How Much Would it Cost to 51% Attack Bitcoin?

Recently, BSV reportedly suffered a ‘massive’ 51% attack beginning on 3rd August and resulting in up to three versions of the chain being mined simultaneously. For over 3 hours, attackers were able to take over the chain. All exchanges that received BSV deposits during that time might have been double-spent.

Will it happen on Bitcoin?

A 51% attack is an attack on a blockchain, which is a type of digital database in ledger form. With blockchain technology, information is collected together in groups or blocks and linked together to create a chain of data. In cryptocurrency trading, blockchain is used to record approved transfers of digital currencies and the mining of crypto coins or tokens.

If “miners” want to attack Bitcoin, they can attempt to add blocks to the chain by solving mathematical problems through the use of a mining machine. These machines are essentially a network of computers. If miners succeed in adding a block to the chain, they receive Bitcoins in return. The speed at which all the mining machines within the network operate is the Bitcoin hashrate. A good hashrate can help gauge the health of the network.

A 51% attack occurs when one or more miners takes control of more than 50% of a network’s mining power, computing power, or hashrate. If a 51 percent attack is successful, the miners responsible essentially control the network and certain transactions that occur within it.

How much would it cost to 51% attack Bitcoin with a physical hashrate?

It is possible to attack BTC through amassing enough ASICs (mining hardware) and power capacity to attack the network with a physical hashrate. Let’s start by analyzing this situation.

Total Hash Rate at 110.28 EH/s from BTC.com

With the current total network hashrate of 110 EH/s, we’ll calculate a rough estimate of the costs necessary to set up 110 EH/s worth of ASICs (assuming the miners with the existing 110 EH/s remain honest and don’t contribute to the attack). In the most favorable case where all hashrate is produced by an equivalent machine to the highest efficiency ASIC on the market today, the Antminer S19 Pro, then the specifications per ASIC would be 110 TH/s and 3250 W consumption.

110,000,000 TH/s / 110 TH/s = approximately 1.00 Million ASICs needed to amass 110 EH/s. With a per-unit consumption of 3250 W, that would put the electricity capacity needed to power all those ASICs at ~3.22 GW of power. That limits the possible candidates to pull off such a huge endeavor to powerful nation states who would work in coordination with large energy producers.

And how much would those 1.00 Million ASICs cost the taxpayers of such a nation state? Well, at a conservative unit price of $4000 each including power supply units, the cost of hardware would exceed $4.00 billion.

In the grand scheme, this may still be a small sum to the likes of the USA or China. However, it doesn’t account for significant obstacles such as the limited capacity of chip manufacturers like Samsung and TSMC to actually produce these high quality hashing chips. (Not to mention the lunacy of a government using that semiconductor manufacturing capacity to build ASICs and attack Bitcoin rather than any number of other valuable applications.)

Overall, attempting to destroy trust in Bitcoin through a mining attack with a physical hashrate just doesn’t make sense anymore, and it hasn’t for years.

How Much Would it Cost to 51% Attack Bitcoin? was originally published in The BTC Blog on Medium, where people are continuing the conversation by highlighting and responding to this story.