<p>No, BCH and BTC transactions were never replayable to the other network.  Starting with the very first BCH block, all BCH transactions were required to use a different <code>SIGHASH_FORKID</code> than used in BTC. This mandatory replay-protection causes BCH transactions to appear invalid to BTC clients, and vice versa, BTC transactions to appear invalid to BCH clients. However, (pre-segwit) addresses remained compatible between the two network, which caused some user confusion.</p>
<p>I assume that the fact that the replay protection was always mandatory may have been lost on some observers, because BCH's replay protection was only made mandatory a couple days before BCH forked off, so a lot of the prior discussion and worries became obsolete last minute. Alternatively, the source of this worry may have been confused by BSV forking off from BCH without any replay-protection whatsoever.</p>

CC BY-SA 4.0
2021-02-09T17:15:23.930Z
2021-02-09T17:15:23.930Z
Murch
<p>Is it true that any UTXO's that are unspent prefork of BCH AUG 2017, has a risk of a replay attack? Say I have 1 BTC in my wallet which has never moved since 2016. Now I load that private key into BCH wallet and now I have 1 BCH. I make a transaction on BCH to a vendor, but now he takes that same transaction and broadcasts it on BTC chain. Now I lost my BTC too. Is this correct?</p>

CC BY-SA 4.0
2021-02-09T17:17:19.087Z
Wasn't this already answered in https://bitcoin.stackexchange.com/q/102397/5406?
Murch
<bitcoin-cash><utxo><replay-attack>
Are unspent UTXO's on Bitcoin from before the AUG 2017 BCH fork at risk to a replay attack?
Patoshi パトシ
# Are unspent UTXO's on Bitcoin from before the AUG 2017 BCH fork at risk to a replay attack?

(Asked by: username_0 on 2021-02-09)

Is it true that any UTXO's that are unspent prefork of BCH AUG 2017, has a risk of a replay attack? Say I have 1 BTC in my wallet which has never moved since 2016. Now I load that private key into BCH wallet and now I have 1 BCH. I make a transaction on BCH to a vendor, but now he takes that same transaction and broadcasts it on BTC chain. Now I lost my BTC too. Is this correct?

**Tags:** bitcoin-cash, utxo, replay-attack

> **Comments:**
> **username_1**: Wasn't this already answered in https://bitcoin.stackexchange.com/q/102397/5406?  

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## 1 answers

### Answer by username_1 on 2021-02-09. Score: 2 | Accepted answer

No, BCH and BTC transactions were never replayable to the other network. Starting with the very first BCH block, all BCH transactions were required to use a different `SIGHASH_FORKID` than used in BTC. This mandatory replay-protection causes BCH transactions to appear invalid to BTC clients, and vice versa, BTC transactions to appear invalid to BCH clients. However, (pre-segwit) addresses remained compatible between the two network, which caused some user confusion.

I assume that the fact that the replay protection was always mandatory may have been lost on some observers, because BCH's replay protection was only made mandatory a couple days before BCH forked off, so a lot of the prior discussion and worries became obsolete last minute. Alternatively, the source of this worry may have been confused by BSV forking off from BCH without any replay-protection whatsoever.


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