In the Web3 space, it is common practice to have sales for tokens to addresses that have been whitelisted off-chain. There are three common on-chain verification mechanisms to validate these users, enabling them to receive the tokens.The three on-chain verification methods (including gas costs of optimiser set to 1,000 runs):storing the address in a mapping (Gas: 23,424)The issues with the mapping is it is very expensive for the seller to store all the addresses.ECDSA Signature Verification (...