Analysts essentially calculate this number by taking cumulative chain work and dividing it by the hash rate at that time. Accordingly, an attacker has to mine a different chain. They can then publish their blocks as soon as the chain has greater proof of work than the main network.
Bitcoin security is at an all-time high as it will take an attacker with complete control of the network over 400 days to rewrite the blockchain even if they have 100% control of the network’s hash rate.
A prospective attacker would, therefore, spend over a year and hundreds of millions if not billions to attack the Bitcoin network. After all this work and resources, the price of Bitcoin could still come crashing down. This means that from an economic standpoint, an attack on Bitcoin makes no sense.
For perspective, a one hour attack will set them back $597,128 per hour at the time of writing.
The amount of time it would take for an attacker with 100% of the Bitcoin network hashrate to rewrite the entire blockchain has reached an all-time high of over 400 days. pic.twitter.com/kCk8ZKlIqH
– Jameson Lopp (@lopp) June 7, 2019
What Does Hash Rate Mean?
Hash rate essentially connotes the frequency that a computer system can guess a string of letter. This is what is called the hash. A cryptographic hash allows a computer to add a block of transactions to the blockchain.
Notably, individual mining units have their own hash rate. Ordinarily, the hash rate of a device is better with its performance. This is why it is no longer profitable to mine bitcoin using your ordinary PC. At the moment, the combined network hash rate makes it difficult to attack the network. This difficulty is certainly higher than it has ever been.
The current hash rate, therefore, means that the potential attack vector is at its most expensive in history.
The Level of Difficulty
Currently, the average hash rate for Bitcoin puts it at its most secure in its relatively short history. As such, an attacker who begins today would need about 400 days to complete more proof of work to than the entire current blockchain. This is, of course, with the assumption that a user has 100 percent of the hash rate. It goes without saying that it is virtually impossible.
That scenario is borderline impossible for a private individual or institution. This would essentially only be possible if you have a scenario where state resources are in play. A great example would be a scenario where the Chinese government seizes all mining farms in China.
As such, the estimate of 400 days is a minimum. No one else should mine Bitcoin in the next 400 days for this to be possible. Moreover, all the hash power goes into building a new blockchain with the same genesis block. Only in that scenario would all the nodes switch to the new chain as the longest chain. This would mean that the current longest chain is left orphaned.
From the aforementioned, the Bitcoin network is still remarkably secure. The fact that it takes this much time and resource to successfully attack the network, defeats the purpose. Moreover, even if you attack the network, it is no guarantee of either stability or profitability. Therefore, we can be sure to have Bitcoin, at least for the next 400 days. This is because the network is historically secure. The future of the decentralized network has never looked more secure. It is upon users and enthusiasts to ensure it gets better in the coming years.
