Is it possible to create unpredictable random number with Solidity?

Question

I have been researching this topic lately and most of the resources are saying that it's impossible to generate a random number on-chain. However, I have come across a post saying that this function can generate a unpredictable number. Is there any way to predict this function?

function rand() public view returns(uint256) {
    uint256 seed = uint256(keccak256(abi.encodePacked(
        block.timestamp + block.difficulty +
        ((uint256(keccak256(abi.encodePacked(block.coinbase)))) / (now)) +
        block.gaslimit + 
        ((uint256(keccak256(abi.encodePacked(msg.sender)))) / (now)) +
        block.number
    )));

    return (seed - ((seed / 1000) * 1000));
}

Answer 1

Is there any way to predict this function?

A miner can publish their block number with a timestamp that fits together with other criteria:

• difficulty is given for some time
• coinbase is given for even longer period of time
• msg.sender (the real transaction sender and signer) can be one of the miner's addresses

There's no way how to generate truly indeterminable random number on-chain. But you can use an oracle that returns an off-chain generated "random" number.