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]
Bitcoin prices were negatively affected by several hacks or thefts from cryptocurrency exchanges, including thefts from Coincheck in January 2018, Coinrail and Bithumb in June, and Bancor in July. For the first six months of 2018, $761 million worth of cryptocurrencies was reported stolen from exchanges.[64] Bitcoin's price was affected even though other cryptocurrencies were stolen at Coinrail and Bancor as investors worried about the security of cryptocurrency exchanges.[65][66][67]
The Ethereum Virtual Machine (EVM) is the runtime environment for smart contracts in Ethereum. It is a 256-bit register stack, designed to run the same code exactly as intended. It is the fundamental consensus mechanism for Ethereum. The formal definition of the EVM is specified in the Ethereum Yellow Paper.[34][37] On February 1, 2018, there were 27,500 nodes in the main Ethereum network.[38] Ethereum Virtual Machines have been implemented in C++, Go, Haskell, Java, JavaScript, Python, Ruby, Rust, Elixir, Erlang, and soon, WebAssembly (currently under development).
Bitcoin is a digital asset designed to work in peer-to-peer transactions as a currency.[4][135] Bitcoins have three qualities useful in a currency, according to The Economist in January 2015: they are "hard to earn, limited in supply and easy to verify."[136] Per some researchers, as of 2015, bitcoin functions more as a payment system than as a currency.[32]
Bitcoin (BTC) is known as the first open-source, peer-to-peer, digital cryptocurrency that was developed and released by a group of unknown independent programmers named Satoshi Nakamoto in 2008. Cryptocoin doesn’t have any centralized server used for its issuing, transactions and storing, as it uses a distributed network public database technology named blockchain, which requires an electronic signature and is supported by a proof-of-work protocol to provide the security and legitimacy of money transactions. The issuing of Bitcoin is done by users with mining capabilities and is limited to 21 million coins. Currently, Bitcoin’s market cap surpasses $138 billion and this is the most popular kind of digital currency. Buying and selling cryptocurrency is available through special Bitcoin exchange platforms or ATMs.
Smart contract is just a phrase used to describe a computer code that can facilitate the exchange of money, content, property, shares, or anything of value. When running on the blockchain a smart contract becomes like a self-operating computer program that automatically executes when specific conditions are met. Because smart contracts run on the blockchain, they run exactly as programmed without any possibility of censorship, downtime, fraud or third-party interference.
Blockchain analysts estimate that Nakamoto had mined about one million bitcoins[28] 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.[29][30] Andresen then sought to decentralize control. This left opportunity for controversy to develop over the future development path of bitcoin, in contrast to the perceived authority of Nakamoto's contributions.[31][30]
• إستثمار البيتكوين يُعتبر مُقامرة: طبقاُ إلى رأى أستاذ الفقه د/جلوى الجميعة أن البيتكوين ما هى إلا عُملات يتم إستخدامها للمقامرة. حيث أن عملة البيتكوين هى عملة إفتراضية إلكترونية ليس لها أى سند أو غطاء من الذهب أو الفضة وبالتالى هى في حُكم الدين تُعتبر سلعة مجهولة المصدر. وبالتالى تتيح حدوث الكثير من عمليات النصب والإحتيال نتيجة لعدم وجود أى جهات رقابية تراقب سير عملية التداول والإستثمار الخاصة بالعملات. كما نهى الرسول تماماً عن مثل هذا النوع من الإستثمار عندما قال ”  صلى الله عليه وسلم عن شراء ما في بطون الانعام حتى تضع، وعما في ضروعها إلا بكيل أو وزن، ونهى عن شراء العبد وهو آبق، وعن شراء المغانم حتى تقسم، وعن شراء الصدقات حتى تقبض، وعن ضربة الغائص”.
Ethereum was announced at the North American Bitcoin Conference in Miami, in January, 2014.[9] During the same time as the conference, a group of people rented a house in Miami Gavin Wood, Charles Hoskinson, and Anthony Di Iorio, a Torontonian who financed the project.[9] Di Iorio invited friend Joseph Lubin, who invited reporter Morgen Peck, to bear witness.[9] Six months later the founders met again in a house in Zug Switzerland, where Buterin told the founders that the project would proceed as a non-profit. Hoskinson left the project at that time.[9]
The domain name "bitcoin.org" was registered on 18 August 2008.[17] On 31 October 2008, a link to a paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System[4] was posted to a cryptography mailing list.[18] Nakamoto implemented the bitcoin software as open-source code and released it in January 2009.[19][20][11] Nakamoto's identity remains unknown.[10]

The rapid price increase of Ethereum has not only attracted investors but developers too. Ethereum has tens of thousands of developers in its open source community, each contributing to the many layers of the “Ethereum stack”. This includes code contributions to the core Ethereum clients, second layer scaling tech and the “decentralized applications” (dApps) that are built on top of the platform. The appeal of Ethereum to developers is unique in that it was the first platform to allow anyone in the world to write and deploy code that would run without the risk of censorship. The community of developers which have formed around these core principles have led to the creation of technologies that could not have existed without the inception of Ethereum, many of which were never predicted. Some of the major use-cases of Ethereum so far have been:


تتمتع عملة البيتكوين بقدر عالٍ من السرية. مبدئيا الأمر صحيح، حيث أن كل ما تحتاجه لإرسال بعض البيتكوينات لشخص آخر هو عنوانه فقط. لكن بحكم أنه يتم تسجيل كل عملية تحويل في سجل بيتكوين فإنه بالرغم من عدم معرفتك لهوية مالك أي عُنوان إلا أنه بمقدورك أن تعرف كم عدد البيتكوينات التي في حوزته وما هي العناوين التي أرسلت بيتكوينات إليه. إن قام أحدهم بالإعلان صراحة عن امتلاكه لعناوين بيتكوين مُعينة فإنه سيُصبح بإمكانك معرفة ما هي العناوين التي قامت بإرسال بيتكوينات إليه وما هي العناوين التي أرسل إليها بيتكوينات. الكشف عن عنوان البيتكوين الخاص بك ليس مُستبعدا، حيث أنك ستحتاج إلى إعطائه لغيرك في حال ما إذا احتجت أن يرسلوا لك بعض المال إليه. يُنصح باستخدام عناوين مُختلفة لعمليات تحويل مُختلفة للحفاظ على مُستوى مُعين من المجهولية، رغم ذلك هناك الكثيرون ممن لا يقومون بذلك. من الناحية التقنية يبقى تتبع مصدر بعض العمليات المشبوهة على شبكة بيتكوين مُمكنا، حيث يكفي تتبع عمليات التحويل إلى غاية وصولها إلى عنوان معروفة هوية صاحبه، وحينها يكفي القيام بعمليات تحقيق عكسية إلى غاية الوصول إلى صاحب الحساب المشبوه. صحيح بأن كم البيانات المُتعلقة بجميع عمليات التحويل ضخم، إلا أن قوة الحواسيب في تزايد مُستمر وإمكانية تتبع هذه العمليات واردة جدا، بل ويُمكن الجزم بأنه تتبع عمليات سرقة البيتكوينات أسهل بكثير من تتبع سرقة الأموال على هيئتها الورقية.
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.
Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. To achieve independent verification of the chain of ownership each network node stores its own copy of the blockchain.[76] About every 10 minutes, a new group of accepted transactions, called a block, is created, added to the blockchain, and quickly published to all nodes, without requiring central oversight. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending. A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.[7]:ch. 5
Ethereum can also be used to build Decentralized Autonomous Organizations (DAO). A DAO is fully autonomous, decentralized organization with no single leader. DAO’s are run by programming code, on a collection of smart contracts written on the Ethereum blockchain. The code is designed to replace the rules and structure of a traditional organization, eliminating the need for people and centralized control. A DAO is owned by everyone who purchases tokens, but instead of each token equating to equity shares & ownership, tokens act as contributions that give people voting rights.
Using Ethereum’s “Turing complete” smart contract language, Solidity, developers are able to deploy a set of instructions to the blockchain that operate indefinitely with a high degree of finality and fraud-resistance. With the first block being mined in July 2015, Ethereum has since become the largest smart contract platform of its kind, and the second largest blockchain of all time as measured by market capitalization.
• إستثمار البيتكوين يُعتبر مُقامرة: طبقاُ إلى رأى أستاذ الفقه د/جلوى الجميعة أن البيتكوين ما هى إلا عُملات يتم إستخدامها للمقامرة. حيث أن عملة البيتكوين هى عملة إفتراضية إلكترونية ليس لها أى سند أو غطاء من الذهب أو الفضة وبالتالى هى في حُكم الدين تُعتبر سلعة مجهولة المصدر. وبالتالى تتيح حدوث الكثير من عمليات النصب والإحتيال نتيجة لعدم وجود أى جهات رقابية تراقب سير عملية التداول والإستثمار الخاصة بالعملات. كما نهى الرسول تماماً عن مثل هذا النوع من الإستثمار عندما قال ”  صلى الله عليه وسلم عن شراء ما في بطون الانعام حتى تضع، وعما في ضروعها إلا بكيل أو وزن، ونهى عن شراء العبد وهو آبق، وعن شراء المغانم حتى تقسم، وعن شراء الصدقات حتى تقبض، وعن ضربة الغائص”.
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]
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