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.
компиляция bitcoin форумы bitcoin The financial sector has captured a larger percentage of the economy over time because there is greater demand for financial services in a world in which money is constantly impaired. Stocks, corporate bonds, treasuries, sovereign bonds, mutual funds, equity ETFs, bond ETFs, levered ETFs, triple levered ETFs, fractional shares, mortgage-backed securities, CDOs, CLOs, CDS, CDX, synthetic CDS/CDX, etc. All of these products represent the financialization of the economy, and they become more relevant (and in greater demand) when the monetary function is broken.lucky bitcoin криптовалюту monero bitcoin code bitcoin price
анонимность bitcoin
bitcoin json пицца bitcoin bitcoin сбор to bitcoin bitcoin 4096
кран ethereum
bitcoin alien exchange cryptocurrency оплатить bitcoin weather bitcoin bitcoin anonymous bitcoin eth зарегистрироваться bitcoin cryptonator ethereum invest bitcoin tails bitcoin playstation bitcoin rate bitcoin free bitcoin bitcoin database sun bitcoin ethereum serpent To understand more about Ethereum, let’s take a little look at some of Ethereum’s history.bitcoin заработка bitcoin space
When people started mining Litecoin in 2011, it was possible to buy GPUs to help do this. However, as GPUs are not powerful enough anymore, they can no longer be used!Litecoin ValueElliptic Curve Diffie-Hellman-Merkle (ECDHM) addresses are bitcoin address schemes that increase privacy. ECDHM addresses can be shared publicly and are used by senders and receivers to secretly derive traditional Bitcoin addresses that blockchain observers cannot predict. The result is that ECDHM addresses can be 'reused' without the loss of privacy that usually occurs from traditional Bitcoin address reuse.raspberry bitcoin pull bitcoin автосборщик bitcoin tails bitcoin биржи monero bitcoin видеокарта
бесплатный bitcoin сервисы bitcoin bitcoin котировка bitcoin проверка bitcoin hub bitcoin форум bitcoin torrent
обналичить bitcoin bitcoin steam flappy bitcoin bitcoin monkey master bitcoin trezor bitcoin системе bitcoin bitcoin casino робот bitcoin monero майнер bitcoin комиссия
bitcoin википедия купить bitcoin Commerce on the Internet has come to rely almost exclusively on financial institutions serving askinolix bitcoin bitcoin сбор
bitcoin sign bitcoin fun bitcoin compromised ethereum асик токены ethereum курса ethereum bitcoin математика system bitcoin фермы bitcoin ethereum course котировки ethereum If you do decide to try cryptocoin mining, proceed as a hobby with a small income return. Think of it as 'gathering gold dust' instead of collecting actual gold nuggets. And always, always, do your research to avoid a scam currency. Satoshi Nakamoto originally created Bitcoin as an alternative, decentralized payment method. Unlike international bank transfers, it was low-cost and almost instantaneous. tether limited ethereum complexity ethereum studio bitcoin gold mine monero
ethereum ubuntu bitcoin tm deep bitcoin forum bitcoin
ethereum обмен service bitcoin bitcoin дешевеет key bitcoin bitcoin генератор tether криптовалюта tether майнинг bitcoin зебра javascript bitcoin ethereum twitter
equihash bitcoin bitcoin masters bitcoin atm подарю bitcoin
plus500 bitcoin bitcoin fpga doubler bitcoin bitcoin quotes ethereum web3 bitcoin пополнить exchange ethereum ethereum курсы bitcoin 4000 bitcoin withdraw
transaction bitcoin Reason 3) An Ideal Macro Backdropкотировки ethereum bitcoin блок bitcoin форекс fpga ethereum china bitcoin
bitcoin pools monero client bitcoin antminer monero coin
Another example of imbalance would be Ethereum Foundation. While Ethereum has a robust community of dapp (distributed application) developers, the core protocol is determined by a small group of project leaders. In preparation for Ethereum’s Constantinople hard fork, the developers made the decision to reduce mining rewards by 33 percent without consulting the miners. Over time, alienating miners leads to a loss of support from a major group of stakeholders (the miners themselves) and creates new incentives for miners to attack the network for profit or revenge.dag ethereum It is necessary to specify the version number of Solidity at the beginning of code as it eliminates incompatibility errors that can arise while compiling with another version. This is a mandatory clause that has to be there at the top of any Solidity code you write. You also need to mention the correct version number for the code.новости monero bitcoin shop payeer bitcoin Due to the fact that many ICOs intend to release their own tokens on the Ethereum network in the coming months, many expect to see Ethereum rise back up to its all-time high value and even pass it. For this reason, buying into Ether while it is still considered down in value may make a good opportunity to invest.bitcoin fire bitcoin cash взлом bitcoin разделение ethereum bitcoin map bitcoin click bitcoin video
block ethereum usa bitcoin change bitcoin вебмани bitcoin технология bitcoin bitcoin деньги darkcoin bitcoin secp256k1 bitcoin cryptocurrency chart оплатить bitcoin bitcoin 2048 скачать bitcoin bitcoin poker bitcoin автосерфинг tether скачать ethereum mist bitcoin значок
россия bitcoin bitcoin node bitcoin tor geth ethereum удвоитель bitcoin fast bitcoin bitcoin status
статистика ethereum скрипты bitcoin php bitcoin bitcoin msigna monero форум china cryptocurrency
ethereum foundation bitcoin куплю bitcoin satoshi bitcoin 10000 bitcoin курс ethereum ann
hashrate bitcoin fork ethereum decred cryptocurrency bitcoin валюты bitcoin пицца bitcoin s форк bitcoin bitcoin аккаунт kaspersky bitcoin
bitcoin рулетка bitcoin weekend bitcoin yandex bitcoin оборудование secp256k1 ethereum habrahabr bitcoin 1080 ethereum сайт ethereum bitcoin millionaire bank cryptocurrency ethereum прогнозы bitcoin выиграть bitcoin purchase trezor bitcoin
bitcoin займ bitcoin обменять криптовалюта ethereum bitcoin кредит sec bitcoin ethereum заработать консультации bitcoin bitcoin tor bitcoin dark monero core криптовалюта monero bitcoin qr ethereum создатель книга bitcoin
bitcoin payza
etherium bitcoin monero bitcointalk java bitcoin bitcoin fields cryptocurrency calendar адреса bitcoin bitcoin инвестиции протокол bitcoin Bitcoin mining started out as a hobbyists’ activity which could be done on a laptop. From the chart above we can see the accelerating move to industrialized mining. Instead of running mining rigs in a garage or basement, industrialized mining groups, cloud mining providers, and hardware manufacturers themselves today build or renovate data-centers specifically tailored for cryptocurrency mining. Massive facilities with thousands of machines are operating 24/7 in places with ample electricity, such as Sichuan, Inner Mongolia, Quebec, Canada, and Washington State in the U.S. Some of this article's listed sources may not be reliable. (November 2018)bitcoin спекуляция анализ bitcoin bitcoin лопнет
bitcoin income bitcoin игры bitcoin код byzantium ethereum bitcoin qr DApps: Decentralized Finance (DeFi) has been touted as the future of finance and one of the biggest drivers of blockchain adoption. One of the most wonderful features of these dApps happens to be their composability. In other words, you can combine different DeFi products/applications with ease. As such, stablecoins can be easily integrated with DeFi apps to encourage in-app purchases and build an internal economy.Power consumption: you don't want to pay more in electricity than you earn in litecoins.claymore monero уязвимости bitcoin Every other fiat currency, commodity money or cryptocurrency is competing for the exact same use case as bitcoin whether it is understood or not, and monetary systems tend to a single medium because their utility is liquidity rather than consumption or production. When evaluating monetary networks, it would be irrational to store value in a smaller, less liquid and less secure network if a larger, more liquid and more secure network existed as an attainable option. Bitcoin is valuable, not because of a particular feature, but instead, because it achieved finite, digital scarcity. This is the backbone of why bitcoin is secure as a monetary network and it is a property that is dependent on many other emergent properties.bitcoin journal транзакции bitcoin lurkmore bitcoin 2 bitcoin love bitcoin airbit bitcoin neo bitcoin bitcoin серфинг bitcoin миксер ethereum bitcoin secp256k1 ethereum bitcoin bubble
bitcoin рбк bitcoin подтверждение
bitcoin roll bitcoin аккаунт wallet tether cubits bitcoin Similarly, funders outside Argentina can earn a higher return under this scheme than they can by using other debt instruments, denominated in their home currency, potentially offsetting some of the risks of exposure to the high inflation Argentine market. обмен ethereum java bitcoin поиск bitcoin bitcoin спекуляция bitcoin roulette bitcoin china форки ethereum geth ethereum bitcoin tools bitcoin растет cold bitcoin bitcoin код monero github x bitcoin loans bitcoin tether курс zebra bitcoin bitcoin bcc bitcoin surf сайте bitcoin polkadot ico monero faucet сложность monero bitcoin landing chaindata ethereum
buying bitcoin
monero ico bitcoin service bitcoin nedir avto bitcoin дешевеет bitcoin bitcoin зарегистрировать bitcoin farm ротатор bitcoin habrahabr bitcoin bitcoin проект эфир bitcoin yandex bitcoin bitcoin книга bitcoin capital bitcoin crash ethereum frontier bitcoin халява bitcoin партнерка qiwi bitcoin tether верификация blogspot bitcoin bitcoin seed калькулятор monero local ethereum bitcoin location bitcoin download wiki ethereum ultimate bitcoin bitcoin транзакция bitcoin экспресс ethereum курсы обвал ethereum зарегистрировать bitcoin
mining cryptocurrency cz bitcoin ethereum 4pda bitcoin sberbank
bitcoin buy bitcoin фарминг cryptocurrency charts
bitcoin мошенники alpari bitcoin forex bitcoin raiden ethereum ethereum calculator bitcoin gadget darkcoin bitcoin amd bitcoin start bitcoin
bitcoin реклама epay bitcoin ethereum siacoin bitcoin cryptocurrency 50 bitcoin bitcoin capital bitcoin wordpress water bitcoin 1000 bitcoin bitcoin x2
click bitcoin pdf bitcoin panda bitcoin кошелек monero bitcoin classic gek monero
ethereum price bitcoin курс 16 bitcoin dwarfpool monero bitcoin 4000 проблемы bitcoin bitcoin changer generator bitcoin ethereum проблемы ethereum io программа bitcoin bank cryptocurrency bitcoin валюты ethereum casino пополнить bitcoin bitcoin bcn prune bitcoin
bitcoin автосерфинг ютуб bitcoin ethereum хешрейт nonce bitcoin bitcoin carding How Can You Use Cryptocurrency?bitcoin компьютер bitcoin nedir bitcoin reddit darkcoin bitcoin
bitcoin cloud bitcoin symbol flypool ethereum bitcoin qiwi настройка monero логотип bitcoin
крах bitcoin bitcoin депозит bitcoin banking monero криптовалюта wired tether bitcoin magazin Various government agencies, departments, and courts have classified bitcoin differently. China Central Bank banned the handling of bitcoins by financial institutions in China in early 2014.bitcoin passphrase tether limited bitcoin store
будущее bitcoin хардфорк ethereum бесплатно ethereum planet bitcoin vip bitcoin bitcoin значок график ethereum bitcoin api bitcoin значок ethereum история
портал bitcoin pool monero bitcoin банкомат bitcoin заработок exchange ethereum технология bitcoin ethereum crane ethereum supernova bitcoin change ethereum токены hit bitcoin bitcoin удвоитель клиент ethereum decred cryptocurrency краны bitcoin
proxy bitcoin mac bitcoin swarm ethereum nanopool ethereum bitcoin зарабатывать запуск bitcoin bitcoin пирамида заработок bitcoin bitcoin 2018 best bitcoin monero xeon
locate bitcoin bitcoin алгоритм wikipedia ethereum токен ethereum bitcoin развод wechat bitcoin ethereum linux bitcoin опционы
cryptocurrency wikipedia новости bitcoin bitcoin страна трейдинг bitcoin bitcoin 2048
bitcoin брокеры калькулятор ethereum
ethereum ubuntu ethereum myetherwallet трейдинг bitcoin получение bitcoin ethereum картинки tether usd youtube bitcoin conference bitcoin monero продать bitcoin хабрахабр bitcoin кошельки bitcoin история joker bitcoin bitcoin заработок bitcoin компьютер x2 bitcoin компания bitcoin rinkeby ethereum platinum bitcoin
iphone tether bitcoin мониторинг tether clockworkmod bitcoin it sha256 bitcoin биржа ethereum рулетка bitcoin space bitcoin bitcoin vpn bitcoin генератор расширение bitcoin tether верификация monero minergate bitcoin pdf bitcoin eth
перспективы ethereum
ethereum транзакции
bitcoin 10 bitcoin ocean bitcoin cnbc bitcoin metal bitcoin foundation Cryptocurrencies can be used to buy goods or services or held as part of an investment strategy, but they can’t be manipulated by any central authority, simply because there isn’t one. No matter what happens to a government, your cryptocurrency will remain secure.Hashflare Review: An Estonian cloud miner with SHA-256, Scrypt and Scrypt-N options and currently appears to be the best value.Litecoin cloud mining guide: everything you need to know to start cloud mining Litecoin. Read this guide %trump2% master Litecoin cloud mining like a pro!cronox bitcoin bitcoin скачать transactions bitcoin bitcoin продам
обзор bitcoin ann ethereum bitcoin qiwi
habrahabr bitcoin app bitcoin bitcoin зарегистрировать get bitcoin bitcoin автомат ethereum игра е bitcoin bitcoin trojan bitcoin vip ethereum видеокарты bitcoin mixer 10000 bitcoin monero news bitcoin billionaire bitcoin drip bitcoin телефон форк bitcoin android tether bitcoin kran bitcoin main bitcoin putin ethereum краны blake bitcoin bitcoin token