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It is alleged that the stolen Bitstamp coins are in this address. In theory, could miners agree to reject all transactions from this address? And if so, would all miners need to agree or just more than half?
Can miners reject transactions from an address?
Answers
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Technically it is possible to blacklist addresses, and it needs just the majority of the mining power to agree.
The problem is arriving at the agreement: Nobody stands to gain from witch-hunts, so a consensus to block an address would have to be carefully built on solid proof, which is hard when there is no central organs with jurisdiction, nor a way to get a statement from the culprit.
Also, blacklisting addresses, just like tracking tainted coins, has a strong implication on what we view Bitcoin to be: One of the sources of Bitcoin's value is that bitcoins are considered fungible – that each individual does not need to care about the history of a bitcoin, because a bitcoin is a bitcoin. If we start treating bitcoins differently in accordance to their transaction history, it will make the bitcoin economy more complicated and less useful.
2People will treat them differently, and are. Bitcoin is not fully fungible. No-one wants dirty bitcoin even less than dirty dollars. Alleged stolen bitcoin are anathema to exchanges and have less value than other bitcoins. – Brad Thomas – 2015-04-17T02:54:06.103
Yes, but I don't think the effect will be pronounced: 1) Exchanges are bound to disagree on perceived taint of coins. 2) It is unlikely that there will be broad consensus to blacklist addresses, so coins will be able to move, hence be mixed with other coins. 3) Through mixing taint either a) spreads or b) dilutes. 4) Punishing users for receiving unwittingly tainted coins would be an undeserved collective punishment for which I can't fathom broad support. 5) Taint will dilute over time. 6) Bitcoins will remain fungible for most uses except directly selling stolen coins on regulated exchanges. – Murch – 2015-04-17T10:47:11.473
TL;DR – Most users will be too lazy to track or in disagreement about taint for it to take a measurable effect. (Unproven opinion.) – Murch – 2015-04-17T15:39:26.653
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I think miners can't refuse any transactions once they're in a block, except those which are invalid right now.
If everyone agreed, there could be a centralized service that would broadcast alert messages to miners, alerting them that the transaction shouldn't be confirmed. But I am not sure this is a good idea. It would definitely go against the decentralization of bitcoin.
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related: Is it technically feasible to “shun” particular bitcoin wallets?, Is it possible for the miners to collude to blackmail a single wealthy address?
– Murch – 2015-01-06T13:22:52.167