change outputs currently going to shuffled wallet, probably wrong or at least very confusing

[fyookball]

[alwaysAn0n]

@fyookball Correct me if I'm misunderstanding but what I think you mean is "change outputs from non-CashShuffle transactions which spend shuffled coins go back into the 'shuffled' wallet".

I agree this is a problem because change from spending shuffled coins shouldn't be considered "shuffled". I don't know how to address this though. Here's the problem. bitcore-wallet-serice will not let you send change to an address outside of the wallet from which you're spending. I checked in the BWS source code. This is by (poor) design. We can do a few things to get around this and they are all a huge pain in the butt.

1. When spending from the CashShuffle wallet, build and broadcast the transaction completely outside of BWS. This will probably be deemed unsafe by the wallet team and might have other negative implications.

2. Keep the change outputs in the CashShuffle wallet but make the UI reflect the adjusted "shuffled balance". Then add a check inside the Wallet that disables the spending of change only if it's in the "CashShuffle spend-only" wallet. This might not be possible without also adding logic that picks the utxos for BWS to use in the transaction. That is because by default BWS makes the utxo choices on server. The client ( bitcoin.com mobile wallet ) just tells BWS how much to send who and from which wallet. BWS picks the inputs, builds the transaction, then hands it back to the client for approval.

3. Add a function that detects new change in the "CashShuffle spend-only" wallet and sends it to a different wallet as soon as it's detected. This is ugly because it will create all kinds of timing mismatches, cost the user more money as they are paying for two transactions, and even further delaying the point at which a coin becomes eligible to shuffle ( since shuffling zero conf coins isn't allowed). Also we would have to know which non-CashShuffle wallet to send the change to. Either by deduction or by keeping track (which weakens privacy when persisted).

4. Change bitcore-wallet-service to allow us to send change to whichever address we want. Although I haven't dug deep into the BWS code, this is almost certainly the best option.