What Is On-Chain Random Number (VRF)? How Do Blockchain Games Ensure Fairness?

Core Conclusion on Blockchain Game Fairness: True fairness is not 'code made up on the spot', but 'verifiable random numbers'.

For blockchain games (including lotteries, blind boxes, PvP matching) to ensure fairness, the core issue is only one:How are random numbers generated, and can players verify they are fair?

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In traditional games, random numbers are generated by the game server, and players cannot verify their authenticity — you never know if this 'luck' is being manipulated behind the scenes. On the blockchain,insecure random number generation methods (such as directly using block hashes or timestamps) can be easily exploited by attackers, rendering fairness completely ineffective. The industry-recognized solution isVRF (Verifiable Random Function), with the most typical implementation beingChainlink VRF.

I. Why Are Ordinary On-Chain Random Numbers 'Not Random'?

The blockchain itself is adeterministic system— each node executing the same code must get the same result to reach consensus. This means that a smart contract cannot directly 'randomly generate' a number. Common developer practice is to use on-chain data as a 'random source':

• blockhash(current block hash)

• block.timestamp(block timestamp)

• block.number(block number)

• block.coinbase(coinbase address)

These data appear random, but can actually be manipulated.Validators or miners know these variables and can choose or influence their values to some extent, thereby gaining 'hidden control' over game results. This is equivalent to a casino knowing the next card before playing with you. Therefore, this insecure random number generation is listed as an important security vulnerability type in smart contract security (OWASP Smart Contract Top 10 SC09:2025 Insecure Randomness).

II. What Is VRF? How Does It Solve the 'Trust' Problem?

The core of VRF (Verifiable Random Function) is not 'more random', but 'verifiable'.

The workflow of Chainlink VRF can be broken down into three steps:

1. Request: The smart contract requests a random number from the Chainlink network.

2. Generation & Fulfillment: Chainlink's oracle generates the random number off-chain, while simultaneously generating acryptographic proofthat this random number was indeed generated by the prescribed algorithm and has not been tampered with.

3. Verification: This proof is sent back on-chain along with the random number. Anyone can use this proof to verify the authenticity of the random number on-chain.

Because the random number is generated off-chain and verified on-chain, itescapes the possibility of manipulation by miners/validators, and the verification process is open and transparent.Even if someone tries to manipulate the data, it will be rejected by the on-chain verification mechanism; manipulation attempts only affect response speed, not the authenticity of the result.

III. Comparison of Mainstream VRF Solutions

Chainlink VRF is currently the most mainstream solution, deployed on Ethereum and major EVM-compatible chains. It offers two payment models:

• Subscription Model: Create a subscription account and pre-deposit LINK or native tokens, suitable for projects that need to generate random numbers frequently.

• Direct Payment Model: Pay per request, suitable for low-frequency scenarios.

IV. For Players: How to Determine If a Chain Game's Random Number Is 'Fair'?

For ordinary players, there is no need to read the code. You can quickly judge by the following points:

1. Check if the project documentation explicitly uses VRF: If a game or NFT project claims to be 'fair', it usually publicly mentions the use of a verifiable random scheme like Chainlink VRF.

2. Check if verification proofs are available: On a block explorer, you can see VRF requests and 'verification passed' records — meaning the source of the random number is publicly verifiable.

3. If a project only says it uses 'blockchain random numbers' but does not specify the implementation method, it is advisable to remain cautious— using insecure on-chain random sources (like block hashes) can still be manipulated by miners or validators.

V. Clarification of Common Misconceptions

• VRF is not 'unpredictable' but 'untamperable': In theory, any random number is unpredictable before it is generated, but the key is whether it can be verified as fair after generation. The value of VRF lies in providing a verifiable proof, not in making the random number itself 'more random'.

• VRF is not zero-latency: Because it involves the two steps of 'request-return-verification', VRF response has some delay and is not suitable for scenarios requiring extremely high-frequency random numbers.

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VI. Result Verification Method

You can verify the VRF call by checking the relevant contract transaction records on a blockchain explorer (such as Etherscan). For Chainlink VRF,the execution of thefulfillRandomWordsfunction means that the random number has been generated and verified, and the accompanying data and cryptographic proof can be independently verified by anyone on-chain.