solidity ecrecover

https://solidity.readthedocs.io/en/latest/units-and-global-variables.html#mathematical-and-cryptographic-functions

ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) returns (address):

recover the address associated with the public key from elliptic curve signature or return zero on error (example usage)

It might be that you run into Out-of-Gas for sha256, ripemd160 or ecrecover on a private blockchain. The reason for this is that those are implemented as so-called precompiled contracts and these contracts only really exist after they received the first message (although their contract code is hardcoded). Messages to non-existing contracts are more expensive and thus the execution runs into an Out-of-Gas error. A workaround for this problem is to first send e.g. 1 Wei to each of the contracts before you use them in your actual contracts. This is not an issue on the official or test net.

ecrecover的思想是，可以计算对应于用于创建ECDSA签名的私钥的公钥，这两个额外的字节通常是由签名提供的。签名本身是椭圆曲线点R和S的两个（编码），而V是恢复公钥所需的两个附加位。

这也解释了为什么返回类型是地址：它返回对应于恢复的公钥（即其sha3/keccak的哈希）的地址。这意味着要实际验证签名，检查返回的地址是否等于相应的私钥应该已经签署哈希的那个地址。

找到了这个接口的代码：

// https://github.com/ethereum/go-ethereum/wiki/Management-APIs#personal_ecRecover
func (s *PrivateAccountAPI) EcRecover(ctx context.Context, data, sig hexutil.Bytes) (common.Address, error) {
    if len(sig) != 65 {
        return common.Address{}, fmt.Errorf("signature must be 65 bytes long")
    }
    if sig[64] != 27 && sig[64] != 28 {
        return common.Address{}, fmt.Errorf("invalid Ethereum signature (V is not 27 or 28)")
    }
    sig[64] -= 27 // Transform yellow paper V from 27/28 to 0/1

    rpk, err := crypto.Ecrecover(signHash(data), sig)
    if err != nil {
        return common.Address{}, err
    }
    pubKey := crypto.ToECDSAPub(rpk)
    recoveredAddr := crypto.PubkeyToAddress(*pubKey)
    return recoveredAddr, nil
}

从这里我们可以看见，如果你使用web3来调用geth,你的v只有27，28两种选择，不会有分叉中的35，36

https://github.com/ethereum/go-ethereum/blob/55599ee95d4151a2502465e0afc7c47bd1acba77/internal/ethapi/api.go#L452-L459

这是所有api接口的内部实现代码，go-ethereum/internal/ethapi/api.go