inputs after the round ends.

‍

Provably fair components at Flush. The server seed hash is your proof the result existed before your bet.

Which Flush Games Are Provably Fair?

Provably fair at Flush applies to all 18 in-house Originals. Each game exposes seeds, hashes, and a verify function from inside the game window:

• Plinko: 16-row pin grid
• Dice: custom under/over slider
• Crash: bitcoin crash game
• Mines: adjustable bomb count
• Keno: picks of 1 to 10
• Wheel: multiple risk tiers
• Video Poker: standard 5-card draw
• Blackjack: classic rules
• Limbo: target multiplier slider
• Baccarat: punto banco rules
• HiLo: adjustable deck settings
• Dragon Tower: multiple risk levels
• Coin Flip
• Cross the Road
• Cross the Lake
• Slider
• Diamonds
• Roulette

‍

How to Verify a Flush Originals Result

You do not need special software. You need a browser and three minutes.

1. Open any Flush Originals game and start a session. The Fairness panel becomes accessible the moment a session is active.
2. Open the Fairness menu. Click the shield icon labeled Fairness in the bottom-right corner of the game window. The panel opens with two tabs: Seeds and Verify.
3. Record the server seed hash before you bet. Go to the Seeds tab and copy the Active Server Seed (Hashed). This is the commitment.
4. Set or rotate your client seed. Any string works. Changing mid-session also reveals the previous server seed for verification.
5. Play the round and note the nonce. The Total bets made with pair counter in the Seeds tab is your nonce.
6. Reveal the server seed. Click Change in the Rotate Seed Pair section. The previous server seed is now accessible for verification.
7. Recompute the HMAC. Open any HMAC-SHA256 calculator. Use the revealed server seed as the key, the string clientSeed:nonce:0 as the message, and read the hex output.
8. Map the hex to an outcome. Each game has a documented mapping in the Provably Fair Document link inside the game.
9. Confirm the outcome matches. If it matches, the round was honest. If it does not, the casino tampered and the seeds prove it.

‍

Four steps to verify any provably fair result at Flush. No special software required.

Worked Example: A Real Plinko Round

Here is a real round played on Plinko at Flush. Every value below was recorded from the Fairness panel before and after the bet.

• Server seed hash (committed before bet): 8c56b7ac3f01f05fcb8d0a318d3b656e032142bc53ae9a0b653bc272a8593c31
• Client seed: 9d16227e50718b9f7f38f0254791b1557217daf735010c706982dfe9702972c4
• Nonce: 1
• Result shown by game: 1.10x

The hash above is the commitment Flush locked in before the round started. To complete verification, rotate your seed pair: the system reveals the original server seed. SHA256-hash it yourself and confirm it produces 8c56b7ac3f... Then run HMAC_SHA256(serverSeed, "clientSeed:1:0") and map the output to the Plinko result using the documented algorithm in the Provably Fair Document inside the game.

‍

Traditional casinos require trust in institutions. Provably fair casinos require only trust in mathematics.

Why Slots and Live Dealer Games Are Not Provably Fair

Provably fair only works when the casino owns the random number generator. Third-party game studios keep their RNG state private. The studio runs the math, the casino displays the result. Flush cannot reveal seeds we never had.

That does not mean those games are untested. Every studio that ships games to a regulated casino is audited by an independent testing lab. The three most respected in the industry are Gaming Laboratories International (GLI), iTech Labs, and eCOGRA. These labs check the RNG output for distribution, look for bias, and certify the published RTP figure against actual long-run outcomes.

The trade-off is real. You cannot verify a single slot spin yourself the way you can verify a single Originals round. Provably fair is a stricter model that Flush applies where it is technically possible: in-house Originals.

‍

What Provably Fair Does Not Prove

Provably fair is a powerful guarantee, but it does not answer every fairness question. Five points worth knowing:

It does not eliminate the house edge. Every Originals game has a published mathematical edge. Provably fair proves no single round was manipulated. It does not change the long-run math built into the game design.

It does not change a game's volatility. Hot streaks and cold streaks are normal in any random system. Provably fair confirms the variance was honest, not that it was kind.

Old rounds remain verifiable after seed rotation. When you rotate a client seed, the system reveals the old server seed. You can still verify every round played under the previous seed pair from your bet history.

Pre-hash collusion is what the commitment prevents. The server seed is hashed and shown before you place a bet. Any claim that the casino picked a different seed after seeing your bet is disproved by the hash.

You do not need to remember your seeds. Every Flush Originals bet stores the server seed (post-reveal), client seed, nonce, and outcome in your account history.

‍

A Short History of Provably Fair

Provably fair was invented by the first generation of crypto-native casinos in the early 2010s. The model emerged because the existing industry trust framework was a poor fit for the Bitcoin community's "verify, do not trust" culture. Engineers borrowed from cryptographic commitment schemes, the same primitive used in Bitcoin transactions, to build a system where a casino could prove fairness on every spin without exposing its internal RNG state.

The standard pattern that emerged, server seed plus client seed plus nonce plus HMAC, has been stable for over a decade. It is the only verification model where the player, not a third party, holds the proof.

‍

FAQ

Is provably fair available on all games at Flush?

No. Provably fair applies to Flush Originals only: Plinko, Dice, Crash, Mines, Keno, Wheel, Video Poker, Blackjack, Limbo, Baccarat, HiLo, Dragon Tower, Coin Flip, Cross the Road, Cross the Lake, Slider, Diamonds, and Roulette. Third-party slot games and live dealer titles use the studios' own RNGs, independently audited by labs including GLI, iTech Labs, and eCOGRA.

How do I verify a provably fair result at Flush?

Open the Fairness menu (shield icon, bottom-right of any Originals game). Copy the server seed hash before you bet, set your client seed, play the round, then rotate seeds to reveal the server seed. Run HMAC-SHA256 yourself or use the built-in Verify tab and confirm the outcome matches.

Can the casino cheat on a provably fair game?

No. The server seed hash is committed before you bet. The casino cannot retroactively change the seed without producing a different hash, which would not match the one you already saw. That hash is the cryptographic anchor.

What is HMAC and why does it matter?

HMAC is a keyed hash function. The server seed is the key, the client seed and nonce form the message, and the output is the random number that determines your outcome. Changing any input changes the output unpredictably, so any tampering becomes visible.

Can I rotate my client seed?

Yes, from the Fairness menu inside any Originals game. Under Rotate Seed Pair, enter a new client seed and click Change. Rotating reveals the previous server seed, which lets you verify every round played under it.

Does provably fair mean the house edge is zero?

No. Provably fair proves no single round was manipulated. Each game keeps its published house edge across long-run play. Provably fair is about per-round integrity, not about changing the underlying math.

Do I need to verify my identity to play at Flush?

No. Flush does not require KYC verification. You connect with a crypto wallet (MetaMask or WalletConnect) and play immediately. No ID upload, no signup form, no document check at any point. Your account is your wallet address.

How fast are withdrawals at Flush?

Withdrawals process in under two minutes to your crypto wallet. No withdrawal limit, no processing fee beyond the network transaction cost. Supported currencies: BTC, ETH, BNB, LTC, USDT, USDC, TRX, POL, and DOGE.

Can I play Flush Originals on mobile?

Yes. All 18 Flush Originals run fully in your mobile browser. No app download required. The Fairness menu and seed verification work on mobile identically to desktop.

‍

Gambling Responsibly

Gambling is entertainment, not a way to make money. Always set a budget before you play and never chase losses. If gambling stops being fun, take a break.

Free help is available 24/7:

• GamCare: gamcare.org.uk | 0808 8020 133
• GamStop: gamstop.co.uk (free self-exclusion for UK players)
• BeGambleAware: begambleaware.org

Flush supports responsible gambling. Players must be 18 or over.

‍

Ready to Try Provably Fair at Flush?

Provably fair lets you trust the math, not the marketing. Browse the Flush Originals lobby to try any of the 18 games free in demo mode, no account needed. Run a verification yourself on your first real round.

Flush supports 9 cryptocurrencies: BTC, ETH, BNB, LTC, USDT, USDC, TRX, POL, and DOGE. Deposits are instant. Withdrawals process in under two minutes. No bank delays, no KYC verification, no maximum withdrawal limits.

‍

‍