What is a 51% Attack?

This article dives into the logistics of a 51% or majority attack.

What is it exactly? Is it feasible? Who could accomplish it? How expensive would it be?

If you misunderstand how attack vector threats like this work, you may fall trap to thought processing like the badger:

What’s interesting is an attack was something carefully considered in the Bitcoin Whitepaper.

The word “attack” is mentioned 25 times.

Fun fact: the word “blockchain” is mentioned 0 times because Satoshi called it a timestamp server (it is a timechain, after all).

Even more interesting, the word “node” is mentioned 38 times.

What does this tell you?

Well, nothing directly, but nodes are the reason a 51% “attack” is nothing more than a pesky scheme, not a nuclear obliteration of the Bitcoin network.

What is a 51% attack?

A 51% attack occurs when a single entity or group gains control of more than 51% of the Bitcoin network's mining hashrate (currently ~ 582.32 EH/s).

This attack is limited and is more of a hindrance than an attack.

A very expensive one for the entity causing the hindrance.

Here is what hoarding this massive amount of hash would allow for:

• Prevent new transactions from gaining confirmations(censoring).
• Reverse transactions to double-spend coins.
• Denial of Service by mining empty blocks.

Here is what obtaining 51% of hashrate will NOT allow for:

• Force nodes to accept blocks
• Steal peoples Bitcoin
• Change consensus rules(increase 21M max supply)

Miners can only build the longest valid chain, and node runners determine if a chain is valid. Miners cannot change the consensus rules.

Is a 51% Attack Feasible?

It is possible to amass 51% of network hash and get reckless, but executing any lasting harm on Bitcoin is extremely challenging due to several factors:

Resource Intensive: To control more than half of the Bitcoin network requires a massive amount of computational power and energy. This would only be possible resource-wise for a nation-state or several nation-states.

Economic Disincentives: It's more profitable for miners to participate honestly in the network than to attack it. The attacker would need an army of ASICs (application-specific integrated circuits), which are expensive and energy-intensive.

Network Resilience: Honest nodes can outpace attackers. The network's structure ensures that even with a significant portion of the hash rate, attackers cannot sustain control indefinitely.

How much would it cost to attack Bitcoin?

Something to the tune of 7 million ASIC mining rigs and would cost around $20 billion. This does not include operational expenditure either.

The reason this would be so foolish is because the entity would get a higher ROI investing the $20B to mine Bitcoin honestly than it would trying to hold up the network.

Even if a nation-state that was not profit-minded wanted to destroy Bitcoin, it would be far more resource-friendly to install legislation that is hostile towards Bitcoin.

And it could backfire and cause people to wonder why the government is anti-Bitcoin.

In reality, a successful attack of transaction censoring, double-spending, and empty blocks would require much more than 51% of hashrate.

It would also make several assumptions:

• Double-spending would occur through an exchange, and for it to work, the exchange would need to be oblivious to the current state of Bitcoin mining.
• The honest 49% would have to get really unlucky and be unable to find blocks and foil the attack.

And the persistent effort becomes more expensive as time goes on.

100% of Bitcoin hashrate was once controlled by one entity, but it was not an attack.

Bitcoin has never got the chance to deflect a devious hashrate plot.

There was a brief 100% hashrate bias when Satoshi was mining Bitcoin honestly on a laptop CPU.

Bitcoin did not die, and it worked fine with the participation of a single honest miner.

If the miner acted dishonestly and prevented people from transacting, transaction fee bid can increase, which can incentivize honest miners to join and include their transaction. If a pool is the culprit, miners can point hash elsewhere.

This is the beauty of the fee market.

So why can’t the US print billions of dollars, accumulate millions of ASICs, and kill BTC?

Because it would require so many resources for such a small benefit and would not kill Bitcoin, but it would be like an annoying bug that would eventually get squashed.

It would be a global advertisement for the security of Bitcoin.

“Nation-state hyperinflates currency and fails to stop Bitcoin”

Bitcoin wins at the end of the day.