Quote from: IggySe7ven on Today at 03:47:46 PM

Guys, I am learning technical side of bitcoin blockchain, I am confused about something.

If it takes 6 blockchain confirmations to confirm a transaction to the network and each confirmation is about 10 minutes, how come sometimes When I recieve bitcoin it came faster like 30 min or less?

The time to mine each block is irregular and proportional to a Poisson distribution. According to this Bitcoin Wiki chart, about 55% of all blocks take 0 to 10 minutes to be made, and somewhere around 5% of blocks take more than 30 minutes to mine. So in your case you probably made a transaction that was included in 6 subsequent blocks all mined quickly.

As others already said, you only need 1 confirmation for the transaction to be in the network. But the more confirmations you wait for, the total waiting time averages out, and the >30 minute waiting times of the 5% compensate for the quickly mined 55%.

Quote from: BlackHatCoiner on Today at 07:12:42 PM

Quote from: bob123 on Today at 06:05:33 PM

If you are dealing with lots of money, wait for 6 confirmations. For standard transactions or transactions with a lower amount (less than a few thousands), 1-3 confirmations are absolutely fine.

Is there any person that lost lots of money by waiting for only 1 confirmation? Because I've heard that a 51% attack has never happened before.

You don't need a 51% attack to break 1 confirmation, there is another attack that works on blocks with one confirmation called a vector76 attack, you need a large stash of bitcoin to create a spending transaction to the node you want to defraud, mine a block, and broadcast it only to the target, and only right after the rest of the miners add another block to their blockchain.

At that point, the spending tx wasn't included in the other miners' blocks so it's invalid to them. As soon as the target makes a transaction to the attacker, which is valid on both chains:

- On the attacker's rejected chain, there is a (not broadcasted) spend, and a broadcasted receive
- On the main chain there is only a broadcasted receive

The broadcasted receive goes to the mempool, is scheduled to be included in the next block which will be visible by all of the nodes, including the attacker and victim. So: The spend wasn't valid on the main chain to begin with, but the receive was, and the victim was cheated out of a lot of bitcoin.

The way I described it, only works on full nodes with few connections to other peers. It can also find a weakly-connected node used by SPV wallets to attack, which will allow them to victimize any of the wallet users connecting to it. And it may or may not work on web wallets, it's unknown which nodes are tied to which web wallets. And this attacking process is extremely difficult to carry out because it's time sensitive and relies on a race condition (which block is seen first) which may not work.