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Yes, a specific transaction needs to be chosen as the consensus transaction. But if there are multiple to choose from (e.g. in the case of an attempted double s
by paulgb 4y ago
Yes, a specific transaction needs to be chosen as the consensus transaction. But if there are multiple to choose from (e.g. in the case of an attempted double spend), the miner can choose either one.
The blockchain doesn’t guarantee, for example, that the transaction which appeared earlier will always be chosen (in practice, it’s likely the one with the highest transaction fee)
- Nursie 4y agoIIRC there were some hacks on bitcoin ATMs using this sort of knowledge. The attacker would set up a withdrawal of (IIRC) CAD on the ATM, then transfer the bitcoin. The ATM would see the transaction, and dispense the cash. However the attacker would immediately, before the next block was generated, send the same BTC to another address which they controlled, with a higher fee. The miner would discard the first one and roll the update into a new block. I may have one or two of the details wrong (is there an explicit way in the bitcoin protocol to mark a transaction as superseding a previous one?), but anyway, like many things, it worked until they got caught.
- FabHK 4y agoATMs would dispense actual cash when a transaction enters the mempool without waiting for (say) 6 confirmations? That seems like a pretty egregious design choice even a decade ago. If that story is true, the ATM designers merited the loss.
- Nursie 4y agohttps://thenextweb.com/news/double-spenders-scam-150000-bitcoin https://thenextweb.com/news/double-spenders-scam-150000-bitc... 2018, and yes, it seems like the Bitcoin arms were dispensing cache as soon as a valid transaction but the mempool.