eth_sign_verify.go

package main

import (
	"fmt"

	"github.com/ethereum/go-ethereum/accounts"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/crypto"
)

func main() {
	fmt.Println(verifySig(
		"0x0EaE3eF6CC7176553E6B45d94e9eFDE2Da7B82a5",
		"0x34850b7e36e635783df0563c7202c3ac776df59db5015d2b6f0add33955bb5c43ce35efb5ce695a243bc4c5dc4298db40cd765f3ea5612d2d57da1e4933b2f201b",
		[]byte("Example `personal_sign` message"),
	))
}

func verifySig(from, sigHex string, msg []byte) bool {
	sig := hexutil.MustDecode(sigHex)

	msg = accounts.TextHash(msg)
	if sig[crypto.RecoveryIDOffset] == 27 || sig[crypto.RecoveryIDOffset] == 28 {
		sig[crypto.RecoveryIDOffset] -= 27 // Transform yellow paper V from 27/28 to 0/1
	}

	recovered, err := crypto.SigToPub(msg, sig)
	if err != nil {
		return false
	}

	recoveredAddr := crypto.PubkeyToAddress(*recovered)

	return from == recoveredAddr.Hex()
}

In our case, the last line had a bug, in which it needs the address to be lower cased, otherwise the comparison fails. Fix this bug lowering the case of the right parameter, like this:

return from == strings.ToLower(recoveredAddress.Hex())

@psmithson

+1

@psmithson
in that case you should use something like

return strings.ToLower(from) == strings.ToLower(recoveredAddress.Hex())

@psmithson in that case you should use something like

return strings.ToLower(from) == strings.ToLower(recoveredAddress.Hex())

or even better

return strings.EqualFold(from, recoveredAddr.Hex())

Very helpful!

here's another example:
https://github.com/verity-team/dws/blob/main/internal/delphi/server/server.go#L127

Sign in with Ethereum - frontend
https://docs.metamask.io/wallet/how-to/sign-data/siwe/

Signature checker in backend with go-ethereum with this code.

@valterlobo Very useful, thanks for sharing