Bitcoin Forum

Is it possible to restart the Bitcoin blockchain from the point where the block was saved? For example, now, as of January 1, 2024, block No. 823.881 has been mined. And I want to restart it from block No. 800,000. Is this real or not?

Yes.

But it would only be for *you* so to speak since the rest of the world would keep happily mining along.
And if you wanted to mine 800,001 by yourself you are going to need a massive amount of hashpower.

https://bitcoin.stackexchange.com/questions/68644/bitcoin-core-go-back-to-a-specific-block

-Dave

No, if you want your blocks to be accepted by others.

Let's say the most recent block is block number 823,881 and you (the attacker) want to replace that with a new block.
To do so, you must mine the block number 823,881 while other miners are trying to mine the block number 823,882. To be successful, you need a big hash power, so that you are fast enough and can build the chain with the most work.

If you want to replace the last two blocks, you have to start from block number 823,880 and the chance of being successful would become much smaller.
The probability of success decreases exponentially, if you want more blocks to be replaced in the blockchain.


Note that given the big total hash rate of the network, even replacing a single block is almost impossible.

Yes, such a scenario, though difficult to implement could be considered  if the total computing power of the attacking (ganged together ) nodes and the nodes they attack exceeds the hashrate of the remaining nodes.


Therefore, in order to prevent their encirclement and isolation, nodes are recommended to carry out a number of activities, namely, increasing the number of connections, selecting peers   randomly and changing  them from time to time, monitor relevant traffic, and so on.