Bitcoin's Decentralised Structure at Threat from Miner with 51% Control of Network

A single pool of bitcoin miners, who combine their computational power to generate new digital coins, has for the first time accounted for over 50% of bitcoin's total cryptographic hashing output for a sustained period of time.

The GHash mining pool provided over half of the power for 12 hours on 12 June, according to researchers from Cornell University, in a situation that threatens bitcoin's status as a decentralised currency.

Any individual or group contributing over half of the hashing output technically has the ability to reject other miners' transactions, spend the same coins twice, or even carry out a distributed denial of service (DDoS) against the bitcoin network.

"Bitcoin mining has been too centralised for years, with just a handful of pool operators controlling well more than 50% of hashing power," said Gavin Andresen, a board member of the Bitcoin Foundation.

"Recently, mining power has become even more centralised, with one mining pool likely controlling somewhere between 40% and 60% of hashing power. That isn't good."

Andresen believes that there is no evidence yet of GHash taking advantage of its position, and any attempt to do so would result in it being caught due to the lack of anonymisation with bitcoin and money transfers.

"I think either attack is extremely unlikely from an economically rational mining pool," Andresen said. "Blockchain history would make it obvious that they were misusing their power, and I'm certain either technical or social solutions would be found to punish the bad behaviour."

GHash has previously quelled concerns about its mining power by claiming it has no intentions to execute any type of attack.

"We would never do anything to harm the Bitcoin economy; we believe in it," Jeffrey Smith, chief information officer of Cex, a cloudhashing service that works alongside GHash, told Cryptocoin news.

"We have invested all our effort, time and money into the development of the bitcoin economy. We agree that mining should be decentralised, but you cannot blame GHash for being the number one mining pool."