How to decode a transaction to verify its signature in Javascript?

Question

I noticed that it's possible to sign a transaction with a wrong private key. I took the following example found at https://github.com/ethereumjs/ethereumjs-tx

const EthereumTx = require('ethereumjs-tx').Transaction
const privateKey = Buffer.from(
  'e331b6d69882b4cb4ea581d88e0b604039a3de5967688d3dcffdd2270c0fd109',
  'hex',
)

const txParams = {
  nonce: '0x00',
  gasPrice: '0x09184e72a000',
  gasLimit: '0x2710',
  to: '0x0000000000000000000000000000000000000000',
  value: '0x00',
  data: '0x7f7465737432000000000000000000000000000000000000000000000000000000600057',
}

// The second parameter is not necessary if these values are used
const tx = new EthereumTx(txParams, { chain: 'mainnet', hardfork: 'petersburg' })
tx.sign(privateKey)
const serializedTx = tx.serialize()

This code does sign the transaction, but how do I verify that the transaction has been correctly signed?

How to use or decode serializedTx and verify that the signature is correct?

Answer 1

This code does sign the transaction, but how do I verify that the transaction has been correctly signed?

How is it possible to verify that the signature is correct?

web3 has an estimateGas method you can use to estimate the gas required for the transaction and If signature is incorrect, that means the transaction is going to fail then it will simply just throw an error.

Also is it possible to programmatically get the private key associated to the address that's logged in (with Metamask)?

Because of security considerations, privateKey is obviously not available. It would be a serious security flaw if you could access metamask accounts that way.

Answer 2

Of course you can sign a transaction with any private key that you want.

But when you finally execute it, the gas required for this transaction (as well as the amount of ether that you have set in the value field) will be taken from the account corresponding with that key.

And if you just choose a random key, then this account will have 0 Ether with a probability of almost 100%, which means that the transaction will subsequently fail for insufficient balance.