Fair warning, part of the reason I'm posting this in the newbie forum is because I've only cursory knowledge as to what I'm talking about. I suppose the question should be phrased more in a "why isn't this an issue?" rather than "Is this a problem?" sort of way.

The reason I hopped between weeks and days is because the difficult changes around every two weeks, just like a block is mined around every two minutes; the difficulty is set for the next two weeks based on the actual hash rate of the network, which in turn determines if 2016 blocks are more likely mined in less or more time than two weeks. I.E.; if 2016 blocks are mined in <2 weeks, then the difficulty increases, if 2016 blocks are mined in >2 weeks, the difficulty drops. At least this is my understanding.

That said, most of what you said makes sense to me. In reality, most miners don't drop out and would operate at a loss, but these sorts of attacks aren't really concerned with what the current mining economy is. I don't think it's an unreasonable prediction that if bitcoin *really* takes off, mining will become far less ideological and speculative, and much more logical and calculated as a necessity to maintain such an (eventually) expensive investment.

Plus, this part is where I think either we disagree or I'm mistaken.

The attack is taken advantage of the fact that (unless I'm mistaken) it takes two weeks for the difficulty to change, meaning it takes two weeks for these miners to be able to respond to that change.

And more along the lines of is the attacker has 40% of the network; they'd need to cause 20.1% of the network to go offline in order to 5% attack. In my understanding of how things work (which could be completely wrong), it sounds a lot more plausible to get 20.1% of the network to drop out due to a 40% increase in difficulty. If this attack could force a number of miners that 1.) comprise 20.1% of the processing power, 2.) cannot operate with a 40% increase in difficulty and have to drop out for two weeks until the difficulty goes back down, then it would be problematic and more feasible than a direct >50% attack, right?

Posted this on reddit, verbatim, but someone suggested I post it over here to possibly get a better response.

Tl;dr Could someone with enough processing power manipulate the difficulty or predicted hashrate in such a way as to force other miners to drop out by strategically going through cycles of mining and not mining, thereby gaining an advantage and eventually 50% of the network?

So, let's say we've got an adversary who's got a sizeable amount of computing power. And lets say he decides to fire up all his hardware for the amount of time it takes to make the difficulty change (let's call this a brick, because I don't know any other name for it; let me know if there's an official name in the comments and I'll change it), and makes the difficulty jump up. In the next brick, he turns off all his hardware and the difficulty jumps back down. And repeats.

As far as I can tell, with the proper set up, here's what would happen:

In the first brick, the time it takes for 2016 blocks to be mined is shorter than the previous brick by some amount. During these this time, our adversary has a slightly better-than-average chance to mine blocks because the network has not yet adapted. Let's say it takes 1.99 weeks for this first brick to process, and the difficulty increases at the end of the first brick.

In the second brick, our adversary stops mining, and it forces the second brick to last 2.01 weeks (making the difficulty go back down) because the network "expects" that computing power to be present. Some of the barely profitable miners drop out mid-brick because of the difficulty change, making the difficulty drop at the rate proportional to both our adversary's and the "fringeminers" computing power.

In the third brick, our adversary and a portion of the fringeminers (who saw the drop in difficulty and decided to give it another go) power back up, but this time our adversary has the advantage of some other miner's dropping out. Let's say enough of the other miners dropped out to make the third brick only last 1.98 days.

And then the fourth brick lasts 2.02 days.

And on and on until the adversary has gone through enough iterations to gain 50% of the computing power by making it unprofitable for others to mine and seizing on the easier difficulty?

I'm well aware that this would still take a ridiculous amount of money, but is there any reason why this couldn't be more feasible than flat out buying hardware to get to 50%?

And this also leads to the question if the 50% attack takes as a figure the actual hashrate or just the hashrate assumed by the network in calculating difficulty. I.e, if the difficulty is calculated to a hashrate of 10, and the actual hashrate when our adversary and some fringe miners pump back up is 20, with our adversary contributing 6, the fringe miners contributing 4, and the rest of the network contributing 10 does this constitute the adversary having 50% control over the network? I can't see why it wouldn't, but I don't know enough to make a definitive call. I feel like the answer to this is also the answer to if you can stop a 50% attack in progress or if you'd have to wait until the difficulty changes again, which of course could have major implications.

What I'm getting from this thread is that shutting down the internet is the best way to shut down bitcoin.

What ever happened to these guyshttp://www.popsci.com/technology/article/2012-01/german-hackers-are-building-diy-space-program-put-their-own-uncensored-internet-space? Something like that would make it a hell of a lot harder to kill bitcoin off...

I don't get what the purpose is... 

But I AM in support of a technocratic bitcult as the new world order.

A quick look says that MPEx and ICBIT are two other big trading platforms. Are there any other big ones I could benefit from knowing about?

It looks to me like ASICminer is going to be operational very soon, and it's looking like a worthwhile investment to pick up some shares in an auction. I read through the first few pages of the ASICminer thread, but they kept mentioning how it was managed through GLBSE, which 1.) I have no experience with, 2.) no longer exists.

So if GLBSE closed down, how are the shares kept track of, traded, etc? Is it just an informal thing, where if I were to buy some shares at auction, I'd just send an email to Bitfountain or whomever and they'd list me as a shareholder/delist the previous owner?  How are the dividends managed?

I'm sure this has been answered elsewhere, but I need more posts to get out of noobjail and I'm too lazy to dig through the 88 pages in the asicminer thread

So I understand the advantage of certain alternative cryptocurrencies over bitcoin, but what's the *point* of competition?

Sure bitcoin has it's shortfalls, but if the ideological end goal is going from fiat currency to decentralized cyrptocurrency, wouldn't it make more sense to try to push the universal adoption of the most popular currency rather than attempting to establish other systems? What do the creators have to gain by pushing a new system that they couldn't gain from simply supporting bitcoin, aside from marginal improvements in terms of things like mining protocols and shorter transaction times?

I'll admit that I'm not very familiar with any other *coins, but it seems that things like litecoin have two main advantages: faster times, and different  (ASIC proof) hashing algorithims.


If these disadvantages of bitcoin are that critical, how long will it be until another currency comes out that has a block solved about every minute? Or how long until ASICs are developed for the litecoin hash algorithm? I'm not convinced that the advantages aren't trivial.

I suppose I'm just unsure of the effects things like litecoin will have on the health of bitcoin in the long run. Part of me wants to say that more competition and decentralization is good, but if it comes at the cost of slowing down the adoption of bitcoin (disadvantages and all), I'm not sure which is the lesser of the two evils.

Regardless, gimme free money : 
LhTULh7acQLdVPbgbmdyk4ZbwcxcGpmaHp

I've been tangentially interested in bitcoin for about two years now, and finally decided to make an account here after lurking around on here and reddit for a while.

Something about bitcoin is absolutely fascinating to me, and I'm finally hoping to make the jump and become a little more active in the community and economy.