Signing transaction for Flashbots MegaBundles

main.go

package main

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"fmt"

	"github.com/ethereum/go-ethereum/accounts"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/crypto/secp256k1"
	"github.com/ethereum/go-ethereum/rlp"
)

type UnsignedMegabundle struct {
	Txs               []hexutil.Bytes
	BlockNumber       uint64
	MinTimestamp      uint64
	MaxTimestamp      uint64
	RevertingTxHashes []common.Hash
}

func main() {

	umb := UnsignedMegabundle{
		Txs: []hexutil.Bytes{
			common.FromHex("0xf86b0184b1c5ad7283061a809474ae21044283ae165c8816832cd3a3ac3bff85ca87038d7ea4c68000802aa041de6b5c5df12bf5eee96da3940cb7e68b9e7d6410d5e777073110c2368ee332a02bdfcc746e7ee020cf7a2db0085541256d767a5a790bc4859f6fad68164d9804"),
		}, // TXs you're submitting
		BlockNumber:       12553628, // decimal block number, not hex
		MinTimestamp:      0,
		MaxTimestamp:      0,
		RevertingTxHashes: []common.Hash{},
	}

	b, _ := rlp.EncodeToBytes(umb)

	msg := accounts.TextHash(b)
	// pub := common.Hex2Bytes("040b4b509bdb077eb274e543c44aa1c27cb3792ae8efcdd7c12c8ca851bdc9edd42bcb125705f2b2e40ae842834def93381bf3cddeceb46e0cacd241b9c7b6753b")
	// secKey := common.Hex2Bytes("66dda74a91924968cec8fcda88a125162b9181b25e7ecf1b1d33900668d77809")

	pub, secKey := generateKeyPair()
	fmt.Printf("pub: %x\n", string(pub))     // save this to reuse easier
	fmt.Printf("priv: %x\n", string(secKey)) // save this to reuse easier

	sig, _ := secp256k1.Sign(msg, secKey)
	sig[64] += 27

	fmt.Printf("sig: %x\n", string(sig)) // use this for the relaySignature
}

func generateKeyPair() (pubkey, privkey []byte) {
	key, err := ecdsa.GenerateKey(secp256k1.S256(), rand.Reader)
	if err != nil {
		panic(err)
	}
	pubkey = elliptic.Marshal(secp256k1.S256(), key.X, key.Y)

	privkey = make([]byte, 32)
	blob := key.D.Bytes()
	copy(privkey[32-len(blob):], blob)

	return pubkey, privkey
}

This allows you to create a signature for the eth_sendMegaBundle RPC endpoint.