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.
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 ..
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.
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]

In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address requires nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second. But the reverse, computing the private key of a given bitcoin address, is mathematically unfeasible. Users can tell others or make public a bitcoin address without compromising its corresponding private key. Moreover, the number of valid private keys is so vast that it is extremely unlikely someone will compute a key-pair that is already in use and has funds. The vast number of valid private keys makes it unfeasible that brute force could be used to compromise a private key. To be able to spend their bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key; the private key is never revealed.[7]:ch. 5

Despite the fallout from The DAO hack, Ethereum is moving forward and looking to a bright future. By providing a user-friendly platform that enables people to harness the power of blockchain technology, Ethereum is speeding up the decentralization of the world economy. Decentralized applications have the potential to profoundly disrupt hundreds of industries including finance, real estate, academia, insurance, healthcare and the public sector amongst many others.

• 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.
• 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.
In March 2017, various blockchain start-ups, research groups, and Fortune 500 companies announced the creation of the Enterprise Ethereum Alliance (EEA) with 30 founding members.[16] By May, the nonprofit organization had 116 enterprise members—including ConsenSys, CME Group, Cornell University's research group, Toyota Research Institute, Samsung SDS, Microsoft, Intel, J. P. Morgan, Cooley LLP, Merck KGaA, DTCC, Deloitte, Accenture, Banco Santander, BNY Mellon, ING, and National Bank of Canada.[17][18][19] By July 2017, there were over 150 members in the alliance, including recent additions MasterCard, Cisco Systems, Sberbank and Scotiabank.[20][21]
Ethereum-based customized software and networks, independent from the public Ethereum chain, are being tested by enterprise software companies.[48] Interested parties include Microsoft, IBM, JPMorgan Chase,[33][49] Deloitte,[50] R3,[51] Innovate UK (cross-border payments prototype).[52] Barclays, UBS and Credit Suisse are experimenting with Ethereum blockchain to automate Markets in Financial Instruments Directive (MiFID) II requirements.
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.
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]
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. 

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.

^ 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.


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].
In March 2013 the blockchain temporarily split into two independent chains with different rules due to a bug in version 0.8 of the bitcoin software. The two blockchains operated simultaneously for six hours, each with its own version of the transaction history from the moment of the split. Normal operation was restored when the majority of the network downgraded to version 0.7 of the bitcoin software, selecting the backward compatible version of the blockchain. As a result, this blockchain became the longest chain and could be accepted by all participants, regardless of their bitcoin software version.[38] During the split, the Mt. Gox exchange briefly halted bitcoin deposits and the price dropped by 23% to $37[38][39] before recovering to previous level of approximately $48 in the following hours.[40] 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 Service Businesses (MSBs), that are subject to registration or other legal obligations.[41][42][43] In April, exchanges BitInstant and Mt. Gox experienced processing delays due to insufficient capacity[44] resulting in the bitcoin price dropping from $266 to $76 before returning to $160 within six hours.[45] The bitcoin price rose to $259 on 10 April, but then crashed by 83% to $45 over the next three days.[36] On 15 May 2013, US authorities seized accounts associated with Mt. Gox after discovering it had not registered as a money transmitter with FinCEN in the US.[46][47] On 23 June 2013, the US Drug Enforcement Administration listed ₿11.02 as a seized asset in a United States Department of Justice seizure notice pursuant to 21 U.S.C. § 881.[48][better source needed] This marked the first time a government agency had seized bitcoin.[49] The FBI seized about ₿30,000[50] in October 2013 from the dark web website Silk Road during the arrest of Ross William Ulbricht.[51][52][53] These bitcoins were sold at blind auction by the United States Marshals Service to venture capital investor Tim Draper.[50] Bitcoin's price rose to $755 on 19 November and crashed by 50% to $378 the same day. On 30 November 2013 the price reached $1,163 before starting a long-term crash, declining by 87% to $152 in January 2015.[36] On 5 December 2013, the People's Bank of China prohibited Chinese financial institutions from using bitcoins.[54] After the announcement, the value of bitcoins dropped,[55] and Baidu no longer accepted bitcoins for certain services.[56] Buying real-world goods with any virtual currency had been illegal in China since at least 2009.[57]
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]
In Charles Stross' 2013 science fiction novel, Neptune's Brood, the universal interstellar payment system is known as "bitcoin" and operates using cryptography.[227] Stross later blogged that the reference was intentional, saying "I wrote Neptune's Brood in 2011. Bitcoin was obscure back then, and I figured had just enough name recognition to be a useful term for an interstellar currency: it'd clue people in that it was a networked digital currency."[228]
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]
To be accepted by the rest of the network, a new block must contain a proof-of-work (PoW).[75] The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash.[85][4] The PoW requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target.[7]:ch. 8 This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is the ascending natural numbers: 0, 1, 2, 3, ...[7]:ch. 8) before meeting the difficulty target.
EthereumPrice.org was developed by Ether0x in March 2016 to allow users to easily track the price of Ethereum both historically and in real-time. The platform has since evolved to include several fiat currencies (EUR, GBP, JPY and others) as well as price data for a number of Ethereum ERC20 tokens and other blockchain currencies. More recently, prediction data from Augur was also added to provide insight into the future price expectations of the Ether market. Price data is currently sourced from multiple exchanges with the weighted average price of these assets being calculated by CryptoCompare.com. For more details on the weighted average calculation, see our FAQ.
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]

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.
Ether is a token whose blockchain is generated by the Ethereum platform. Ether can be transferred between accounts and used to compensate participant mining nodes for computations performed.[3] Ethereum provides a decentralized virtual machine, the Ethereum Virtual Machine (EVM), which can execute scripts using an international network of public nodes.[4] The virtual machine's instruction set, in contrast to others like Bitcoin Script, is thought to be Turing-complete. "Gas", an internal transaction pricing mechanism, is used to mitigate spam and allocate resources on the network.[4]
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.
Both blockchains have the same features and are identical in every way up to a certain block where the hard-fork was implemented. This means that everything that happened on Ethereum up until the hard-fork is still valid on the Ethereum Classic Blockchain. From the block where the hard fork or change in code was executed onwards, the two blockchains act individually.

On 1 August 2017, a hard fork of bitcoin was created, known as Bitcoin Cash.[111] Bitcoin Cash has a larger block size limit and had an identical blockchain at the time of fork. On 24 October 2017 another hard fork, Bitcoin Gold, was created. Bitcoin Gold changes the proof-of-work algorithm used in mining, as the developers felt that mining had become too specialized.[112]
Augur is an open-source prediction & forecasting market platform that allows anyone to forecast events and get rewarded for predicting them correctly. Predictions on future real world events, like who will win the next US election, are carried out by trading virtual shares. If a person buys shares in a winning prediction, they receive monetary rewards.
^ Jump up to: a b c d e Joshua A. Kroll; Ian C. Davey; Edward W. Felten (11–12 June 2013). "The Economics of Bitcoin Mining, or Bitcoin in the Presence of Adversaries" (PDF). The Twelfth Workshop on the Economics of Information Security (WEIS 2013). Archived (PDF) from the original on 9 May 2016. Retrieved 26 April 2016. A transaction fee is like a tip or gratuity left for the miner.
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