Myth. Double-spending requires having more than half of the network hashrate.
As long as the attacker can use their hashpower to confirm a block that contains the double spend then the attack will be successful. The success rate of executing this attack increases as your hashrate increases until being 100% success when you control more then 1/2 the network. Are you agreeing this is a myth or disagreeing? Anyway, it's not just "confirm a block", it's make an alternative longer chain after the seller waited for n confirmation. Myth. The important factor is the amount of time spent waiting for confirmations, rather than the number of blocks. (Still a myth if instead of actual time you look at #blocks * average time per block). This could be true if the seller was willing to accept a 0/unconfirmed transaction. A seller would want to wait some time for the transaction to propagate throughout the network prior to releasing gods as an attacker could potentially release a TX to a very well connected node then one second later release a transaction to a poorly connected node that the "attackee" is suppose to believe will go through. For some period of time both transactions will appear to be valid on some parts of the network but after some time the TX will likely fall out of the pending pool on nodes. Note that this is an analysis of hashrate-based double spending, not double-spends of 0-conf based on network topology. |
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We've had our fair share of Bitcoin coverage on TV; but for the first time, there was a story about Bitcoin in a central news edition in Israeli TV, on channel 2, June 10 2014 (the program starts at 19:58). The story focused on a new Bitcoin ATM placed in the "Town House" hotel in Tel Aviv (a Robocoin machine, operated by the Israeli BitBox). For various reasons the program referred to it as "the first Bitcoin ATM in Israel", despite the fact that we already have a Lamassu ATM. In addition, the Bitcoin Embassy in Tel Aviv was shown, along with some general discussion about Bitcoin. Video link (in Hebrew of course, but some parts are interesting regardless of language): https://www.youtube.com/watch?v=C6-YF0_jWzU&list=PLiOFfTVghPYhGSnmImJBDd7Ul7BqgRkAd&index=35How is the political situation around bit coin there? Would you consider it a friendly country for crypto currencies? Probably not the friendliest, but we're working on it. |
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We've had our fair share of Bitcoin coverage on TV; but for the first time, there was a story about Bitcoin in a central news edition in Israeli TV, on channel 2, June 10 2014 (the program starts at 19:58). The story focused on a new Bitcoin ATM placed in the "Town House" hotel in Tel Aviv (a Robocoin machine, operated by the Israeli BitBox). For various reasons the program referred to it as "the first Bitcoin ATM in Israel", despite the fact that we already have a Lamassu ATM. In addition, the Bitcoin Embassy in Tel Aviv was shown, along with some general discussion about Bitcoin. Video link (in Hebrew of course, but some parts are interesting regardless of language): https://www.youtube.com/watch?v=C6-YF0_jWzU&list=PLiOFfTVghPYhGSnmImJBDd7Ul7BqgRkAd&index=35 |
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If the mining is memoryless, then does it make another popular paper published last year less meaningful? ( http://arxiv.org/abs/1311.0243). They argue that if a selfish miner get a block, they can hide it and starts to mine the next block based on it earlier than others so they can have an advantage. What's the advantage then? The only advantage is that they have a slight chance to find the block before others having a chance to work on it. If they publish the block before finding the next one, then no matter how long they have worked on it, they don't have any advantage. That paper correctly treats block finding as memoryless (it may or may not be correct about other things). You'd need to examine their analysis to understand why the attack works. The basic idea is that the attackers are attempting to build a long chain which is unknown to the network. If they manage to find 2 blocks in a row, they have the ability to evaporate a block found by the honest network, by releasing their longer, previously hidden chain. |
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When you find a block earlier, your opponents do not need to start from the scratch. They keep on working on their current block, on which they have spent , so the probability for they to get the next block earlier than you is much much higher than 'p'.
It seems that if all these words in this paper make sense, actually the author assumes the mining block is a memoryless process. It means no matter how much time you have spent on mining the current block, the expecting time from now to the moment you get the block is always the same (around 10 minutes). Begin computing early does not bring you any advantage. This is quite counter-intuitive.
Therefore, now I really doubt the correctness of this paper.
It's a well-known fact that block finding is memoryless. Miners "start from scratch" every fraction of a second. They try a hash, and it being a valid block is completely random and independent. If the hash is not valid, it does not make the next hashes any more likely to be valid. If a miner mines for 20 minutes and finds no block, he is not any closer to finding one than when he began. I have a question about this paper.
We will not
use this assumption, but rather model m more accurately as a negative binomial variable; it
is the number of successes (blocks found by the attacker) before n failures (blocks found by
the honest network), with a probability q of success. The probability for a given value of m
is
P(m) = (m + n − 1) p ^n * q ^m
m
I doubt this is correct. When the attacker is preparing a fork, he is not competing with the others. There are two completely independent mining process. I don't know why this can be modelled as a negative binomial variable.
When others find a block, it's not the attacker's failure. He will not restart a mining based on other's block, but has to continue mining based on his own previous block.
Moreover
"We will denote by az the probability that the attacker will be able to catch up when he is
currently z blocks behind. Clearly, if z < 0 then az = 1 as the attacker already has a longer
branch. To find az when z ≥ 0, we condition on the first step. If the next block found will
be by the honest network, which happens with probability p, the attacker will now be z + 1
blocks behind and his probability of success will be az+1. If the next block found will be by
the attacker, which happens with probability q, his probability of success will be az−1. It
follows that az satisfies the recurrence relation
az = paz+1 + qaz−1."
This is also not so straightforward. As I said, there's no competition, so what's the meaning of 'next block'. They are working on two different chains.
"Failure" is the standard term used when discussing negative binomial distributions. It doesn't mean anything. If you look at continuous time these are two separate process. However, we are certainly allowed to introduce an abstraction that puts all the blocks found in a sequence. Each such block will have probability p to be honest and q to be the attackers (independent of other blocks). The rest of the analysis follows. |
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Bitcoin is just a tulip bulb scenario in which an ever-increasing number of new investors is required to keep up the hype, and once there are no more greater fools left, it will crash
...
it's not like I'm investing in something that provides a real value to people.
...
a tiny bit of value... in a best-case scenario... which is highly unlikely to happen.
If you believe this, then it is unethical for you to profit from Bitcoin. But, in this case, it is also silly for you to believe you will profit by buying bitcoins, as the logical conclusion is the Bitcoin will go down in value soon. Luckily for the rest of us, we understand that Bitcoin is a revolutionary technology that will bring the world to a new era of transparency, free trade and personal empowerment; and that any profit we will make while dealing with it is a token reward for our contribution to the betterment of humanity. |
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only now?? I thought that they were accepting bitcoin before..
They started 2 weeks ago. If you recall something from before that, you might be thinking about Namecheap. |
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I think it's solvable in the following way: The node will require that the miner pays him some fee in the generation transaction. When the miner finds a valid nonce, the node will only release the full block if the miner shows him that the nonce matches a generation transaction paying the required fee. This way the node guarantees a fair share of the revenue enabled by his contribution.
Actually, there isn't supposed to be anything secret in the data that the node prepared, right? So in the rare occasion that the miner solves the block, he can broadcast it immediately to the network, and then he (or other members of the pool) can collect the transactions that the node used to create the block, and send all these txns to Bitcoin peers so that the solved block would be valid? In fact, the users who created those txns (and other Bitcoin nodes who just wish to see smooth continuation of the blockchain) have an interest to also pitch in and help with making the solved block valid? The only way to avoid this freeloading issue is if the node that created the block will incorporate a "dummy" txn that has never been broadcasted to the network? That might be messy because of the headers-first sync optimization that Bitcoin clients will probably have by default, i.e. while the broadcasted solved block is considered to be a valid candidate by the network, the miner could say to the node that he agrees to pay only half the fee in exchange for releasing the dummy transaction, or other such forms of abusive behavior? Edit2: Actually I was very much confused, the data is indeed not secret, but I missed the point that the miner only has one branch of the Merkle tree, therefore it should be infeasible to try different permutations with unconfirmed txns, especially if the volume of unconfirmed txns is high (which is one reason why we need multi-PPS in the first place). Right, as I was reading your comment, my first thought was that even if the miner knows which txs went into the block, there are still 2^n possibly orderings which only the node knows. The extra round-trips of communication between the node and the miner imply that the current form of centralized pools will have an advantage over multi-PPS, especially if the average blocktime is less than 10 minutes as with Litecoin etc., right? Wouldn't this advantage override the benefits of multi-PPS, meaning that miners will prefer not to use multi-PPS because of this?
I don't think it's a significant overhead, because the data that needs to be communicated is small, and because there will likely be nodes in physical proximity to the miner, so latency shouldn't be high. Furthermore, the advantage of Multi-PPS is significant, commensurable with several percent of the revenue. For example, if miner-node latency is 0.1s, and time between blocks is 600 s, the lost revenue is 0.017% while the gain is 3%. This does indeed worsen with faster block times, however this might be solvable with new block graph structures. |
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1) So far this proposal doesn't explicitly describe how to pay the nodes who construct a block that contains all the transactions minus the coinbase, for their service. If it should be some sort of a subscription service where the PoW miner pays in advance, then this adds to the overhead because the miner has to identify himself when requesting a new block, and there's room for abuse/freeloading i.e. one miner pays and then shares his account (login/password) with other miners, or shares the constructed block (minus the coinbase) with other miners. Another option is that it'd be some kind of an honor system, where miners donate some portion of their profits to the nodes who provide this service, but I'm not sure if that'd be sustainable.
I think it's solvable in the following way: The node will require that the miner pays him some fee in the generation transaction. When the miner finds a valid nonce, the node will only release the full block if the miner shows him that the nonce matches a generation transaction paying the required fee. This way the node guarantees a fair share of the revenue enabled by his contribution. 2) In an old thread the issue of performance was discussed, slush's reply ( link) is rather pessimistic. He considers the straightforward setting where the miner submits the entire block to the pool, unlike your followup post about quizzing or using SNARK/SCIP as an improvement. Though unlike the old thread, with multi-PPS there's the added complexity of interacting with separate nodes that construct blocks for the miners, and this should also be taken into account since the miner might request several such blocks during the average 10 minutes interval, as new transactions are being broadcasted over the network. I think that BIP0022 (which probably isn't being used by anyone yet?) was inspired in part by that old thread, so I'm not sure what should be the current assessment regarding the severity of the performance issues. I think slush is simply wrong in that post (either that or remarkably forward-thinking), as he ignores the Merkle tree structure. For the foreseeable future, the mining revenue will consist primarily of newly minted coins - and in this case, protection against directly profitable attacks (though not against sabotage) is easy by sending Merkle branches, without quizzing or advanced methods. And, statistical quizzing methods do exist, and by the time this is relevant I hope SCIP will be practical. (Actually GBT and similar methods like Stratum are the norm currently, they're needed to deal with the rapid rate at which ASICs exhaust nonce ranges). |
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what is the position of Israel right now about Bitcoin?
looks like you taking it really serious there..
Currently there are no Bitcoin-related guidlines or rules from Israeli authorities. |
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Critical Update: The conference has been cancelled. See http://bitcoin.org.il/files/Israel%20Bitcoin%20Conference%20Cancellation%20Notice.pdf. Instead, we will be having a conference on October 19-20: https://bitcointalk.org/index.php?topic=734556Hi all, On July 28-29 we will be holding a Bitcoin conference in Tel Aviv, a joint work of the Israeli Bitcoin Association and Media Bistro's "Inside Bitcoins" brand. More details about the event are available at http://bitcointlv.com/. We expect hundreds of people from around the world to participate, and we have ~30 confirmed speakers consisting of both Bitcoin's worldwide experts (including, for example, slush, Stefan Thomas and Vitalik Buterin) and Israel's local talent. We're designing the conference to have something for everyone, with topics covering both Bitcoin's industry (businesses, start-ups, commerce, communities, regulation and authorities) and technology (core protocol, software, features, algorithms and academic research). The tentative agenda is available on the site, but it is still actively developed with new sessions added and existing sessions being finalized. The early bird registration price is $259 for the whole conference, though there are some discounted ticket options. The deadline for enjoying the best rates will end soon, so make sure not to miss this opportunity to network, learn about developments in the Bitcoin world, and visit the Bitcoin empire that is Israel. We're also looking for more sponsors for the event, so if this is relevant for your company you're welcome to contact our team to discuss the sponsorship opportunities. I hope to see you all there!
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And at this point we are discussing semantics
Of course we are. However, I do believe there's a fundamental difference between this and other examples you've given such as the oak tree. Bitcoin, being a currency - and a purely digital one at that - is defined by what people think it is. If the system continues to work as it does now, but people stop believing in it, it becomes meaningless. Whereas the oak tree is still there regardless of whether we look at it, talk about it, call it different names. With the oak tree, the specific configuration of atoms matters. With Bitcoin, the agreement of people matters. Hence, we have the power to mutate Bitcoin with the power of thought and agreement, in a way we cannot with the oak tree. Notably, this has happened before (P2SH and some bug fixes come to mind). People agreed that Bitcoin should be changed, and viola, Bitcoin was changed, without anyone supposing we're now using an alt. This discussion has practical consequences beyond the OP's opinion. When I accept bitcoins as payment, I do so because I believe they will have value now and in the future (as with any other currency). I believe this because I believe Bitcoin will be used, and that there will be no more than 21M bitcoins. "Used" is a human-centric concept and thus is influenced by perception and marketing. If people use the name "Bitcoin" to refer to a new protocol, it has a different effect on the survivability of the old protocol than if people used a different name. So "will a protocol that has a different inflation schedule than the current Bitcoin exist" is a different question from "will a protocol that has a different inflation schedule than the current Bitcoin exist and be called 'Bitcoin'". A positive answer to the latter doesn't bode well to the value of bitcoins I can currently obtain, thus a negative answer to it is what I need to be assured in accepting bitcoins. This again is a practical consideration, not a purely philosophical one. |
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