Extracting the Public Key from a transaction hash

Question

I've seen a variety of questions and answers in this forum about extracting the public key from a signed transaction hash. I am able to get the correct answer from newer transactions, but unable to with older transactions and am curious if anyone has any ideas.

https://etherscan.io/tx/0x8aa30f7d95cd5f22dd02e59434c0e66794c6e370ed2659ea532ed6fe49f9cce5

This is the signed transaction I am attempting to generate the public key for. Any help would be appreciated!

Answer 1

It essentially comes down to the three methods constructing transactions through the Ethereum history until now.

Below is a piece a tiny bit modified Python script originally published in this gist (full credit should go to the original author) covering the three types.

Explanation:

• type_0_keys — legacy transactions before EIP-155.
• type_1_keys — EIP-155 transactions.
• type_2_keys — EIP-1559 transactions.

Replace NODE_ENDPOINT and TX_HASH with your values. Note also tx["chainId"] = 1 set for the Ethereum mainnet.

import web3
from eth_account._utils.signing import extract_chain_id, to_standard_v
from eth_account._utils.legacy_transactions import serializable_unsigned_transaction_from_dict

w3 = web3.Web3(web3.HTTPProvider("NODE_ENDPOINT"))
tx = w3.eth.get_transaction("TX_HASH")
tx = dict(tx)

type_0_keys = ['chainId', 'gas', 'gasPrice', 'nonce', 'to', 'value']
type_1_keys = ["to",
    "nonce",
    "value",
    "gas",
    'gasPrice',
    "chainId",
    "type"]
type_2_keys = ["to",
    "nonce",
    "value",
    "gas",
    "chainId",
    "maxFeePerGas",
    "maxPriorityFeePerGas",
    "type"]

s = w3.eth.account._keys.Signature(vrs=(
    to_standard_v(extract_chain_id(tx["v"])[1]),
    w3.to_int(tx["r"]),
    w3.to_int(tx["s"])
))

if tx["type"] == 0:
    keys_to_get = type_0_keys
elif tx["type"] == 1:
    keys_to_get = type_1_keys
elif tx["type"] == 2:
    keys_to_get = type_2_keys

if "chainId" not in tx:
    tx["chainId"] = 1

tt = {k:tx[k] for k in keys_to_get}
tt["data"] = tx["input"]

ut = serializable_unsigned_transaction_from_dict(tt)

public_key = s.recover_public_key_from_msg_hash(ut.hash())

if hasattr(public_key, 'to_hex'):
    public_key_hex = public_key.to_hex()
else:
    public_key_bytes = public_key.to_bytes()
    public_key_hex = public_key_bytes.hex()

print(public_key_hex)