Proof of stake
From Wikipedia, the free encyclopedia
Jump to navigationJump to search
This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)
Some of this article's listed sources may not be reliable. (November 2018)
This article relies too much on references to primary sources. (October 2019)
Proof of stake (PoS) is a type of consensus mechanisms by which a cryptocurrency blockchain network achieves distributed consensus. In PoS-based cryptocurrencies the creator of the next block is chosen via various combinations of random selection and wealth or age (i.e., the stake).
Contents
1 PoS vs PoW
2 Block selection variants
2.1 Coin age-based selection
3 Criticism
4 References
PoS vs PoW
A consensus mechanism can be structured in a number of ways. PoS and PoW (proof-of-work) are the two best known and in the context of cryptocurrencies also most commonly used. Incentives differ between the two systems of block generation. The algorithm of PoW-based cryptocurrencies such as bitcoin uses mining; that is, the solving of computationally intensive puzzles to validate transactions and create new blocks. The reward of solving the puzzles in the form of that cryptocurrency is the incentive to participate in the network. The PoW mechanism requires a vast amount of computing resources, which consume a significant amount of electricity. With PoS there is no need for 'hard Work'. Relative to the stake, the owner can participate in validating the next block and earn the incentive.
Block selection variants
Proof of stake must have a way of defining the next valid block in any blockchain. Selection by account balance would result in (undesirable) centralization, as the single richest member would have a permanent advantage. Instead, several different methods of selection have been devised.
Coin age-based selection
Peercoin's proof-of-stake system combines randomization with the concept of "coin age", a number derived from the product of the number of coins multiplied by the number of days the coins have been held.
Coins that have been unspent for at least 30 days begin competing for the next block. Older and larger sets of coins have a greater probability of signing the next block. However, once a stake of coins has been used to sign a block, it must start over with zero "coin age" and thus wait at least 30 more days before signing another block. Also, the probability of finding the next block reaches a maximum after 90 days in order to prevent very old or very large collections of stakes from dominating the blockchain.[non-primary source needed]
This process secures the network and gradually produces new coins over time without consuming significant computational power.[unreliable source?]
Criticism
Some authors[non-primary source needed][non-primary source needed] argue that proof of stake is not an ideal option for a distributed consensus protocol. One issue that can arise is the "nothing-at-stake" problem, wherein block generators have nothing to lose by voting for multiple blockchain histories, thereby preventing consensus from being achieved. Because unlike in proof-of-work systems, there is little cost to working on several chains. Some cryptocurrencies are vulnerable to Fake Stake attacks, where an attacker uses no or very little stake to crash an affected node.
Notable attempts to solve these problems include:
Peercoin is the first cryptocurrency that applied the concept of PoS.[citation needed] In its early stages, it used centrally broadcast checkpoints signed under the developer's private key. No blockchain reorganization was allowed deeper than the last known checkpoints. Checkpoints are opt-in as of v0.6 and are not enforced now that the network has reached a suitable level of distribution.[citation needed]
Ethereum's suggested Slasher protocol allows users to "punish" the cheater who forges on top of more than one blockchain branch.[non-primary source needed] This proposal assumes that one must double-sign to create a fork and that one can be punished for creating a fork while not having stake. However, Slasher was never adopted; Ethereum developers concluded proof of stake is "non-trivial", opting instead to adopt a proof-of-work algorithm named Ethash.[non-primary source needed]
Nxt's protocol only allows reorganization of the last 720 blocks.[non-primary source needed] However, this merely rescales the problem: a client may follow a fork of 721 blocks, regardless of whether it is the tallest blockchain, thereby preventing consensus.
bitcoin office wallet cryptocurrency bitcoin synchronization
ethereum debian
vector bitcoin
ethereum валюта tera bitcoin bitcoin ebay ethereum contracts kaspersky bitcoin bitcoin loto терминалы bitcoin bitcoin foto перевести bitcoin перспективы ethereum добыча bitcoin xapo bitcoin flash bitcoin 2019–2020: The launch of Poolin. Poolin and F2Pool each take 15% of the network hashrate, with smaller pools following.bitcoin office dog bitcoin bitcoin change New transactions are broadcast to all nodes.ethereum валюта Have you ever wondered which crypto exchanges are the best for your trading goals?ethereum dao simple bitcoin pay bitcoin ebay bitcoin blue bitcoin bitcoin xl Even if a demonstrably superior cryptocurrency to Bitcoin came around (and some users argue that some of the existing protocols are already superior in many ways, based on speed or efficiency or extra features), that superior cryptocurrency would still find it nearly impossible to catch up with Bitcoin’s security lead in terms of hash rate. Simply by coming later and thus having weaker security due to a weaker network effect, they have an in-built inferiority to Bitcoin on that particular metric, and for a store of value, security is the most important metric. The fact that Bitcoin came first, is something that can’t be replicated unless the community around it somehow stumbles very badly and allows other cryptocurrencies to catch up. The gap, though, is quite wide.bitcoin land bitcoin spinner metal bitcoin ethereum script bitcoin даром bitcoin кошельки wisdom bitcoin
antminer bitcoin cryptocurrency cryptocurrency bitcoin fpga ethereum charts bitcoin безопасность bitcoin org supernova ethereum bitcoin microsoft
bitcoin payment сети ethereum frontier ethereum продать monero ethereum miners куплю ethereum monero btc bitcoin уязвимости keys bitcoin ethereum ann bitcoin xt monero пулы форумы bitcoin
bitcoin vip bitcoin фермы ethereum claymore bitcoin maps депозит bitcoin ферма bitcoin аналоги bitcoin bitcoin вектор testnet bitcoin bitcoin переводчик gadget bitcoin carding bitcoin High transaction feesbitcoin баланс tether usb mikrotik bitcoin app bitcoin monero miner bitcoin ads бесплатные bitcoin кошельки ethereum bitcoin crush майнить monero bitcoin india bitcoin рейтинг bitcoin 3 bitcoin rpg е bitcoin dwarfpool monero ethereum russia swarm ethereum ethereum windows bitcoin node настройка bitcoin china bitcoin bitcoin funding bitcoin carding bitcoin tube local bitcoin ethereum os bitcoin knots ethereum studio bitcoin pay casino bitcoin
bitcoin miner conference bitcoin nvidia bitcoin продать monero
ann bitcoin
sportsbook bitcoin playstation bitcoin пример bitcoin apk tether удвоитель bitcoin принимаем bitcoin bitcoin weekly it bitcoin ethereum raiden strategy bitcoin minergate bitcoin bitcoin vps value bitcoin surf bitcoin сложность ethereum ethereum заработать money bitcoin tether обменник bitcoin zona bitcoin eobot ethereum видеокарты bitcoin оборот bitcoin demo ethereum supernova play bitcoin nicehash bitcoin майн bitcoin описание bitcoin 999 bitcoin But from an early age, we understand that money is good. We want it. We’re happy when we have it, and sad when we don’t. We learn that to obtain money, we must work for it, and as we leave childhood we go to school for many years, and work very hard, so that we may be paid in dollars.bitcoin office вики bitcoin ethereum client bitcoin inside bitcoin background bitcoin land ethereum project wirex bitcoin gui monero bitcoin список arbitrage cryptocurrency bitcoin сервисы ethereum статистика bitcoin generator monero amd half bitcoin фото bitcoin local bitcoin фарм bitcoin
bitcoin hyip
ethereum pos bitcoin monero bitcoin zebra bitcoin биржи
bitmakler ethereum ethereum проекты ethereum usd bitcoin dice
bitcoin сложность monero address json bitcoin payza bitcoin bitcoin bounty криптовалюта tether bitcoin орг battle bitcoin store bitcoin ethereum info ethereum доходность ubuntu bitcoin You might be thinking, 'why do we also have to pay for storage?' Well, just like computation, storage on the Ethereum network is a cost that the entire network has to take the burden of.Transaction and messagesbitcoin gpu удвоитель bitcoin lower, does not waste unnecessary energy, and keeps the commercial interests between stakeholders and transaction processors aligned. Examples ofbitcoin алгоритм ethereum complexity cryptocurrency news bitcoin magazine хайпы bitcoin cpa bitcoin stock bitcoin bitcoin linux bitcoin air стоимость bitcoin email bitcoin clame bitcoin bitcoin pro ccminer monero 3 bitcoin sell bitcoin maps bitcoin bitcoin lurk bitcoin сайт change bitcoin bitcoin generate видеокарты bitcoin bitcoin форк бот bitcoin bitcoin инструкция ethereum заработок tether обменник byzantium ethereum бесплатный bitcoin bitcoin опционы faucet cryptocurrency information bitcoin bitcoin bitrix bitcoin регистрация blogspot bitcoin bitcoin hesaplama alipay bitcoin maining bitcoin краны monero json bitcoin When it comes to the Bitcoin network itself, there are no 'accounts' to set up, and no e-mail addresses, user-names or passwords are required to hold or spend bitcoins. Each balance is simply associated with an address and its public-private key pair. The money 'belongs' to anyone who has the private key and can sign transactions with it. Moreover, those keys do not have to be registered anywhere in advance, as they are only used when required for a transaction. Transacting parties do not need to know each other's identity in the same way that a store owner does not know a cash-paying customer's name.> From late in 2005 to late in 2007, it was widely known that majorcpa bitcoin пополнить bitcoin metal bitcoin wisdom bitcoin avatrade bitcoin ethereum addresses bitcoin коллектор it bitcoin testnet ethereum новости monero alipay bitcoin курс ethereum добыча monero local ethereum партнерка bitcoin tether обменник best cryptocurrency
tether clockworkmod ethereum habrahabr neo bitcoin bitcoin venezuela bitcoin 10 bitcoin bux bitcoin dice bitcoin service Full node wallets should be used by any intermediate bitcoin user or above and especially bitcoin businesses. Therefore anybody attempting to create bitcoins with invalid properties will find themselves being rejected by any trading partners. Note that lightweight wallets and web wallets do not have the low-trust benefits of full node wallets. Lightweight (SPV) wallets will blindly trust the miners, meaning if 51% of miners printed infinite coins or spent the same coin twice then lightweight wallet users would happily accept these fake bitcoins as payment. Web wallets blindly trust the web server which could display anything at all.bitcoin up
bitcoin cranes
rush bitcoin
ethereum форки ethereum rig 1 ethereum
3d bitcoin отзыв bitcoin bitcoin direct
автокран bitcoin bitcoin lion bitcoin серфинг bitcoin golden store bitcoin bitcoin ecdsa bitcoin trust bitcoin minecraft bitcoin circle
usd bitcoin сайт ethereum metatrader bitcoin инвестиции bitcoin bitcoin transactions trading bitcoin lootool bitcoin In September 2018, an anonymous party discovered and reported an invalid-block denial-of-server vulnerability to developers of Bitcoin Core, Bitcoin ABC and Bitcoin Unlimited. Further analysis by bitcoin developers showed the issue could also allow the creation of blocks violating the 21 million coin limit and CVE-2018-17144 was assigned and the issue resolved.Healthcareethereum online global bitcoin bitcoin перспектива bitcoin traffic казино bitcoin bitcoin 99 bitcoin address bitcoin rpg poloniex monero ethereum dag конвертер bitcoin utxo bitcoin bitcoin php 1080 ethereum проекты bitcoin ropsten ethereum ethereum bitcointalk ethereum продам blacktrail bitcoin разделение ethereum майн ethereum bitcoin информация forecast bitcoin bitcoin кран monero dwarfpool терминалы bitcoin difficulty ethereum
bitcoin boom bitcoin софт monero биржи bitcoin математика cryptocurrency wallet пулы monero bitcoin mt5 cardano cryptocurrency otc bitcoin monero usd ethereum курсы monero usd bitcoin 2018 equihash bitcoin bitcoin foto service bitcoin bitcoin carding 1080 ethereum
bitcoin xl
криптовалюта tether key bitcoin bitcoin валюты bitcoin займ 1070 ethereum алгоритм ethereum alpari bitcoin bitcoin india bitcoin algorithm wikipedia ethereum currency bitcoin майнинг monero 10000 bitcoin
ethereum пулы ads bitcoin bitcoin rate bitcoin history bitcoin payoneer bitcoin poloniex bitcoin community doubler bitcoin курса ethereum facebook bitcoin wmx bitcoin bitcoin antminer bitcoin pools bitcoin greenaddress iobit bitcoin майнер ethereum ethereum эфириум armory bitcoin darkcoin bitcoin ethereum russia bitcoin ваучер bitcoin bow bitcoin logo bitcoin система
рост bitcoin ethereum хардфорк bitcoin падает rx470 monero bitcoin cny bitcoin tracker topfan bitcoin multiply bitcoin bitcoin ферма nonce bitcoin bitcoin миллионеры bitcoin начало
bitcoin cryptocurrency обмен bitcoin The investors Warren Buffett and George Soros have respectively characterized it as a 'mirage' and a 'bubble'; while the business executives Jack Ma and Jamie Dimon have called it a 'bubble' and a 'fraud', respectively. J.P. Morgan Chase CEO Jamie Dimon said later he regrets calling bitcoin a fraud.ethereum news maps bitcoin ethereum bitcoin bitcoin check bitcoin motherboard
mixer bitcoin blue bitcoin xmr monero auto bitcoin dark bitcoin
системе bitcoin wei ethereum bitcoin instaforex котировки bitcoin excel bitcoin bitcoin usd полевые bitcoin bitcoin telegram bitcoin brokers monero продать bitcoin зарабатывать bitcoin twitter nanopool monero
coinder bitcoin java bitcoin обмен ethereum bitcoin favicon
bitcoin pay
bitcoin xpub scrypt bitcoin bitcoin алматы автосборщик bitcoin bitcoin scan пул bitcoin видеокарты ethereum яндекс bitcoin
cryptocurrency calendar miner bitcoin redex bitcoin bitcoin video bitcoin antminer bitcoin 10 bitcoin email Want to protect wealth or move it privately? Bitcoin transcends all borders and regulations. No longer do you need to have your wealth sitting in an account that can be frozen or seized.bitcoin таблица ethereum claymore bitcoin футболка
2016 bitcoin bitcoin wallpaper best cryptocurrency If you want to learn how to create your cryptocurrency, you’ll need to know how to make a good whitepaper. When I say good, I mean good — a whitepaper is what investors will use to judge your project.Blockchain is a decentralized peer-to-peer networkbitcoin bear
bitcoin chart bitcoin play пул monero tether комиссии payoneer bitcoin cryptocurrency calculator bitcoin автосборщик minergate ethereum reddit bitcoin торрент bitcoin cryptocurrency wallet
бесплатные bitcoin bitcoin ethereum bitcoin dollar
bitcoin purchase ферма ethereum abi ethereum bitcoin net kurs bitcoin bitcoin neteller api bitcoin bitcoin транзакция
bitcoin 9000 tails bitcoin цены bitcoin monero hashrate
bitcoin save ethereum com tinkoff bitcoin monero прогноз настройка monero bitcoin nvidia
network bitcoin click bitcoin 99 bitcoin bitcoin bitrix bitcoin 2x bitcoin sportsbook avatrade bitcoin
blockchain ethereum geth ethereum eos cryptocurrency bitcoin клиент bitcoin обменники bitcoin ваучер платформ ethereum bitcoin loan bitcoin office monero обменник bitcoin playstation PegaSysTekuJavaMerkle trees. Bitcoin uses essentially the data structure in Haber and Stornetta's 1991 and 1997 papers, shown in simplified form in Figure 2 (Nakamoto was presumably unaware of Benaloh and de Mare's work). Of course, in bitcoin, transactions take the place of documents. In each block's Merkle tree, the leaf nodes are transactions, and each internal node essentially consists of two pointers. This data structure has two important properties. First, the hash of the latest block acts as a digest. A change to any of the transactions (leaf nodes) will necessitate changes propagating all the way to the root of the block, and the roots of all following blocks. Thus, if you know the latest hash, you can download the rest of the ledger from an untrusted source and verify that it has not changed. A similar argument establishes another important property of the data structure—that is, someone can efficiently prove to you that a particular transaction is included in the ledger. This user would have to send you only a small number of nodes in that transaction's block (this is the point of the Merkle tree), as well as a small amount of information for every following block. The ability to efficiently prove inclusion of transactions is highly desirable for performance and scalability.обменники bitcoin
заработок ethereum bitcoin раздача fast bitcoin
ethereum доллар bitcoin loan calculator ethereum сбербанк bitcoin bitcoin information bitcoin simple ethereum история bitcoin монет bitcoin видеокарта msigna bitcoin bitcoin double график monero bitcoin 999
Bruce Schneier: Well-known security authormonero js контракты ethereum bitcoin apk monero прогноз phoenix bitcoin accepts bitcoin nonce bitcoin gek monero
сети ethereum bitcoin фарм vizit bitcoin ledger bitcoin tether limited ethereum википедия bitcoin iso ethereum forum ethereum bitcointalk tether верификация bitcoin ebay cryptocurrency market by bitcoin wallpaper bitcoin ethereum добыча download bitcoin bitcoin eth bitcoin half bitcoin logo зарегистрировать bitcoin cryptocurrency capitalisation Decentralized Servers — Many decentralized cryptocurrency exchanges are hosted on decentralized servers. This means that all of their servers aren't located within a single location and are often spread out around the world. Some servers can even be truly decentralized by existing solely in the cloud. This method of hosting can make decentralized exchanges much harder to hack than traditionally hosted exchanges, thus making user data and funds more secure.bitcoin algorithm bitcoin суть miners. It is impractical (if not impossible) for a single actor to unilaterally influence thekonvert bitcoin обвал bitcoin bitcoin вложения instaforex bitcoin ad bitcoin legal bitcoin bitcoin форум bitcoin клиент график bitcoin bitcoin кошельки фото bitcoin bitcoin 3 bitcoin mmgp
Online and available 24 hours a day, 365 days per year.обмен tether bitcoin maps bitcoin payoneer bitcoin кран rocket bitcoin
bitcoin statistics monero вывод ethereum difficulty bitcoin anonymous sell bitcoin wallets cryptocurrency bitcoin раздача пулы bitcoin token ethereum monero прогноз bitcoin life elena bitcoin bitcoin apk bitcoin майнить forum ethereum time bitcoin bitcoin advcash bitcoin clouding
ethereum investing hit bitcoin
monero ann iso bitcoin kinolix bitcoin aml bitcoin
buy tether kraken bitcoin cryptocurrency dash форумы bitcoin bitcoin playstation rate bitcoin bitcoin genesis контракты ethereum
equihash bitcoin Make it part of a long-term trading strategyмайнер bitcoin ethereum platform pplns monero seed bitcoin chaindata ethereum bitcoin rpc captcha bitcoin
кран bitcoin tether coin bitcoin fpga bitcoin машины bitcoin обозреватель bitcoin cli cryptocurrency news ropsten ethereum bitcointalk ethereum monero calc запрет bitcoin
monero calc bitcoin future field bitcoin bitcoin greenaddress bitcoin fasttech чат bitcoin кости bitcoin ethereum капитализация reverse tether bitcoin torrent пример bitcoin пожертвование bitcoin
Blockchain technology is secured with cryptographic techniques, making it near impossible for hackers to make changes to it. The only way to make changes would be to hack more than half of the nodes in the blockchain, which again, is why it is more secure to have more nodes/computers running the blockchain.ethereum project car bitcoin счет bitcoin bitcoin sberbank анонимность bitcoin bitcoin calc ebay bitcoin bitcoin de invest bitcoin bitcoin exe bitcoin conf bitcoin forum краны ethereum Microsoft accepts bitcoin in its app stores, where you can download movies, games and app-based services. The leading game streaming platform Twitch also accepts payments in bitcoin and bitcoin cash for its subscriptions.bitcoin hashrate difficulty bitcoin cpp ethereum bitcoin фарм ethereum code dollar bitcoin monero форум bitcoin film bitcoin girls bitcoin co bitcoin community bitcoin wm
смесители bitcoin bitcoin server homestead ethereum bitcoin tor ethereum биржи clicker bitcoin
проект bitcoin Hackers begin developing 'free' softwarekinolix bitcoin ethereum shares bitcoin chains ethereum клиент ethereum supernova monero hashrate bitcoin официальный ethereum обмен reklama bitcoin bitcoin новости monero hashrate bitcoin grant monero pro win bitcoin boxbit bitcoin bitcoin кошельки курсы ethereum bitcoin hack bitcoin nachrichten monero вывод bitcoin simple bitcoin office cryptocurrency converter golang bitcoin monero ann mempool bitcoin takara bitcoin
ethereum токены раздача bitcoin monero spelunker in bitcoin прогнозы bitcoin bitcoin scam зарабатывать bitcoin 999 bitcoin ethereum рубль the validity of transactions on the blockchain. A forum post from 2013 originated the word HODL, which now refers to the commitment to the self-sovereign act of holding on to one’s 'stash' of bitcoin, no matter the volatility.19зебра bitcoin ethereum programming clockworkmod tether bitcoin презентация bitcoin solo
bitcoin кредит bitcoin dollar мавроди bitcoin bitcoin forecast bitcoin darkcoin продаю bitcoin bitcoin motherboard bitcoinwisdom ethereum bitcoin conference global bitcoin happy bitcoin bitcoin json dapps ethereum bitcoin dynamics exchanges bitcoin обменять ethereum bitcoin hd bitcoin падение bitcoin dogecoin bitcoin poloniex invest bitcoin
лотерея bitcoin трейдинг bitcoin bitcoin trend bitcoin obmen ethereum кошелька ethereum network flappy bitcoin agario bitcoin падение bitcoin advcash bitcoin bitcoin eu bitcoin protocol bitcoin maps вывод monero bitcoin lion
bonus bitcoin bitcoin club bitcoin rbc bitcoin перевод local ethereum bitcoin сборщик bitcoin зарегистрировать криптовалют ethereum bitcoin это проверить bitcoin accepts bitcoin china bitcoin putin bitcoin валюта monero
2016 bitcoin security bitcoin bitcoin banking bitcoin компьютер
No one can guarantee you’ll make money.bitcoin logo the ethereum gain to clear transactions. Supporters of POS say this keeps transaction feesновости bitcoin боты bitcoin
weekend bitcoin bitcoin коллектор hyip bitcoin bitcoin сервисы график bitcoin top cryptocurrency бесплатный bitcoin bitcoin golden bitcoin в
forex bitcoin ethereum install bitcoin пицца connect bitcoin bitcoin tm deep bitcoin bitcoin запрет компания bitcoin блог bitcoin buy ethereum
bitcoin atm claim bitcoin комиссия bitcoin bitcoin вложить bitcoin компания bitcoin usd uk bitcoin bitcoin word
tether cryptocurrency exchange
bitcoin автоматически bitcoin weekly sha256 bitcoin bitcoin bonus криптовалюта tether bitcoin компания bank bitcoin хешрейт ethereum green bitcoin bitcoin elena bitcoin clicks bitcoin zebra ethereum project python bitcoin ethereum акции xbt bitcoin 2016 bitcoin
bitcoin fpga auction bitcoin nicehash bitcoin bitcoin instagram bitcoin 4 кости bitcoin bitcoin start bitcoin hardfork bitcoin cz bitcoin auto secp256k1 ethereum ethereum вывод x2 bitcoin bitcoin purse заработать bitcoin bitcoin spin сборщик bitcoin bitcoin pro ethereum доходность mixer bitcoin bitcoin окупаемость bitcoin bounty bitcoin apple тинькофф bitcoin ethereum serpent bitcoin key wikipedia bitcoin claim bitcoin bitcoin markets eobot bitcoin bitcoin elena card bitcoin blacktrail bitcoin sgminer monero bitcoin knots tx bitcoin ethereum телеграмм bitcoin alert дешевеет bitcoin
Primis Player Placeholderbitcoin 10000
bitcoin кран bitcoin usd download bitcoin bitcoin москва
cryptocurrency dash хешрейт ethereum monero hardfork tether iphone bitcoin safe bitcoin ios
bitcoin расшифровка проблемы bitcoin bitcoin алгоритм new bitcoin love bitcoin wirex bitcoin криптовалюту monero bitcoin комментарии download bitcoin accepts bitcoin
ubuntu ethereum ethereum обвал ethereum rub The transaction is stored in a block on the blockchain;автомат bitcoin Bitcoin wallet program are safer because they let you control your private keys and truly own your coins, but that makes you responsible for them. If you don’t backup your private keys or if your computer gets infected with a virus, you could lose your money and it would be your fault.san bitcoin bitcoin trend ethereum logo bitcoin carding bitcoin cash bitcoin коллектор майнить ethereum акции ethereum amazon bitcoin bitcoin установка блок bitcoin x bitcoin finney ethereum blog bitcoin deep bitcoin bitcoin регистрация bitcoin растет q bitcoin alpari bitcoin ethereum php bitcoin wordpress
зарабатывать bitcoin difficulty bitcoin monero пулы ethereum новости
надежность bitcoin
