What is the reason for bitcoin

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She may instead transfer this value by first entrusting her currency to a bank who promises to store and protect Alice's currency notes. The bank gives Alice a written promise called a "bank statement" that entitles her to withdraw the same number of currency bills that she deposited.

Since the money is still Alice's, she is entitled to do with it whatever she pleases, and the bank like most banks , for a small fee, will do Alice the service of passing on the currency bills to Bob on her behalf. This is done by Alice's bank by giving the dollar bills to Bob's bank and informing them that the money is for Bob, who will then see the amount the next time he checks his balance or receives his bank statement.

Since banks have many customers, and bank employees require money for doing the job of talking to people and signing documents, banks in recent times have been using machines such as ATMs and web servers that do the job of interacting with customers instead of paid bank employees.

The task of these machines is to learn what each customer wants to do with their money and, to the extent that it is possible, act on what the customer wants for example, ATMs can hand out cash. Customers can always know how much money they have in their accounts, and they are confident that the numbers they see in their bank statements and on their computer screens accurately reflect the number of dollars that they can get from the bank on demand.

They can be so sure of this that they can accept those numbers in the same way they accept paper banknotes this is similar to the way people started accepting paper dollars when they had been accepting gold or silver. Bitcoin is a system of owning and voluntarily transferring amounts of so-called bitcoins , in a manner similar to online banking, but pseudonymously and without reliance on a central authority to maintain account balances.

If bitcoins are valuable, it is because they are useful and limited in supply. How to buy Bitcoin? There are many ways to buy Bitcoin cryptocurrency, with debit or credit card, PayPal, online on cryptocurrency exchange, with bank transfers and etc. It's difficult to say what is the best way to buy Bitcoin. After the opening Bitcoin address-account you can start buying coins. Buying and selling coins to individuals is carried on specialized sites, such as LocalBitcoins.

User should select the country and the city in the special window, fill in the information on the number of coins and select the purchase payment method. Seller should be chosen according to the grade level on the site. Purchasing Bitcoins at the unaccredited sites or from individuals is not recommended due to the high fraud risk.

New coins are slowly mined into existence by following a mutually agreed-upon set of rules. A user mining bitcoins is running a software program that searches tirelessly for a solution to a very difficult math problem whose difficulty is precisely known. The difficulty is automatically adjusted regularly so that the number of solutions found globally, by everyone, for a given unit of time is constant: an average of 6 per hour.

When a solution is found, the user may tell everyone of the existence of this newly found solution, along with other information, packaged together in what is called a " block ". Blocks create This amount, known as the block reward, is an incentive for people to perform the computation work required for generating blocks. Originally the block reward was 50 bitcoins; it halved in November and then once more in July Any block that is created by a malicious user that does not follow this rule or any other rules will be rejected by everyone else.

In the end, no more than 21 million bitcoins will ever exist. Because the block reward will decrease over the long term, miners will some day instead pay for their hardware and electricity costs by collecting transaction fees. The sender of money may voluntarily pay a small transaction fee which will be kept by whoever finds the next block.

Paying this fee will encourage miners to include the transaction in a block more quickly. Bitcoin Mining is the process of adding transaction records to Bitcoin's public ledger of past transactions and a mining rig is a colloquial metaphor for a single computer system that performs the necessary computations for mining. This ledger of past transactions is called the block chain as it is a chain of blocks.

The block chain serves to confirm transactions to the rest of the network as having taken place. Bitcoin nodes use the block chain to distinguish legitimate Bitcoin transactions from attempts to re-spend coins that have already been spent elsewhere.

Bitcoin mining' is intentionally designed to be resource-intensive and difficult so that the number of blocks found each day by miners remains steady. Individual blocks must contain a proof of work to be considered valid. This proof of work is verified by other Bitcoin nodes each time they receive a block. Bitcoin uses the hashcash proof-of-work function. The primary purpose of mining is to allow Bitcoin nodes to reach a secure, tamper-resistant consensus.

Bitcoin Mining is also the mechanism used to introduce Bitcoins into the system: Miners are paid any transaction fees as well as a subsidy of newly created coins. This both serves the purpose of disseminating new coins in a decentralized manner as well as motivating people to provide security for the system. Bitcoin mining is so called because it resembles the mining of other commodities: it requires exertion and it slowly makes new currency available at a rate that resembles the rate at which commodities like gold are mined from the ground.

To guarantee that a third-party, let's call her Eve, cannot spend other people's bitcoins by creating transactions in their names, Bitcoin uses public key cryptography to make and verify digital signatures. In this system, each person, such as Alice or Bob, has one or more addresses each with an associated pair of public and private keys that they may hold in a wallet. Only the first two steps require human action. The rest is done by the Bitcoin client software.

Looking at this transaction from the outside, anyone who knows that these addresses belong to Alice and Bobcan see that Alice has agreed to transfer the amount to Bob, because nobody else has Alice's private key.

Alice would be foolish to give her private key to other people, as this would allow them to sign transactions in her name, removing funds from her control. Only Bob can do this because only he has the private key that can create a valid signature for the transaction. So if Charlie accepts that the original coin was in the hands of Alice, he will also accept the fact that this coin was later passed to Bob, and now Bob is passing this same coin to him. The process described above does not prevent Alice from using the same bitcoins in more than one transaction.

The following process does; this is the primary innovation behind Bitcoin. When Bob sees that his transaction has been included in a block, which has been made part of the single longest and fastest-growing blockchain extended with significant computational effort , he can be confident that the transaction by Alice has been accepted by the computers in the network and is permanently recorded, preventing Alice from creating a second transaction with the same coin.

In order for Alice to thwart this system and double-spend her coins, she would need to muster more computing power than all other Bitcoin users combined. When it comes to the Bitcoin network itself, there are no "accounts" to set up, and no e-mail addresses, user-names or passwords are required to hold or spend bitcoins. Each balance is simply associated with an address and its public-private key pair. The money "belongs" to anyone who has the private key and can sign transactions with it.

Moreover, those keys do not have to be registered anywhere in advance, as they are only used when required for a transaction. 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: even in Somalia, where the government collapsed 20 years ago, Somali shillings are still accepted as payment.

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: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again.

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: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy?

Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. 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: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

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. Don't panic! 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.

See also: Address reuse. 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: both can be put into jeopardy when addresses are used for more than a single transaction only. 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. Fees do not depend on the BTC amount of the transaction -- it's entirely possible for a 0. Basic intro to how Bitcoin transactions work: If you receive BTC in three separate transactions of say 1, 5, and 10 BTC, then you can think of your wallet as containing three gold coins with sizes 1, 5, and 10 BTC.

In Bitcoin's technical vocabulary, these objects are literally called input and output coins. In the rest of this section, when we say "coin" we mean these objects, not the amount of BTC value. Transaction data sizes, and therefore fees, are proportional to the number not value of input and output coins in a transaction. If your wallet estimates a very high fee, it is most likely because your wallet is full of a whole bunch of tiny coins, so your transaction will need to take very many coins as inputs, increasing the cost.

On the bright side, fees will go down once you make a few transactions, since you will end up "melting down" these many small coins into a few larger ones. Sometimes you can significantly reduce the fee by sending less BTC: if you have like tiny faucet payments totaling 0. Fees also fluctuate depending on network conditions. All unconfirmed transactions compete with each other to be picked up by miners. If there are a lot of high-fee transactions being sent right now, then you will need to pay higher fees to out-bid them.

On the other hand, if speed is less important to you, you can pay a somewhat smaller fee, and your transaction will float around until there is a period of reduced network usage. Sometimes even transactions with zero fee will be confirmed after a very long period of time, though this requires a perfect set of conditions, beyond what is explained here ie.

Oftentimes wallets will have an "express" fee configuration, but note that confirmation times are naturally random and unreliable. At any given point in time, the probability that no transactions will be confirmed in the next hour is about 0. Bitcoin users should avoid getting into situations where their transactions absolutely must get 1 confirmation in the next couple of hours, even if high-fee transactions usually take less than 10 minutes to get 1 confirmation.

Bitcoins are not actually "sent" to your wallet; the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received. If you are sent coins when your wallet client program is not running, and you later launch the wallet client program, the coins will eventually appear as if they were just received in the wallet.

That is to say, when the client program is started it must download blocks and catch up with any transactions it did not already know about. The popular Bitcoin client software from bitcoin. One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system.

During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed. In normal operation, after synchronizing, the software should use a hardly noticeable amount of your computer's resources. When the wallet client program is first installed, its initial validation requires a lot of work from your computer's hard disk, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed.

It can take anywhere from a few hours to a day or so. On a slow computer it could take more than 40 hours of continuous synchronization, so check your computer's power-saving settings to ensure that it does not turn its hard disk off when unattended for a few hours. You can use the Bitcoin software during synchronization, but you may not see recent payments to you until the client program has caught up to the point where those transactions happened. If you feel that this process takes too long, you can try an alternative lightweight node such as Electrum , though these clients have weaker security and privacy.

See also: Why should you use a full node wallet. Bitcoin will connect to other nodes, usually on TCP port You will need to allow outgoing TCP connections to port if you want to allow your Bitcoin client to connect to many nodes. Testnet uses TCP port instead of If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the fallback nodes list. Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use.

In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a built-in list which is updated from time to time in new versions of the software.

In the reference software initial peers can also be specified manually by adding an addr. Mining is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system [1]. Technically speaking, mining is the calculation of a hash of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a nonce.