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Chainlink VRF is a service using the VRF(Verifiable random function) to generate verifiable randomness on-chain, a smart contract supplies a seed (which should be unpredictable to the oracles to whom it is provided), and the seed in turn is used to generate a random number that is sent back to the contract.

I read documents and some codes, function RequestRandomWords in smart contract VRFCoordinator supplies preseed to event log. Then Oracle node takes the preseed and a blockhash as input to generate a seed for VRF. At last, VRF uses the seed and its private key to generate verifiable randomness.

My question is:

Which blockhash is used to generate seed in VRF? It looks like the next block after the block where VRF request was made but I do not see the details in document.

Thanks in advance.

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In its source code, see VRFCoordinatorV2#getRandomnessFromProof:


bytes32 blockHash = blockhash(rc.blockNum);
if (blockHash == bytes32(0)) {
  blockHash = BLOCKHASH_STORE.getBlockhash(rc.blockNum);
  if (blockHash == bytes32(0)) {
    revert BlockhashNotInStore(rc.blockNum);
  }
}

The hash of the block which contains the request, is used.

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