Re: Are there protections built-in against 51% attack?
⭐ Merited by Quickseller (2)
Since majority of the hashing power is controlled by the adversary in the case of 51% attack, they can literally do anything for as long as they can sustain the attack.
I don't know how you understand double-spending, but I'm imagining it like that. Some nodes will receive the red transaction first and some others the green. Therefore, they will reject the invalid transactions. The problem is that not all nodes agree to the same transaction.
Even with a 51% attack, you can't double-spend bitcoins. You can reverse transactions, which is different.
Are there any capabilities built into the code of Bitcoin or Bitcoin mining node softwares to tackle a scenario like this?
Unfortunately, no. I had made the same question on this thread: A solution to every 51% attack. The reason why this can't happen is pretty dumb in my opinion and it has to do with the already written consensus rules. If the developers change them, they're officially turning bitcoin into a fork. Sooner or later, though, they'll have to change some consensus rules, because technology evolves.Transactions <100, 500, 1000 or whatever> blocks deep should remain in the blockchain forever.