Bitcoin Forum

I guess I don't understand the relationship between the rising difficulty, the 51% thing, and all this chatter about ASIC disrupting the market.

Is there a set limit on how many btc can be produced by the global community of miners in a single day?

http://www.youtube.com/watch?v=D-OGsSb0BPU
Over 9000........IN THE FUTURE

The Bitcoin network automatically adjusts the difficulty so that a new block is produced roughly every 10 minutes.

1440 minutes in a day / 10 minutes per block = 144 blocks per day
Every block currently creates 50 bitcoins, so 144 * 50 = 7200 BTC

It should be noted that this is an approximation and will differ depending on luck.

the system is designed so that on average a block is solved every 10minutes
difficulty is what regulates this and is adjusted very 2016blocks - roughly a fortnight

24hours x 6blocks x 50BTC = 7200BTC/day on average

if/when asics arrive and block solving skyrockets the 2016 blocks will be found much quicker than a fortnight and difficulty will increase (and the time to block reward halving will come forward).
In this window of rapidly rising difficulty early adopters of asic will do very well.

If 1Thash asics are released. well today the network is ~ 12.5Thash, it would take 7 1Thash asics to have over 51% of the network hashpower, not really a huge cost to disrupt the bitcoin network if one really wanted to.

It would take more than 7TH/s to have 51% of the network, unless existing miners drop out.

@OP: You could have much more than 7200 BTC in a day if you had a large increase in hashing power. Say BFL gets their initial batch of ASIC rigs together and decides to do some live testing. If they had 45TH/s of hashing power, you would expect that 576 blocks would be found that day instead of 144, so 28800 with 21600 going to BFL.

currently the network is under 13Thash , 7Thash is >51% (7Thash is 50% of 14Thash) as the network stands today. I imagine it will be more by october/december/whenever /ifever asics are delivered...

Graet, your math is retarded. If you add 7 more Thash to 13Thash, then you have 20 Thash total of network hashing power. 7 is not 51% of 20. What Mr. Teal is saying is correct. Current miners would have to drop out while the 7 Thash are added in order for the ASIC's to be 50% of the network hashing power (If there are 13Thash now, then 7Thash would have to stop mining as 7Thash of ASIC's commence mining).

Once the attacker starts mining on the main network, the total will be 20 Thps, and their 7 just won't cut it anymore.

Aye, an attacker will have to add atleast as much as the existing hash rate +1% of that total in order to achieve 51%


And just wtf does anyone think someone could actually accomplish with 51% besides a bit of harrassment with orphaned blocks from some of the other miners? A double spend? Really, what is the likelihood of 2 merchants having anything large enough to offer that it would be worthwhile to spend twice at the same time. And then what are the odds they will ship anything before they noticed the transaction disappeared?

Maybe I forgot some other nasty side affect to a short-term 51%. I assume a long term one would cause the need for a fork in order to get legit transactions reporting again. shrug.

If some magical device came along that could do petahashes per second, keep in mind the following information: Blocks can be created as fast as your hardware will go, you could create 100 of them within 10 seconds if your hardware was that fast.

However, there are 2016 blocks per retarget interval, so the maximum number of blocks that could be created before the difficulty was adjusted would be 2016. Currently, that is BTC100,800.00 plus fees, at BTC50 per block. If you created all 2016 blocks within 1 day, the difficulty would jump in order to fix the generation speed.

But there is another factor to contend with: The difficulty cannot rise more than four times the current value per retarget interval - so the current value is 1726566.5591935 and four times that would be 6906266.236774. It would continue to rise in 4x jumps until the block creation rate was 2016 blocks per 2 weeks, as it should be.

Just for laughs, I'll use my 2016 blocks per day example for some calculations. 2016 blocks per day is 14 times as fast as the network wants to go, so at the end of day one the diff would rise at the max rate of 4x. Now that 2016 blocks takes 4x as long to create, it will be 4 days before the next retarget interval. 4 days is still 3.5x as fast as the network wants to go, so at the end of 4 more days the diff will rise again, but this time by 3.5x. Now, the diff is 14 times higher than it was 5 days ago, and the block creation time is now back on track to where it should be. Therefore, in 5 days of mining, the network has adjusted the difficulty to neutralize this hashing monster, and keep the block flowing at a steady pace.

The trick now is what happens when he stops mining. At that point, the network is 14x higher than it should be, so it could take a while to get back to normal....

P.S. If I have made any blatant mathematical errors, I'm sure the smarter folks here will helpfully point them out. Please and thank you ;)

Double-spending isn't spending to 2 merchants. It's spending to a merchant and yourself, or sending to an eWallet and yourself (e.g., send to an eWallet, wait until it is confirmed, withdraw and get some other coins, reverse the original transaction).

Or he can prevent any transaction from confirming.

>50% at the hands of a malicious entity really is pretty bad.

The correct answer is: however many the developers code into the client. This can be changed, but right now we have no reason to believe it will.

The question was about how many bitcoins can be produced. If someone (be it Gavin or anyone else) releases a piece of software that generates more than 50/block + retarget for 2016=14 days, whatever it generates isn't Bitcoin.

Thanks for that. It's been a while since I read any serious discussions on the topic. I would be fairly concerned about the transactions not confirming. This it would seem could be more devistating to the BTC economy than the potential to 'spoof' BTCs(sorry for the bad terminology. I'm still having a hard time grasping just how double spend would benefit the perp in the end)

edit; sorry for sidetracking the OP a bit. As RJk and others have pointed out the difficulty adjestment would correct the increased generation on its own.

Yes. They would be mining on a worthless chain.

Think chargebacks... for Bitcoin.

/me weeps

aye, I get the concept. But wouldn't they need to receive something in return from the soon to be charge backed transaction to benefit from it?

They wait with the "chargeback" until the merchant is satisfied with the amount of confirmations and gives them the product or service, at which point the attacker "charges back" the transaction and gets to keep both. There is no limit as to the amount of merchants they can screw over, so the potential for damage is huge.

Aye, so pretty much like I'm imagining then. Sooo, how many merchants are able to deliver a product before the blocks resume and the chargeback happens. I mean if the 51% is sustained long enough to be noticed by devs would we not be able to fork from it?

edit; don't get me wrong, I see the potential for this to happen with the 51%. It seems seems they would need too many others things to fall perfectly into place for it to work.

Remember that even with 51%, no attacker can spend your or others' coins. They can only spend their own, prevent your transactions from occurring, and roll back your and others' transactions at will. That last part becomes more and more difficult with the passing of time, and depending on how much hash power the attacker has.

Between each difficulty increase, the network produces 2016 blocks. 


So if you've increased 3 times in 5 days, you've made 3x2016 blocks in 5 days.  That's 6048 blocks or 302,400 bitcoins.  Now you see why people are having wet dreams.

aye, if they had 51% they definitly would not have a shortage of BTC to play with. ;p  And yea, the rolling back of a huge volume of transactions seems very concerning.

This is where I fail in my understanding of the double spend.  Suppose someone gets the hashpower (costly) and goes through with this 'attack', wouldn't it be self defeating? I mean everyone can follow the transaction trees so they would know when/if it happened and at that point wouldn't bitcoin become completely useless as everyone loses trust and pulls out? The attacker only really has one attempt to profit on this before the house of cards falls down correct?

Or is it a case of blind denial and people will try to fix the attackers changes and keep bitcoin limping along even though the trust is now shattered?

Have fun cashing out. ;D

You don't know until it's too late. The attacker starts mining on a chain of their own, without broadcasting the blocks to the outside world. They could be 100 blocks ahead of us right now, and you wouldn't know it. On their chain they're still in possession of their bitcoins, while they spend them all on our chain. When they're happy with the fruits of their spending frenzy, they unleash upon us their chain, which is immediately accepted because it is longer.

ahhhh, I see.  edit; But, how would they spend coins on our chain before overwriting the chain?

So the only other hurdle for them is building a chain to match the length of the current one before joining? Of course they can likely do this all at difficulty 1?

Or something a bit more subtle.. like refusing to include transactions unless a higher transaction fee is paid.  Sure other people could try to mine them, but eventually, they'll be orphaned.

The chain building must conform to the current network parameters, including difficulty. It must be built without leaking onto the internet at any point (slightly difficult), and if it doesn't match what the network expects when it is released, that would cause it to be rejected and all that hash power wasted.

Meh, they would make more from screwing over a single merchant with a double-spend than a lifetime of transaction fee extortion, and people would abandon Bitcoin in both cases.

ahh, thought they could atleast cheat the difficulty. Soo, if they had the hash power to build a matching chain would they not make more money by just mining thereal  chain? Or would the benefit have to be not neccesairly motivated by money then?

haha, I love the fee extortion idea. ;p  Why not, it seems someone actually doing this would have to be a bit bonkers to begin with. ;p

Eventually this will happen anyway once the rewarding drops further.  You'll see further consolidation as mining margins shrink which will slowly give the mining companies much more say with what goes on.

Well at that point, they would have all the coins mined from their fake chain which has now been accepted as real, as well as whatever they were able to bilk out of the merchants that they fleeced with a double-spend.

In other words, a shit ton of coins.

Actually, they sort of can. There is the "Zeitgeist attack". (I prefer "Time travel attack", but that's beside the point.)

It works on the premise of artificially modifying the block timestamps so as to "confuse" the algorithm that retargets the difficulty. ArtForz describes it here (https://bitcointalk.org/index.php?topic=43692.msg521772#msg521772).

tl;dr: an attacker can perform the attack with marginally less hashing power

Once all this new 'allegedly' available asic tech comes online the network will be a shit ton stronger against this sort of attack.

so    BFL = savior of the blockchain
and  BFL = destroyer of miner's dreams

If it materializes, then yes pretty much. Along with Vladimir's proposed ASIC farm, the difficulty in the future is going to be damn high.

I'm trying to visualize what this all means.  Soon the 7200 bitcoins per day max will be halved to 3600.

So now we have 3600 bitcoins spread out among...what would people guess...200TH/s once ASIC hits?  2,000TH/s?

aye, it's really hard to speculate now and comes down to just how much miners are willing to spend to buy asics. The preorders currently put the new hash rate at maybe 45TH by reward halving(much citation needed still). And will be largely influenced by how well the release goes and whether that encourages more miners to buy equipment or not.

BFL won't get to 2000TH/s any time soon. If you think about it, using the current SC ASICs that would be 2000 MiniRigs or 50,000 singles. Given the little we know about BFL's production and assuming that the new singles/minirigs take as long to produce as the old ones, how long do you think it will take to get 50,000 singles out the door? Of course, the $70M that would bring in at current prices finance quite the expansion.

We know via Bit-Pay that they got at least a quarter million dollars yesterday alone.

http://www.marketwatch.com/story/bitpay-shatters-record-for-bitcoin-payment-processing-2012-06-26

That buys 8.3 minirigs or 8.3 Terahashes.

Do you think they'll be able to ship out 8.3TH/s worth of gear in one day?

If I was a malicious attacker with 51%, I'd prevent everyone's transactions from happening and ask for a significant ransom.  Once the ransom is paid, then I'd resume normal activity.  And maybe rinse and repeat a little while later.

That's the only way I can see that I'd be potentially profitable without being traceable.  I can't imagine a double-spend actually working.  I'd probably end up getting caught and going to jail.  It'd be hard to buy ANY physical good without leaving some sort of trail.  And asking for higher transaction fees might work, but it'd be the lower-profit option, I believe.

Now, if I was a reasonable person with 51%, I'd just mine the heck out of Bitcoins and have a nice pile of them to do whatever I want with.  Seriously, if you're money-motivated, and have 51%, THAT is the best option.  It won't reduce confidence in Bitcoin (and thus your Bitcoin net worth), and it would continue to be profitable long into the future (whereas a double-spend or ransom attack would only be profitable in the short term).

Basically, I would completely eliminate the possibility of a 51% attack happening.  I don't see why any reasonable person would do it.  It would make them less money than simply mining with that hashing power.

I see it pretty much the way you do. That does still leave us with an entity that is not motivated by money and simply wanted to destroy bitcoin.

'Some men just want to see the world burn.'    ;D Sorry I couldn't resist

This is true.  I should have concluded my post with "I would completely eliminate the possibility of a 51% attack happening by any profit-motivated malicious attacker."

It's a good question given their track record. That said, in the past they were new at this and selling to a skeptical client base. I assume if they are smart enough to build and ASIC they are smart enough to solve their supply chain bottlenecks.

Assuming killed the cat.. or something.

Technically... the rest of them. But really just a few times the normal amount in a day will send difficulty skyrocketing and bring it back to the average amount quickly.

1. Take a short position on BTC.
2. Destroy Bitcoin with a 51% attack.
3. Profit.

mhmm
Is there anything you don't think of? =)