Quote from: o_e_l_e_o on July 13, 2023, 07:52:28 AM

Anything above 6 confirmations doesn't require 51% of the hashrate either. Even with, say, 30% of the hashrate, you still have a 4.2% chance of reversing 10 confirmations and a 0.2% chance of reversing 20 confirmations.

I tried, but got different numbers. How did you calculate this?

Either way, it's very costly. You'd risk losing 6 blocks (of 6.25 Bitcoin block reward plus fees each) for a 4% chance of reversing a transaction. That means it costs tens of millions of dollars on average to pull this off.

Quote from: ranochigo on July 13, 2023, 08:05:05 AM

Quote from: o_e_l_e_o on July 13, 2023, 07:52:28 AM

You might also be interested to read this post, which describes how a miner can double spend a transaction with one confirmation: https://bitcointalk.org/index.php?topic=36788.msg463391#msg463391.

The caveat being that the amount that you're depositing has to be more than your block reward at least for the attack to the worthwhile.

It's nice to read how simple things in 2011 were: I assume the guy was talking about a very large deposit (in Bitcoin), followed by a very quick withdrawal (after 1 confirmation). Nowadays, nobody in their right mind accepts such a deposit right after 1 confirmation.

Quote from: vector76 on August 17, 2011, 05:37:56 PM

Eventually, I succeed in creating a valid block. I do not broadcast it immediately, but instead I wait until someone else mines a block

Vector76 didn't even mention the loss of a block (back then worth about $500) if his plan failed and his block become orphaned.
Nowadays this means you're gambling with a $200,000 block reward.