What “Provably Fair 2.0” means
Early “provably fair” systems relied on server–client seeds and hash commitments. In Web3, the bar is higher: randomness must be unbiasable and auditable on-chain; code must be publicly verified; secret game state (like hidden cards) should be provably correct; and custody or collateral should be transparently monitored. This article breaks down the technology stack—VRFs, public randomness beacons, zero-knowledge shuffles, open contract verification, and proof-of-reserves—with actionable checklists for players and builders.
Layer 1 — Verifiable randomness for draws and rolls
Verifiable Random Functions (VRFs) return a random value plus a cryptographic proof that contracts verify on-chain before using it, which prevents operators or oracles from tampering with outcomes. Chainlink VRF v2.x/v2.5 is widely used and adds practical features like simpler upgrades and paying fees in LINK or native tokens.
Developers should avoid “homegrown RNG” from block variables (block.timestamp, blockhash, etc.), which are miner/validator-influenced and explicitly flagged as insecure in industry guidance.
Layer 2 — Public randomness beacons and hybrid RNG
Public randomness beacons (e.g., drand’s League of Entropy) publish unpredictable, publicly verifiable random values at fixed intervals using threshold cryptography across independent operators. Some protocols combine beacon outputs with in-contract randomness for defense in depth.
Research and practitioner write-ups discuss beacon design, operator diversity, and update cadence (e.g., ~30-second rounds in documented deployments), offering an auditable, neutral randomness source that games can reference.
Layer 3 — Zero-knowledge proofs for hidden information games
Card games need secrecy and fairness at once. Zero-knowledge (ZK) “verifiable shuffle” protocols prove that a deck was properly shuffled and dealt without revealing card order, a technique rooted in peer-reviewed cryptography and now demonstrated in on-chain poker prototypes. These zk shuffles let anyone verify the game logic while players keep hands private.
ZK systems used in gaming are also supported by modern rollups and zk tooling, making on-chain verification feasible as costs fall.
Layer 4 — Open code, verified builds, transparent upgrades
“Trust the code” only works if users can match source to deployed bytecode. Explorers like Etherscan and decentralized services like Sourcify let developers verify contracts so anyone can audit the exact code that’s running; verification can be automated across chains for consistency. Prefer verified code paths and disclosed upgrade mechanisms (timelocks, roles).
Layer 5 — Payout integrity and bankroll solvency
Fair odds aren’t enough if the bankroll can’t pay. When solvency depends on off-chain collateral (e.g., wrapped assets, custodial treasuries), “proof of reserves” oracles continuously attest to backing, giving users on-chain, near-real-time collateralization checks. That model is used broadly in DeFi and can inform gambling platforms that rely on off-chain assets.
Known pitfalls (and how 2.0 addresses them)
Insecure randomness from block properties lets validators bias outcomes; use VRF or beacon-based randomness instead.
Naïve commit-reveal is vulnerable to “last-revealer” bias (withholding the reveal to skew results). Current research proposes two-phase, randomized reveal ordering and other mitigations; VDF-backed approaches also remove timing advantages.
Opaque or unverified code erodes trust; require Etherscan/Sourcify verification, clear upgrade policies, and public audits.
Player checklist: verify fairness in minutes
- Check randomness. Look for VRF calls or documented beacon use; confirm the contract verifies proofs before settlement.
- Inspect the contract. On the explorer, confirm the “verified” badge and review key functions (bet, payout, withdrawal).
- Watch for insecure RNG red flags such as
block.timestamporblockhash-based draws. - If prizes depend on off-chain collateral (wrapped assets, custodians), look for a proof-of-reserves feed.
- Prefer games that document zk shuffles or equivalent proofs for hidden-information mechanics.
Builder checklist: quick wins for “Provably Fair 2.0”
Use VRF v2.x/v2.5 or a well-documented randomness beacon; never rely on block variables.
For card games, implement a verifiable shuffle (e.g., Neff-style/ZK-SNARK-based) and publish verifier code.
Verify contracts on Etherscan and Sourcify; document upgrade roles/timelocks and publish audits.
When solvency is off-chain, integrate a proof-of-reserves oracle and expose the feed to users.
Document your threat model, including last-revealer and MEV considerations; consider commit-reveal mitigations or VDF designs where appropriate.
FAQs
Why isn’t “blockhash for randomness” good enough?
Because block attributes can be influenced within bounds by block producers; guidance classifies such sources as insecure for randomness. Use VRF or a public beacon instead.
What’s new in VRF v2.5 that matters to games?
Operational upgrades like paying in LINK or native tokens and easier upgrades reduce friction and help standardize secure randomness in production.
Do zk shuffles make poker fully trustless?
They provide strong guarantees that shuffles and deals are correct without revealing cards. You still need verified contracts, sound bankroll management, and careful front-end integrity.
How can I verify a platform’s solvency?
If off-chain collateral is involved, look for a proof-of-reserves feed monitored by independent oracle nodes and visible on-chain.
