Every 2UP Originals outcome is cryptographically committed before you place your bet, and you can independently verify it afterwards. This article explains the mechanism behind that claim.
Key takeaways
Before you bet, 2UP Originals publish a cryptographic hash of the secret server seed. This is a commitment: the outcome is fixed and can no longer be altered.
Your client seed is combined into every outcome, so you co-generate the result.
After the round, the server seed is revealed so you can verify the commitment.
All 10,000,000 Crash rounds were committed publicly and anchored to Bitcoin block #971288 before it was mined.
Provably fair verifies integrity, not odds. RTP and house edge are unchanged.
1. The trust problem with server-side randomness
In online gaming, outcomes are generated server-side, where you cannot observe them. Provably fair replaces trust with cryptographic verification: instead of asking you to believe a result was fair, it gives you the evidence to check.
2. Commit-then-reveal: locking the outcome before the bet
A commitment scheme locks in a value before it is revealed. In plain terms: a pundit posts the final score before kick-off, somewhere it can't be edited, and everyone checks it after the match.
On 2UP Originals, the committed value is the server seed. Its hash is published before you bet; the seed itself is revealed afterwards. Verification is two checks:
Hash the revealed seed. It must match the hash shown before the round.
Recompute the outcome from the seed and your inputs. It must match your result.
If both pass, the outcome existed before your bet and was never modified.
3. SHA-256 and HMAC_SHA256: why the commitment is binding
2UP Originals commit the server seed with SHA-256, the hash function that secures the Bitcoin blockchain, and generate outcomes with HMAC_SHA256, a keyed variant of the same function. Two properties make the commitment binding:
Pre-image resistance (one-way): a hash cannot be reversed to recover its input, so seeing the hash tells you nothing about the outcome.
Avalanche effect (tamper-evident): changing a single character of the input produces a completely different hash. Example: SHA-256 of "2UP" begins 01ece222…, while SHA-256 of "2up" begins 38c2f63e…. A substituted seed would be detected immediately.
4. Server seed, client seed, nonce: three inputs, one deterministic outcome
Input | Provided by | Role | Can you change it? |
Server seed | 2UP Originals | Secret random value, committed by hash before play and revealed afterwards | No |
Client seed | You | Your contribution to every outcome | Yes, at any time |
Nonce | Automatic | Counter that increments with every bet, so each outcome is unique even with the same seed pair | No |
Because the server seed is committed before your client seed is applied, no outcome can be pre-computed or targeted at you.
5. Crash: a hash chain anchored to the Bitcoin blockchain
Crash is a shared-outcome game: every player in a round sees the same multiplier, so no single client seed can govern the result. 2UP Originals therefore use a different mechanism:
Hash chain: 10,000,000 round hashes were pre-generated, each one the SHA-256 hash of the round that follows it. Altering any round breaks the chain. Anyone can verify a link by hashing one round's hash to obtain the previous round's.
Public commitment: the chain's final hash was announced before launch: https://x.com/play2upio/status/2110017766732231084
External entropy: every outcome also incorporates the hash of Bitcoin block #971288, mined after the commitment. A block hash is produced by the Bitcoin network, so neither 2UP Originals nor anyone else could predict or select it: https://mempool.space/block/971288
6. The boundaries of the guarantee
Provably fair | Scope |
Verifies | Outcomes were committed before your bet and were not altered |
Does not change | The odds. RTP and house edge apply as published; 2UP Originals offer RTP of up to 99.5% |
Applies to | 2UP Originals. Third-party slots and live casino games use RNGs certified by independent testing laboratories |
7. Verifying a round in under a minute
8. Frequently asked questions
Can an outcome be changed after I bet? No. A substituted seed would not match the hash you already hold.
Why is the server seed hidden until later? Revealing it during play would expose upcoming outcomes.
Does my client seed affect my odds? No. It guarantees outcomes cannot be pre-computed; it does not alter probabilities.
Why a Bitcoin block? Its hash is generated by the Bitcoin network and cannot be predicted or controlled by any single party.
Is a provably fair game easier to win? No. Same odds, same RTP.
Verify it yourself
Don't take our word for it. Full technical detail you may check here.
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