Topic: Manipulating the difficulty? (Read 4147 times)

True, but Bitcoin is subject to overwelming computations anyway.  Which is why the system is designed to encourage participation in the hashing that keeps the blockchain strong.

Hypothetically if they had that much power and were trying to destroy not just manipulate the btc economy they could easily right? Obviously it can come back etc but they could cause some serious problems.

This sounds like the old joke, "I always give 100% of my efforts at work!  10% on Mondays, 25% on Tuesdays, 50% on Wendsdays...."

Tell me this, if any single entity had access to the kind of hashing power to make this work, why bother with such a complex attack vector?  Why not just simply dominate the network?

Seems like it's a big part of it is motivation and the goal. It's going to be a lot easier to damage bitcoin than rip it off. Just like it's easier to break the windows on a bank than it is to rob it.
With the expensive of damaging it though I don't see anyone out side of governments or maybe a competing currency if google started one that would go to that effort.
Obviously if it were super villain that just did evil things you could explain it but I doubt anyone with that power just throws it around.

If someone had access to 100 tera hashes per second... they could user 10 for the first 2016 blocks, 25 for the next, 50 for the next, and 100 for the next 2016 blocks... and then leave... placing us in a predicament that takes more than a few hours to allow a transaction through the network...

For the attack to work once, it already requires that the attacker have control of at least one of the blocks wherein the difficulty is adjusted (perhaps both) that buffet a 2016 block set.  To do this attack twice in a row requires that the attacker be able to reliablely control at least two of these critical blocks in succession.  If the attacker has that kind of processing power at hand, then the 50% takeover issue is probably within reach.

The majority rules cannot be changed in such a fashion.  The only way that the protocol rules can be changed is if the majority of the potential generating userbase (which is larger than that actuall generating base) we to agree to change the rules, and vote by downloading a new client that repected those rules.  It couldn't just happen during a relatively short time frame, because once that attack ended, which it must eventually, the entire network would revert to the existing protocol stack, and any temporary changes made by the attacker by brute force would simply be undone, and all of the attacker's new blocks rejected.  Resulting in the atacker gaining nothing for his efforts.

Honestly, it probably woulnd't harm the Bitcoin network at this point, but in the future it might make getting honest tranasctions into the blockchain difficult, which could impact further adoption.

Motive questions moved aside.

The factor four thing wont really help, I think, because google could just do the attack for 2 consecutive difficulty adjustment periods and raise the difficulty by up to a factor of 16.

Also, in such a scenario, it should be possible for the majority of nodes to decide to change the rules to somehow adjust the difficulty more quick. This might bring up some trustworthiness issues, since we keep saying the rules cannot be changed easily, but I think in such a case a majority could form. On the other hand: we've got quite a few coins in circulation, doesn't really hurt to have mining slowed for half a year, does it?

Not really, it was just a spike and follow-up drop in the hashrate a couple of weeks ago.  Someone just referred to it as our "mystery miner" and it just stuck.  We don't have any evidence that it was a single entity, or several with bad timing.  My best guess about the whole thing is that someone tried renting out the cloud to mine for a bit, before having the facepalm moment when they finally realize that it's going to be hard for them to pay rent five times higher than the value of the bitcoins and make it up on volume.  Another credible possibility was that someone with a botnet was benchmarking their network.  The truth is that it is actually impossible for us to ever know any details, so we are all just guessing.

http://bitcoinwatch.com/

It's near the bottom on the left column.

Where did you find that figure? I've been thinking about analyzing the P2P network's combined hash power, but if someone else has already done it I won't bother.

I think the Mystery Miner predates me. Got a link to discussions on it/him/her?

Not at all. I just thought I remembered seeing this exploit being kicked around a bit during that period, that's all. The Mystery Miner does, however, show that it is possible (however unlikely) for a single, determined user to manipulate the network's difficulty.


Well, there's that double-spend vector that keeps getting kicked about. Also...