Nostr Web Client

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nostrnaut

does consolidating already-coinjoined UTXOs affect privacy in any deleterious way?

no, right?

#asknostr

#coinjoin

#UTXO

Max 1y ago

It depends...

Let's say you have 10 coinjoined utxos worth each 0.1 bitcoin.

When you consolidate all 10 inputs in a single user transaction, then everyone knows that these 10 inputs belong to the same person, this is new knowledge that wasn't public before the transaction.

However, it's not so obvious which other coinjoin outputs you have, and which pre-coinjoin inputs you have.

There are like 3000 "fresh" bitcoin joining the wabisabi pool each month, so there are hundreds of new "1 bitcoin users" in this month along. Since 2018 Wasabi had over 300000 fresh bitcoin, and even the first user could have coinjoined for all these five years, only to now make a 1 bitcoin consolidation transaction.

It is however not great to reveal your entire wallet balance by a full wallet consolidation, better to make two or three separate transactions that spend a small portion of the wallet balance.

Finally, with WabiSabi this isn't a problem at all anymore, because you can anonymously register multiple inputs in the same coinjoin transaction, and thus consolidate privately without revealing common input ownership heuristic. Payments in coinjoin is a further improvement.

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Discussion

Ralphy 1y ago

I didn’t follow the last part, “because you can anonymously register multiple inputs”. Does that mean you can in fact coinjoin your whole wallet balance (let’s say currently comprised of 10 different utxos) without a loss of privacy?

Max 1y ago

It depends...

Generally speaking yes, but for example if all those 10 coins were created on the exact same day 10 years ago, and all 10 coins are in the same coinjoin transaction, even with 300 other inputs, it is quite unlikely that two or more different users created coins on the same day back then, and are online at the same time now to spend them.

In this case the coinjoin at least adds some plausible deniabiliy, but the most obvious guess is the correct one, so any serious adversary will likely figure it out that those 10 coins belong to one person.

If you're really paranoid, it's best to not even consolidate non-private coins in a coinjoin, Wasabi does this with the "red coin isolation" setting, on by default in the optimize for privacy profile.

Lee 1y ago

Samourai is same or different in your opinion?

IntuitiveGuy☯️ 1y ago

Thanks for this 🤙