I have a question:
When I am doing a transaction and I send my signed tx to the network. Could someone else take that transaction and add a additional signed input to the tx. So this would mean that my tx gets coinjoined without my approval, would that be accepted by the network?
Greets
From what I understand, that is not possible; or not practical. You'll have to coinjoin your transactions first before sending it to the network.
It may be possible with the replace-with-fee thingie, but if the first transaction gets confirmed, then the second one won't work anymore as it will be a double-spend.
For CoinJoin to work, people need to join their signed tx first. The only way I see this working is some sort of third-party that does the joining, or some app that does it for everyone involved, at the same time, or waiting within a set time.
I think what's happening is people meet up and then agree to do a CoinJoin, either in chat or through some app or website, the third-party not being able to steal any coins in the process.