Transactions are defined using a Forth-like scripting language.[7]:ch. 5 Transactions consist of one or more inputs and one or more outputs. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output. To prevent double spending, each input must refer to a previous unspent output in the blockchain.[77] The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs (coins used to pay) can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer.[77] Any input satoshis not accounted for in the transaction outputs become the transaction fee.[77]


As the industry continues to investigate blockchain platforms, it’s apparent that Ethereum is becoming a de facto leader. For example, a few days ago JPMorgan publicly open-sourced its Quorum platform, architected and developed around the Go Ethereum client by Jeff Wilcke and his team. Several other major banks are using Ethereum, and Microsoft is anchoring its Bletchley platform on it as the foundational blockchain element. Industry, both publicly and confidentially, continues to contribute to Ethereum and work with us and others to help our promising, toddler-age codebase reach maturity. Stay tuned for news on this front.

As the industry continues to investigate blockchain platforms, it’s apparent that Ethereum is becoming a de facto leader. For example, a few days ago JPMorgan publicly open-sourced its Quorum platform, architected and developed around the Go Ethereum client by Jeff Wilcke and his team. Several other major banks are using Ethereum, and Microsoft is anchoring its Bletchley platform on it as the foundational blockchain element. Industry, both publicly and confidentially, continues to contribute to Ethereum and work with us and others to help our promising, toddler-age codebase reach maturity. Stay tuned for news on this front.


Ethereum is the pioneer for blockchain based smart contracts. When running on the blockchain a smart contract becomes like a self-operating computer program that automatically executes when specific conditions are met. On the blockchain, smart contracts allow for code to be run exactly as programmed without any possibility of downtime, censorship, fraud or third-party interference. It can facilitate the exchange of money, content, property, shares, or anything of value. The Ethereum network went live on July 30th, 2015 with 72 million Ethereum premined.
^ Mooney, Chris; Mufson, Steven (19 December 2017). "Why the bitcoin craze is using up so much energy". The Washington Post. Archived from the original on 9 January 2018. Retrieved 11 January 2018. several experts told The Washington Post that bitcoin probably uses as much as 1 to 4 gigawatts, or billion watts, of electricity, roughly the output of one to three nuclear reactors.
Ethereum has recently created a new standard called the ERC721 token for tracking unique digital assets. One of the biggest use cases currently for such tokens is digital collectibles, as the infrastructure allows for people to prove ownership of scarce digital goods. Many games are currently being built using this technology, such as the overnight hit CryptoKitties, a game where you can collect and breed digital cats.
The bitcoin blockchain is a public ledger that records bitcoin transactions.[75] It is implemented as a chain of blocks, each block containing a hash of the previous block up to the genesis block[c] of the chain. A network of communicating nodes running bitcoin software maintains the blockchain.[32]:215–219 Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications.
An official investigation into bitcoin traders was reported in May 2018.[177] The U.S. Justice Department launched an investigation into possible price manipulation, including the techniques of spoofing and wash trades.[178][179][180] Traders in the U.S., the U.K, South Korea, and possibly other countries are being investigated.[177] Brett Redfearn, head of the U.S. Securities and Exchange Commission's Division of Trading and Markets, had identified several manipulation techniques of concern in March 2018.
Lightweight clients consult full clients to send and receive transactions without requiring a local copy of the entire blockchain (see simplified payment verification – SPV). This makes lightweight clients much faster to set up and allows them to be used on low-power, low-bandwidth devices such as smartphones. When using a lightweight wallet, however, the user must trust the server to a certain degree, as it can report faulty values back to the user. Lightweight clients follow the longest blockchain and do not ensure it is valid, requiring trust in miners.[96]
The price of bitcoins has gone through cycles of appreciation and depreciation referred to by some as bubbles and busts.[159] In 2011, the value of one bitcoin rapidly rose from about US$0.30 to US$32 before returning to US$2.[160] In the latter half of 2012 and during the 2012–13 Cypriot financial crisis, the bitcoin price began to rise,[161] reaching a high of US$266 on 10 April 2013, before crashing to around US$50. On 29 November 2013, the cost of one bitcoin rose to a peak of US$1,242.[162] In 2014, the price fell sharply, and as of April remained depressed at little more than half 2013 prices. As of August 2014 it was under US$600.[163] During their time as bitcoin developers, Gavin Andresen[164] and Mike Hearn[165] warned that bubbles may occur.
The bitcoin blockchain is a public ledger that records bitcoin transactions.[75] It is implemented as a chain of blocks, each block containing a hash of the previous block up to the genesis block[c] of the chain. A network of communicating nodes running bitcoin software maintains the blockchain.[32]:215–219 Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications. 

“A DAO consists of one or more contracts and could be funded by a group of like-minded individuals. A DAO operates completely transparently and completely independently of any human intervention, including its original creators. A DAO will stay on the network as long as it covers its survival costs and provides a useful service to its customer base” Stephen Tual, Slock.it Founder, former CCO Ethereum.
Several news outlets have asserted that the popularity of bitcoins hinges on the ability to use them to purchase illegal goods.[135][222] Nobel-prize winning economist Joseph Stiglitz says that bitcoin's anonymity encourages money laundering and other crimes, "If you open up a hole like bitcoin, then all the nefarious activity will go through that hole, and no government can allow that." He's also said that if "you regulate it so you couldn't engage in money laundering and all these other [crimes], there will be no demand for Bitcoin. By regulating the abuses, you are going to regulate it out of existence. It exists because of the abuses."[223][224]
Lightweight clients consult full clients to send and receive transactions without requiring a local copy of the entire blockchain (see simplified payment verification – SPV). This makes lightweight clients much faster to set up and allows them to be used on low-power, low-bandwidth devices such as smartphones. When using a lightweight wallet, however, the user must trust the server to a certain degree, as it can report faulty values back to the user. Lightweight clients follow the longest blockchain and do not ensure it is valid, requiring trust in miners.[96]
An official investigation into bitcoin traders was reported in May 2018.[177] The U.S. Justice Department launched an investigation into possible price manipulation, including the techniques of spoofing and wash trades.[178][179][180] Traders in the U.S., the U.K, South Korea, and possibly other countries are being investigated.[177] Brett Redfearn, head of the U.S. Securities and Exchange Commission's Division of Trading and Markets, had identified several manipulation techniques of concern in March 2018.

البيتكوين عملة رقمية ذات مجهولية، حيث أن عملية التحويل عبرها يتطلب فقط معرفة رقم محفظة الشخص المحول إليه ويتم تخزين عملية التحويل في سلسلة الكتل برقم تسلسلي خاص ولا يتضمن هذا اسم المرسل او المتلقي او اي بيانات اخرى خاصة بهما، مما يجعل منها فكرة رائجة لدى كل من المدافعين عن الخصوصية، أو بائعي البضائع غير المشروعة (مثل المخدرات) عبر الإنترنت على حد سواء.[9]
Until relatively recently, building blockchain applications has required a complex background in coding, cryptography, mathematics as well as significant resources. But times have changed. Previously unimagined applications, from electronic voting & digitally recorded property assets to regulatory compliance & trading are now actively being developed and deployed faster than ever before. By providing developers with the tools to build decentralized applications, Ethereum is making all of this possible.
يقصد بتعدين البتكوين هو استخراجه وتنقيبه ولتبسيط المفهوم فالعملية تشبه استخراج الذهب، الذهب لاستخراجه من باطن الأرض يتطلب معدات معينة مخصصة لذلك الغرض وجهد كبير، الأمر مشابه لتعدين البتكوين فهو يتطلب معدات وبرامج مخصصة تقوم بفك الشفرات والعمليات الحسابية المعقدة ، هذه البرامج مجانية على الانترنت تستطيع تعدين البيتكوين الان على جهازك ولكن للاسف جهازك مهما كانت قوته لن يستحمل الضغط الكهربائي الهائل وسيصاب بالتلف أضف إلى ذلك فاتورة الكهرباء التي ستتسبب بها ، احد الحلول يكمن في التعدين السحابي وهذا التعدين السحابي وهو يتمثل ببساطة أن شركات متخصصة في المجال وتسمى بالمسبح (بالانجليزية: Pool) وهو أن يجتمع مجموعة من الأشخاص لهم نفس الهدف كل يدفع نسبة من المال عبارة عن استثمار وعند الربح يأخذ المال على حسب النسبة التي وضعها.
الجدير بالذكر بأن بعض المواقع كانت تنشر سابقا تقديرا لمقدار الخسارة/ الربح الذي يُسجله المنقبون لكن يبدو بأنهم توقفوا عن القيام بذلك لأسباب نجهلها. قد يعتقد البعض بأنه لم يكن بالإمكان إعطاء تقدير دقيق لمقدار الخسارة أو الربح الذي يُسجله المنقبون، ولذلك تم التخلص من ذلك. إلا أنه من المُمكن جدا أنه تم التخلص من ذلك لكيلا يتم تنفير المُنقبين من عمليات التنقيب.
Ethereum blockchain applications are usually referred to as DApps (decentralized application), since they are based on the decentralized Ethereum Virtual Machine, and its smart contracts.[46] Many uses have been proposed for Ethereum platform, including ones that are impossible or unfeasible.[47][33] Use case proposals have included finance, the internet-of-things, farm-to-table produce, electricity sourcing and pricing, and sports betting. Ethereum is (as of 2017) the leading blockchain platform for initial coin offering projects, with over 50% market share.
^ Iansiti, Marco; Lakhani, Karim R. (January 2017). "The Truth About Blockchain". Harvard Business Review. Harvard University. Retrieved 17 January 2017. The technology at the heart of bitcoin and other virtual currencies, blockchain is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way.
بروتوكول التوجيه بين البوابات (BGP)   بروتوكول التهيئة الآليّة للمضيفين (DHCP) بروتوكول التطبيقات المقيدة (CoAP) نظام أسماء النطاقات (DNS) بروتوكول نقل النصّ الفائق (HTTP) بروتوكول الوصول إلى رسائل الإنترنت (IMAP) بروتوكول النفاذ إلى الدليل البسيط (LDAP) برتوكول نقل أخبار الشبكة (NNTP) بروتوكول التوقيت في الشبكة (NTP) بروتوكول مكتب البريد (POP) بروتوكول معلومات التوجيه (RIP) بروتوكول التدفق في الزمن حقيقي (RTSP) بروتوكول وصف الجلسة (SDP) بروتوكول بدء جلسة (SIP) بروتوكول نقل الملفات (FTP) بروتوكول نقل الملفات البسيط (TFTP) بروتوكول إرسال البريد البسيط (SMTP) بروتوكول إدارة الشبكات البسيط (SNMP) بروتوكول الاتصال الآمن (SSH) بروتوكول تل نت (Telnet) سبيدي (SPDY) مزيد ..
Despite bringing a number of benefits, decentralized applications aren’t faultless. Because smart contract code is written by humans, smart contracts are only as good as the people who write them. Code bugs or oversights can lead to unintended adverse actions being taken. If a mistake in the code gets exploited, there is no efficient way in which an attack or exploitation can be stopped other than obtaining a network consensus and rewriting the underlying code. This goes against the essence of the blockchain which is meant to be immutable. Also, any action taken by a central party raises serious questions about the decentralized nature of an application.
Researchers have pointed out at a "trend towards centralization". Although bitcoin can be sent directly from user to user, in practice intermediaries are widely used.[32]:220–222 Bitcoin miners join large mining pools to minimize the variance of their income.[32]:215, 219–222[115]:3[116] Because transactions on the network are confirmed by miners, decentralization of the network requires that no single miner or mining pool obtains 51% of the hashing power, which would allow them to double-spend coins, prevent certain transactions from being verified and prevent other miners from earning income.[117] As of 2013 just six mining pools controlled 75% of overall bitcoin hashing power.[117] In 2014 mining pool Ghash.io obtained 51% hashing power which raised significant controversies about the safety of the network. The pool has voluntarily capped their hashing power at 39.99% and requested other pools to act responsibly for the benefit of the whole network.[118] Between 2017 and 2019 over 70% of the hashing power and 90% of transactions were operating from China.[119]
بروتوكول التوجيه بين البوابات (BGP)   بروتوكول التهيئة الآليّة للمضيفين (DHCP) بروتوكول التطبيقات المقيدة (CoAP) نظام أسماء النطاقات (DNS) بروتوكول نقل النصّ الفائق (HTTP) بروتوكول الوصول إلى رسائل الإنترنت (IMAP) بروتوكول النفاذ إلى الدليل البسيط (LDAP) برتوكول نقل أخبار الشبكة (NNTP) بروتوكول التوقيت في الشبكة (NTP) بروتوكول مكتب البريد (POP) بروتوكول معلومات التوجيه (RIP) بروتوكول التدفق في الزمن حقيقي (RTSP) بروتوكول وصف الجلسة (SDP) بروتوكول بدء جلسة (SIP) بروتوكول نقل الملفات (FTP) بروتوكول نقل الملفات البسيط (TFTP) بروتوكول إرسال البريد البسيط (SMTP) بروتوكول إدارة الشبكات البسيط (SNMP) بروتوكول الاتصال الآمن (SSH) بروتوكول تل نت (Telnet) سبيدي (SPDY) مزيد ..
سعر البيتكوين غير مستقر ومن المُحتمل جدا أنك سمعت بأخبار تجاوز بيتكوين لحاجز 11000 دولار صعودا أو نزولا. هناك من يعتقد بأن هذا السعر مُبالغ فيه، لكن هناك كثيرون يعتقدون بأنه سعر لا يُعطي للبيتكوين حقه. من بين الأسباب التي تدفع إلى اعتقاد ذلك هو كون البيتكوين سلعة تحتاج إلى قدر كبير من الكهرباء لإنتاجها ويُفترض أن يكون سعرها على الأقل مُقاربا لسعر الكهرباء التي تم استهلاكها لإنتاجها أو أعلى بقليل بحكم قيام المُنقبين بدور حيوي لشبكة بيتكوين، وبالتالي يجب أن يكون هناك ما يدفعهم للقيام ذلك. بإمكاننا معرفة ما يربحه المنقبون من العمليات التي يقومون بها بشكل دقيق، حيث هناك مواقع تنشر هذه الإحصائيات جاهزة، لكن يُمكن التحقق من ذلك عبر تحليل سجل حسابات بيتكوين أيضا. لدى كتابة هذه السطور استطاع المُنقبون تحقيق $3,925,863 خلال الساعات الـ24 الماضية، قد يبدو هذا المبلغ ضخما، لكن القيام بعمليات التنقيب تلك احتاجت إلى 11,388,578 جيجا هاش /الثانية وهو أيضا رقم كبير جدا ويحتاج إلى قدر ضخم من الكهرباء للقيام بذلك. ليس من السهل معرفة تكلفة القيام بذلك لكن يُمكن القيام ببعض الحسابات التي ستعطينها فهما تقريبيا للوضع.
Like Bitcoin, Ethereum is a distributed public blockchain network. Although there are some significant technical differences between the two, the most important distinction to note is that Bitcoin and Ethereum differ substantially in purpose and capability. Bitcoin offers one particular application of blockchain technology, a peer to peer electronic cash system that enables online Bitcoin payments. While the Bitcoin blockchain is used to track ownership of digital currency (bitcoins), the Ethereum blockchain focuses on running the programming code of any decentralized application.
Physical wallets can also take the form of metal token coins[102] with a private key accessible under a security hologram in a recess struck on the reverse side.[103]:38 The security hologram self-destructs when removed from the token, showing that the private key has been accessed.[104] Originally, these tokens were struck in brass and other base metals, but later used precious metals as bitcoin grew in value and popularity.[103]:80 Coins with stored face value as high as ₿1000 have been struck in gold.[103]:102–104 The British Museum's coin collection includes four specimens from the earliest series[103]:83 of funded bitcoin tokens; one is currently on display in the museum's money gallery.[105] In 2013, a Utahn manufacturer of these tokens was ordered by the Financial Crimes Enforcement Network (FinCEN) to register as a money services business before producing any more funded bitcoin tokens.[102][103]:80

A wallet stores the information necessary to transact bitcoins. While wallets are often described as a place to hold[93] or store bitcoins, due to the nature of the system, bitcoins are inseparable from the blockchain transaction ledger. A wallet is more correctly defined as something that "stores the digital credentials for your bitcoin holdings" and allows one to access (and spend) them.[7]:ch. 1, glossary Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated.[94] At its most basic, a wallet is a collection of these keys.

The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC[a] and XBT.[b][72]:2 Its Unicode character is ₿.[1] Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), and satoshi (sat). Named in homage to bitcoin's creator, a satoshi is the smallest amount within bitcoin representing 0.00000001 bitcoins, one hundred millionth of a bitcoin.[2] A millibitcoin equals 0.001 bitcoins; one thousandth of a bitcoin or 100,000 satoshis.[73]


Mining is a record-keeping service done through the use of computer processing power.[e] Miners keep the blockchain consistent, complete, and unalterable by repeatedly grouping newly broadcast transactions into a block, which is then broadcast to the network and verified by recipient nodes.[75] Each block contains a SHA-256 cryptographic hash of the previous block,[75] thus linking it to the previous block and giving the blockchain its name.[7]:ch. 7[75]
There is ongoing research on how to use formal verification to express and prove non-trivial properties. A Microsoft Research report noted that writing solid smart contracts can be extremely difficult in practice, using The DAO hack to illustrate this problem. The report discussed tools that Microsoft had developed for verifying contracts, and noted that a large-scale analysis of published contracts is likely to uncover widespread vulnerabilities. The report also stated that it is possible to verify the equivalence of a Solidity program and the EVM code.[41]
^ Iansiti, Marco; Lakhani, Karim R. (January 2017). "The Truth About Blockchain". Harvard Business Review. Harvard University. Retrieved 17 January 2017. The technology at the heart of bitcoin and other virtual currencies, blockchain is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way.
To lower the costs, bitcoin miners have set up in places like Iceland where geothermal energy is cheap and cooling Arctic air is free.[205] Bitcoin miners are known to use hydroelectric power in Tibet, Quebec, Washington (state), and Austria to reduce electricity costs.[204][206] Miners are attracted to suppliers such as Hydro Quebec that have energy surpluses.[207] According to a University of Cambridge study, much of bitcoin mining is done in China, where electricity is subsidized by the government.[208][209]
On 3 January 2009, the bitcoin network was created when Nakamoto mined the first block of the chain, known as the genesis block.[21][22] Embedded in the coinbase of this block was the text "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks".[11] This note references a headline published by The Times and has been interpreted as both a timestamp and a comment on the instability caused by fractional-reserve banking.[23]:18
بيتكوين ليست العملة الافتراضية الوحيدة المتواجدة حاليًا في الأسواق الافتراضية. فقد برزت بفضل نجاحات ال بيتكوين ، مجموعة متنوعة من ما يسمى ب "altcoins" أو العملات الافتراضية البديلة ذات قيمة جيدة في الأسواق. أهم الفروقات بين البيتكوين وهذه العملات البديلة هي: البتكوين الأصعب في التعدين والأكثر غلاءً بينما العملات البديلة يمكن الحصول عليها عادةً بطريقة أسهل وأرخص، ويمكن أن يكون سعرها أكثر ثباتًا من سعر البتكوين ذات السعر المتقلب، كما أنّ الكثير من هذه العملات تم إنشاؤها لتلافي المشاكل الحاصلة في نظام بتكوين.[20] هذه لائحة بست عملات رقمية بديلة :
The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and the media.[218] In the United States, the FBI prepared an intelligence assessment,[219] the SEC issued a pointed warning about investment schemes using virtual currencies,[218] and the U.S. Senate held a hearing on virtual currencies in November 2013.[220] The U.S. government claimed that bitcoin was used to facilitate payments related to Russian interference in the 2016 United States elections.[221]
Third-party internet services called online wallets offer similar functionality but may be easier to use. In this case, credentials to access funds are stored with the online wallet provider rather than on the user's hardware.[97] As a result, the user must have complete trust in the online wallet provider. A malicious provider or a breach in server security may cause entrusted bitcoins to be stolen. An example of such a security breach occurred with Mt. Gox in 2011.[98]
The U.S. federal investigation was prompted by concerns of possible manipulation during futures settlement dates. The final settlement price of CME bitcoin futures is determined by prices on four exchanges, Bitstamp, Coinbase, itBit and Kraken. Following the first delivery date in January 2018, the CME requested extensive detailed trading information but several of the exchanges refused to provide it and later provided only limited data. The Commodity Futures Trading Commission then subpoenaed the data from the exchanges.[181][182]
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