Provably Fair Verifier

When you play at a provably fair crypto casino, every single bet generates a cryptographic proof that the result was determined fairly. But that proof is only valuable if you actually check it. Most players never do — they trust the casino's word that the system works. Our free Provably Fair Verifier changes that by giving you a simple, independent way to recalculate any game result yourself.

Provably fair gambling is one of the most significant innovations in online gaming. Unlike traditional online casinos where you have to trust that a Random Number Generator (RNG) was properly audited by a third party, provably fair systems use cryptographic hash functions to create a mathematical guarantee of fairness. Before each bet, the casino commits to a server seed by publishing its hash. You provide (or accept) a client seed. Together with a nonce that increments with each bet, these three values are combined through a hash function to produce the game result. After the bet, the casino reveals the original server seed so you can verify everything independently.

This tool supports all major algorithms used by crypto casinos: SHA-256, SHA-512, HMAC-SHA-256, and HMAC-SHA-512. Whether you play at Stake, BC.Game, Roobet, BitStarz, or any other provably fair casino, you can paste in your seeds and nonce and instantly see the computed hash and derived game results — dice rolls, crash multipliers, and card values.

Every calculation happens entirely in your browser using the Web Crypto API. No data is transmitted to our servers. Your seeds, nonces, and results never leave your device. This is not just a privacy feature — it's fundamental to the verification process. If a third-party server were involved, you'd have to trust that server too, defeating the purpose of independent verification.

Below the tool, you'll find a comprehensive guide explaining exactly how provably fair systems work, how to obtain your seeds from popular casinos, and how to interpret the results. Whether you're a seasoned crypto gambler who verifies every bet or a newcomer trying to understand what "provably fair" actually means, this tool and guide have you covered.

Complete Guide to Provably Fair Verification

What Is Provably Fair Gaming?

Provably fair gaming is a transparency mechanism unique to cryptocurrency casinos. It leverages cryptographic hash functions — the same mathematics that secure Bitcoin and Ethereum — to create an auditable trail for every single bet. The core principle is simple: neither the casino nor the player can predict or manipulate the game outcome after the bet has been placed, and both parties can verify this independently after the fact.

Traditional online casinos rely on Random Number Generators (RNGs) that are audited by third-party firms like eCOGRA or iTech Labs. While these audits provide some assurance, players must trust both the casino and the auditor. Provably fair systems eliminate the need for this trust by making the mathematics transparent and independently verifiable. It's the difference between "trust us, we were audited" and "here's the math — check it yourself."

How the Cryptographic System Works

The provably fair system follows a commit-reveal pattern common in cryptographic protocols:

1. Commitment phase: Before any bets are placed, the casino generates a random server seed. It then creates a SHA-256 hash of this seed and shows you the hash. This hash acts as a commitment — the casino has locked in its seed but hasn't revealed it. Changing the seed later would produce a completely different hash.
2. Player input: You are assigned or choose a client seed — a random string that you control. Some casinos let you type anything you want; others generate one that you can change. This ensures the casino cannot predict your contribution to the final result.
3. Result generation: For each bet, the server seed, client seed, and a nonce (bet counter) are combined and hashed using an algorithm like HMAC-SHA-256. The resulting hash determines the game outcome — for a dice game, the first few hex characters are converted to a number between 0 and 100; for a crash game, the hash determines the multiplier; for cards, it maps to a specific card in the deck.
4. Reveal and verification: When you rotate to a new server seed (which you can do at any time), the previous server seed is revealed in full. You can now hash it yourself and confirm it matches the commitment hash you were shown. Then you can recompute every single bet result from that seed rotation to verify they were all fair.

Understanding Hash Algorithms

Different casinos use different cryptographic algorithms. Here's what each one in our tool does:

• SHA-256: A one-way hash function from the SHA-2 family. It takes any input and produces a fixed 256-bit (64 hex character) output. Used by some simpler provably fair implementations where the server seed and client seed are concatenated before hashing.
• SHA-512: Similar to SHA-256 but produces a 512-bit (128 hex character) output. Provides more bits of entropy, useful for games that need to derive multiple random values from a single hash (e.g., shuffling an entire deck of cards).
• HMAC-SHA-256: The most common algorithm in provably fair casinos. HMAC (Hash-based Message Authentication Code) uses the server seed as a secret key to authenticate a message (the client seed and nonce). This is more cryptographically sound than simple concatenation because it prevents length-extension attacks. Stake, BC.Game, and Roobet all use HMAC-SHA-256.
• HMAC-SHA-512: HMAC variant using SHA-512 for longer output. Used when games need more random bytes from a single computation.

How Game Results Are Derived

Once the hash is computed, the hex string must be converted into a game result. The exact method varies by game type:

Dice Roll (0–100)

The first 8 hex characters of the hash are converted to a decimal number (0 to 4,294,967,295). This is divided by the maximum value (0xFFFFFFFF) and multiplied by 100 to produce a result between 0.00 and 100.00. Most dice games let you bet over or under a target number, with the payout calculated from the probability.

Crash Multiplier

The crash multiplier uses a similar conversion of the first 8 hex characters, but applies a formula that produces a distribution where most results are low (1×–2×) but occasionally very high (100×, 1000×+). A typical formula incorporates a house edge (usually 3–4%) and calculates: max(1, (1 - houseEdge) × 2³² / (rawValue + 1)). This ensures a minimum multiplier of 1× (instant crash) and an unbounded maximum.

Card Value

For card games, the hash value is mapped to a position in a standard 52-card deck. The raw number modulo 13 gives the rank (Ace through King), and integer division by 13 modulo 4 gives the suit. For full shuffles, additional bytes from the hash are used for each subsequent card using a Fisher-Yates shuffle seeded by the hash.

How to Get Your Seeds from Popular Casinos

Each casino has a slightly different interface for accessing your provably fair seeds:

• Stake: Click your avatar → Settings → Fairness. You'll see your active client seed and the hashed server seed. Click "Unhash" or rotate to reveal the previous server seed.
• BC.Game: Go to your profile → Fairness Verification. Your active and previous seeds are listed there along with a built-in verifier.
• Roobet: Click the fairness shield icon during any provably fair game, or go to Settings → Fairness.
• BitStarz: Look for the "Provably Fair" option in supported games. Click to reveal seed information and past bet verification.

Common Verification Mistakes

If your result doesn't match the casino's displayed result, check these common issues:

• Using the hashed server seed: You need the revealed (unhashed) server seed, not the SHA-256 hash shown before the reveal.
• Wrong algorithm: Make sure you've selected the correct algorithm for your casino. Most use HMAC-SHA-256, but some use plain SHA-256.
• Incorrect nonce: The nonce must match the exact bet number. If you placed 47 bets with a seed pair, the first bet is nonce 0 (or 1, depending on the casino) and the last is nonce 46 (or 47).
• Different result derivation: Our tool uses a standard derivation method, but some casinos use proprietary formulas. The hash itself should always match — if it does, the underlying randomness is verified even if the game result conversion differs slightly.

Limitations of Provably Fair

While provably fair systems are a massive improvement over blind trust, they have limitations worth understanding. Provably fair only proves that the specific game result was generated from the committed seeds — it doesn't prove the overall house edge is as advertised, that the game logic is correct, or that the casino will actually pay your winnings. It also doesn't cover non-provably-fair games at the same casino (many crypto casinos offer both provably fair originals and traditional third-party slots that rely on conventional RNG audits).

Additionally, provably fair is only as trustworthy as the implementation. A casino could theoretically generate millions of server seeds, pick one that produces favourable results, and use that. Good implementations mitigate this by letting you set your own client seed (adding unpredictability) and by using sequential nonces (preventing cherry-picking). Always verify, and always use your own client seed.

Frequently Asked Questions