How to create multisignature transaction?

Question

I have to create a multisignature transaction which the transaction should get signed with at least 2 private keys. Could anyone explain how to do it? I am using web3.py

import rlp

    from ethereum.transactions import Transaction
    tx = Transaction(
        nonce=web3.eth.getTransactionCount(web3.eth.coinbase),
        gasprice=web3.eth.gasPrice,
        startgas=100000,
        to='0xd3cda913deb6f67967b99d67acdfa1712c293601',
        value=12345,
        data=b'',
    )
    tx.sign(the_private_key_for_the_from_account)
    raw_tx = rlp.encode(tx)
    raw_tx_hex = web3.toHex(raw_tx)
    web3.eth.sendRawTransaction(raw_tx_hex)

In the above code, I am only signing with one private key. Could anyone explain how to sign with multiple private keys?

Answer 1

An Ethereum transaction should have only one signature, representing the account that will pay the gas for it. If you want to control a resource with multiple signatures, you have two options:

• Make a contract that requires multiple transactions to make whatever it is happen. See this contract for an example.
• Instead of checking the transaction signature (in practice, msg.sender) like you would with a simple transaction, sign the data to the transaction and have your contract check it using ecrecover. This allows you to collect the signatures out-of-band and submit all the signature data in a single transaction. See this contract for an example.