Could someone explain to me about 51% attacks and if bitcoin is vulnerable to one?
Hypothetically, a government decides to put forward enough resources to perform a 51% attack on bitcoin. Is that possible? If not, why? And is this something to actually worry about, or could something be done to combat it?
Basically the security assumption in Bitcoin is that at least 50% of miners are honest and work for a profit. A 51% attacker can recreate the latest blocks and remove all transactions from them, effectively the ability to reverse payments.
Hypothetically the government can gain 51% hashrate. For example China could take control of all miners there (currently more than 50%) and use them to attack the chain.
This type of attack can be detected. An extreme type of defense is to change the proof-of-work algorithm, making all existing miners worthless. This has been done several times in Monero for example.
[0]: https://whycryptocurrencies.com/how_do_cryptocurrencies_work...
There's two ways to do this either tactically to reverse your own transactions or randomly to essentially screw over everyone and sow FUD in the reliability of BTC transactions.
One good note is as far as I know the Lightning network shouldn't really be vulnerable to this (except maybe for channel opening?) because either party can submit the most recent transaction and have it reflect on the BTC chain.
The problem there is that then people lose faith in the network, and don't honor transactions, and it collapses in value.
No you can't. You have the power to prevent or revert transactions, and that's it. You cannot print unlimited money for yourself or steal coins from an address you don't control.
https://forum.bitcoingold.org/t/anatomy-of-a-double-spend-51...
Edit: a word