Chapter 9: Signature Verification

The sig parameter of the move() function is the player's signature. If the signature is not verified, anyone can call the contract's move() method to move the piece.

The following example is the most common contract in the Bitcoin network: pay to public key hash.

contract P2PKH {
    Ripemd160 pubKeyHash;

    public function unlock(Sig sig, PubKey pubKey) {
        require(hash160(pubKey) == this.pubKeyHash);
        require(checkSig(sig, pubKey));
    }
}

The signature and public key of pay to public key hash are both passed in from the unlock parameter. In the TicTacToe contract, only the signature is passed in from the unlock parameter, and the player's public key has been stored in the contract's PubKey alice and PubKey bob properties.

Put it to the test

1. Verify the sig signature parameter of the move() function.