The Ethereum Classic network, which was 51% attacked three times in August, has implemented a finality system to protect against 51% attacks: Modified Exponential Subjective Scoring (MESS).
MESS was implemented on October 11th at block height 11,380,000 and is supposed to reduce the likelihood of 51% attacks taking place on the ETC network.
“First proposed by Vitalik in 2014, MESS changes this rule so nodes will prefer chain segments they see first over segments they see later,” said ETC Labs in their blog post announcing MESS.
The key principle: Large reorganizations(reorgs) are usually bad, small reorganizations are usually good. If the preferred chain is the first one the node sees, building a super long chain in secret is no longer an attack vector.”
MESS makes it ~31x more expensive to attack the chain than it currently is; according to ETC Labs, a 3,000 block reorg protected by MESS would cost over $20,000,000 and makes the amount of hash power required to pull off the 51% attack impossible to acquire through NiceHash, the hash provider that allows individuals to rent hash power.
Will this be the end of the ETC 51% attacks?
In August, the ETC network was 51% attacked three times which resulted in millions of dollars being lost by way of double-spends. To gain control of more than 51% of the network, the attacker rented hash-power from NiceHash–which only cost them a few thousand dollars–and subsequently broadcasted a fraudulent version of the ETC blockchain to the other nodes on the network which they quickly accepted as the legitimate chain. Because Ethereum Classic has a low amount of hash power supporting it but is liquid across digital currency exchanges, it is a prime target for attackers.
Although the ETC network has implemented MESS and claims that the cost of conducting a 51% attack on the ETC network now costs millions of dollars, Crypto51, a website that calculates the cost of conducting a 51% attack on a blockchain for one hour, says the current cost of attacking the ETC network for one hour is only $4,844. Unless the data on Crypto51 has yet to be updated to account for the MESS implementation, there is a chance that it is still possible to purchase the hash power needed to 51% attack the ETC network.
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