In a Purge attack, an attacker replaces blocks full of transactions with empty blocks. As a result, previously confirmed transactions are sent back into the mempools (the "waiting area" for Bitcoin transactions.)
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Once in the mempools, anyone with a minimum of technical knowledge or access to public tools can opportunistically double-spend their transactions back to themselves.pic.twitter.com/WvK01iV1RB
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Double-spends of unconfirmed transactions are made possible by transaction replacement. For that reason, zero-confirmation transactions are widely regarded as unsafe.
In a Purge attack, an attacker retroactively applies a zero-conf policy to the entire network.Prikaži ovu nit -
When is a Purge attack a good idea? We are unlikely to see it if the attacker himself wants to double-spend. The more people he affects, the more he increases the range and likelihood of triggering a violent response (e.g. PoW change)
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A Purge attack is a form of sabotage, aiming to undermine trust in Bitcoin's assurances, e.g. the future finality of transactions.
We named it after the dystopian movie The Purge, where all crime is legal for one night every year.Prikaži ovu nit -
The Purge attack differs from other sabotage attacks (e.g. full DoS) in that it specifically disrupts the coordination process among Bitcoin users in response to the attack. By giving some users a chance to benefit from the attack, the attacker turns them into supporters.
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How to defend against this? Purge attacks are similar to all other forms of sabotage attacks in this case. 1. Bitcoin’s first wall of defense is the sum of its future block rewards. It represents the amount of money an attacker has to burn to sabotage the network.
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2. Its second wall of defense is the strength of Bitcoin’s pre-coordination in the face of attack. A leaderless group of people can carry out their defense more easily if the right response is self-evident to most people.
this is what the attacker wants to disruptPrikaži ovu nit -
All in all, Purge attacks probably don’t constitute a bigger risk than other known forms of sabotage attacks, but represent an interesting spin where the attacker specifically targets the pre-coordination of defenders.
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Virtually all attacks on cryptocurrencies to date have tried to double-spend. Two reasons that could change in the future: 1) as the sum of future block rewards decreases, the cost of attack goes down 2) as Bitcoin becomes more important, the incentive to sabotage goes up
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