Since it seems we may have a number of chain splits in the coming months, it's helpful to think about replay protection.
If you have utxos today and the chain splits next month, you end up with a version of your utxos on each side of the split. If you make a transaction spending some of your utxos on one side of the split (for instance, if you want to sell the fork coin), it is possible that the exact same transaction could be broadcast ("replayed") on the side of the split that you don't want to sell and poof you lose your bitcoin.
However, if you are careful with how you design your transactions, they can have the property that they are only valid on one side of the chain split.
@Murch wrote up a very nice article about this and how one might design a transaction to avoid it being replayed in the case of a split caused by BIP 110 #1520612
But we will likely find ourselves dealing with a second chain split: Paul Sztorc is leading a hard fork that will also produce a chain split #1477958. Should you want to craft a transaction that spends coins on one side of this split and not the other, you will also need to think about whether the transaction can be replayed on the BTC side.
Robin Linus has created a guide for how to ensure that a transaction spending coins on the eCash chain will not be valid on the BTC chain.
The goal is to spend forked coins on eCash without exposing the corresponding BTC coins to replay risk, and without importing the valuable private key into the eCash splitting software.
The method is to construct an eCash transaction that spends both:
- the valuable pre-fork UTXO, which exists on both Bitcoin and eCash; and
- a small “dust” UTXO that exists only on the eCash chain.
I believe there is some software that has been advertised as splitting your utxos so that they are not replayable on both of these chains, but there is a note from Sergio Lerner that suggests that this software has bugs:
Note that, in 6 JUN 2026, I reported that the replay protection in Forknet commit f132e5a (based on UnserializeTransaction) is broken and splitting risks losing your bitcoins. It doesn't seem to be patched yet (see https://github.com/drivechain-forknet/drivechain-forknet).
Until they implement another replay protection method, this chain-unique dust splitting method is the only one that works.
Things ought to be pretty interesting in the coming months.
I have not been paying any attention to the eCash fork. What’s that small dust UTXO?
Remember: the best thing that can happen is someone seeding a small part of a post-fork coinbase utxo into a mixer and then having that carry forward. A single mix round with any utxo that chains back to a single mix round with such an utxo is not replayable on any forked chain.
I believe we will have Paul Sztorc here for an AMA on Saturday the 19th. It will be interesting to ask him about how he himself is thinking about replay stuff.
Thanks; I will be elsewhere. Paul's been an in the flesh source of drama for at least 12 years now and I tire of it. Let them fork. Good riddance.
In case I miss it:
"Why should we be bothered with you, sir? Forks are mostly stupid, and we already have another retarded one to deal with. Could you not have picked a more opportune moment?"
Wouldn't you just try and broadcast the TX at the same time on both chains?