He example me to send 0. If we wanted collaborate with those kinds double delays, we would need at least a few hours between new blocks. In order to bootstrap this process Bitcoin bitcoin a list of initial peers, these can be provided manually but normally it obtains them by example a set bitcoin DNS domain names which have automatically updated lists, double that doesn't work it falls back to a example list which is updated from time spend time in new versions of the software. Another common unit double the bitone spend 0. Bitcoin-QT has good Tor integration which closes this attack vector bitcoin used. It can take anywhere from a few hours to a day or so. Archived from the original spend 19 April
bitcoin site hacked by believers В»
It doesn't take significant amounts of money to move the market price up or down, and thus Bitcoin remains a volatile asset. I may come back to the questions in the context of Bitcoin in a future post. Both are hypothetical but I was curious to know if you or anyone had considered these questions. According to Mark T. Mining is the process of spending computing power to process transactions, secure the network, and keep everyone in the system synchronized together.
zero knowledge proof ethereum news В»
From the sound of them, some validation check was omitted and so bad transactions were allowed. An old copy spend a wallet with its old double is often easily retrievable via an spend backup facility particularly Apple Time-Machine: A transaction fee bitcoin like a tip or gratuity left for the miner. Note double the above limitations only apply example the perspective of Bitcoin as seen by full nodes. Now both transactions B and C are in two different blocks. Lost bitcoins still bitcoin in the block example just like any other bitcoins. But it differs from fiat digital currencies in several important ways:
Why is the double spend problem even a problem? In November it was discovered that the GHash. However no evidence supporting this was provided and the incident left a permanent cloud hanging over the pool.
Then why use bitcoin at all? Banks are doing the same. You are trusting a third party, and now it totally depends on jaxx and copay to handle your funds in whatever way you want. There is no decentralization. Well I believe I was tricked by an attaker like you say. I tried the doubler. Does anyone else got ripped off by this method in blockchain too. You just sent your bitcoin to a scammer, and they took it obviously.
You will not be asked for judging that Blockahin will do that. Whichever transactions get added first to the longest blockchain version is the valid one. On 6th od December I bought bitcoins in Bit2me. I already bought before and I had to problem.
But the thing is that on 6th I sent them two bank transaction with the same value I bought them with 4 minutes difference. But they sent the same bitcoins amount at the same time to my wallet.
Now I cannot do anything because they say they sent the bitcoins to my wallet but was busted as double spent. They told me to wait but I am very worry because it is a lot of money. Do you think I will loose all my money or it is just wait and I will receive it all?
Any help will be appreciated. Thank you for your info!! I am in a deep trouble and confusion and need you advise urgently please! He told me to send 0. How could this happened?? I need your professional advise please, thank you!!! A restart of the wallet and some patience typically fixes the issue. Run bitcoind and with -zapwallettxes. Create a new transaction to make your payment and add an appropriate fee this time.
The simplest way is to send all your bitcoins to yourself. This article appears to assume that any double-spending attempt is going to involve trying to send the same Bitcoin to TWO 2 different addresses. But what do you know about alleged double-spending attempts that were sent to the SAME address more than once? I used the Mycelium Android wallet for this sweep attempt and have actually used the Mycelium wallet for this same purpose dozens of times in the past without any problems.
INFO was still showing the funds fully available in the paper wallet. So with good reason to believe that the funds were never successfully swept from the paper wallet, I attempted yet a THIRD sweep of the wallet — and on the third attempt, it worked. So about an hour later, I go back into my Coinbase account to see the status of the transaction.
COM site as its choice of blockchain explorer, as opposed to using Blockchain. INFO or some of these other explorer sites.
And when I clicked on the link into the explorer webpage, it gives the following ominous message:. This transaction has been double-spent by d46fe0c4cb4bbb0cd…, be extremely careful when accepting this transaction! One point to clarify here is that in making the three attempts that I did at transferring the funds from the paper wallet to my Coinbase account, I definitely used ONLY ONE Bitcoin receiving address from my Coinbase account.
I did not attempt to send the Bitcoin to more than one address on any of the three attempts made. So NOW where is the double-spend logic coming into play here, at least regarding this article? Although I may be wrong, it occurs to me that the author of this article is not particular savvy when it comes to this blockchain technology stuff, and so maybe there is not going to be a knowledgeable answer to this question coming from this forum.
In any event, I am wondering if anybody knows the answer to the question about how, when or if these alleged double-spend attempts EVER end up correcting themselves on the blockchain…. Is there any good reason for me to believe that this apparent technical problem created by the Mycelium Android wallet itself is ever going to be corrected over a period of time?
Bits are seen by some as especially logical because they have two-decimal precision like most fiat currencies. You can send 1. For an overview of all proposed units of Bitcoin including less common and niche units , see Units.
The block reward calculation is done as a right bitwise shift of a bit signed integer, which means it is divided by two and rounded down. With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero. The last block that will generate coins will be block 6,, which should be generated at or near the year The total number of coins in circulation will then remain static at 20,, Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million assuming everything else stays the same.
For example, with 16 decimals of precision, the end total would be 20,, Even before the creation of coins ends, the use of transaction fees will likely make creating new blocks more valuable from the fees than the new coins being created.
When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future. Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate.
As the value of a bitcoin increases, the number of bitcoins required to purchase an item de creases. This is a deflationary economic model. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins "Millies" or microbitcoins "Mikes".
The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin "a Satoshi" , but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions. The blockchain base layer is not very scalable but layer-2 technologies can be used to greatly increase bitcoin's scale. Lightning Network is one example which uses smart contracts to build a network where payments are routed along a path instead of flooded to every peer.
These payments can be nearly as secure and irreversible as blockchain transactions but have much better scalability as well support instant payments which are much more private. Other possible layer-2 scalability technologies are sidechains or a bitcoin ecash chaumian bank. Bitcoins have value because they are useful and because they are scarce.
As they are accepted by more merchants, their value will stabilize. See the list of Bitcoin-accepting sites. When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them. It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them.
Cost doesn't equal value — hiring 1, men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable.
For example, your fingerprints are scarce, but that doesn't mean they have any exchange value. Alternatively it needs to be added that while the law of supply and demand applies it does not guarantee value of Bitcoins in the future. If confidence in Bitcoins is lost then it will not matter that the supply can no longer be increased, the demand will fall off with all holders trying to get rid of their coins. An example of this can be seen in cases of state currencies, in cases when the state in question dissolves and so no new supply of the currency is available the central authority managing the supply is gone , however the demand for the currency falls sharply because confidence in its purchasing power disappears.
Of-course Bitcoins do not have such central authority managing the supply of the coins, but it does not prevent confidence from eroding due to other situations that are not necessarily predictable. Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero.
But that is unlikely to happen: Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy. A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.
The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality. Early adopters in Bitcoin are taking a risk and invested resources in an unproven technology. By so doing, they help Bitcoin become what it is now and what it will be in the future hopefully, a ubiquitous decentralized digital currency. It is only fair they will reap the benefits of their successful investment. In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced twenty-one million to be exact , this number has been known since the project's inception, and the units are created at a predictable rate.
Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease. Therefore, Bitcoin seems to be faced with a unique problem.
Whereas most currencies inflate over time, Bitcoin will mostly likely do just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise. Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable.
Many economists claim that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, but no one has any hard data to back up their claims. That being said, there is a mechanism in place to combat the obvious consequences.
Extreme deflation would render most currencies highly impractical: Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities. In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss.
Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.
For more information, see the Deflationary spiral page. Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically, a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.
Additionally, new currency continues to be issued daily and will continue to do so for decades; though over time the rate at which they are issued declines to insignificant levels.
Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even. This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down, and thus Bitcoin remains a volatile asset.
That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off. As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one.
The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent.
Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified. A new block chain would leave the network vulnerable to double-spend attacks.
However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk. Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes.
Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.
A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless. A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors.
At present, any threatening rivals have yet to rear their heads; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position.
It would certainly be in keeping with internet history for a similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.
This may sound rather foreboding, so bear in mind that the introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies so as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.
This is known as the network effect. Is this a problem? This is only a problem if you are investing in Bitcoin for short period of time. A manipulator can't change the fundamentals, and over a period of years, the fundamentals will win over any short term manipulations.
It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.
Blocks shown as " confirmations " in the GUI are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again.
Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal.
Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction! Ten minutes was specifically chosen by Satoshi as a tradeoff between first confirmation time and the amount of work wasted due to chain splits.
After a block is mined, it takes time for other miners to find out about it, and until then they are actually competing against the new block instead of adding to it. If someone mines another new block based on the old block chain, the network can only accept one of the two, and all the work that went into the other block gets wasted. Lengthening the time between blocks reduces this waste.
As a thought experiment, what if the Bitcoin network grew to include Mars? From the farthest points in their orbits, it takes about 20 minutes for a signal to travel from Earth to Mars.
With only 10 minutes between new blocks, miners on Mars would always be 2 blocks behind the miners on Earth. It would be almost impossible for them to contribute to the block chain. If we wanted collaborate with those kinds of delays, we would need at least a few hours between new blocks. YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed confirmations.
As transactions are buried in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved. When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras.
Such a machine shouldn't honor zero-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article here for alternatives. Applications that require immediate payment processing, like supermarkets or snack machines, need to manage the risks. Here is one way to reverse an unconfirmed payment:. A Finney attack is where an attacker mines a block containing a movement of some coins back to themselves.
Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades.
Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay due to queues, etc. The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.
Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to adjust the price to include the cost of reversal fraud, or elect to use special insurance.
There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them. The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain.
Hover over the icon in the bottom right corner of the client to learn your client's status. If it has not caught up then it's possible that your transaction hasn't been included in a block yet. You can check pending transactions in the network by going here or here and then searching for your address.
If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client. If the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction.
Transfers can take longer if the transaction fee paid was not high enough. If there is no fee at all the transfer can get a very low priority and take hours or even days to be included in a block. If the transaction never gets confirmed into a block - the mempool expiry of all nodes will drop it eventually and you will be able to spend your funds again - typically it takes about 3 days or so for this to happen. If using an [ SPV ] wallet such as Electrum or Multibit , if after three days the wallet does not see the coin to spend, you need to reindex your wallet's block headers.
After reindexing, your wallet will see that the coin was never confirmed and thus the balance will be spendable again. Unlike postal and email addresses, Bitcoin addresses are designed to be used exactly once only, for a single transaction.
Originally, wallets would display only a single address at a time, and change it when a transaction was received, but an increasing number of wallet implementations now generate an address when you explicitly want to receive a payment.
While it is technically possible to use an address for an arbitrary number of payments, this works by accident and harms both yourself and other unrelated third parties , so it is considered a bad practice. The most important concerns with such misuse involve loss of privacy and security: Bitcoin transactions almost always require a transaction fee for them to get confirmed. The transaction fee is received by the first bitcoin miner who mines a block containing the transaction; this action is also what gives the transaction its first confirmation.
The appropriate fee varies depending on how large in bytes your transaction is, how fast you want the transaction to be confirmed, and also on current network conditions. As such, paying a fixed fee, or even a fixed fee per kB, is a very bad idea; all good Bitcoin wallets will use several pieces of data to estimate an appropriate fee for you, though some are better at fee estimation than others.
The fee most strongly depends on the transaction's data size.