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Why are bitcoin hacks not reverted? (self.Buttcoin)

moonshine_is が 投稿

I only keep up with the comedy aspect of buttcoins and I've never got into the technical side because who cares I'm not using it. So if there is a blockchain, and it registers all these transactions etc, everyone has to accept transactions, why is it when an exchange goes down, or something is hacked that they don't just revert the blockchain, they have a record of all these coins right?

Sorry if it's a dumb question.

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[–]magcius 7ポイント8ポイント  (1子コメント)

They've done this before, back when Bitcoin was super early on and everybody lost a bunch of money because of dumb technical glitches.

The way that the blockchain works, you actually can't revert one transaction, you can only bring the ledger back to a previous state in time. So if somebody steals my coins, then waits for six months, when it reverts, everybody's transactions since six months ago would get reverted. And that's a major issue.

Also, the developers themselves really don't have any power to do this, unless they convince the miners who are maintaining the ledger.

[–]rydan 0ポイント1ポイント  (0子コメント)

They could just make a client that after block X it only accepts certain bitcoin version numbers as valid. This forks bitcoin and you have to convince everybody on /r/bitcoin that your client is the one true client.

[–]ZZ9ZA 4ポイント5ポイント  (1子コメント)

Who is this "they"?

[–]zom-ponks 3ポイント4ポイント  (0子コメント)

This would require network consensus, so that's an impossibility currently. Not to mention that it would undermine the whole point of the blockchain, this Satoshi'sPBUH immutable gift to mankind.

But... if I remember correctly, it has in fact happened at least once: https://en.bitcoin.it/wiki/Value_overflow_incident

Someone with better knowledge of bit Coins' history might want to chime in here.

[–]NoThisIsActuallyGood 3ポイント4ポイント  (0子コメント)

Because hacks are a feature

[–]JeSuisEuphorique 0ポイント1ポイント  (0子コメント)

It's against everyone else's self interest

[–]jstolfi 0ポイント1ポイント  (0子コメント)

If you can convince enough miners to secure more than half of the total hashpower in the world, you can "rewind" the blockchain to an arbitrarily remote past. However, the further back you want to go, the longer it will take for the blockchain to be up-to-date again.

For example, if you have 75% of the hashpower, and you want to rewind to 1 month ago, it may take 2 months for the new branch to overtake the old one. (But if the other miners realize what you are doing, and do not object to it, they may join you, and then it will take only another month.)

Of course you will have to pay from your pocket for all the coins that those miners had mined in the old branch that got discarded.

Also, if you wanted to rewind all the way back to genesis (e.g. to steal Satoshiś coins), you would not have to churn for 6 years. Since the difficulty then was much lower, you could do it in maybe only 2 or 3 years, using all the hashpower available today.

That happened twice already, in 2010 and 2013; IIRC, several tens of blocks were discarded and re-mined in each case. Since those rewinds were meant to fix nasty bugs, the devs at the time easily convinced most miners to cooperate.

When such a rewind omits some transaction that was confirmed in the old branch (e. g. a transaction that stole coins from an exchange), it must also omit any transaction that used the outputs of that one, and so on recursively. If the thief sent the coins to an exchange, then the exchange's hot wallet will become "tainted", and all subsequent withdrawals from that exachange would have to be canceled too. If he bought something through BitPay, BitPayś hot wallet will be tainted, and so all the other coins that Bitpay sold from then on will go back to that hot wallet. It would be a royal mess...