1. The only accepted callback function is fulfillRandomness(bytes32 _reqId, uint256 _random) with the function selector being 0x1f1f897f. This is required in order to avoid malicious callbacks.
2. The fulfillRandomness function is able to verify the VRF value and minimize the amount of keep3rs that can fulfill data with the following check functions:
require(isFulfiller[msg.sender], "Must is fulfiller"): fulfillRandomness function makes sure that only a fixxed amount of keep3rs are allowed to fulfil data ;
require(isNode(validator), "Forbidden validator"): The random value is guaranteed to be generated from Oraichain's validators.
3. The gas limit is 800,000. This means that any fulfilling or callback request exceeding the limit amount can lead to tx getting reverted, at which case the oracle will ignore and refuse to execute such request.