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Actually the transaction wasn't reversed, a distinct cryptocurrency was created (a "fork") which reversed the transaction. The new cryptocurrency adopted the na

Actually the transaction wasn't reversed, a distinct cryptocurrency was created (a "fork") which reversed the transaction. The new cryptocurrency adopted the name Ethereum and it became way more popular than the original, so the original had to rebrand to "Ethereum Classic" to avoid confusion. The new cryptocurrency was successful largely thanks to Ethereum founder Vitalik Buterin endorsing it. Similar "attacks" were attempted on Bitcoin multiple times (e.g. Bitcoin Cash) but they never quite succeeded and are unlikely to succeed thanks to Bitcoin lacking some sort of active founder/leader. For a Bitcoin hard fork to succeed, there would need to be a large consensus not only among miners, but among users, merchants, exchanges, etc.

wpietri 5y ago
So it sounds like we agree: It's unlikely but impossible, and so patio11 is correct to say that finality does not exist, and that it's just a probability distribution for each channel.
- olalonde 5y ago
  I disagree that the Ethereum fork confirms the idea that the transaction wasn't final. It was final and still is. That being said, I do think patio11 is technically correct, given his unconventionally strict definition of "finality". Probability is at the core of Bitcoin's proof of work security mechanism. There is a non zero probability that I could rewrite the whole Bitcoin transaction history in the next 15 minutes, if my miner gets really, really, really lucky. The chances of that happening are of course abysmally small and not worth considering. For all practical purposes, Bitcoin transactions are final past a few confirmations.
  - wpietri 5y ago
    I think you are using a very technical definition of "final". Both the purpose and the real-world effect of the fork was to make an apparently final transaction no longer final. That it is still "final" in at best a distraction to the general-audience meaning of "final". I estimate the probability of a similar Bitcoin action to be small, but much larger than the "miner gets really, really, really lucky" scenario you propose. Do you disagree?
    - olalonde 5y ago
      I wouldn't say it's just technical. The Ethereum Classic chain, where the transaction lives on, still exists and is now worth ~3x more than it was at the time of the hack. If the hacker kept their ETC (not sure if they did) they would still have 118M$ USD today. And regardless, the probability that any one transaction will be reversed by a fork of the Bitcoin blockchain are vastly smaller. There have been tons of hacks in Bitcoin's history already and no transactions were reversed. Bitcoin doesn't have a clear head. > I estimate the probability of a similar Bitcoin action to be small, but much larger than the "miner gets really, really, really lucky" scenario you propose. Do you disagree? Of course, I agree. That being said, I'd still put the probability in the vanishingly small category, especially for any individual transaction that isn't an exploit, and not worth considering in the context of "finality", as the term is commonly used (and not as patio11 defines it).

wpietri 5y ago

So it sounds like we agree: It's unlikely but impossible, and so patio11 is correct to say that finality does not exist, and that it's just a probability distribution for each channel.

olalonde 5y ago
I disagree that the Ethereum fork confirms the idea that the transaction wasn't final. It was final and still is. That being said, I do think patio11 is technically correct, given his unconventionally strict definition of "finality". Probability is at the core of Bitcoin's proof of work security mechanism. There is a non zero probability that I could rewrite the whole Bitcoin transaction history in the next 15 minutes, if my miner gets really, really, really lucky. The chances of that happening are of course abysmally small and not worth considering. For all practical purposes, Bitcoin transactions are final past a few confirmations.
- wpietri 5y ago
  I think you are using a very technical definition of "final". Both the purpose and the real-world effect of the fork was to make an apparently final transaction no longer final. That it is still "final" in at best a distraction to the general-audience meaning of "final". I estimate the probability of a similar Bitcoin action to be small, but much larger than the "miner gets really, really, really lucky" scenario you propose. Do you disagree?
  - olalonde 5y ago
    I wouldn't say it's just technical. The Ethereum Classic chain, where the transaction lives on, still exists and is now worth ~3x more than it was at the time of the hack. If the hacker kept their ETC (not sure if they did) they would still have 118M$ USD today. And regardless, the probability that any one transaction will be reversed by a fork of the Bitcoin blockchain are vastly smaller. There have been tons of hacks in Bitcoin's history already and no transactions were reversed. Bitcoin doesn't have a clear head. > I estimate the probability of a similar Bitcoin action to be small, but much larger than the "miner gets really, really, really lucky" scenario you propose. Do you disagree? Of course, I agree. That being said, I'd still put the probability in the vanishingly small category, especially for any individual transaction that isn't an exploit, and not worth considering in the context of "finality", as the term is commonly used (and not as patio11 defines it).