4 ms·

Hmm. The humans at the exchanges seem to be able to tell the difference. I wonder if it could be encoded.

AgentME 8y ago
The "legitimate" fork can only be identified if you were online when the 51% attack started. Users who have started up their ETC client after the attack started will just see two forks and will pick the one with more blocks (which will be the 51% attacker's fork). No one wants a permanent fork, so the clients that were online the whole time disregard their knowledge of the previous "legitimate" fork and adopt the attacker's fork because it has more work and because that's the one everyone else is using. Also, if you have clients follow the rule "never switch forks" to protect against 51% attacks, then any network partitions will cause a permanent fork.
leevlad 8y ago
I don't think that's feasible, to be honest. I'd imagine that you would want to look for evidence of a double spend as that's the most likely goal of a 51% attack. But then the blockchain must have up-to-date knowledge of likely double spend targets (such as exchanges, OTC desks, etc), and be able to algorithmically and deterministically prove malicious intent with high certainty. Only then will you be able to maintain consensus and prevent unnecessary or accidental forks. But since this is all open-source anyway, it would only be a matter of time before a slightly more sophisticated attacker read through the updated consensus algorithm and figured out how to game it. And so the cycle continues. In truth, the only real strategy for mitigating attacks in PoW blockchains is hash power. It has proven to be very effective if you have enough of it (see BTC), and looking for other 51% resistance measures isn't really that productive unless you start from the ground up and rebuild the consensus mechanism on a different paradigm (e.g. PoS, which is still unproven afaik).

The "legitimate" fork can only be identified if you were online when the 51% attack started. Users who have started up their ETC client after the attack started will just see two forks and will pick the one with more blocks (which will be the 51% attacker's fork). No one wants a permanent fork, so the clients that were online the whole time disregard their knowledge of the previous "legitimate" fork and adopt the attacker's fork because it has more work and because that's the one everyone else is using. Also, if you have clients follow the rule "never switch forks" to protect against 51% attacks, then any network partitions will cause a permanent fork.

leevlad 8y ago

I don't think that's feasible, to be honest. I'd imagine that you would want to look for evidence of a double spend as that's the most likely goal of a 51% attack. But then the blockchain must have up-to-date knowledge of likely double spend targets (such as exchanges, OTC desks, etc), and be able to algorithmically and deterministically prove malicious intent with high certainty. Only then will you be able to maintain consensus and prevent unnecessary or accidental forks. But since this is all open-source anyway, it would only be a matter of time before a slightly more sophisticated attacker read through the updated consensus algorithm and figured out how to game it. And so the cycle continues. In truth, the only real strategy for mitigating attacks in PoW blockchains is hash power. It has proven to be very effective if you have enough of it (see BTC), and looking for other 51% resistance measures isn't really that productive unless you start from the ground up and rebuild the consensus mechanism on a different paradigm (e.g. PoS, which is still unproven afaik).