Polygon ecrecover header example

ecrecover.org

The signer can be recovered by taking a block, constructoring the headers and then using the Ecrecover of the go-ethereum crypto library.

First, we’ll download a block, extract the result using jq and then save the response in block.json.

curl -s -H 'Content-Type: application/json' -d '{"jsonrpc":"2.0", "id": 1, "method": "eth_getBlockByNumber", "params": ["0x31b7feb", true]}' https://polygon-rpc.com | jq '.result' | tee block.json

Now that we have the block saved locally in json format, we can parse it and output the signer with go

package main

import (
	"encoding/hex"
	"fmt"
	"log/slog"
	"os"

	"github.com/ethereum/go-ethereum/consensus/clique"
	ethtypes "github.com/ethereum/go-ethereum/core/types"
	ethcrypto "github.com/ethereum/go-ethereum/crypto"
)

func main() {
	blockData, err := os.ReadFile("block.json")
	if err != nil {
		slog.Error("Could not open file", "error", err.Error())
		os.Exit(1)
	}
	_, signer, err := ecrecover(blockData)
	if err != nil {
		slog.Error("Unable to recover signer", "error", err.Error())
		os.Exit(1)
	}
	fmt.Println(hex.EncodeToString(signer))
}

func ecrecover(data []byte) (*ethtypes.Header, []byte, error) {
	header := new(ethtypes.Header)
	err := header.UnmarshalJSON(data)
	if err != nil {
		return header, nil, err
	}
	sigStart := len(header.Extra) - ethcrypto.SignatureLength
	if sigStart < 0 || sigStart > len(header.Extra) {
		return header, nil, fmt.Errorf("Unable to recover signature")
	}
	signature := header.Extra[sigStart:]
	pubkey, err := ethcrypto.Ecrecover(clique.SealHash(header).Bytes(), signature)
	if err != nil {
		return header, nil, err
	}
	signer := ethcrypto.Keccak256(pubkey[1:])[12:]

	return header, signer, nil
}