Transfer With Timeout

One interesting use case of Nexa is using it for paper tips. With paper tips, you send a small amount of money to an address, and print the corresponding private key on a piece of paper. Then you can hand out these pieces of paper as a tip or gift to people in person. In practice, however, people might not know what to do with these gifts or they might lose or forget about it.

As an alternative, a smart contract can be used for these kinds of gifts. This smart contract allows the recipient to claim their gift at any time, but if they don't claim it in time, the sender can reclaim it.

pragma nexscript ^0.1.0;

contract TransferWithTimeout(pubkey sender, pubkey recipient, int timeout) {
    // Require recipient's signature to match
    function transfer(sig recipientSig) {
        require(checkSig(recipientSig, recipient));
    }

    // Require timeout time to be reached and sender's signature to match
    function timeout(sig senderSig) {
        require(checkSig(senderSig, sender));
        require(tx.time >= timeout);
    }
}