What is Verifiable Onchain Randomness or VRF?

Why is VRF Needed?

• Blockchains are deterministic systems, making it difficult to generate secure random numbers on-chain.
• Naive methods (like using block hashes) can be manipulated by miners or validators, leading to unfair outcomes.
• Off-chain solutions lack transparency and cannot prove that the randomness was not tampered with.

How Does VRF Work?

• A VRF combines unpredictable blockchain data (such as block data) with a private key held by an oracle node to generate a random number and a cryptographic proof.
• The random number and its proof are published on-chain.
• Smart contracts verify the proof before accepting the random number, ensuring that the result is fair and cannot be manipulated by any party, including oracle operators, miners, users, or developers123.

Use Cases

• Blockchain games and NFTs (e.g., random loot drops, lottery winners)
• Random assignment of duties or resources (e.g., assigning judges to cases)
• Consensus mechanisms (e.g., selecting validators or committee members)
• Any application requiring unpredictable, fair outcomes

Examples in Practice

• Chainlink VRF is the most widely used implementation, servicing millions of requests across thousands of smart contracts4.
• Polkadot and Algorand use VRF in their consensus mechanisms to randomly select validators or committee members, ensuring fairness and security in block production.

Key Benefits

• Provably Fair: Every random number comes with a cryptographic proof that can be verified on-chain.
• Tamper-Proof: No single entity can manipulate the outcome.
• Transparent: Anyone can verify the randomness and its proof on the blockchain.