In Ethereum all smart contracts are stored publicly on every node of the blockchain, which has costs.[57] Being a blockchain means it is secure by design and is an example of a distributed computing system with high Byzantine fault tolerance. The downside is that performance issues arise in that every node is calculating all the smart contracts in real time, resulting in lower speeds.[57] As of January 2016, the Ethereum protocol could process about 25 transactions per second.[57] In comparison, the Visa payment platform processes 45,000 payments per second leading some to question the scalability of Ethereum.[58] On 19 December 2016, Ethereum exceeded one million transactions in a single day for the first time.[59]
Izabella Kaminska, the editor of FT Alphaville, has pointed out that criminals are using Ethereum to run Ponzi schemes and other forms of investment fraud.[67] The article was based on a paper from the University of Cagliari, which placed the number of Ethereum smart contracts which facilitate Ponzi schemes at nearly 10% of 1384 smart contracts examined. However, it also estimated that only 0.05% of the transactions on the network were related to such contracts.[68]
تسمح تطبيقات بيتكوين والتي يُطلق عليها أحيانا اسم عميل بيتكوين للمُستخدمين بالتعامل مع شبكة بيتكوين. في شكله القاعدي يسمح التطبيق بتوليد وحفظ مفاتيح خاصة بالمُستخدم والاتصال بشبكة الند للند الخاص بالعُملة. تم إطلاق أول تطبيق بيتكوين سنة 2009 من طرف ساتوشي ناكاموتو مُؤسس عُملة بيتكوين كتطبيق مجاني ومفتوح المصدر. يُستخدم هذا التطبيق -والذي يُطلق عليه عادة اسم تطبيق ساتوشي- كمحفظة على الحواسيب الشخصية للقيام بعمليات دفع إلكترونية أو كخادوم لاستقبال تلك المدفوعات ولخدمات أخرى مُتعلقة بالدفع. أما تطبيق Bitcoin-Qt فيتم اعتباره كتطبيق مرجعي بحكم أنه يُمثل الآلية التي يعمل من خلالها بروتوكول بيتكوين ويُعتبر مثالا يُحتذى به لغيره من التطبيقات. لدى القيام بعمليات شراء باستخدام الهواتف الذكية فإنه عادة ما يتم استخدام تطبيقات بيتكوين تقوم بتوليد و/أو قراءة QR codes لتسهيل مهمة التحويل والدفع. كما تتوفر حاليا عدة تطبيقات تعمل كخواديم تقوم بتأكيد الإجراءات التي تتم على الشبكة وتقوم بإضافتها كتلة تحويلات.
Full clients verify transactions directly by downloading a full copy of the blockchain (over 150 GB As of January 2018).[95] They are the most secure and reliable way of using the network, as trust in external parties is not required. Full clients check the validity of mined blocks, preventing them from transacting on a chain that breaks or alters network rules.[7]:ch. 1 Because of its size and complexity, downloading and verifying the entire blockchain is not suitable for all computing devices.
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]
Bloomberg reported that the largest 17 crypto merchant-processing services handled $69 million in June 2018, down from $411 million in September 2017. Bitcoin is "not actually usable" for retail transactions because of high costs and the inability to process chargebacks, according to Nicholas Weaver, a researcher quoted by Bloomberg. High price volatility and transaction fees make paying for small retail purchases with bitcoin impractical, according to economist Kim Grauer. However, bitcoin continues to be used for large-item purchases on sites such as Overstock.com, and for cross-border payments to freelancers and other vendors.[141]
• غطاء تمويلى للمنظمات الإرهابية: قامت دار الإفتاء المصرية بتصريح أن عمليات الإستثمار والتداول في البيتكوين تُعتبر عمليات مُحرمة من قبل الدين والشرع حيث إنها تعمل كغطاء لتمويل المنظمات الإرهابية وعصابات المُخدرات. كما لعدم وجود هيئات حكومية وبنوك مركزية كان لذلك آثر رهيب على استخدام إستثمارات البيتكوين في عمليات غسيل الأموال والتى بالطبع نهانا الرسول عنها، بل ويُحاسب عليها القانون أيضاً.
As with other cryptocurrencies, the validity of each ether is provided by a blockchain, which is a continuously growing list of records, called blocks, which are linked and secured using cryptography.[30][31] By design, the blockchain is inherently resistant to modification of the data. It is an open, distributed ledger that records transactions between two parties efficiently and in a verifiable and permanent way.[32] Unlike Bitcoin, Ethereum operates using accounts and balances in a manner called state transitions. This does not rely upon unspent transaction outputs (UTXOs). State denotes the current balances of all accounts and extra data. State is not stored on the blockchain, it is stored in a separate Merkle Patricia tree. A cryptocurrency wallet stores the public and private "keys" or "addresses" which can be used to receive or spend ether. These can be generated through BIP 39 style mnemonics for a BIP 32 "HD Wallet". In Ethereum, this is unnecessary as it does not operate in a UTXO scheme. With the private key, it is possible to write in the blockchain, effectively making an ether transaction. 

Ethereum was initially described in a white paper by Vitalik Buterin,[10] a programmer involved with Bitcoin Magazine, in late 2013 with a goal of building decentralized applications.[11][12] Buterin had argued that Bitcoin needed a scripting language for application development. Failing to gain agreement, he proposed development of a new platform with a more general scripting language.[4]:88
Cameron and Tyler Winklevoss, the founders of the Gemini Trust Co. exchange, reported that they had cut their paper wallets into pieces and stored them in envelopes distributed to safe deposit boxes across the United States.[101] Through this system, the theft of one envelope would neither allow the thief to steal any bitcoins nor deprive the rightful owners of their access to them.[100]
The successful miner finding the new block is allowed by the rest of the network to reward themselves with newly created bitcoins and transaction fees.[88] As of 9 July 2016,[89] the reward amounted to 12.5 newly created bitcoins per block added to the blockchain, plus any transaction fees from payments processed by the block. To claim the reward, a special transaction called a coinbase is included with the processed payments.[7]:ch. 8 All bitcoins in existence have been created in such coinbase transactions. The bitcoin protocol specifies that the reward for adding a block will be halved every 210,000 blocks (approximately every four years). Eventually, the reward will decrease to zero, and the limit of 21 million bitcoins[f] will be reached c. 2140; the record keeping will then be rewarded solely by transaction fees.[90]
بيتكوين (بالإنجليزية: Bitcoin) هي عملة معماة ونظام دفع عالمي يمكن مقارنتها بالعملات الأخرى مثل الدولار أو اليورو، لكن مع عدة فوارق أساسية، من أبرزها أن هذه العملة هي عملة إلكترونية بشكل كامل تتداول عبر الإنترنت فقط من دون وجود فيزيائي لها.[1] وهي أول عملة رقمية لامركزية - فهي نظام يعمل دون مستودع مركزي أو مدير واحد، أي أنها تختلف عن العملات التقليدية بعدم وجود هيئة تنظيمية مركزية تقف خلفها. وتتم المعاملات بشبكة الند للند بين المستخدمين مباشرة دون وسيط من خلال استخدام التشفير. يتم التحقق من هذه المعاملات عن طريق عُقد الشبكة وتسجيلها في دفتر حسابات موزع وعام يسمى سلسلة الكتل. اخترع البيتكوين شخص غير معروف أو مجموعة من الناس عرف باسم ساتوشي ناكاموتو وأُصدِر كبرنامج مفتوح المصدر في عام 2009.
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.
• لا حرج من دفع عمولات تحويل العملات: كما هو شائع بالنسبة للبعض أن دفع العُمولات عبر شبكات الإنترنت مقابل خدمات تحويل أو شراء عُملات البيتكوين يُعد شكل من أشكال الربا غير المسموح بها. لكن إستناداُ إلى ما تم ذكره بحسب الفتوى رقم 259576 أن لا هناك أى حرج على دفع مثل هذه العمولات. حيث إنك تدفع مُقابل حصولك على خدمة معينة بما فيها خدمات تحويل وشراء عُملات البيتكوين الإفتراضية.
^ Jump up to: a b c d "Statement of Jennifer Shasky Calvery, Director Financial Crimes Enforcement Network United States Department of the Treasury Before the United States Senate Committee on Banking, Housing, and Urban Affairs Subcommittee on National Security and International Trade and Finance Subcommittee on Economic Policy" (PDF). fincen.gov. Financial Crimes Enforcement Network. 19 November 2013. Archived (PDF) from the original on 9 October 2016. Retrieved 1 June 2014.
Ethereum was proposed in late 2013 by Vitalik Buterin, a cryptocurrency researcher and programmer. Development was funded by an online crowdsale that took place between July and August 2014.[4] The system then went live on 30 July 2015, with 72 million coins "premined". This accounts for about 68 percent of the total circulating supply in 2019. [5]
حاليا لا يُملك مالكو عملات بيتكوين خيارات كثيرة لإنفاق أموالهم من خلالها، وهو ما يدفع ببعضهم إلى استبدالها مقابل العملات التقليدية. يتم ذلك عادة عبر منصات خاصة بذلك حيث يتم استبدال البيتكوينات مع مُستخدمين آخرين لها. يبدو أنه وفي حال ما إذا رغبت الحكومات في معرفة هويات أصحاب بعض الحسابات فما عليها سوى أن تقوم بتقنين عمليات التحويل بدل منعها، حيث سيصبح بالإمكان معرفة اسم صاحب كل حساب بُمجرد أن يرغب في استبدال ما بحوزته مقابل عملات تقليدية، وهو ما يُمثل نقطة انطلاق لتتبع الأموال المسروقة.
لضمان صحّة عمليات التحويل، يقوم نظام البيتكوين بالاحتفاظ بسجل حسابات تُسجل فيه جميع الإجراءات التي تتم على الشبكة يُطلق عليه اسم سلسلة الكُتل (بالإنجليزية: block chain). تتشارك جميع العُقد المتواجدة على شبكة البيتكوين هذا السجل عبر نظام يعتمد على بروتوكول بِتكُيِن. تحتوي سلسلة الكُتل على جميع الإجراءات التي تمت باستخدام بِتكُيِن، وهو ما يُمكن من معرفة الرصيد الذي يملكه كل عنوان على هذه الشبكة. يُطلق على هذا المفهوم وصف السلسلة للترابط المتواجد ما بين الكُتل، حيث تحتوي كل كُتلة على هاش الكُتلة التي تسبقها ويتواصل الأمر إلى غاية الوصول إلى الكُتلة الأولى التي يُطلق عليها اسم "كتلة التكوين" (بالإنجليزية: genesis block) . تكوين السلسلة بهذه الطريقة يجعل من مهمة تغيير أي كُتلة بعد مرور مُدة مُعينة على إنشائها في غاية الصعوبة، حيث أن تغيير أي كُتلة يتطلب تغيير كل الكُتل التي تليها بسبب الحاجة إلى إعادة حساب هاش كل كُتلة لتحديث قيمة هاش الكُتلة السابقة فيها. هذه الخاصية هي ما يجعل من مُشكل الإنفاق المُتكرر لنفس العُملات في غاية الصعوبة على بِتكُيِن، بل ويُمكن اعتبار سلسلة الكُتل العمود الفقري الذي لا يُمكن لعُملة بِتكُيِن الوقوف من دونه[10].
^ 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.

Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoin was invented by an unknown person or group of people using the name Satoshi Nakamoto[10] and was released as open-source software in 2009.[11] Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services.[12] Research produced by University of Cambridge estimates that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.[13]
As with other cryptocurrencies, the validity of each ether is provided by a blockchain, which is a continuously growing list of records, called blocks, which are linked and secured using cryptography.[30][31] By design, the blockchain is inherently resistant to modification of the data. It is an open, distributed ledger that records transactions between two parties efficiently and in a verifiable and permanent way.[32] Unlike Bitcoin, Ethereum operates using accounts and balances in a manner called state transitions. This does not rely upon unspent transaction outputs (UTXOs). State denotes the current balances of all accounts and extra data. State is not stored on the blockchain, it is stored in a separate Merkle Patricia tree. A cryptocurrency wallet stores the public and private "keys" or "addresses" which can be used to receive or spend ether. These can be generated through BIP 39 style mnemonics for a BIP 32 "HD Wallet". In Ethereum, this is unnecessary as it does not operate in a UTXO scheme. With the private key, it is possible to write in the blockchain, effectively making an ether transaction.
According to the Library of Congress, an "absolute ban" on trading or using cryptocurrencies applies in eight countries: Algeria, Bolivia, Egypt, Iraq, Morocco, Nepal, Pakistan, and the United Arab Emirates. An "implicit ban" applies in another 15 countries, which include Bahrain, Bangladesh, China, Colombia, the Dominican Republic, Indonesia, Iran, Kuwait, Lesotho, Lithuania, Macau, Oman, Qatar, Saudi Arabia and Taiwan.[169]
تُعتبر بيتكوين عُملة معمّاة (بالإنجليزية: cryptocurrency) ويُقصد بذلك أنها تعتمد بشكل أساسي على مبادئ التشفير في جميع جوانبها، كما أنها تُعتبر أيضا العُملة الأولى من نوعها والأكثر شهرة وانتشارًا لكن رغم ذلك ليست العُملة التشفيرية الوحيدة الموجودة على شبكة الإنترنت حاليًا. حيث يتوفر ما يزيد عن 60 عُملة تشفيرية مُختلفة[6] منها 6 عُملات يُمكن وصفها بالرئيسية [7] وذلك اعتمادًا على عدد المُستخدمين وبنية كل شبكة، إضافة إلى الأماكن التي يُمكن استبدال وشراء هذه العُملات التشفيرية مُقابل عُملات أخرى. جميع العُملات التشفيرية الحالية مبنية على مبدأ عمل عُملة بيتكوين نفسها باستثناء عُملة Ripple [8]، وبما أن عُملة بيتكوين مفتوحة المصدر فإنه من المُمكن استنساخها وإدخال بعض التعديلات عليها ومن ثم إطلاق عُملة جديدة.
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]
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]
^ 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.
Wallets and similar software technically handle all bitcoins as equivalent, establishing the basic level of fungibility. Researchers have pointed out that the history of each bitcoin is registered and publicly available in the blockchain ledger, and that some users may refuse to accept bitcoins coming from controversial transactions, which would harm bitcoin's fungibility.[123] For example, in 2012, Mt. Gox froze accounts of users who deposited bitcoins that were known to have just been stolen.[124]
As with other cryptocurrencies, the validity of each ether is provided by a blockchain, which is a continuously growing list of records, called blocks, which are linked and secured using cryptography.[30][31] By design, the blockchain is inherently resistant to modification of the data. It is an open, distributed ledger that records transactions between two parties efficiently and in a verifiable and permanent way.[32] Unlike Bitcoin, Ethereum operates using accounts and balances in a manner called state transitions. This does not rely upon unspent transaction outputs (UTXOs). State denotes the current balances of all accounts and extra data. State is not stored on the blockchain, it is stored in a separate Merkle Patricia tree. A cryptocurrency wallet stores the public and private "keys" or "addresses" which can be used to receive or spend ether. These can be generated through BIP 39 style mnemonics for a BIP 32 "HD Wallet". In Ethereum, this is unnecessary as it does not operate in a UTXO scheme. With the private key, it is possible to write in the blockchain, effectively making an ether transaction.
David Golumbia says that the ideas influencing bitcoin advocates emerge from right-wing extremist movements such as the Liberty Lobby and the John Birch Society and their anti-Central Bank rhetoric, or, more recently, Ron Paul and Tea Party-style libertarianism.[132] Steve Bannon, who owns a "good stake" in bitcoin, considers it to be "disruptive populism. It takes control back from central authorities. It's revolutionary."[133]
Ethereum is also being used as a platform to launch other cryptocurrencies. Because of the ERC20 token standard defined by the Ethereum Foundation, other developers can issue their own versions of this token and raise funds with an initial coin offering (ICO). In this fundraising strategy, the issuers of the token set an amount they want to raise, offer it in a crowdsale, and receive Ether in exchange. Billions of dollars have been raised by ICOs on the Ethereum platform in the last two years, and one of the most valuable cryptocurrencies in the world, EOS, is an ERC20 token.
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]
Ethereum's blockchain uses Merkle trees, for security reasons, to improve scalability, and to optimize transaction hashing.[61] As with any Merkle tree implementation, it allows for storage savings, set membership proofs (called "Merkle proofs"), and light client synchronization. The Ethereum network has at times faced congestion problems, for example, congestion occurred during late 2017 in relation to Cryptokitties.[62]

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]
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