tokenpocket安卓版免费下载|btc network

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Bitcoin price today, BTC to USD live price, marketcap and chart | CoinMarketCap

oin price today, BTC to USD live price, marketcap and chart | CoinMarketCapCryptos: 2.2M+Exchanges: 723Market Cap: $2.62T0.70%24h Vol: $104.88B10.95%Dominance: BTC: 52.1% ETH: 17.9% ETH Gas: 71 Gwei Fear & Greed: 89/100CryptocurrenciesCryptocurrenciesRankingCategoriesGlobal ChartsHistorical SnapshotsBitcoin ETFsLeaderboardsTrendingRecently AddedGainers & LosersMost VisitedNFTOverall NFT StatsTop CollectionsUpcoming SalesOn Chain DataDex PairsChain RankingHot DEX PairsExchangesSpotDerivativesDEXCommunityFeedsTopicsLivesArticlesProductsPRODUCTSConverterCMC LabsTelegram BotAdvertiseCrypto APISite WidgetsCAMPAIGNSAirdropsDiamond RewardsLearn & EarnCALENDARSICO CalendarEvents CalendarLearnNewsAcademyResearchVideosGlossaryHalving: 37DWatchlistPortfolioSearch/Bitcoin price BTC$69,547.08 1.79% (1d)Bitcoin to USD ChartLoading DataPlease wait a moment. Add to watchlist Bitcoin statisticsMarket cap 1.71%$1,365,549,566,707#1Volume (24h) 18.44%$32,392,765,635#2Volume/Market cap (24h) 2.37%Circulating supply 19,650,431 BTC93.57%Total supply 19,650,431 BTCMax. supply 21,000,000 BTCFully diluted market cap $1,459,333,940,352Official linksWebsiteWhitepaperGitHubSocialsRedditRating · Based on 2 institutional ratings4.9 Network informationChain explorersSupported walletsUCID1 BTC to USD ConverterBTCUSDPrice performance24h Low$68,164.70High$70,005.20All-time highMar 08, 2024 (2 days ago)$70,083.05-0.84%All-time lowJul 14, 2010 (14 years ago)$0.04865+142850948.39%See historical dataPopularityIn watchlists4,642,791x27th / 9.0KTagsMineablePoWSHA-256Show allMore informationDo you own this project? Update Token Info Loading DataPlease wait a moment. Bitcoin community Bitcoin marketsALLCEXDEXSpotPerpetualFuturesAll pairsLoading data...Show full widthDisclaimer: This page may contain affiliate links. CoinMarketCap may be compensated if you visit any affiliate links and you take certain actions such as signing up and transacting with these affiliate platforms. Please refer to Affiliate DisclosureBitcoin news About BitcoinWhat Is Bitcoin (BTC)?Bitcoin is a decentralized cryptocurrency originally described in a 2008 whitepaper by a person, or group of people, using the alias Satoshi Nakamoto. It was launched soon after, in January 2009.Bitcoin is a peer-to-peer online currency, meaning that all transactions happen directly between equal, independent network participants, without the need for any intermediary to permit or facilitate them. Bitcoin was created, according to Nakamoto’s own words, to allow “online payments to be sent directly from one party to another without going through a financial institution.”Some concepts for a similar type of a decentralized electronic currency precede BTC, but Bitcoin holds the distinction of being the first-ever cryptocurrency to come into actual use.Who Are the Founders of Bitcoin?Bitcoin’s original inventor is known under a pseudonym, Satoshi Nakamoto. As of 2021, the true identity of the person — or organization — that is behind the alias remains unknown.On October 31, 2008, Nakamoto published Bitcoin’s whitepaper, which described in detail how a peer-to-peer, online currency could be implemented. They proposed to use a decentralized ledger of transactions packaged in batches (called “blocks”) and secured by cryptographic algorithms — the whole system would later be dubbed “blockchain.”Just two months later, on January 3, 2009, Nakamoto mined the first block on the Bitcoin network, known as the genesis block, thus launching the world’s first cryptocurrency. Bitcoin price was $0 when first introduced, and most Bitcoins were obtained via mining, which only required moderately powerful devices (e.g. PCs) and mining software. The first known Bitcoin commercial transaction occurred on May 22, 2010, when programmer Laszlo Hanyecz traded 10,000 Bitcoins for two pizzas. At Bitcoin price today in mid-September 2021, those pizzas would be worth an astonishing $478 million. This event is now known as “Bitcoin Pizza Day.” In July 2010, Bitcoin first started trading, with the Bitcoin price ranging from $0.0008 to $0.08 at that time.However, while Nakamoto was the original inventor of Bitcoin, as well as the author of its very first implementation, he handed the network alert key and control of the code repository to Gavin Andresen, who later became lead developer at the Bitcoin Foundation. Over the years a large number of people have contributed to improving the cryptocurrency’s software by patching vulnerabilities and adding new features.Bitcoin’s source code repository on GitHub lists more than 750 contributors, with some of the key ones being Wladimir J. van der Laan, Marco Falke, Pieter Wuille, Gavin Andresen, Jonas Schnelli and others.What Makes Bitcoin Unique?Bitcoin’s most unique advantage comes from the fact that it was the very first cryptocurrency to appear on the market.It has managed to create a global community and give birth to an entirely new industry of millions of enthusiasts who create, invest in, trade and use Bitcoin and other cryptocurrencies in their everyday lives. The emergence of the first cryptocurrency has created a conceptual and technological basis that subsequently inspired the development of thousands of competing projects.The entire cryptocurrency market — now worth more than $2 trillion — is based on the idea realized by Bitcoin: money that can be sent and received by anyone, anywhere in the world without reliance on trusted intermediaries, such as banks and financial services companies.Thanks to its pioneering nature, BTC remains at the top of this energetic market after over a decade of existence. Even after Bitcoin has lost its undisputed dominance, it remains the largest cryptocurrency, with a market capitalization that surpassed the $1 trillion mark in 2021, after Bitcoin price hit an all-time high of $64,863.10 on April 14, 2021. This is owing in large part to growing institutional interest in Bitcoin, and the ubiquitousness of platforms that provide use-cases for BTC: wallets, exchanges, payment services, online games and more.How Much Bitcoin Is in Circulation?Bitcoin’s total supply is limited by its software and will never exceed 21,000,000 coins. New coins are created during the process known as “mining”: as transactions are relayed across the network, they get picked up by miners and packaged into blocks, which are in turn protected by complex cryptographic calculations.As compensation for spending their computational resources, the miners receive rewards for every block that they successfully add to the blockchain. At the moment of Bitcoin’s launch, the reward was 50 bitcoins per block: this number gets halved with every 210,000 new blocks mined — which takes the network roughly four years. As of 2020, the block reward has been halved three times and comprises 6.25 bitcoins.Bitcoin has not been premined, meaning that no coins have been mined and/or distributed between the founders before it became available to the public. However, during the first few years of BTC’s existence, the competition between miners was relatively low, allowing the earliest network participants to accumulate significant amounts of coins via regular mining: Satoshi Nakamoto alone is believed to own over a million Bitcoin.Mining Bitcoins can be very profitable for miners, depending on the current hash rate and the price of Bitcoin. While the process of mining Bitcoins is complex, we discuss how long it takes to mine one Bitcoin on CoinMarketCap Alexandria — as we wrote above, mining Bitcoin is best understood as how long it takes to mine one block, as opposed to one Bitcoin. As of mid-September 2021, the Bitcoin mining reward is capped to 6.25 BTC after the 2020 halving, which is roughly $299,200 in Bitcoin price today.How Is the Bitcoin Network Secured?Bitcoin is secured with the SHA-256 algorithm, which belongs to the SHA-2 family of hashing algorithms, which is also used by its fork Bitcoin Cash (BCH), as well as several other cryptocurrencies.What Is Bitcoin’s Role as a Store of Value?Bitcoin is the first decentralized, peer-to-peer digital currency. One of its most important functions is that it is used as a decentralized store of value. In other words, it provides for ownership rights as a physical asset or as a unit of account. However, the latter store-of-value function has been debated. Many crypto enthusiasts and economists believe that high-scale adoption of the top currency will lead us to a new modern financial world where transaction amounts will be denominated in smaller units.The smallest units of Bitcoin, 0.00000001 BTC, are called Satoshis (or Sats in short), in a nod to the pseudonymous creator. At Bitcoin price now, 1 Satoshi is equivalent to roughly $0.00048.The top crypto is considered a store of value, like gold, for many — rather than a currency. This idea of the first cryptocurrency as a store of value, instead of a payment method, means that many people buy the crypto and hold onto it long-term (or HODL) rather than spending it on items like you would typically spend a dollar — treating it as digital gold.How Is Bitcoin’s Technology Upgraded?A hard fork is a radical change to the protocol that makes previously invalid blocks/transactions valid, and therefore requires all users to upgrade. For example, if users A and B are disagreeing on whether an incoming transaction is valid, a hard fork could make the transaction valid to users A and B, but not to user C.A hard fork is a protocol upgrade that is not backward compatible. This means every node (computer connected to the Bitcoin network using a client that performs the task of validating and relaying transactions) needs to upgrade before the new blockchain with the hard fork activates and rejects any blocks or transactions from the old blockchain. The old blockchain will continue to exist and will continue to accept transactions, although it may be incompatible with other newer Bitcoin clients.A soft fork is a change to the Bitcoin protocol wherein only previously valid blocks/transactions are made invalid. Since old nodes will recognise the new blocks as valid, a soft fork is backward-compatible. This kind of fork requires only a majority of the miners upgrading to enforce the new rules.Some examples of prominent cryptocurrencies that have undergone hard forks are the following: Bitcoin’s hard fork that resulted in Bitcoin Cash, Ethereum’s hard fork that resulted in Ethereum Classic.Bitcoin Cash has been hard forked since its original forking, with the creation of Bitcoin SV. Read more about the difference between Bitcoin, Bitcoin Cash and Bitcoin SV here.What Is Taproot?Taproot is a soft fork that bundles together BIP 340, 341 and 342 and aims to improve the scalability, efficiency, and privacy of the blockchain by introducing several new features.The two major changes are the introduction of the Merkelized Abstract Syntax Tree (MAST) and Schnorr Signature. MAST introduces a condition allowing the sender and recipient of a transaction to sign off on its settlement together. Schnorr Signature allows users to aggregate several signatures into one for a single transaction. This results in multi-signature transactions looking the same as regular transactions or more complex ones. By introducing this new address type, users can also save on transaction fees, as even complex transactions look like simple, single-signature ones.Although HODLers will probably not notice a big impact, Taproot could become a key milestone to equipping the network with smart contract functionality. In particular, Schnorr Signatures would lay the foundation for more complex applications to be built on top of the existing blockchain, as users start switching to Taproot addresses primarily. If adopted by users, Taproot could, in the long run, result in the network developing its own DeFi ecosystem that rivals those on alternative blockchains like Ethereum.What Is the Lightning Network?The Lightning Network is an off-chain, layered payment protocol that operates bidirectional payment channels which allows instantaneous transfer with instant reconciliation. It enables private, high volume and trustless transactions between any two parties. The Lightning Network scales transaction capacity without incurring the costs associated with transactions and interventions on the underlying blockchain.Who Are the Largest Corporate Holders of Bitcoin?A few years ago, the idea that a publicly traded company might hold Bitcoin on its balance sheets seemed highly laughable. The flagship cryptocurrency was considered to be too volatile to be adopted by any serious business. Many top investors, including Warren Buffett, labeled the asset a “bubble waiting to pop.”This negative sentiment appears to have been broken, with a number of corporate behemoths buying up Bitcoin since 2020. In particular, business intelligence firm MicroStrategy set the pace after it bought $425 million worth of Bitcoin in August and September 2020. Since then, many others have followed suit, including EV manufacturer Tesla.MicroStrategy has by far the largest Bitcoin portfolio held by any publicly-traded company. The business analytics platform has adopted Bitcoin as its primary reserve asset, aggressively buying the cryptocurrency through 2021 and 2022. As of August 30, 2022, the company had 129,699 Bitcoin in its reserve, equivalent to just over $2.5 billion.Other top corporate holders include Marathon Digital Holdings, with 10,054 BTC, Coinbase (9,000), Square Inc. (8,027), and Hut 8 Mining Corp. (7,078).Is Bitcoin Political?Bitcoin is becoming more political by the day, particularly after El Salvador began accepting the currency as legal tender. The country's president, Nayib Bukele, announced and implemented the decision almost unilaterally, dismissing criticism from his citizens, the Bank of England, the IMF, Vitalik Buterin and many others. Since the Bitcoin legal tender law was passed in September 2021, Bukele has also announced plans to build Bitcoin City, a city fully based on mining Bitcoin with geothermal energy from volcanoes.Countries like Mexico, Russia and others have been rumored to be candidates also to accept Bitcoin as legal tender, but thus far, El Salvador stands alone.On the flip side, countries like China have moved to heavily clamp down on Bitcoin mining and trading activities. In May 2021, the Chinese government declared that all crypto-related transactions are illegal. This was followed by a heavy crackdown on Bitcoin mining operations, forcing many crypto-related businesses to flee to friendlier regions.Surprisingly, the anti-crypto stance of the Chinese government has done little to stop the industry. According to data by the University of Cambridge, China is now the second-biggest contributor to Bitcoin's global hash rate, only behind the United States.How Much Is Bitcoin?The current valuation of Bitcoin is constantly moving, all day every day. It is a truly global asset. From a start of under one cent per coin, BTC has risen in price by thousands of percent to the numbers you see above. The prices of all cryptocurrencies are quite volatile, meaning that anyone’s understanding of how much Bitcoin is will change by the minute. However, there are times when different countries and exchanges show different prices and understanding how much Bitcoin is will be a function of a person’s location.Where Can You Buy Bitcoin (BTC)?Bitcoin is, in many regards, almost synonymous with cryptocurrency, which means that you can buy Bitcoin on virtually every crypto exchange — both for fiat money and other cryptocurrencies. Some of the main markets where BTC trading is available are:BinanceCoinbase ProOKExKrakenHuobi GlobalBitfinexIf you are new to crypto, use CoinMarketCap’s own educational portal — Alexandria — to learn how to start buying Bitcoin and other cryptocurrencies.Related Pages:Looking for market and blockchain data for BTC? Visit our block explorer.Want to buy Bitcoin? Use CoinMarketCap’s guide.Want to keep track of Bitcoin prices live? Download the CoinMarketCap mobile app!Want to convert Bitcoin price today to your desired fiat currency? Check out CoinMarketCap exchange rate calculator.Should you buy Bitcoin with PayPal?What is wrapped Bitcoin?Will Bitcoin volatility ever reduce?How to use a Bitcoin ATMBitcoin Energy ConsumptionOver the past few decades, consumers have become more curious about their energy consumption and personal effects on climate change. When news stories started swirling regarding the possible negative effects of Bitcoin’s energy consumption, many became concerned about Bitcoin and criticized this energy usage. A report found that each Bitcoin transaction takes 1,173 KW hours of electricity, which can “power the typical American home for six weeks.” Another report calculates that the energy required by Bitcoin annually is more than the annual hourly energy usage of Finland, a country with a population of 5.5 million.The news has produced commentary from tech entrepreneurs to environmental activists to political leaders alike. In May 2021, Tesla CEO Elon Musk even stated that Tesla would no longer accept the cryptocurrency as payment, due to his concern regarding its environmental footprint. Though many of these individuals have condemned this issue and move on, some have prompted solutions: how do we make Bitcoin more energy efficient? Others have simply taken the defensive position, stating that the Bitcoin energy problem may be exaggerated.At present, miners are heavily reliant on renewable energy sources, with estimates suggesting that Bitcoin’s use of renewable energy may span anywhere from 40-75%. However, to this point, critics claim that increasing Bitcoin’s renewable energy usage will take away from solar sources powering other sectors and industries like hospitals, factories or homes. The Bitcoin mining community also attests that the expansion of mining can help lead to the construction of new solar and wind farms in the future.Furthermore, some who defend Bitcoin argue that the gold and banking sector — individually — consume twice the amount of energy as Bitcoin, making the criticism of Bitcoin’s energy consumption a nonstarter. Moreover, the energy consumption of Bitcoin can easily be tracked and traced, which the same cannot be said of the other two sectors. Those who defend Bitcoin also note that the complex validation process creates a more secure transaction system, which justifies the energy usage.Another point that Bitcoin proponents make is that the energy usage required by Bitcoin is all-inclusive such that it encompasess the process of creating, securing, using and transporting Bitcoin. Whereas with other financial sectors, this is not the case. For example, when calculating the carbon footprint of a payment processing system like Visa, they fail to calculate the energy required to print money or power ATMs, or smartphones, bank branches, security vehicles, among other components in the payment processing and banking supply chain.What exactly are governments and nonprofits doing to reduce Bitcoin energy consumption? Earlier this year in the U.S., a congressional hearing was held on the topic where politicians and tech figures discussed the future of crypto mining in the U.S, specifically highlighting their concerns regarding fossil fuel consumption. Leaders also discussed the current debate surrounding the coal-to-crypto trend, particularly regarding the number of coal plants in New York and Pennsylvania that are in the process of being repurposed into mining farms.Aside from congressional hearings, there are private sector crypto initiatives dedicated to solving environmental issues such as the Crypto Climate Accord and Bitcoin Mining Council. In fact, the Crypto Climate Accord proposes a plan to eliminate all greenhouse gas emissions by 2040, And, due to the innovative potential of Bitcoin, it is reasonable to believe that such grand plans may be achieved.Crypto WalletsThe most popular wallets for cryptocurrency include both hot and cold wallets. Cryptocurrency wallets vary from hot wallets and cold wallets. Hot wallets are able to be connected to the web, while cold wallets are used for keeping large amounts of coins outside of the internet.Some of the top crypto cold wallets are Trezor, Ledger and CoolBitX. Some of the top crypto hot wallets include Exodus, Electrum and Mycelium.Still not sure of which wallet to use? Check out CoinMarketCap Alexandria’s guide on the top cold wallets of 2021 and top hot wallets of 2021. Bitcoin analyticsLoading...Most Visited CryptocurrenciesCatgirlCATGIRL$0.00000000107539.04%TABOO TOKENTABOO$0.00289818.84%EggdogEGG$0.0093949.42%RichQUACK.comQUACK$0.0000000012722.43%OpSecOPSEC$2.1217.75%MAGATRUMP$7.9812.81%Osaka ProtocolOSAK$0.000000363115.12%Baby ElonBABYELON$0.0000000000172417.50%L7LSD$7.405.75%Niza GlobalNIZA$0.0103614.11%Pepe 2.0PEPE2.0$0.000000071764.52%MinuMINU$0.0000007380.58%Script NetworkSCPT$0.0466528.68%beobleBBL$0.22919.61%BitcoinBTC$69,455.731.63%Bonk 2.0BONK2.0$0.0000000606244.36%ArtyfactARTY$1.742.31%Shiba InuSHIB$0.000033353.40%ATOR ProtocolATOR$2.7524.92%EthereumETH$3,900.650.28%Global PricesBTC/USDUnited States Dollar$69,547.08BTC/EUREuro€63,551.01BTC/GBPPound Sterling£54,088.57BTC/CNYChinese Yuan¥499,744.44BTC/CADCanadian Dollar$94,079.81BTC/AUDAustralian Dollar$104,678.78BTC/JPYJapanese Yen¥10,227,940.13BTC/KRWSouth Korean Won₩91,590,024.13BTC/RUBRussian Ruble₽6,325,307.42BTC/INRIndian Rupee₹5,755,183.85BTC/BRLBrazilian RealR$346,373.66BTC/TRYTurkish Lira₺2,215,074.36BTC/PHPPhilippine Peso₱3,861,497.59People also watchEthereum$3,904.580.17%yearn.finance$10,036.12.36%Band Protocol$2.631.18%Gather$0.0032760.53%1irstcoin$0.000.00%GoldMint$0.063481.06%Uniswap$14.071.69%Firo$2.082.98%Chainlink$19.672.93%Oasis Network$0.17571.19%TrendingPepe$0.0000083955.06%Childrens Aid Foundation$0.400320.36%FLOKI$0.000223510.93%Digiverse$1.1236.25%Shiba Inu$0.000033343.36%Bitcoin Price Live DataThe live Bitcoin price today is $69,492.09 USD with a 24-hour trading volume of $32,392,765,635 USD. We update our BTC to USD price in real-time. Bitcoin is up 1.70% in the last 24 hours. The current CoinMarketCap ranking is #1, with a live market cap of $1,365,549,566,707 USD. It has a circulating supply of 19,650,431 BTC coins and a max. supply of 21,000,000 BTC coins.If you would like to know where to buy Bitcoin at the current rate, the top cryptocurrency exchanges for trading in Bitcoin stock are currently Binance, BlueBit, OKX, LBank, and Bybit. You can find others listed on our crypto exchanges page.CryptocurrenciesCoinsBitcoinProductsCMC LabsChatGPT PluginCrypto APICrypto IndicesDoodlesSitemapAdvertiseCompanyAbout usTerms of usePrivacy PolicyCookie preferencesCookie policyCommunity RulesDisclaimerMethodologyCareersWe’re hiring!SupportRequest FormContact SupportFAQGlossarySocialsX (Twitter)CommunityTelegramInstagramFacebookRedditLinkedIn© 2024 CoinMarketCap. All rights reserved

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SANG Infrastructure

To support the DWDM Network stability which is the backbone infrastructure for all Saudi Arabian National Guard (SANG) networks Kingdome wide carrying the service demands for all networks.

The Saudi Arabian National Guard (SANG) was looking forward for a solution which will ensure network stability and to overcome the disrupts in Nationwide Fiber in a timely manner without affecting the running services Kingdome wide.

Madinah Development Authority

A Saudi Arabian governmental organization focused on developing the city of Madinah, the second holiest city in the Muslim world, to meet the expectations of its permanent residents and visitors. BTC was entrusted to build Data Center Structured Cabling System, Campus Network LAN solution, Hyperconverged Infrastructure, and Data Center SDN Solution.

Ministry of Justice

The main objective of the project is to facilitate the judicial procedure for all parties by documenting trials sessions and conversation between all parties, ensuring that Trials are executed with the best practices, and in case of any complaint the system should support the Investigation Board efficiently to clear all issues related to the judiciary process

ATC 270° Simulators

In 2019 , BTC complete one of the important projects in Aviation Training sector for GACA-SACA (General Authority of civil aviation- Saudi Academy of civil aviation) through one top worldwide simulator manufacturers ADACEL Inc. which will lead Jeddah – KSA to be one of the important destinations for global Air Tower Controllers to get the latest training on 4 Simulator 270°angle view.

NEOM

NEOM is a centerpiece of Saudi Arabia’s 2030 Vision plan to grow and diversify the Saudi economy and position the country to play a leading role in global development. NEOM is being built on the Red Sea in northwest Saudi Arabia, and it will be a destination for people who want to be part of building a new model for sustainable living and prospering. BTC is working implementing Command & Control Center, Network infrastructure and Two-way radio systems.

Digital Mobile Radio

BTC had the honor serving SAUDIA by one of the latest technologies in Digital Mobile Radio, used in all SAUDIA terminals over kingdom Airports

Unified platform for world-class customer experience

A financial institute that is one of the largest banks in the Middle East with more than 70 branches in the Kingdom and 40 branches outside. Has been leading the industry in innovation, playing a major role in the modern transformation of banking in Saudi Arabia. This financial institute wanted to modernize its Contact Center to provide best customer experience using a unified solution.

Debt Recovery with Automated Dialing

This Financial Institute is one of the leading banks in the Kingdom of Saudi Arabia with more than 80 branches and 3000 plus employees, whose objective is to become the most modern, innovative and experience focused bank in the region. Being one of the leading lenders, the bank was facing challenge to reach out to the delinquent customers and recover debt on time. The bank was not able to efficiently utilize their resources with the legacy process.

Exceptional Customer Experience

A company is the largest health insurance provider in the Kingdom of Saudi Arabia. It differentiates themselves by rendering quality services that grant their customers access to the best healthcare facilities and that facilitate a more comfortable experience.

Tamkeen

Tamkeen Technologies is a government owned IT Service Provider. Tamkeen Technologies was using a traditional Data Center that provides IT Products & Services including Cloud Services. To be aligned with the National Transformation program and to meet customer requirements, Tamkeen Technologies decided to build two State of Art Data Centers using the latest technologies.

Integrated Security System

BTC has been awarded one of the prestigious projects to provide Integrated Security System & secure the substations across Kingdom of Saudi Arabia.

SANG Infrastructure

To support the DWDM Network stability which is the backbone infrastructure for all Saudi Arabian National Guard (SANG) networks Kingdome wide carrying the service demands for all networks.

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This does not include coins returned as change.Market SignalsMarket Value to Realised ValueMVRV is calculated by dividing Market Value by Realised Value. In Realised Value, BTC prices are taken at the time they last moved, instead of the current price like in Market ValueNetwork Value to TransactionsNVT is computed by dividing the Network Value (= Market Value) by the total transactions volume in USD over the past 24hour.Network Value to Transactions SignalNVTS is a more stable measure of NVT, with the denominator being the moving average over the last 90 days of NVT's denominatorExplore top crypto assets

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Bitcoin protocol - Wikipedia

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1Blockchain

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1.1Transactions

2Mining

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2.1Difficulty and mining pools

2.2Environmental effects

2.3Mined bitcoins

3Payment verification

4Protocol features

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4.1Decentralization

4.2Security

4.2.1Unauthorized spending

4.2.2Double spending

4.2.3Race attack

4.2.4History modification

4.3Scalability

4.4Privacy

4.4.1Deanonymisation of clients

5Consensus mechanism and upgrades

6Impact and influence

7See also

8References

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From Wikipedia, the free encyclopedia

Rules that govern the functioning of Bitcoin

For broader coverage of this topic, see Bitcoin.

A diagram of a bitcoin transfer

The Bitcoin protocol is the set of rules that govern the functioning of Bitcoin. Its key components and principles are: a peer-to-peer decentralized network with no central oversight; the blockchain technology, a public ledger that records all Bitcoin transactions; mining and proof of work, the process to create new bitcoins and verify transactions; and cryptographic security.

Users broadcast cryptographically signed messages to the network using Bitcoin cryptocurrency wallet software. These messages are proposed transactions, changes to be made in the ledger. Each node has a copy of the ledger's entire transaction history. If a transaction violates the rules of the Bitcoin protocol, it is ignored, as transactions only occur when the entire network reaches a consensus that they should take place. This "full network consensus" is achieved when each node on the network verifies the results of a proof-of-work operation called mining. Mining packages groups of transactions into blocks, and produces a hash code that follows the rules of the Bitcoin protocol. Creating this hash requires expensive energy, but a network node can verify the hash is valid using very little energy. If a miner proposes a block to the network, and its hash is valid, the block and its ledger changes are added to the blockchain, and the network moves on to yet unprocessed transactions. In case there is a dispute, then the longest chain is considered to be correct. A new block is created every 10 minutes, on average.

Changes to the Bitcoin protocol require consensus among the network participants. The Bitcoin protocol has inspired the creation of numerous other digital currencies and blockchain-based technologies, making it a foundational technology in the field of cryptocurrencies.

Blockchain[edit]

This section is empty. You can help by adding to it. (November 2023)

Blockchain technology is a decentralized and secure digital ledger that records transactions across a network of computers. It ensures transparency, immutability, and tamper resistance, making data manipulation difficult. Blockchain is the underlying technology for cryptocurrencies like Bitcoin and has applications beyond finance, such as supply chain management and smart contracts.[1]

Transactions[edit]

The best chain consists of the longest series of transaction records from the genesis block to the current block or record. Orphaned records exist outside of the best chain.

The network requires minimal structure to share transactions. An ad hoc decentralized network of volunteers is sufficient. Messages are broadcast on a best-effort basis, and nodes can leave and rejoin the network at will. Upon reconnection, a node downloads and verifies new blocks from other nodes to complete its local copy of the blockchain.[2][3]

Mining[edit]

GPU-based mining rig, 2012

A Bitcoin mining farm, 2018

To form a distributed timestamp server as a peer-to-peer network, bitcoin uses a proof-of-work system.[3] This work is often called bitcoin mining.

During mining, practically the entire computing power of the Bitcoin network is used to solve cryptographic tasks, the proof of work. Their purpose is to ensure that the generation of valid blocks involves a certain amount of effort, so that subsequent modification of the block chain, such as in the 51% attack scenario, can be practically ruled out. Because of the difficulty, miners form "mining pools" to get payouts despite these high power requirements, costly hardware deployments, and/or hardware under their own control. As a result of the Chinese ban on Bitcoin mining in 2021, the United States currently holds the largest share of Bitcoin mining pools.[4][5]

Requiring a proof of work to accept a new block to the blockchain was Satoshi Nakamoto's key innovation. The mining process involves identifying a block that, when hashed twice with SHA-256, yields a number smaller than the given difficulty target. While the average work required increases in inverse proportion to the difficulty target, a hash can always be verified by executing a single round of double SHA-256.

For the bitcoin timestamp network, a valid proof of work is found by incrementing a nonce until a value is found that gives the block's hash the required number of leading zero bits. Once the hashing has produced a valid result, the block cannot be changed without redoing the work. As later blocks are chained after it, the work to change the block would include redoing the work for each subsequent block. If there is a deviation in consensus then a blockchain fork can occur.

Majority consensus in bitcoin is represented by the longest chain, which required the greatest amount of effort to produce. If a majority of computing power is controlled by honest nodes, the honest chain will grow fastest and outpace any competing chains. To modify a past block, an attacker would have to redo the proof-of-work of that block and all blocks after it and then surpass the work of the honest nodes. The probability of a slower attacker catching up diminishes exponentially as subsequent blocks are added.[3]

Mining difficulty has increased significantly.

To compensate for increasing hardware speed and varying interest in running nodes over time, the difficulty of finding a valid hash is adjusted roughly every two weeks. If blocks are generated too quickly, the difficulty increases and more hashes are required to make a block and to generate new bitcoins.[3]

Difficulty and mining pools[edit]

Further information: Mining pool

Early bitcoin miners used GPUs for mining, as they were better suited to the proof-of-work algorithm than CPUs.[6]Later amateurs mined bitcoins with specialized FPGA and ASIC chips. The chips pictured have become obsolete due to increasing difficulty.Today, bitcoin mining companies dedicate facilities to housing and operating large amounts of high-performance mining hardware.[7]

The largest Bitcoin mining pools as of April 2020 by nation in which the pools are based

Bitcoin mining is a competitive endeavor. An "arms race" has been observed through the various hashing technologies that have been used to mine bitcoins: basic central processing units (CPUs), high-end graphics processing units (GPUs), field-programmable gate arrays (FPGAs) and application-specific integrated circuits (ASICs) all have been used, each reducing the profitability of the less-specialized technology. Bitcoin-specific ASICs are now the primary method of mining bitcoin and have surpassed GPU speed by as much as 300-fold. The difficulty of the mining process is periodically adjusted to the mining power active on the network. As bitcoins have become more difficult to mine, computer hardware manufacturing companies have seen an increase in sales of high-end ASIC products.[8]

Computing power is often bundled together or "pooled" to reduce variance in miner income. Individual mining rigs often have to wait for long periods to confirm a block of transactions and receive payment. In a pool, all participating miners get paid every time a participating server solves a block. This payment depends on the amount of work an individual miner contributed to help find that block, and the payment system used by the pool.[9]

Environmental effects[edit]

This section is an excerpt from Environmental effects of bitcoin.[edit]

Bitcoin mining facility in Quebec, Canada

The environmental effects of bitcoin are significant. Bitcoin mining, the process by which bitcoins are created and transactions are finalized, is energy-consuming and results in carbon emissions as about half of the electricity used is generated through fossil fuels.[10] Moreover, bitcoins are mined on specialized computer hardware with a short lifespan, resulting in electronic waste.[11] The amount of e-waste generated by bitcoin mining is comparable to the one of the Netherlands.[11] Scholars argue that Bitcoin mining could support renewable energy development by utilizing surplus electricity from wind and solar.[12] Bitcoin's environmental impact has attracted the attention of regulators, leading to incentives or restrictions in various jurisdictions.[13]

Avalon ASIC-based mining machine

Mined bitcoins[edit]

Diagram showing how bitcoin transactions are verified

By convention, the first transaction in a block is a special transaction that produces new bitcoins owned by the creator of the block. This is the incentive for nodes to support the network.[2] It provides the way to move new bitcoins into circulation. The reward for mining halves every 210,000 blocks. It started at 50 bitcoin, dropped to 25 in late 2012 and to 12.5 bitcoin in 2016. The most recent halving, which occurred in May 2020 (with block number 630,000), reduced the block reward to 6.25 bitcoin. This halving process is programmed to continue a maximum 64 times before new coin creation ceases.[14]

Payment verification[edit]

Main article: Online transaction processing

Each miner can choose which transactions are included in or exempted from a block.[15] A greater number of transactions in a block does not equate to greater computational power required to solve that block.[15]

As noted in Nakamoto's whitepaper, it is possible to verify bitcoin payments without running a full network node (simplified payment verification, SPV). A user only needs a copy of the block headers of the longest chain, which are available by querying network nodes until it is apparent that the longest chain has been obtained; then, get the Merkle tree branch linking the transaction to its block. Linking the transaction to a place in the chain demonstrates that a network node has accepted it, and blocks added after it further establish the confirmation.[2]

Protocol features[edit]

Decentralization[edit]

This section is empty. You can help by adding to it. (November 2023)

Security[edit]

Various potential attacks on the bitcoin network and its use as a payment system, real or theoretical, have been considered. The bitcoin protocol includes several features that protect it against some of those attacks, such as unauthorized spending, double spending, forging bitcoins, and tampering with the blockchain. Other attacks, such as theft of private keys, require due care by users.[16][17]

Unauthorized spending[edit]

Unauthorized spending is mitigated by bitcoin's implementation of public-private key cryptography. For example, when Alice sends a bitcoin to Bob, Bob becomes the new owner of the bitcoin. Eve, observing the transaction, might want to spend the bitcoin Bob just received, but she cannot sign the transaction without the knowledge of Bob's private key.[17]

Double spending[edit]

A specific problem that an internet payment system must solve is double-spending, whereby a user pays the same coin to two or more different recipients. An example of such a problem would be if Eve sent a bitcoin to Alice and later sent the same bitcoin to Bob. The bitcoin network guards against double-spending by recording all bitcoin transfers in a ledger (the blockchain) that is visible to all users, and ensuring for all transferred bitcoins that they have not been previously spent.[17]: 4

Race attack[edit]

If Eve offers to pay Alice a bitcoin in exchange for goods and signs a corresponding transaction, it is still possible that she also creates a different transaction at the same time sending the same bitcoin to Bob. By the rules, the network accepts only one of the transactions. This is called a race attack, since there is a race between the recipients to accept the transaction first. Alice can reduce the risk of race attack stipulating that she will not deliver the goods until Eve's payment to Alice appears in the blockchain.[18]

A variant race attack (which has been called a Finney attack by reference to Hal Finney) requires the participation of a miner. Instead of sending both payment requests (to pay Bob and Alice with the same coins) to the network, Eve issues only Alice's payment request to the network, while the accomplice tries to mine a block that includes the payment to Bob instead of Alice. There is a positive probability that the rogue miner will succeed before the network, in which case the payment to Alice will be rejected. As with the plain race attack, Alice can reduce the risk of a Finney attack by waiting for the payment to be included in the blockchain.[19]

History modification[edit]

Each block that is added to the blockchain, starting with the block containing a given transaction, is called a confirmation of that transaction. Ideally, merchants and services that receive payment in bitcoin should wait for at least a few confirmations to be distributed over the network before assuming that the payment was done. The more confirmations that the merchant waits for, the more difficult it is for an attacker to successfully reverse the transaction—unless the attacker controls more than half the total network power, in which case it is called a 51% attack, or a majority attack.[20]

Although more difficult for attackers of a smaller size, there may be financial incentives that make history modification attacks profitable.[21]

Scalability[edit]

This section is an excerpt from Bitcoin scalability problem.[edit]

Number of transactions per month, on a logarithmic scale

The Bitcoin scalability problem refers to the limited capability of the Bitcoin network to handle large amounts of transaction data on its platform in a short span of time.[22] It is related to the fact that records (known as blocks) in the Bitcoin blockchain are limited in size and frequency.[23]

Bitcoin's blocks contain the transactions on the bitcoin network.[24]: ch. 2 The on-chain transaction processing capacity of the bitcoin network is limited by the average block creation time of 10 minutes and the original block size limit of 1 megabyte. These jointly constrain the network's throughput. The transaction processing capacity maximum estimated using an average or median transaction size is between 3.3 and 7 transactions per second.[23] There are various proposed and activated solutions to address this issue.

Privacy[edit]

Deanonymisation of clients[edit]

Deanonymisation is a strategy in data mining in which anonymous data is cross-referenced with other sources of data to re-identify the anonymous data source. Along with transaction graph analysis, which may reveal connections between bitcoin addresses (pseudonyms),[16][25] there is a possible attack[26] which links a user's pseudonym to its IP address. If the peer is using Tor, the attack includes a method to separate the peer from the Tor network, forcing them to use their real IP address for any further transactions. The cost of the attack on the full bitcoin network was estimated to be under €1500 per month, as of 2014.[26]

Consensus mechanism and upgrades[edit]

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Impact and influence[edit]

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1History

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1.1Background

1.22008–2009: Creation

1.32010–2012: Early growth

1.42013–2014: First regulatory actions

1.52015–2019

1.62020–present

2Design

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2.1Units and divisibility

2.2Blockchain

2.3Addresses and transactions

2.4Mining

2.5Privacy and fungibility

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2.7Scalability and decentralization challenges

3Economics and usage

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3.1Bitcoin's theoretical roots and ideology

3.2Recognition as a currency and legal status

3.3Use for payments

3.4Use for investment and status as an economic bubble

4See also

5Notes

6References

7Further reading

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Decentralized digital currency

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BitcoinLogo of BitcoinDenominationsPluralBitcoinsSymbol₿(Unicode: U+20BF ₿ BITCOIN SIGN)[1]CodeBTC[a]Precision10−8Subunits 1⁄1000Millibitcoin 1⁄1000000Microbitcoin 1⁄100000000Satoshi[b][2]DevelopmentOriginal author(s)Satoshi NakamotoWhite paper"Bitcoin: A Peer-to-Peer Electronic Cash System"Implementation(s)Bitcoin CoreInitial release0.1.0 / 9 January 2009 (15 years ago) (2009-01-09)Latest release25.1 / 19 October 2023 (4 months ago) (2023-10-19)[3]Code repositorygithub.com/bitcoin/bitcoinDevelopment statusActiveWritten inC++Source modelFree and open-source softwareLicenseMIT LicenseLedgerLedger start3 January 2009 (15 years ago) (2009-01-03)Timestamping schemeProof of work (partial hash inversion)Hash functionSHA-256 (two rounds)Issuance scheduleDecentralized (block reward)Initially ₿50 per block, halved every 210,000 blocksBlock reward₿6.25 (as of 2023[update])Block time10 minutesCirculating supply₿19,591,231 (as of 6 January 2024[update])Supply limit₿21,000,000[c]ValuationExchange rateFloatingDemographicsOfficial user(s)El Salvador[4]

This article contains special characters. Without proper rendering support, you may see question marks, boxes, or other symbols.

Bitcoin (abbreviation: BTC[a]; sign: ₿) is the first decentralized cryptocurrency. Nodes in the peer-to-peer bitcoin network verify transactions through cryptography and record them in a public distributed ledger, called a blockchain, without central oversight. Consensus between nodes is achieved using a computationally intensive process based on proof of work, called mining, that requires increasing quantities of electricity and guarantees the security of the bitcoin blockchain.[5]

Based on a free market ideology, bitcoin was invented in 2008 by Satoshi Nakamoto, an unknown person.[6] Use of bitcoin as a currency began in 2009,[7] with the release of its open-source implementation.[8]: ch. 1 In 2021, El Salvador adopted it as legal tender.[4] Bitcoin is currently used more as a store of value and less as a medium of exchange or unit of account. It is mostly seen as an investment and has been described by many scholars as an economic bubble.[9] As bitcoin is pseudonymous, its use by criminals has attracted the attention of regulators, leading to its ban by several countries as of 2021[update].[10]

History

Main article: History of bitcoin

Background

Before bitcoin, several digital cash technologies were released, starting with David Chaum's ecash in the 1980s.[11] The idea that solutions to computational puzzles could have some value was first proposed by cryptographers Cynthia Dwork and Moni Naor in 1992.[11] The concept was independently rediscovered by Adam Back who developed Hashcash, a proof-of-work scheme for spam control in 1997.[11] The first proposals for distributed digital scarcity-based cryptocurrencies came from cypherpunks Wei Dai (b-money) and Nick Szabo (bit gold) in 1998.[12] In 2004, Hal Finney developed the first currency based on reusable proof of work.[13] These various attempts were not successful:[11] Chaum's concept required centralized control and no banks wanted to sign on, Hashcash had no protection against double-spending, while b-money and bit gold were not resistant to Sybil attacks.[11]

2008–2009: Creation

External image Cover page of The Times 3 January 2009 showing the headline used in the genesis block

Bitcoin logos made by Satoshi Nakamoto in 2009 (left) and 2010 (right) depict bitcoins as gold tokens.

The domain name bitcoin.org was registered on 18 August 2008.[14] On 31 October 2008, a link to a white paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System was posted to a cryptography mailing list.[15] Nakamoto implemented the bitcoin software as open-source code and released it in January 2009.[7] Nakamoto's identity remains unknown.[6] All individual components of bitcoin originated in earlier academic literature.[11] Nakamoto's innovation was their complex interplay resulting in the first decentralized, Sybil resistant, Byzantine fault tolerant digital cash system, that would eventually be referred to as the first blockchain.[11][16] Nakamoto's paper was not peer reviewed and was initially ignored by academics, who argued that it could not work, based on theoretical models, even though it was working in practice.[11]

On 3 January 2009, the bitcoin network was created when Nakamoto mined the starting block of the chain, known as the genesis block.[17] Embedded in this block was the text "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks", which is the date and headline of an issue of The Times newspaper.[7] Nine days later, Hal Finney received the first bitcoin transaction: ten bitcoins from Nakamoto.[18] Wei Dai and Nick Szabo were also early supporters.[17] In 2010, the first known commercial transaction using bitcoin occurred when programmer Laszlo Hanyecz bought two Papa John's pizzas for ₿10,000.[19]

2010–2012: Early growth

Blockchain analysts estimate that Nakamoto had mined about one million bitcoins[20] before disappearing in 2010 when he handed the network alert key and control of the code repository over to Gavin Andresen. Andresen later became lead developer at the Bitcoin Foundation,[21][22] an organization founded in September 2012 to promote bitcoin.[23]

After early "proof-of-concept" transactions, the first major users of bitcoin were black markets, such as the dark web Silk Road. During its 30 months of existence, beginning in February 2011, Silk Road exclusively accepted bitcoins as payment, transacting ₿9.9 million, worth about $214 million.[24]: 222

2013–2014: First regulatory actions

In March 2013, the US Financial Crimes Enforcement Network (FinCEN) established regulatory guidelines for "decentralized virtual currencies" such as bitcoin, classifying American bitcoin miners who sell their generated bitcoins as money services businesses, subject to registration and other legal obligations.[25] In May 2013, US authorities seized the unregistered exchange Mt. Gox.[26] In June 2013, the US Drug Enforcement Administration seized ₿11.02 from a man attempting to use them to buy illegal substances. This marked the first time a government agency had seized bitcoins.[27] The FBI seized about ₿30,000 in October 2013 from Silk Road, following the arrest of its founder Ross Ulbricht.[28]

In December 2013, the People's Bank of China prohibited Chinese financial institutions from using bitcoin.[29] After the announcement, the value of bitcoin dropped,[30] and Baidu no longer accepted bitcoins for certain services.[31] Buying real-world goods with any virtual currency had been illegal in China since at least 2009.[32]

2015–2019

Research produced by the University of Cambridge estimated that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.[33] In August 2017, the SegWit software upgrade was activated. Segwit was intended to support the Lightning Network as well as improve scalability.[34] SegWit opponents, who supported larger blocks as a scalability solution, forked to create Bitcoin Cash, one of many forks of bitcoin.[35]

In December 2017, the first futures on bitcoin was introduced by the CME.[36]

In February 2018, price crashed after China imposed a complete ban on Bitcoin trading.[37] The percentage of bitcoin trading in the Chinese renminbi fell from over 90% in September 2017 to less than 1% in June 2018.[38] During the same year, Bitcoin prices were negatively affected by several hacks or thefts from cryptocurrency exchanges.[39]

2020–present

Bitcoin price in US dollars

In 2020, some major companies and institutions started to acquire bitcoin: MicroStrategy invested $250 million in bitcoin as a treasury reserve asset,[40] Square, Inc., $50 million,[41] and MassMutual, $100 million.[42] In November 2020, PayPal added support for bitcoin in the US.[43]

In February 2021, Bitcoin's market capitalization reached $1 trillion for the first time.[44] In November 2021, the Taproot soft-fork upgrade was activated, adding support for Schnorr signatures, improved functionality of smart contracts and Lightning Network.[45] Before, Bitcoin only used a custom elliptic curve with the ECDSA algorithm to produce signatures.[46]: 101 In September 2021, Bitcoin became legal tender in El Salvador, alongside the US dollar.[4] In October 2021, the first bitcoin futures ETF, called BITO, from ProShares was approved by the SEC and listed on the Chicago Mercantile Exchange.[47]

In May and June 2022, the bitcoin price fell following the collapses of TerraUSD, a stablecoin,[48] and the Celsius Network, a cryptocurrency loan company.[49][50]

In 2023, ordinals, non-fungible tokens (NFTs) on Bitcoin, went live.[51] In January 2024, the first 11 US spot bitcoin exchange-traded funds (ETFs) began trading, offering direct exposure to bitcoin for the first time on American stock exchanges.[52][53]

Design

Main article: Bitcoin protocol

Units and divisibility

The unit of account of the bitcoin system is the bitcoin. It is most commonly represented with the currency code BTC[a] as well as the symbol ₿.[1] XBT, a code that conforms to ISO 4217 though not officially part of it, is used by Bloomberg L.P.[54]

No uniform capitalization convention exists; some sources use Bitcoin, capitalized, to refer to the technology and network, and bitcoin, lowercase, for the unit of account.[55] The Oxford English Dictionary advocates the use of lowercase bitcoin in all cases.[56]

One bitcoin is divisible to eight decimal places.[8]: ch. 5 Units for smaller amounts of bitcoin are the millibitcoin (mBTC), equal to 1⁄1000 bitcoin, and the satoshi[b] (sat), representing 1⁄100000000 (one hundred millionth) bitcoin, the smallest amount possible.[2] 100,000 satoshis are one mBTC.[57]

Blockchain

Further information: Blockchain § Structure and design

As a decentralized system, bitcoin operates without a central authority or single administrator,[58] so that anyone can create a new bitcoin address and transact without needing any approval.[8]: ch. 1 This is accomplished through a specialized distributed ledger called a blockchain that records bitcoin transactions.[59]

The blockchain is implemented as an ordered list of blocks. Each block contains a SHA-256 hash of the previous block,[59] "chaining" them in chronological order.[8]: ch. 7 [59] The blockchain is maintained by a peer-to-peer network.[24]: 215–219 Individual blocks, public addresses, and transactions within blocks are public information, and can be examined using a blockchain explorer.[60]

Nodes validate and broadcast transactions, each maintaining a copy of the blockchain for ownership verification.[61] A new block is created every 10 minutes on average, updating the blockchain across all nodes without central oversight. This process tracks bitcoin spending, ensuring each bitcoin is spent only once. Unlike a traditional ledger that tracks physical currency, bitcoins exist digitally as unspent outputs of transactions.[8]: ch. 5

Addresses and transactions

Simplified chain of ownership. In practice, a transaction can have more than one input and more than one output.[62]

In the blockchain, bitcoins are linked to specific addresses that are hashes of a public key. Creating an address involves generating a random private key and then computing the corresponding address. This process is almost instant, but the reverse (finding the private key for a given address) is nearly impossible.[8]: ch. 4 Publishing a bitcoin address does not risk its private key, and it is extremely unlikely to accidentally generate a used key with funds. To use bitcoins, owners need their private key to digitally sign transactions, which are verified by the network using the public key, keeping the private key secret.[8]: ch. 5

Bitcoin transactions use a Forth-like scripting language,[8]: ch. 5 involving one or more inputs and outputs. When sending bitcoins, a user specifies the recipients' addresses and the amount for each output. This allows sending bitcoins to several recipients in a single transaction. To prevent double-spending, each input must refer to a previous unspent output in the blockchain.[62] Using multiple inputs is similar to using multiple coins in a cash transaction. As in a cash transaction, the sum of inputs can exceed the intended sum of payments. In such a case, an additional output can return the change back to the payer.[62] Unallocated input satoshis in the transaction become the transaction fee.[62]

Losing a private key means losing access to the bitcoins, with no other proof of ownership accepted by the protocol.[24] For instance, in 2013, a user lost ₿7,500, valued at US$7.5 million, by accidentally discarding a hard drive with the private key.[63] It is estimated that around 20% of all bitcoins are lost.[64] The private key must also be kept secret as its exposure, such as through a data breach, can lead to theft of the associated bitcoins.[8]: ch. 10 [65] As of December 2017[update], approximately ₿980,000 had been stolen from cryptocurrency exchanges.[66]

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P2P Network¶

The Bitcoin network protocol allows full nodes (peers) to collaboratively maintain a peer-to-peer network for block and transaction exchange.

Introduction¶

Full nodes download and verify every block and transaction prior to relaying them to other nodes. Archival nodes are full nodes which store the entire blockchain and can serve historical blocks to other nodes. Pruned nodes are full nodes which do not store the entire blockchain. Many SPV clients also use the Bitcoin network protocol to connect to full nodes.

Consensus rules do not cover networking, so Bitcoin programs may use alternative networks and protocols, such as the high-speed block relay network used by some miners and the dedicated transaction information servers used by some wallets that provide SPV-level security.

To provide practical examples of the Bitcoin peer-to-peer network, this section uses Bitcoin Core as a representative full node and BitcoinJ as a representative SPV client. Both programs are flexible, so only default behavior is described. Also, for privacy, actual IP addresses in the example output below have been replaced with RFC5737 reserved IP addresses.

Peer Discovery¶

When started for the first time, programs don’t know the IP addresses of any active full nodes. In order to discover some IP addresses, they query one or more DNS names (called DNS seeds) hardcoded into Bitcoin Core and BitcoinJ. The response to the lookup should include one or more DNS A records with the IP addresses of full nodes that may accept new incoming connections. For example, using the Unix ``dig` command `__:

;; QUESTION SECTION:

;seed.bitcoin.sipa.be. IN A

;; ANSWER SECTION:

seed.bitcoin.sipa.be. 60 IN A 192.0.2.113

seed.bitcoin.sipa.be. 60 IN A 198.51.100.231

seed.bitcoin.sipa.be. 60 IN A 203.0.113.183

[...]

The DNS seeds are maintained by Bitcoin community members: some of them provide dynamic DNS seed servers which automatically get IP addresses of active nodes by scanning the network; others provide static DNS seeds that are updated manually and are more likely to provide IP addresses for inactive nodes. In either case, nodes are added to the DNS seed if they run on the default Bitcoin ports of 8333 for mainnet or 18333 for testnet.

DNS seed results are not authenticated and a malicious seed operator or network man-in-the-middle attacker can return only IP addresses of nodes controlled by the attacker, isolating a program on the attacker’s own network and allowing the attacker to feed it bogus transactions and blocks. For this reason, programs should not rely on DNS seeds exclusively.

Once a program has connected to the network, its peers can begin to send it addr (address) messages with the IP addresses and port numbers of other peers on the network, providing a fully decentralized method of peer discovery. Bitcoin Core keeps a record of known peers in a persistent on-disk database which usually allows it to connect directly to those peers on subsequent startups without having to use DNS seeds.

However, peers often leave the network or change IP addresses, so programs may need to make several different connection attempts at startup before a successful connection is made. This can add a significant delay to the amount of time it takes to connect to the network, forcing a user to wait before sending a transaction or checking the status of payment.

To avoid this possible delay, BitcoinJ always uses dynamic DNS seeds to get IP addresses for nodes believed to be currently active. Bitcoin Core also tries to strike a balance between minimizing delays and avoiding unnecessary DNS seed use: if Bitcoin Core has entries in its peer database, it spends up to 11 seconds attempting to connect to at least one of them before falling back to seeds; if a connection is made within that time, it does not query any seeds.

Both Bitcoin Core and BitcoinJ also include a hardcoded list of IP addresses and port numbers to several dozen nodes which were active around the time that particular version of the software was first released. Bitcoin Core will start attempting to connect to these nodes if none of the DNS seed servers have responded to a query within 60 seconds, providing an automatic fallback option.

As a manual fallback option, Bitcoin Core also provides several command-line connection options, including the ability to get a list of peers from a specific node by IP address, or to make a persistent connection to a specific node by IP address. See the -help text for details. BitcoinJ can be programmed to do the same thing.

Resources: Bitcoin Seeder, the program run by several of the seeds used by Bitcoin Core and BitcoinJ. The Bitcoin Core DNS Seed Policy. The hardcoded list of IP addresses used by Bitcoin Core and BitcoinJ is generated using the makeseeds script.

Connecting To Peers¶

Connecting to a peer is done by sending a “version” message, which contains your version number, block, and current time to the remote node. The remote node responds with its own “version” message. Then both nodes send a “verack” message to the other node to indicate the connection has been established.

Once connected, the client can send to the remote node getaddr and “addr” messages to gather additional peers.

In order to maintain a connection with a peer, nodes by default will send a message to peers before 30 minutes of inactivity. If 90 minutes pass without a message being received by a peer, the client will assume that connection has closed.

Initial Block Download¶

Before a full node can validate unconfirmed transactions and recently-mined blocks, it must download and validate all blocks from block 1 (the block after the hardcoded genesis block) to the current tip of the best block chain. This is the Initial Block Download (IBD) or initial sync.

Although the word “initial” implies this method is only used once, it can also be used any time a large number of blocks need to be downloaded, such as when a previously-caught-up node has been offline for a long time. In this case, a node can use the IBD method to download all the blocks which were produced since the last time it was online.

Bitcoin Core uses the IBD method any time the last block on its local best block chain has a block header time more than 24 hours in the past. Bitcoin Core 0.10.0 will also perform IBD if its local best block chain is more than 144 blocks lower than its local best header chain (that is, the local block chain is more than about 24 hours in the past).

Blocks-First¶

Bitcoin Core (up until version 0.9.3) uses a simple initial block download (IBD) method we’ll call blocks-first. The goal is to download the blocks from the best block chain in sequence.

Overview Of Blocks-First Method¶

The first time a node is started, it only has a single block in its local best block chain—the hardcoded genesis block (block 0). This node chooses a remote peer, called the sync node, and sends it the “getblocks” message illustrated below.

First GetBlocks Message Sent During IBD¶

In the header hashes field of the “getblocks” message, this new node sends the header hash of the only block it has, the genesis block (6fe2…0000 in internal byte order). It also sets the stop hash field to all zeroes to request a maximum-size response.

Upon receipt of the “getblocks” message, the sync node takes the first (and only) header hash and searches its local best block chain for a block with that header hash. It finds that block 0 matches, so it replies with 500 block inventories (the maximum response to a “getblocks” message) starting from block 1. It sends these inventories in the “inv” message illustrated below.

First Inv Message Sent During IBD¶

Inventories are unique identifiers for information on the network. Each inventory contains a type field and the unique identifier for an instance of the object. For blocks, the unique identifier is a hash of the block’s header.

The block inventories appear in the “inv” message in the same order they appear in the block chain, so this first “inv” message contains inventories for blocks 1 through 501. (For example, the hash of block 1 is 4860…0000 as seen in the illustration above.)

The IBD node uses the received inventories to request 128 blocks from the sync node in the “getdata” message illustrated below.

First GetData Message Sent During IBD¶

It’s important to blocks-first nodes that the blocks be requested and sent in order because each block header references the header hash of the preceding block. That means the IBD node can’t fully validate a block until its parent block has been received. Blocks that can’t be validated because their parents haven’t been received are called orphan blocks; a subsection below describes them in more detail.

Upon receipt of the “getdata” message, the sync node replies with each of the blocks requested. Each block is put into serialized block format and sent in a separate “block” message. The first “block” message sent (for block 1) is illustrated below.

First Block Message Sent During IBD¶

The IBD node downloads each block, validates it, and then requests the next block it hasn’t requested yet, maintaining a queue of up to 128 blocks to download. When it has requested every block for which it has an inventory, it sends another “getblocks” message to the sync node requesting the inventories of up to 500 more blocks. This second “getblocks” message contains multiple header hashes as illustrated below:

Second GetBlocks Message Sent During IBD¶

Upon receipt of the second “getblocks” message, the sync node searches its local best block chain for a block that matches one of the header hashes in the message, trying each hash in the order they were received. If it finds a matching hash, it replies with 500 block inventories starting with the next block from that point. But if there is no matching hash (besides the stopping hash), it assumes the only block the two nodes have in common is block 0 and so it sends an inv starting with block 1 (the same “inv” message seen several illustrations above).

This repeated search allows the sync node to send useful inventories even if the IBD node’s local block chain forked from the sync node’s local block chain. This fork detection becomes increasingly useful the closer the IBD node gets to the tip of the block chain.

When the IBD node receives the second “inv” message, it will request those blocks using “getdata” messages. The sync node will respond with “block” messages. Then the IBD node will request more inventories with another “getblocks” message—and the cycle will repeat until the IBD node is synced to the tip of the block chain. At that point, the node will accept blocks sent through the regular block broadcasting described in a later subsection.

Blocks-First Advantages & Disadvantages¶

The primary advantage of blocks-first IBD is its simplicity. The primary disadvantage is that the IBD node relies on a single sync node for all of its downloading. This has several implications:

Speed Limits: All requests are made to the sync node, so if the sync node has limited upload bandwidth, the IBD node will have slow download speeds. Note: if the sync node goes offline, Bitcoin Core will continue downloading from another node—but it will still only download from a single sync node at a time.

Download Restarts: The sync node can send a non-best (but otherwise valid) block chain to the IBD node. The IBD node won’t be able to identify it as non-best until the initial block download nears completion, forcing the IBD node to restart its block chain download over again from a different node. Bitcoin Core ships with several block chain checkpoints at various block heights selected by developers to help an IBD node detect that it is being fed an alternative block chain history—allowing the IBD node to restart its download earlier in the process.

Disk Fill Attacks: Closely related to the download restarts, if the sync node sends a non-best (but otherwise valid) block chain, the chain will be stored on disk, wasting space and possibly filling up the disk drive with useless data.

High Memory Use: Whether maliciously or by accident, the sync node can send blocks out of order, creating orphan blocks which can’t be validated until their parents have been received and validated. Orphan blocks are stored in memory while they await validation, which may lead to high memory use.

All of these problems are addressed in part or in full by the headers-first IBD method used in Bitcoin Core 0.10.0.

Resources: The table below summarizes the messages mentioned throughout this subsection. The links in the message field will take you to the reference page for that message.

Message

From→To

Payload

“getblocks”

IBD→Sync

One or more header hashes

“inv”

Sync→IBD

Up to 500 block inventories (unique identifiers)

“getdata”

IBD→Sync

One or more block inventories

“block”

Sync→IBD

One serialized block

Headers-First¶

Bitcoin Core 0.10.0 uses an initial block download (IBD) method called headers-first. The goal is to download the headers for the best header chain, partially validate them as best as possible, and then download the corresponding blocks in parallel. This solves several problems with the older blocks-first IBD method.

Overview Of Headers-First Method¶

The first time a node is started, it only has a single block in its local best block chain—the hardcoded genesis block (block 0). The node chooses a remote peer, which we’ll call the sync node, and sends it the “getheaders” message illustrated below.

First getheaders message¶

In the header hashes field of the “getheaders” message, the new node sends the header hash of the only block it has, the genesis block (6fe2…0000 in internal byte order). It also sets the stop hash field to all zeroes to request a maximum-size response.

Upon receipt of the “getheaders” message, the sync node takes the first (and only) header hash and searches its local best block chain for a block with that header hash. It finds that block 0 matches, so it replies with 2,000 header (the maximum response) starting from block 1. It sends these header hashes in the “headers” message illustrated below.

First headers message¶

The IBD node can partially validate these block headers by ensuring that all fields follow consensus rules and that the hash of the header is below the target threshold according to the nBits field. (Full validation still requires all transactions from the corresponding block.)

After the IBD node has partially validated the block headers, it can do two things in parallel:

Download More Headers: the IBD node can send another “getheaders” message to the sync node to request the next 2,000 headers on the best header chain. Those headers can be immediately validated and another batch requested repeatedly until a “headers” message is received from the sync node with fewer than 2,000 headers, indicating that it has no more headers to offer. As of this writing, headers sync can be completed in fewer than 200 round trips, or about 32 MB of downloaded data.

Once the IBD node receives a “headers” message with fewer than 2,000 headers from the sync node, it sends a “getheaders” message to each of its outbound peers to get their view of best header chain. By comparing the responses, it can easily determine if the headers it has downloaded belong to the best header chain reported by any of its outbound peers. This means a dishonest sync node will quickly be discovered even if checkpoints aren’t used (as long as the IBD node connects to at least one honest peer; Bitcoin Core will continue to provide checkpoints in case honest peers can’t be found).

Download Blocks: While the IBD node continues downloading headers, and after the headers finish downloading, the IBD node will request and download each block. The IBD node can use the block header hashes it computed from the header chain to create “getdata” messages that request the blocks it needs by their inventory. It doesn’t need to request these from the sync node—it can request them from any of its full node peers. (Although not all full nodes may store all blocks.) This allows it to fetch blocks in parallel and avoid having its download speed constrained to the upload speed of a single sync node.

To spread the load between multiple peers, Bitcoin Core will only request up to 16 blocks at a time from a single peer. Combined with its maximum of 8 outbound connections, this means headers-first Bitcoin Core will request a maximum of 128 blocks simultaneously during IBD (the same maximum number that blocks-first Bitcoin Core requested from its sync node).

Simulated Headers-First Download Window¶

Bitcoin Core’s headers-first mode uses a 1,024-block moving download window to maximize download speed. The lowest-height block in the window is the next block to be validated; if the block hasn’t arrived by the time Bitcoin Core is ready to validate it, Bitcoin Core will wait a minimum of two more seconds for the stalling node to send the block. If the block still hasn’t arrived, Bitcoin Core will disconnect from the stalling node and attempt to connect to another node. For example, in the illustration above, Node A will be disconnected if it doesn’t send block 3 within at least two seconds.

Once the IBD node is synced to the tip of the block chain, it will accept blocks sent through the regular block broadcasting described in a later subsection.

Resources: The table below summarizes the messages mentioned throughout this subsection. The links in the message field will take you to the reference page for that message.

Message

From→To

Payload

“getheaders”

IBD→Sync

One or more header hashes

“headers”

Sync→IBD

Up to 2,000 block headers

“getdata”

IBD→Many

One or more block inventories derived from header hashes

“block”

Many→IBD

One serialized block

Block Broadcasting¶

When a miner discovers a new block, it broadcasts the new block to its peers using one of the following methods:

Unsolicited Block Push: the miner sends a “block” message to each of its full node peers with the new block. The miner can reasonably bypass the standard relay method in this way because it knows none of its peers already have the just-discovered block.

Standard Block Relay: the miner, acting as a standard relay node, sends an “inv” message to each of its peers (both full node and SPV) with an inventory referring to the new block. The most common responses are:

Each blocks-first (BF) peer that wants the block replies with a “getdata” message requesting the full block.

Each headers-first (HF) peer that wants the block replies with a “getheaders” message containing the header hash of the highest-height header on its best header chain, and likely also some headers further back on the best header chain to allow fork detection. That message is immediately followed by a “getdata” message requesting the full block. By requesting headers first, a headers-first peer can refuse orphan blocks as described in the subsection below.

Each Simplified Payment Verification (SPV) client that wants the block replies with a “getdata” message typically requesting a merkle block.

The miner replies to each request accordingly by sending the block in a “block” message, one or more headers in a “headers” message, or the merkle block and transactions relative to the SPV client’s bloom filter in a “merkleblock” message followed by zero or more “tx” messages.

Direct Headers Announcement: a relay node may skip the round trip overhead of an “inv” message followed by getheaders by instead immediately sending a “headers” message containing the full header of the new block. A HF peer receiving this message will partially validate the block header as it would during headers-first IBD, then request the full block contents with a “getdata” message if the header is valid. The relay node then responds to the getdata request with the full or filtered block data in a block or “merkleblock” message, respectively. A HF node may signal that it prefers to receive headers instead of inv announcements by sending a special “sendheaders” message during the connection handshake.

This protocol for block broadcasting was proposed in BIP 130 and has been implemented in Bitcoin Core since version 0.12.

By default, Bitcoin Core broadcasts blocks using direct headers announcement to any peers that have signalled with “sendheaders” and uses standard block relay for all peers that have not. Bitcoin Core will accept blocks sent using any of the methods described above.

Full nodes validate the received block and then advertise it to their peers using the standard block relay method described above. The condensed table below highlights the operation of the messages described above (Relay, BF, HF, and SPV refer to the relay node, a blocks-first node, a headers-first node, and an SPV client; any refers to a node using any block retrieval method.)

Message

From→To

Payload

“inv”

Relay→Any

The inventory of the new block

“getdata”

BF→Relay

The inventory of the new block

“getheaders”

HF→Relay

One or more header hashes on the HF node’s best header chain (BHC)

“headers”

Relay→HF

Up to 2,000 headers connecting HF node’s BHC to relay node’s BHC

“block”

Relay→BF/HF

The new block in serialized format

“merkleblock”

Relay→SPV

The new block filtered into a merkle block

“tx”

Relay→SPV

Serialized transactions from the new block that match the bloom filter

Orphan Blocks¶

Blocks-first nodes may download orphan blocks—blocks whose previous block header hash field refers to a block header this node hasn’t seen yet. In other words, orphan blocks have no known parent (unlike stale blocks, which have known parents but which aren’t part of the best block chain).

Difference Between Orphan And Stale Blocks¶

When a blocks-first node downloads an orphan block, it will not validate it. Instead, it will send a “getblocks” message to the node which sent the orphan block; the broadcasting node will respond with an “inv” message containing inventories of any blocks the downloading node is missing (up to 500); the downloading node will request those blocks with a “getdata” message; and the broadcasting node will send those blocks with a “block” message. The downloading node will validate those blocks, and once the parent of the former orphan block has been validated, it will validate the former orphan block.

Headers-first nodes avoid some of this complexity by always requesting block headers with the “getheaders” message before requesting a block with the “getdata” message. The broadcasting node will send a “headers” message containing all the block headers (up to 2,000) it thinks the downloading node needs to reach the tip of the best header chain; each of those headers will point to its parent, so when the downloading node receives the “block” message, the block shouldn’t be an orphan block—all of its parents should be known (even if they haven’t been validated yet). If, despite this, the block received in the “block” message is an orphan block, a headers-first node will discard it immediately.

However, orphan discarding does mean that headers-first nodes will ignore orphan blocks sent by miners in an unsolicited block push.

Transaction Broadcasting¶

In order to send a transaction to a peer, an “inv” message is sent. If a getdata response message is received, the transaction is sent using tx. The peer receiving this transaction also forwards the transaction in the same manner, given that it is a valid transaction.

Memory Pool¶

Full peers may keep track of unconfirmed transactions which are eligible to be included in the next block. This is essential for miners who will actually mine some or all of those transactions, but it’s also useful for any peer who wants to keep track of unconfirmed transactions, such as peers serving unconfirmed transaction information to SPV clients.

Because unconfirmed transactions have no permanent status in Bitcoin, Bitcoin Core stores them in non-persistent memory, calling them a memory pool or mempool. When a peer shuts down, its memory pool is lost except for any transactions stored by its wallet. This means that never-mined unconfirmed transactions tend to slowly disappear from the network as peers restart or as they purge some transactions to make room in memory for others.

Transactions which are mined into blocks that later become stale blocks may be added back into the memory pool. These re-added transactions may be re-removed from the pool almost immediately if the replacement blocks include them. This is the case in Bitcoin Core, which removes stale blocks from the chain one by one, starting with the tip (highest block). As each block is removed, its transactions are added back to the memory pool. After all of the stale blocks are removed, the replacement blocks are added to the chain one by one, ending with the new tip. As each block is added, any transactions it confirms are removed from the memory pool.

SPV clients don’t have a memory pool for the same reason they don’t relay transactions. They can’t independently verify that a transaction hasn’t yet been included in a block and that it only spends UTXOs, so they can’t know which transactions are eligible to be included in the next block.

Misbehaving Nodes¶

Take note that for both types of broadcasting, mechanisms are in place to punish misbehaving peers who take up bandwidth and computing resources by sending false information. If a peer gets a banscore above the -banscore= threshold, he will be banned for the number of seconds defined by -bantime=, which is 86,400 by default (24 hours).

Alerts¶

Removed inBitcoin Core 0.13.0

Earlier versions of Bitcoin Core allowed developers and trusted community members to issue Bitcoin alerts to notify users of critical network-wide issues. This messaging system was retired in Bitcoin Core v0.13.0; however, internal alerts, partition detection warnings and the -alertnotify option features remain.

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