One of the bigger headlines last week concerned mining pool Ghash.IO and the amount of hashing power they have. In fact, they actually reached 42% network power at one point, triggering a mini-panic and small campaign to get miners into a diversified group of pools.
The fear? A 51% attack on the bitcoin network. And for as long as bitcoin has existed, this threat has loomed overhead, with little that could be done to prevent it.
But if we go back to May 2012, Bitcoin core developer Gavin Andresen :
Something like “ignore a longer chain orphaning the current best chain if the sum(priorities of transactions included in new chain) is much less than sum(priorities of transactions in the part of the current best chain that would be orphaned)” would mean a 51% attacker would have to have both lots of hashing power AND lots of old, high-priority bitcoins to keep up a transaction-denial-of-service attack. And they’d pretty quickly run out of old, high-priority bitcoins and would be forced to either include other people’s transactions or have their chain rejected.
In Andresen’s post, he notes that such a solution would be “Not To Be Used Except In Case of Emergency”, which begs the question: could we what have seen last week be considered an emergency? The community managed to alert each other to move to other pools. And sure, Ghash.IO says they have no interest in carrying out a 51% attack, but should we believe them?
Is it time to put Andresen’s solution to work? What do you think?
Justin Goro 
While vested interests have no incentive to corrupt the network, the group we all hate (central banks) have every incentive and the resources to do so. Gavin’s priority check does sound like a good way to identify a centralized attack though.