Mining 5 blocks in a row! Is this a real problem?? \ stacker news ~bitcoin

pull down to refresh

Mining 5 blocks in a row! Is this a real problem??

400 sats \ 8 comments \ @028eda39e4 22 Dec bitcoin_Mining

The miners have no incentive to disrupt the blockchain (e.g., no reward for doing so and everything to lose due to the trust damage this would cause), despite the lack of motivation to harm the network, could they technically pull this off?

I mean, in this case as shown in the image, could they actually "rewrite" the blockchain history for those blocks. For example, they could perform a double-spend attack by reversing transactions in those blocks?

Would love to hear your thoughts on this! Thanks.

view all related items

286 sats \ 3 replies \ @nullcount 22 Dec

For a malicious miner to cause a deep reorg, they would have to first "withhold" those blocks from the network.

Example:

Suppose Foundry was evil and wanted to reorg any chance they could get.

Suppose Foundry found a valid block at blockheight 900,000. Meaning, they found a nonce such that when combined with the previous block's hash (block 899,999) the resulting hash is below the difficulty target.

Instead of broadcasting block 900k, they hold it themselves and begin mining their next block on top of this withheld block 900k.

Now suppose some other (honest) miner found and broadcast their version of block 900k. All the nodes will accept this block. Suppose this block contained a tx of yours and you already received the goods/services you paid for.

Now suppose Foundry found block 900,001 but this block is only valid if you use Foundry's block 900k, not the block 900k that was accepted by the network.

Foundry can broadcast BOTH their withheld blocks and cause the original block 900k to be orphaned.

If your tx was "confirmed" in the honest block 900k, but does not exist in either of foundry's new blocks, then its like your tx never happened, but you still received the goods/services.

If any miner wants to be malicious and they have enough power (or get lucky) they could reorg blocks.

20 sats \ 2 replies \ @nullcount 22 Dec

This is why many places of business require 3-6 block confirmations to render goods/services. However, as miners get more centralized, this should really be raised to 10-30 block confirmations, if you don't trust the miners to play nice.

10 sats \ 0 replies \ @Skipper 22 Dec

Or just use Lightning...

0 sats \ 0 replies \ @028559d218 23 Dec

My understanding... is that Foundry in this case (or any miner) would need to effectively mine 7 blocks consecutively (before any group of miners could collectively) without broadcasting any of them.

Then after the 6th block in the 'honest' chain is broadcast (6th block or 'confirmation' after a transaction occurs) Foundry would have to suddenly broadcast all 7 blocks which would not include some or many of the transactions that just took place 6 blocks before.

This would basically be... a 're-org' after 6 blocks (how long it takes for full confirmation.)

Basically, just mine 7 consecutive blocks in sequence, without announcing any of them, before 7 blocks can be added to the chain consecutively (by any number of miners). Then 'suddenly' announce the 7 blocks, potentially not including transactions that people had waited 6 confirmations for.

In order to 'double-spend' or 're-spend' UTXOs that are now unspent.

I believe that's my understanding.

145 sats \ 2 replies \ @freetx 22 Dec

The "51% attack", while theoretically possible, ignores most adult game theory analysis.

So the premise is, a company will spend billions of dollars and take on tons of debt in order to destroy bitcoin and then rule over a worthless chain? Then they can payback their debt and shareholders with what??

Further, a public company, with public officers are going to engage in provable fraud? There will be criminal charges over that.

The moment mining complicity in double spend attacks was detected, bitcoin would crash by 70-90%. There is literally no value in the network at that point....

There was a time, when "51% attacks" did make sense....when the total cost to achieve it was in the few million dollar range...that is, it could still be funded by single actor...at the current investment levels required, there are too many legal entanglements that prevent that.

10 sats \ 1 reply \ @028eda39e4 OP 22 Dec

I understand and I agree, but regardless the game theory and the disincentives to destroy bitcoin for miners, technically speaking mining 5 blocks in a row could give them the chance to "rewrite" the blockchain history for those blocks?

29 sats \ 0 replies \ @freetx 22 Dec

I suppose technically, but they can't predict ahead of time when they will ever get "5 blocks in a row".

Its like being able to predict: Starting now, I'm going to flip a coin and get heads to come up 8 times in row. Certainly theoretically possible but very very unlikely.

0 sats \ 0 replies \ @kristapsk 22 Dec

6+ confirmations are considered "safe" in Bitcoin Core wallet.