How to recover Ethereum Public Key from Transaction

Question

How can I recover the Ethereum Public Key from a Transaction?

web3.eth.accounts.recoverTransaction("0x02f87501833c636a843b9aca008512a05f200082520894f5c238dd768de69c0f4f9d1e08bbf497029326698741ca84c07b6a0080c080a02d49f0b49cb718f8ef403e22b21ff8f488553a4f96f77482e08912e3b24d8647a008faa0e1caafff5ddf1366248e590eee99612b1d0b590ee41af7a2c3d92bfeed") '0x00192Fb10dF37c9FB26829eb2CC623cd1BF599E8'

returns the address only. However, I am looking for a programmatic way to recover the public key from an existing transaction.

Answer 1

As far as I know, Web3.js doesn't expose such functionalities directly. You could however do it by relying on one of its dependencies (@ethereumjs/tx).

Here is an example code heavily inspired by the recoverTransaction implementation :

const Web3 = require("web3"); // Optional : here only for the address recovery example
const { TransactionFactory } = require("@ethereumjs/tx");

const TX_DATA = "0x02f87501833c636a843b9aca008512a05f200082520894f5c238dd768de69c0f4f9d1e08bbf497029326698741ca84c07b6a0080c080a02d49f0b49cb718f8ef403e22b21ff8f488553a4f96f77482e08912e3b24d8647a008faa0e1caafff5ddf1366248e590eee99612b1d0b590ee41af7a2c3d92bfeed";

function recoverPublicKey(rawTx) {
  const data = Buffer.from(rawTx.slice(2), "hex");
  const tx = TransactionFactory.fromSerializedData(data);

  return tx.getSenderPublicKey().toString("hex");
}

const publicKey = recoverPublicKey(TX_DATA);
console.log("Public key : " + publicKey);

// To compute the address from the public key :
const pubHash = Web3.utils.soliditySha3("0x" + publicKey);
console.log("Address : " + "0x" + pubHash.slice(-40));
// 0x00192fb10df37c9fb26829eb2cc623cd1bf599e8