可以参考 https://programtheblockchain.com/posts/2018/02/17/signing-and-verifying-messages-in-ethereum/
Summary
Signed messages provide a way to authenticate a message to a smart contract.
Signed messages may need a nonce to protect against replay attacks.
Signed messages may need to include the contracts’s address to protect against replay attacks.
Until a better signature standard is adopted,I recommend following the behavior of theeth_sign JSON-RPC method.
主要用到了ecrecover(message, v, r, s)，ecrecover 是 solidity 内置指令
具体的合约实现：
pragma solidity ^0.4.20;
contract ReceiverPays {
address owner = msg.sender;
mapping(uint256 => bool) usedNonces;
// Funds are sent at deployment time.
function ReceiverPays() public payable { }
function claimPayment(uint256 amount,uint256 nonce,bytes sig) public {
require(!usedNonces[nonce]);
usedNonces[nonce]= true;
// This recreates the message that was signed on the client.
bytes32 message = prefixed(keccak256(msg.sender,amount,nonce,this));
require(recoverSigner(message,sig)== owner);
msg.sender.transfer(amount);
}
// Destroy contract and reclaim leftover funds.
function kill()public {
require(msg.sender == owner);
selfdestruct(msg.sender);
}
// Signature methods
function splitSignature(bytes sig)
internal
pure
returns(uint8,bytes32,bytes32)
{
require(sig.length == 65);
bytes32 r;
bytes32 s;
uint8 v;
assembly {
// first 32 bytes, after the length prefix
r := mload(add(sig,32))
// second 32 bytes
s := mload(add(sig,64))
// final byte (first byte of the next 32 bytes)
v := byte(0,mload(add(sig,96)))
}
return(v,r,s);
}
function recoverSigner(bytes32 message,bytes sig)
internal
pure
returns(address)
{
uint8 v;
bytes32 r;
bytes32 s;
(v,r,s)= splitSignature(sig);
return ecrecover(message,v,r,s);
}
// Builds a prefixed hash to mimic the behavior of eth_sign.
function prefixed(bytes32 hash)internal pure returns(bytes32){
return keccak256("\x19Ethereum Signed Message:\n32",hash);
}
}
