Apparently, it can be very secure. If “pieces” of a secure key are stored in multiple places, for example, only changing one link in the “chain” means it won’t match with the others. They ALL have to be changed at the same time, which is virtually impossible to do in secret.
Please note that I am far from an expert on the subject. I’m paraphrasing an article I read months ago.
Can’t you takeover a blockchain by owning the majority of a block chain, or by having a majority of the processing power to compute hashes?
Yes which is part of why the major chains are owned and controlled by companies, but then that makes the whole thing pointless. IMO, a company controlled blockchain may as well just be a DB cluster, it would be faster and more efficient.
If you had 51% of the world’s computing power (to blockchains using proof of work) yes you could forge records, from what I could wrap my head around about blockchains.
You don’t need 51% of the world’s power though, just 51% of the power of people who care about how the system works. Most people using block chain cryptos don’t care at all, so the threshold is a tiny percentage of the user base.
This would just create a fork in the blockchain where 51% of the network doesn’t match the correct state of the blockchain that the 49% have. The 49% would effectively stop working because they could never validate the transactions that the 51% takeover has falsely created. The node operators of the 49% of the network would need to reach consensus for how to deal with the problem, but essentially they would just adopt code that ignores the 51% data, so they could continue to process blocks of transactions. Without manual intervention the 49% would be frozen. The 51% is just fake, they haven’t really changed anything because every real node operator would know it’s false data.
