When splitting coins from a hard fork and signing the transaction on the forked coin, is there a time/block limit when the transaction gets invalid on the BTC chain, so a potentially possible replay attack gets invalid forever?

Imagine this scenario: You successfully split 1 BTC and 1 BXX (which has no replay protection) from address A to B and C. At some later point you forget about it and send 2 BTC to address A. Can the old 1 BXX transaction be used to replay A -> C in BTC?

1 Answer 1


Bitcoin is not an account based currency like Ethereum, which track the balance in addresses. Instead it is a UTXO based currency. In a UTXO-based currency, funds are tracked in portions called "Unspent Transaction Outputs", these are uniquely identified through their history, specifically through the transaction id that created them. Any new money moved to the same address would have a different history and thus would not be replayable.

  • Thanks! What about the same scenario but you never moved your original 1 BTC away, is a replay attack possible at any point in time or does the "window" expire at some point?
    – A1m
    Commented Nov 28, 2017 at 6:10
  • When the UTXO has not been moved, the replay attack remains possible indefinitely. However, that's in conflict with "having split successfully". ;)
    – Murch
    Commented Nov 28, 2017 at 13:32
  • Yes, I understand. Thus for a successful split, you have to move both values to new addresses, other than that you could never be sure to not be replayed at some point. This answers my question, thanks!
    – A1m
    Commented Nov 28, 2017 at 15:18

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