RBF and full blocks make 0-conf useless, because it's easy to override. Wasn't it once useful? I've heard without those it's more secure than Visa in terms of double spending.

  • I don't know how one would measure "more secure than Visa". Certainly there are no formal security guarantees for zero-conf transactions. Someone might have gathered statistics on what fraction of transactions were actually double-spent, and compared it to Visa chargeback rates, but it's not clear that this is a valid comparison; for instance, lots of Bitcoin transactions involve people sending money to themselves. – Nate Eldredge Feb 17 '18 at 2:57

No. A zero-confirmation transaction is not useful for anything. Satoshi used PoW specifically, because he was trying to answer how to trust a transaction(double-spending problem).

Secondly, transaction replacement was introduced by Satoshi in the first release of the Bitcoin software, but was later removed due to denial-of-service problems.

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  • Sources, please. – Lubo Kanev Feb 18 '18 at 6:11

RBF is optional and it can be seen if a particular transaction has RBF enabled or not. For transactions without RBF enabled, they are as 0-conf secure as they were previously.

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  • Except when blocks are full. – Lubo Kanev Feb 18 '18 at 6:11
  • @LuboKanev Whether or not blocks are full has not changed how secure 0-conf is or is not. It was always recommended to wait for six confirmations. Otherwise, you just accept that a transaction exists and suppose that it will be included in a block eventually. – Willtech Feb 18 '18 at 7:07
  • Small merchants always used 0-conf so far. If blocks are not full, your transaction doesn't just get in eventually, it get's in in the very next block. When they are full it may never get in, or perhaps 6-conf can take days. – Lubo Kanev Feb 18 '18 at 8:53
  • @LuboKanev True, except, there was never any guarantee the transaction would be in the next block, even if that was what always happened. – Willtech Feb 18 '18 at 9:01
  • I agree. But that's why it's only used for small purchases. – Lubo Kanev Feb 20 '18 at 19:47

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