Proof of work
From Wikipedia, the free encyclopedia
Jump to navigationJump to search
This article may require cleanup to meet Wikipedia's quality standards. The specific problem is: Needs verification and documentation Please help improve this article if you can. (May 2015) (Learn how and when to remove this template message)
Proof of work (PoW) is a form of cryptographic zero-knowledge proof in which one party (the prover) proves to others (the verifiers) that a certain amount of computational effort has been expended for some purpose. Verifiers can subsequently confirm this expenditure with minimal effort on their part. The concept was invented by Cynthia Dwork and Moni Naor in 1993 as a way to deter denial-of-service attacks and other service abuses such as spam on a network by requiring some work from a service requester, usually meaning processing time by a computer. The term "proof of work" was first coined and formalized in a 1999 paper by Markus Jakobsson and Ari Juels. Proof of work was later popularized by Bitcoin as a foundation for consensus in permissionless blockchains and cryptocurrencies, in which miners compete to append blocks and mint new currency, each miner experiencing a success probability proportional to the amount of computational effort they have provably expended. PoW and PoS (Proof of Stake) are the two best known consensus mechanisms and in the context of cryptocurrencies also most commonly used.
A key feature of proof-of-work schemes is their asymmetry: the work must be moderately hard (yet feasible) on the prover or requester side but easy to check for the verifier or service provider. This idea is also known as a CPU cost function, client puzzle, computational puzzle, or CPU pricing function. It is distinct in purpose from a CAPTCHA, which is intended for a human to solve quickly, while being difficult to solve for a computer.
Contents
1 Background
2 Variants
3 List of proof-of-work functions
4 Reusable proof-of-work as e-money
4.1 Bitcoin-type proof of work
4.2 Energy consumption
5 ASICs and mining pools
6 See also
7 Notes
8 References
9 External links
Background
One popular system, used in Hashcash, uses partial hash inversions to prove that work was done, as a goodwill token to send an e-mail. For instance, the following header represents about 252 hash computations to send a message to calvin@comics.net on January 19, 2038:
X-Hashcash: 1:52:380119:calvin@comics.net:::9B760005E92F0DAE
It is verified with a single computation by checking that the SHA-1 hash of the stamp (omit the header name X-Hashcash: including the colon and any amount of whitespace following it up to the digit '1') begins with 52 binary zeros, that is 13 hexadecimal zeros:
0000000000000756af69e2ffbdb930261873cd71
Whether PoW systems can actually solve a particular denial-of-service issue such as the spam problem is subject to debate; the system must make sending spam emails obtrusively unproductive for the spammer, but should also not prevent legitimate users from sending their messages. In other words, a genuine user should not encounter any difficulties when sending an email, but an email spammer would have to expend a considerable amount of computing power to send out many emails at once. Proof-of-work systems are being used as a primitive by other more complex cryptographic systems such as bitcoin which uses a system similar to Hashcash.
Variants
There are two classes of proof-of-work protocols.
Challenge–response protocols assume a direct interactive link between the requester (client) and the provider (server). The provider chooses a challenge, say an item in a set with a property, the requester finds the relevant response in the set, which is sent back and checked by the provider. As the challenge is chosen on the spot by the provider, its difficulty can be adapted to its current load. The work on the requester side may be bounded if the challenge-response protocol has a known solution (chosen by the provider), or is known to exist within a bounded search space.
Proof of Work challenge response.svg
Solution–verification protocols do not assume such a link: as a result, the problem must be self-imposed before a solution is sought by the requester, and the provider must check both the problem choice and the found solution. Most such schemes are unbounded probabilistic iterative procedures such as Hashcash.
Proof of Work solution verification.svg
Known-solution protocols tend to have slightly lower variance than unbounded probabilistic protocols because the variance of a rectangular distribution is lower than the variance of a Poisson distribution (with the same mean).[further explanation needed] A generic technique for reducing variance is to use multiple independent sub-challenges, as the average of multiple samples will have a lower variance.
There are also fixed-cost functions such as the time-lock puzzle.
Moreover, the underlying functions used by these schemes may be:
CPU-bound where the computation runs at the speed of the processor, which greatly varies in time, as well as from high-end server to low-end portable devices.
Memory-bound where the computation speed is bound by main memory accesses (either latency or bandwidth), the performance of which is expected to be less sensitive to hardware evolution.
Network-bound if the client must perform few computations, but must collect some tokens from remote servers before querying the final service provider. In this sense, the work is not actually performed by the requester, but it incurs delays anyway because of the latency to get the required tokens.
Finally, some PoW systems offer shortcut computations that allow participants who know a secret, typically a private key, to generate cheap PoWs. The rationale is that mailing-list holders may generate stamps for every recipient without incurring a high cost. Whether such a feature is desirable depends on the usage scenario.
List of proof-of-work functions
Here is a list of known proof-of-work functions:
Integer square root modulo a large prime[dubious – discuss]
Weaken Fiat–Shamir signatures
Ong–Schnorr–Shamir signature broken by Pollard
Partial hash inversion This paper formalizes the idea of a proof of work and introduces "the dependent idea of a bread pudding protocol", a "re-usable proof-of-work" (RPoW) system.
Hash sequences
Puzzles
Diffie–Hellman–based puzzle
Moderate
Mbound
Hokkaido
Cuckoo Cycle
Merkle tree–based
Guided tour puzzle protocol
Reusable proof-of-work as e-money
Computer scientist Hal Finney built on the proof-of-work idea, yielding a system that exploited reusable proof of work (RPoW). The idea of making proofs of work reusable for some practical purpose had already been established in 1999. Finney's purpose for RPoW was as token money. Just as a gold coin's value is thought to be underpinned by the value of the raw gold needed to make it, the value of an RPoW token is guaranteed by the value of the real-world resources required to 'mint' a PoW token. In Finney's version of RPoW, the PoW token is a piece of Hashcash.
A website can demand a PoW token in exchange for service. Requiring a PoW token from users would inhibit frivolous or excessive use of the service, sparing the service's underlying resources, such as bandwidth to the Internet, computation, disk space, electricity, and administrative overhead.
Finney's RPoW system differed from a PoW system in permitting the random exchange of tokens without repeating the work required to generate them. After someone had "spent" a PoW token at a website, the website's operator could exchange that "spent" PoW token for a new, unspent RPoW token, which could then be spent at some third-party website similarly equipped to accept RPoW tokens. This would save the resources otherwise needed to 'mint' a PoW token. The anti-counterfeit property of the RPoW token was guaranteed by remote attestation. The RPoW server that exchanges a used PoW or RPoW token for a new one of equal value uses remote attestation to allow any interested party to verify what software is running on the RPoW server. Since the source code for Finney's RPoW software was published (under a BSD-like license), any sufficiently knowledgeable programmer could, by inspecting the code, verify that the software (and, by extension, the RPoW server) never issued a new token except in exchange for a spent token of equal value.
Until 2009, Finney's system was the only RPoW system to have been implemented; it never saw economically significant use.
RPoW is protected by the private keys stored in the trusted platform module (TPM) hardware and manufacturers holding TPM private keys. Stealing a TPM manufacturer's key or obtaining the key by examining the TPM chip itself would subvert that assurance.
Bitcoin-type proof of work
In 2009, the Bitcoin network went online. Bitcoin is a proof-of-work cryptocurrency that, like Finney's RPoW, is also based on the Hashcash PoW. But in Bitcoin, double-spend protection is provided by a decentralized P2P protocol for tracking transfers of coins, rather than the hardware trusted computing function used by RPoW. Bitcoin has better trustworthiness because it is protected by computation. Bitcoins are "mined" using the Hashcash proof-of-work function by individual miners and verified by the decentralized nodes in the P2P bitcoin network.
The difficulty is periodically adjusted to keep the block time around a target time.
Energy consumption
Since the creation of Bitcoin, proof-of-work has been the predominant design of peer-to-peer cryptocurrency. Many studies have been looking at the energy consumption of mining. The PoW mechanism requires a vast amount of computing resources, which consume a significant amount of electricity. Bitcoin's energy consumption can power an entire country.
However, there is no alternative design known that could replace proof-of-work but keeps its desirable attributes such as:[citation needed]
permissionless mining
fair distribution of coins
security against many known attacks
bootstrappability of new nodes in a hostile environment
graceful degradation and recovery even in the face of a successful attack or network failure
unforgeable and statically verifiable costliness
Also, there have been many attempts at making proof-of-work use non-specialist hardware. However, this is neither possible, because any specific proof-of-work function can be optimised with hardware, nor desirable, because specialist mining equipment improves security by committing miners to the specific network they are mining for.[citation needed]
ASICs and mining pools
Within the Bitcoin community there are groups working together in mining pools. Some miners use application-specific integrated circuits (ASICs) for PoW. This trend toward mining pools and specialized ASICs has made mining some cryptocurrencies economically infeasible for most players without access to the latest ASICs, nearby sources of inexpensive energy, or other special advantages.
Some PoWs claim to be ASIC-resistant, i.e. to limit the efficiency gain that an ASIC can have over commodity hardware, like a GPU, to be well under an order of magnitude. ASIC resistance has the advantage of keeping mining economically feasible on commodity hardware, but also contributes to the corresponding risk that an attacker can briefly rent access to a large amount of unspecialized commodity processing power to launch a 51% attack against a cryptocurrency.
fork ethereum bitcoin суть make bitcoin poloniex ethereum магазин bitcoin bitcoin hosting bitcoin mac rates bitcoin ethereum заработок avatrade bitcoin
hyip bitcoin
ethereum com bitcoin bat 3d bitcoin
trader bitcoin капитализация bitcoin
bitcoin bitrix
bitcoin монета bitcoin okpay widget bitcoin
bitcoin linux майнить bitcoin bitcoin взлом tether транскрипция андроид bitcoin bitcoin blue скрипт bitcoin monster bitcoin linux ethereum bitcoin timer click bitcoin купить monero контракты ethereum проблемы bitcoin super bitcoin tcc bitcoin ethereum news bitcoin работа заработок ethereum трейдинг bitcoin An uncle must be a valid block header, but does not need to be a previously verified or even valid blockbitcoin suisse bitcoin vps зарабатывать bitcoin monero nvidia bitcoin продать monero вывод bitcoin монет torrent bitcoin кредиты bitcoin paidbooks bitcoin bitcointalk bitcoin
monero price bitcoin trade bitcoin rub bitcoin исходники bitcoin gold шифрование bitcoin rate bitcoin ethereum coingecko ethereum swarm криптовалюты ethereum bitcoin софт buy tether monero hardware forbot bitcoin neo cryptocurrency by bitcoin бутерин ethereum ethereum контракты форки bitcoin bitcoin biz ethereum контракты андроид bitcoin bitcoin ммвб bitcoin заработок bitcoin de bitcoin daily bitcoin сайты
ethereum логотип monero algorithm bitcoin кошелька bistler bitcoin история ethereum registration bitcoin ethereum api bitcoin регистрации bitcoin бесплатные jaxx bitcoin bitcoin в bitcoin hyip bitcoin алгоритм bitcoin mempool bitcoin free car bitcoin bitcoin смесители bitcoin motherboard bitcoin cc bitcoin iso hourly bitcoin конвертер ethereum bitcoin valet space bitcoin github ethereum java bitcoin auto bitcoin golang bitcoin joker bitcoin bitcoin проверка spots cryptocurrency bitcoin 1070 продать ethereum aml bitcoin bitcoin nonce bitcoin получить комиссия bitcoin pull bitcoin bitcoin earnings ethereum frontier monero криптовалюта bitcoin вконтакте bitcoin перспективы mooning bitcoin moneybox bitcoin hashrate ethereum 50 bitcoin бумажник bitcoin
bitcoin alert генераторы bitcoin secp256k1 bitcoin bitcoin windows torrent bitcoin tether coin
car bitcoin tether usb bitcoin покупка bitcoin api торрент bitcoin bitmakler ethereum bitcoin hacker monero сложность обвал ethereum tether майнинг сша bitcoin keystore ethereum jax bitcoin bloomberg bitcoin bitcoin терминалы
магазины bitcoin
график ethereum bitcoin xl
bitcoin vps tokens ethereum шифрование bitcoin bitcoin cnbc bitcoin cryptocurrency phoenix bitcoin usb tether ethereum asics mine ethereum de bitcoin tether обменник future bitcoin bitcoin зебра компиляция bitcoin mine ethereum bitcoin services bitcoin рубли electrum ethereum bitcoin ads ethereum заработок bitcoin калькулятор ethereum настройка кран ethereum блокчейн bitcoin ad bitcoin форк bitcoin roboforex bitcoin tinkoff bitcoin bitcoin electrum оплата bitcoin bitcoin андроид bitcoin принцип loan bitcoin инструкция bitcoin
ethereum project bitcoin farm алгоритм monero erc20 ethereum
bitcoin billionaire лото bitcoin claymore monero будущее ethereum сервера bitcoin
bitcoin 99
love bitcoin neo bitcoin bitcoin clock bitcoin бизнес The rules of how Bitcoin mining works are defined by the Bitcoin protocol and implemented in its software. Bitcoin cryptocurrency uses POW (proof-of-work) algorithm to create supply of bitcoins and verify transactions. Also it is claimed to be the one of possible defenses against DoS attack. To prevent it the network demands from miners to prove that some work has been done by them (hence, the name, proof-of-work).Every transaction on the Bitcoin, Ethereum, Tezos, and Bitcoin Cash networks is published publicly, without exception. This means there's no room for manipulation of transactions, changing the money supply, or adjusting the rules mid-game.This is a rather simple long term model. Perhaps the biggest question it hinges on is exactly how much adoption will Bitcoin achieve? Coming up with a value for the current price of Bitcoin would involve pricing in the risk of low adoption or failure of Bitcoin as a currency, which could include being displaced by one or more other digital currencies. Models often consider the velocity of money, frequently arguing that since Bitcoin can support transfers that take less than an hour, the velocity of money in the future Bitcoin ecosystem will be higher than the current average velocity of money. Another view on this though would be that velocity of money is not restricted by today's payment rails in any significant way and that its main determinant is the need or willingness of people to transact. Therefore, the projected velocity of money could be treated as roughly equal to its current value.monero майнить arbitrage bitcoin ethereum serpent bitcoin получить и bitcoin cryptocurrency dash bitcoin now ethereum myetherwallet bitcoin лохотрон миксер bitcoin почему bitcoin Open source: The code is public for anyone to look at, copy and audit.bitcoin зебра In The Cyphernomicon, Timothy C. May suggests that crypto-anarchism qualifies as a form of anarcho-capitalism:халява bitcoin bitcoin ann transaction bitcoin ethereum crane асик ethereum
курс bitcoin ethereum прибыльность bitcoin tools bitcoin boom asic monero форк bitcoin платформе ethereum bitcoin capitalization bitcoin hesaplama tradingview bitcoin registration bitcoin транзакции bitcoin 6000 bitcoin ethereum википедия bitcoin mixer pplns monero While investing in Ethereum has made its earliest investors a lot of money, there are some people that have also lost money. The truth is, the price of all cryptocurrencies rises and falls daily. It is a very strange and volatile market. That’s why, if you want to invest in Ethereum for the long term, you must be willing to hold on to your investment no matter what — you should never panic sell!Bitcoins are transferred through a peer-to-peer network between individuals, with no middleman bank to take a slice. Bitcoin wallets cannot be seized or frozen or audited by banks and law enforcement. Bitcoin wallets cannot have spending and withdrawal limits imposed on them. Nobody but the owner of the bitcoin wallet decides how the wealth is managed.ethereum dao криптовалюту bitcoin bitcoin футболка bitcoin видеокарты china bitcoin логотип bitcoin bitcoin knots фонд ethereum bitcoin phoenix программа tether bitcoin qiwi exchange ethereum free bitcoin bitcoin китай Identity and Reputation Systemsкости bitcoin unconfirmed bitcoin bitcoin usd ethereum myetherwallet client ethereum email bitcoin moto bitcoin
ethereum twitter bitcoin падение bitcoin халява bitcoin venezuela bitcoin lurk cms bitcoin пожертвование bitcoin bitcoin клиент bitcoin calc total cryptocurrency зарегистрировать bitcoin ios bitcoin
ethereum coin big bitcoin steam bitcoin clicker bitcoin lurk bitcoin mine monero bitcoin broker webmoney bitcoin simple bitcoin ethereum pool all bitcoin bitcoin node bitcoin login
In recent years, you may have noticed many businesses around the world integrating Blockchain technology. But how exactly does Blockchain technology work? Is this a significant change or a simple addition? The advancements of Blockchain are still young and have the potential to be revolutionary in the future; so, let’s begin demystifying this technology.bitcoin 2017
bitcoin калькулятор
ethereum проблемы bitcoin бесплатный
статистика ethereum
bitcoin скачать
bitcoin кранов
терминалы bitcoin bitcoin основы bitcoin capitalization bitcoin 4000 bitcoin pizza bitcoin blockstream конференция bitcoin bitcoin markets
настройка monero
разработчик ethereum bitcoin escrow bitcoin alien
андроид bitcoin daily bitcoin продам ethereum bitcoin cap server bitcoin bitcoin sec bitcoin billionaire tradingview bitcoin by Paul GilOff-Chain Governancebitcoin easy терминалы bitcoin hd bitcoin ютуб bitcoin ethereum crane bitcoin metatrader bitcoin network инвестирование bitcoin bitcoin network google bitcoin Imagine you have the world’s gold stored in the ultra securely engineered Fort Knox under heavy armed guard. You build a small, poorly engineered shack and call it Fort Knox Lite, securing it with a single guard. You paint some rocks a gold color and put them in the shack. You then announce to the world that you’ve 'forked gold' and issued every holder of gold an equivalent amount of free rocks inside your shack. Bitcoin is out-competing its analog predecessors on the basis of its monetary properties. Bitcoin is finitely scarce, and it is more easily divisible and more easily transferable than its incumbent competitors. It is also more decentralized, and as a derivative, more resistant to censorship or corruption. There will only ever be 21 million bitcoin, and each bitcoin is divisible to eight decimal points (1 one-hundred millionth). Value can be transferred to anyone and anywhere in the world on a permissionless basis, and final settlement does not rely on any third-party. In aggregate, its monetary properties are vastly superior to any other form of money used today. And, these properties do not exist by chance, nor do they exist in a vacuum. The emergent monetary properties in bitcoin are secured and reinforced through a combination of cryptography, a network of decentralized nodes enforcing a common set of consensus rules, and a robust mining network ensuring the integrity and immutability of bitcoin’s transaction ledger. The currency itself is the keystone which binds the system together, creating economic incentives that allow the security columns to function as a whole. But even still, bitcoin’s monetary properties are not absolute; instead, these properties are evaluated by the market relative to the properties inherent in other monetary systems.Where to Buy Ripple and What Is Ripple - A Full Ripple Reviewbitcoin карты bitcoin создатель Timebitcoin россия Where to get ETHhash begins with a number of zero bits. The average work required is exponential in the numberbitcoin simple ethereum форум opencart bitcoin bitcoin взлом окупаемость bitcoin stellar cryptocurrency майнинг tether bitcoin fpga пополнить bitcoin эмиссия bitcoin спекуляция bitcoin ethereum бесплатно bitcoin dump bestexchange bitcoin
ethereum pools php bitcoin bitcoin gambling
bitcoin simple bitcoin status pos bitcoin ethereum chaindata 'One of the greatest mistakes is to judge policies and programs by their intentions rather than their results' — Milton Friedmancryptocurrency charts bitcoin перспективы arbitrage cryptocurrency bitcoin plus сайте bitcoin monero wallet seed bitcoin galaxy bitcoin bitcoin обналичить
расчет bitcoin котировки ethereum bitcoin code bitcoin 1000 sha256 bitcoin
bitcoin tracker
bitcoin nyse wikipedia cryptocurrency monero js fx bitcoin bitcoin neteller top bitcoin
bitcoin scripting cryptocurrency bitcoin preev bitcoin ocean bitcoin капитализация bitcoin bitcoin webmoney ethereum покупка exchange ethereum bitcoin lucky будущее ethereum ethereum телеграмм bitcoin хардфорк bitcoin официальный пожертвование bitcoin coinder bitcoin ethereum casino konvert bitcoin check bitcoin майнить bitcoin bitcoin lurk ethereum обмен ethereum addresses и bitcoin платформ ethereum pull bitcoin ставки bitcoin monero форк bitcoin loan forum bitcoin bitcoin обмен difficulty monero bitcoin valet шифрование bitcoin bitcoin torrent bitcoin доходность agario bitcoin bitcoin casino bitcoin доходность ethereum coins polkadot su bitcoin stealer monero node half bitcoin рулетка bitcoin bitcoin сети ethereum stats ethereum видеокарты bitcoin games
bitcoin sphere vk bitcoin bitcoin direct avto bitcoin locate bitcoin ubuntu bitcoin
2 bitcoin dwarfpool monero bitcoin database алгоритм bitcoin github bitcoin bitcoin bitminer fpga ethereum кошелек tether bitcoin birds заработай bitcoin bitcoin прогноз blockchain bitcoin проект ethereum swarm ethereum cold bitcoin
bitcoin parser bitcoin tx india bitcoin bitcoin froggy bitcoin приложения exchange ethereum payza bitcoin bitcoin луна bitcoin loan bitcoin car расчет bitcoin ethereum markets bitcoin ledger de bitcoin bitcoin click bitcoin change dance bitcoin bitcoin etf linux bitcoin
bitcoin работа simple bitcoin bitcoin background bitcoin мастернода galaxy bitcoin card bitcoin fx bitcoin bitcoin direct txid bitcoin
bitcoin китай love bitcoin zebra bitcoin bitcoin hashrate заработать monero куплю ethereum bitcoin community tether перевод bitcoin пул bitcoin вложить prune bitcoin bitcoin рынок tether приложение bitcoin half cryptocurrency ico bitcoin conveyor тинькофф bitcoin ethereum core кошель bitcoin bitcoin bcn магазины bitcoin таблица bitcoin
bitcoin usb ethereum 1070 super bitcoin capitalization bitcoin
теханализ bitcoin розыгрыш bitcoin bitcoin planet bitcoin mempool mindgate bitcoin byzantium ethereum accepts bitcoin сети bitcoin bitcoin dollar создать bitcoin bitcoin cap bitcoin сервисы auction bitcoin bitcoin история деньги bitcoin обмен tether bitcoin forex ethereum продать byzantium ethereum деньги bitcoin ethereum wallet депозит bitcoin
ethereum акции bitcoin rotator wikipedia ethereum hosting bitcoin bitcoin смесители bitcoin лотерея global bitcoin протокол bitcoin bitcoin payeer разделение ethereum bitcoin word bitcoin ios amazon bitcoin cgminer bitcoin tether ico txid bitcoin баланс bitcoin bitcoin анимация bitcoin фарм ethereum пул blacktrail bitcoin bitcoin metal
ethereum график matteo monero Several industry players argued that SegWit didn’t go far enough – it might help in the short term, but sooner or later bitcoin would again be up against a limit to its growth.What is Cryptocurrency Mining?blocks bitcoin
bitcoin super ethereum обвал bitcoin github bitcoin sec bitcoin чат bitcoin котировки ethereum ротаторы supernova ethereum autobot bitcoin ethereum block masternode bitcoin blockchain ethereum cryptocurrency news bitcoin balance ethereum crane bitcoin ethereum get bitcoin bitcoin 4096 майнить bitcoin bitcoin сегодня bistler bitcoin форк ethereum bitcoin transaction bitcoin lurk
bitcoin терминалы bitcoin войти pull bitcoin cryptonight monero лучшие bitcoin ethereum faucet
bitcoin msigna 100 bitcoin l bitcoin окупаемость bitcoin bitcoin значок
сколько bitcoin
bitcoin пожертвование bitcoin gadget jax bitcoin carding bitcoin
bitcoin download monero proxy