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20 sats \ 4 replies \ @petertodd 15 Nov 2022 \ parent \ on: Binance clogging the mempool? bitcoin
Basically the simplest way to double spend an unconfirmed transaction is to just broadcast a new one with a higher fee. Nodes running full-rbf will replace the lower fee tx with the higher fee; nodes not running full-rbf will only do that if the transaction opts into replacement (about 30% of txs do).
When the mempool is full, lower fee txs get kicked out to make room for new ones with higher fees. This happens on all nodes, so it's particularly easy to double spend.
tl;dr: don't rely on unconfirmed transactions. Wait until at least one confirmation before treating them as a real payment.
Thanks I understand! This is how the police in a recent SN article tricked those ransomware people recently to send the decryption keys without it being confirmed. 'Double Spend by accident' that the poster mentioned above is not an issue with Bitcoin, but a human error when people do not wait for the confirmation to happen.
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As long as I have a few confirmations, I am not at risk of this, correct?
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Correct. 1 confirmation is usually enough for most day to day things. 2/3 confirmations is forever IMO.
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I'm gonna give you the technical answer first, which is read the whitepaper:
Every block mined makes a reorg 2x less likely doubling with every block (source: https://bitcoin.org/bitcoin.pdf)
"Section 5 under "Network": "Nodes always consider the longest chain to be the correct one and will keep working on
extending it. If two nodes broadcast different versions of the next block simultaneously, some
nodes may receive one or the other first. In that case, they work on the first one they received,
but save the other branch in case it becomes longer. The tie will be broken when the next proof of-work is found and one branch becomes longer; the nodes that were working on the other
branch will then switch to the longer one."
Realistically, this 1 block reorg still happens on Bitcoin sometimes (example: https://www.coindesk.com/tech/2021/01/21/the-bitcoin-double-spend-that-never-happened/) however, I don't know of any cases in recent times when we've had deeper than a 1 block reorg. If you happen upon a 2 block reorg, we'll all be very interested to read about it.
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