Recently we looked at the case of Bitcoin Gold, which came under a 51% attack that cost exchanges millions of dollars (see http://telegra.ph/All-that-glitters-is-not-Gold-05-24). It seems other community members have found the topic interesting, with someone going so far as to create www.crypto51.app. This is a site that lists the major proof-of-work cryptos and the cost of carrying out a 51% attack on them for one hour.

What immediately strikes us is the low cost of an attack. Attack costs are based on the price to rent the required hashrate from Nicehash, and in many cases there simply isn’t enough hashrate to do the job, but it’s still a useful overall metric. The price to attack Bitcoin is just $600,000, whilst for smaller cryptos it’s less than $1,000 – easily what someone might pay to mess around with a blockchain ‘for the lulz’ or to settle a grudge with the devs, let alone to profit from playing havoc with the market.

Having 51% of hashrate for one hour generally wouldn’t be enough to cause real damage. An attacker would need significantly more than that to rewrite the chain with any degree of confidence and permanence. Double-spend attacks would probably fail on such a short-term scale. Still, though, this should be a wake-up call to networks with lower hashrate: they need to adapt to a world where hashrate is cheap.

One of the easiest solutions for new blockchain projects is proof-of-stake. The equivalent attack for this involves buying 51% of total coins, and the mechanics of supply and demand make that incredibly expensive (the more you buy, the higher the price goes – and you then kill the value of your own stake when you attack the chain). Another is linking blockchains, such as Komodo’s approach of notarising its blockchain on the bitcoin blockchain. And, of course, there’s the solution of launching new coins on an existing and secure blockchain, whether that is PoS or PoW.

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