I had to implement this ecreover extencion on a project I been working because I had trouble recovering the signer from a signature on Ethereum using solidity, here is how I fixed it reusing the ECVerify Lib
pragma solidity ^0.4.8;
library ECRecover {
// ECRecovery Methods
// Duplicate Solidity's ecrecover, but catching the CALL return value
function safer_ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) internal returns (bool, address) {
// We do our own memory management here. Solidity uses memory offset
// 0x40 to store the current end of memory. We write past it (as
// writes are memory extensions), but don't update the offset so
// Solidity will reuse it. The memory used here is only needed for
// this context.
// FIXME: inline assembly can't access return values
bool ret;
address addr;
assembly {
let size := mload(0x40)
mstore(size, hash)
mstore(add(size, 32), v)
mstore(add(size, 64), r)
mstore(add(size, 96), s)
// NOTE: we can reuse the request memory because we deal with
// the return code
ret := call(3000, 1, 0, size, 128, size, 32)
addr := mload(size)
}
return (ret, addr);
}
function ecrecovery(bytes32 hash, bytes sig) returns (address) {
bytes32 r;
bytes32 s;
uint8 v;
if (sig.length != 65)
return (address(0));
assembly {
r := mload(add(sig, 32))
s := mload(add(sig, 64))
v := byte(0, mload(add(sig, 96)))
// Alternative solution:
// 'byte' is not working due to the Solidity parser, so lets
// use the second best option, 'and'
// v := and(mload(add(sig, 65)), 255)
}
// albeit non-transactional signatures are not specified by the YP, one would expect it
// to match the YP range of [27, 28]
//
// geth uses [0, 1] and some clients have followed. This might change, see:
// https://github.com/ethereum/go-ethereum/issues/2053
if (v < 27)
v += 27;
if (v != 27 && v != 28)
return (address(0));
bool ret;
address addr;
(ret, addr) = safer_ecrecover(hash, v, r, s);
return addr;
}
}
