Compatibilidade do signo de peixes e aries
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Bitcoin [ note 5 ] is an online payment system invented by Satoshi Nakamoto , [ note 6 ] who published his invention in , [ 12 ] and released it as open-source software in Bitcoins are created as a reward for payment processing work in which users offer their computing power to verify and record payments into the public ledger. This activity is called mining and is rewarded by transaction fees and newly created bitcoins.
The European Banking Authority [ 28 ] and other sources [ 14 ]: The use of bitcoin by criminals has attracted the attention of financial regulators, [ 29 ] legislative bodies, [ 30 ] law enforcement, [ 31 ] and media. As of [update] , the criminal activities centered around theft and black markets. Officials in countries such as the United States also recognized that bitcoin can provide legitimate financial services to customers. The block chain is a public ledger that records bitcoin transactions.
A novel solution accomplishes this without any trusted central authority: Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. Approximately six times per hour, a new group of accepted transactions, a block, is created, added to the block chain, and quickly published to all nodes.
This allows bitcoin software to determine when a particular bitcoin amount has been spent, which is necessary in order to prevent double-spending in an environment without central oversight. Whereas a conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, the block chain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.
The unit of account of the bitcoin system is bitcoin. Named in homage to bitcoin's creator, a satoshi is the smallest multiple of bitcoin representing 0. A microbitcoin is sometimes referred to as a bit. Ownership of bitcoins implies that a user can spend bitcoins associated with a specific address.
To do so, a payer must digitally sign the transaction using the corresponding private key. Without knowledge of the private key the transaction cannot be signed and bitcoins cannot be spent. The network verifies the signature using the public key. A transaction must have one or more inputs. For the transaction to be valid, every input must be an unspent output of a previous transaction.
Every input must be digitally signed. The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. A transaction can also have multiple outputs, allowing one to make multiple payments in one go.
A transaction output can be specified as an arbitrary multiple of satoshi. Similarly as in a cash transaction, the sum of inputs coins used to pay can exceed the intended sum of payments. In such case, an additional output is used, returning the change back to the payer. To send money to a bitcoin address, users can click links on webpages; this is accomplished with a provisional Bitcoin URI scheme using a template registered with IANA.
Mobile clients recognize Bitcoin URIs in QR codes , so that the user does not have to type the bitcoin address and amount in manually.
The QR code is generated from the user input based on the payment amount. The QR code is displayed on the mobile device screen and can be scanned by a second mobile device. Mining is a record-keeping service. A new block contains information that "chains" it to the previous block thus giving the block chain its name. It is a cryptographic hash of the previous block, using the SHA hashing algorithm. A new block must also contain a so-called proof-of-work.
The proof-of-work consists of a number called a difficulty target and a number called a nonce , which is jargon for "a number used only once". Miners have to find a nonce that yields a hash of the new block numerically smaller than the number provided in the difficulty target. When the new block is created and distributed to the network, every network node can easily verify the proof. The fact that the hash of the new block is smaller than the difficulty target serves as a proof that this tedious work has been done, hence the name "proof-of-work".
By changing the difficulty target number, the average time required to find a nonce can be shortened or extended A smaller number reduces the range of accepted nonces and increases the time required.
The bitcoin system adjusts the difficulty target number every blocks so that the average time the entire network needs to find a nonce always remains about ten minutes.
In this way the bitcoin protocol ensures that it will always take about ten minutes to add a new block regardless of the size of the network or the sophistication of the mining hardware it employs. The proof-of-work system alongside the chaining of blocks makes modifications of the block chain extremely hard as an attacker must modify all subsequent blocks in order for modifications of one block to be accepted.
As new blocks are mined all the time, the difficulty of modifying a block increases as time passes and the number of subsequent blocks increases. The environmental cost of mining includes the generation of electricity. Even if all miners used energy efficient processes, the combined electricity consumption would be 1. As of [update] , it has become common for miners to join organized mining pools , [ 44 ] which are used primarily to reduce variance.
The reward is then split among the members creating a more steady stream of income without necessarily lowering the total expected amount of rewards for each miner when averaged over time, although a fee may be charged for the service. The successful miner finding the new block is rewarded with newly created bitcoins and transaction fees. To claim the reward, a special transaction called a coinbase is included with the processed payments.
The bitcoin protocol specifies that the reward for adding a block will be halved approximately every four years. Eventually, the reward will be removed entirely when an arbitrary limit of 21 million bitcoins is reached c. Paying a transaction fee is optional, but may speed up confirmation of the transaction.
Fees are based on the storage size of the transaction generated, which in turn is dependent on the number of inputs used to create the transaction. Furthermore, priority is given to older unspent inputs. A wallet stores the information necessary to transact bitcoins.
While wallets are often described as a place to hold [ 54 ] or store bitcoins, [ 55 ] due to the nature of the system, bitcoins are inseparable from the block chain transaction ledger. Perhaps a better way to describe a wallet is something that "stores the digital credentials for your bitcoin holdings" [ 55 ] and "allows you to access and spend them". Bitcoin uses public-key cryptography , in which two cryptographic keys, one public and one private, are generated.
There are several types of wallet. Software wallets connect to the network and allow spending bitcoins in addition to holding the credentials that prove ownership. Others are simply paper printouts. Another type of wallet called a hardware wallet keeps credentials offline while facilitating transactions. The first wallet program, called Bitcoin-Qt, was released in by Satoshi Nakamoto as open-source code. Bitcoin-Qt, also called Satoshi client, is sometimes referred to as the reference client because it serves to define the bitcoin protocol and acts as a standard for other implementations.
Privacy is achieved by not identifying owners of bitcoin addresses while making other transaction data public. Bitcoin users are not identified by name, but transactions can be linked to individuals and companies.
Users concerned about privacy can use so-called mixing services that swap coins they own for coins with different transaction histories. Wallets and similar software technically handle bitcoins as equivalent, establishing the basic level of fungibility. Researchers have pointed out that the history of every single bitcoin is registered and publicly available in the block chain ledger, and that some users may refuse to accept bitcoins coming from controversial transactions, which would harm bitcoin's fungibility.
Bitcoin was invented by Satoshi Nakamoto, [ note 6 ] who published his invention on 31 October in a research paper called "Bitcoin: A Peer-to-Peer Electronic Cash system". Bitcoin is often called the first cryptocurrency [ 19 ] although prior proposals existed.
One of the first supporters, adopters, contributor to bitcoin and receiver of the first bitcoin transaction was programmer Hal Finney. Finney downloaded the bitcoin software the day it was released, and received 10 bitcoins from Nakamoto in the world's first bitcoin transaction.
Other early supporters were Wei Dai, creator of bitcoin predecessor b-money , and Nick Szabo, creator of bitcoin predecessor bit gold. In , an exploit in an early bitcoin client was found that allowed large numbers of bitcoins to be created. Based on bitcoin's open source code, other cryptocurrencies started to emerge in In March , a technical glitch caused a fork in the block chain, with one half of the network adding blocks to one version of the chain and the other half adding to another.
For six hours two bitcoin networks operated at the same time, each with its own version of the transaction history. The core developers called for a temporary halt to transactions, sparking a sharp sell-off.
Normal operation was restored when the majority of the network downgraded to version 0. In some mainstream websites began accepting bitcoins. In October , Chinese internet giant Baidu had allowed clients of website security services to pay with bitcoins. Gox and the Europe-based Bitstamp to become the largest bitcoin trading exchange by trade volume. As of [update] mining had become quite competitive and was compared to an arms race as ever-more-specialized technology was being utilized.
The most efficient mining hardware makes use of custom designed application-specific integrated circuits , which outperform general purpose CPUs and also use less power. In the US two men were arrested in January on charges of money-laundering using bitcoins; one was Charlie Shrem , the head of now defunct bitcoin exchange BitInstant and a vice chairman of the Bitcoin Foundation.
Shrem allegedly allowed the other arrested party to purchase large quantities of bitcoins for use on black-market websites. In early February , one of the largest bitcoin exchanges, Mt. Gox , [ ] suspended withdrawals citing technical issues. Gox had filed for bankruptcy protection in Japan amid reports that , bitcoins had been stolen.
The Gathering cards, [ ] Mt. Gox had once been the dominant bitcoin exchange but its popularity had waned as users experienced difficulties withdrawing funds. On June 18, , it was announced that bitcoin payment service provider BitPay would become the new sponsor of St.
Petersburg Bowl under a two-year deal, renamed the Bitcoin St. Bitcoin was to be accepted for ticket and concession sales at the game as part of the sponsorship, and the sponsorship itself was also paid for using bitcoin.
Less than one year after the collapse of Mt.