It seems like it would be useful to avoid replay attacks if your wallet could specify that a transaction must be confirmed before say the (current+100)th block before broadcasting it

I guess there could be a problem with this scheme if the tx was no longer able to be included into a block after a reorg (esp for dependent txs)

  • I don't know of any way to accomplish that. Can you be more specific as to what kind of "replay attack" you are worried about? Mar 4, 2016 at 2:42
  • here is an example qntra.net/2016/03/a-miner-problem
    – djp
    Mar 4, 2016 at 6:33
  • This is not an attack. This is total misunderstaning how the Bitcoin network works.
    – amaclin
    Mar 4, 2016 at 6:41
  • In a scenario of permanent backlog of transactions this scenario will need better strategies however
    – djp
    Mar 6, 2016 at 22:05

1 Answer 1


No, there isn't a way to make a transaction that has to be included before a certain block number.

And there's a good reason for this: such a transaction would not be what is known as reorg-safe. Generally, transactions should be able to be included in either side of a block chain fork. If you make a transaction that can only be included before a certain block number, and then a fork occurs that makes a chain that doesn't include it before the designated block number, then that transaction gets reversed and so do all transactions that depend on the base transaction.

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