Proof of work (PoW) is a form of cryptographic proof in which one party proves to others that a certain amount of a specific computational effort has been expended. Verifiers can subsequently confirm this expenditure with minimal effort on their part. The concept was invented by Moni Naor and Cynthia Dwork 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. The concept was adapted to digital tokens by Hal Finney in 2004 through the idea of "reusable proof of work" using the 160-bit secure hash algorithm 1 (SHA-1).
Double-spending is a fundamental flaw in a digital cash protocol in which the same single digital token can be spent more than once. Due to the nature of information space, in comparison to physical space, a digital token is inherently almost infinitely duplicable or falsifiable, leading to ownership of said token itself being undefinable unless declared so by a chosen authority. As with counterfeit money, such double-spending leads to inflation by creating a new amount of copied currency that did not previously exist. Like all increasingly abundant resources, this devalues the currency relative to other monetary units or goods and diminishes user trust as well as the circulation and retention of the currency.
A cryptocurrency, crypto-currency, or crypto is a digital currency designed to work as a medium of exchange through a computer network that is not reliant on any central authority, such as a government or bank, to uphold or maintain it.
Proof-of-stake (PoS) protocols are a class of consensus mechanisms for blockchains that work by selecting validators in proportion to their quantity of holdings in the associated cryptocurrency. This is done to avoid the computational cost of proof-of-work (POW) schemes. The first functioning use of PoS for cryptocurrency was Peercoin in 2012, although the scheme, on the surface, still resembled a POW.
Ethereum is a decentralized blockchain with smart contract functionality. Ether is the native cryptocurrency of the platform. Among cryptocurrencies, ether is second only to bitcoin in market capitalization. It is open-source software.
A blockchain is a distributed ledger with growing lists of records (blocks) that are securely linked together via cryptographic hashes. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data. Since each block contains information about the previous block, they effectively form a chain, with each additional block linking to the ones before it. Consequently, blockchain transactions are irreversible in that, once they are recorded, the data in any given block cannot be altered retroactively without altering all subsequent blocks.
A decentralised application is an application that can operate autonomously, typically through the use of smart contracts, that run on a decentralized computing, blockchain or other distributed ledger system. Like traditional applications, DApps provide some function or utility to its users. However, unlike traditional applications, DApps operate without human intervention and are not owned by any one entity, rather DApps distribute tokens that represent ownership. These tokens are distributed according to a programmed algorithm to the users of the system, diluting ownership and control of the DApp. Without any one entity controlling the system, the application is therefore decentralised.
Ethereum Classic is a blockchain-based distributed computing platform that offers smart contract (scripting) functionality. It is open source and supports a modified version of Nakamoto consensus via transaction-based state transitions executed on a public Ethereum Virtual Machine (EVM).
Cardano is a public blockchain platform. It is open-source and decentralized, with consensus achieved using proof of stake. It can facilitate peer-to-peer transactions with its internal cryptocurrency, ADA.
The Bitcoin scalability problem refers to the limited capability of the Bitcoin network to handle large amounts of transaction data on its platform in a short span of time. It is related to the fact that records in the Bitcoin blockchain are limited in size and frequency.
Gavin James Wood is an English computer scientist, a co-founder of Ethereum and creator of Polkadot and Kusama.
Tezos is an open-source blockchain that can execute peer-to-peer transactions and serve as a platform for deploying smart contracts. The native cryptocurrency for the Tezos blockchain is the tez. The Tezos network achieves consensus using proof-of-stake. Tezos uses an on-chain governance model that enables the protocol to be amended when upgrade proposals receive a favorable vote from the community. Its testnet was launched in June 2018, and its mainnet went live in September 2018.
Avalanche is a decentralized, open-source proof of stake blockchain with smart contract functionality. AVAX is the native cryptocurrency of the platform.
Ouroboros is a family of proof-of-stake consensus protocols used in the Cardano and Polkadot blockchains. It can run both permissionless and permissioned blockchains.
Aggelos Kiayias FRSE is a Greek cryptographer and computer scientist, currently a professor at the University of Edinburgh and the Chief Science Officer at Input Output Global, the company behind Cardano.
Algorand is a cryptocurrency protocol providing proof-of-stake on a blockchain. Algorand's native cryptocurrency is called ALGO.
ICON is a decentralized, open-source blockchain with smart contract functionality. ICX is the native cryptocurrency of the platform.
Polygon is a blockchain platform which aims to create a multi-chain blockchain system compatible with Ethereum. As with Ethereum, it uses a proof-of-stake consensus mechanism for processing transactions on-chain. Polygon's native token is named MATIC. Matic is an ERC-20 token, allowing for compatibility with other Ethereum cryptocurrencies.
Nervos Network is a blockchain platform which consists of multiple blockchain layers that are designed for different functions. The foundational layer is known as the Common Knowledge Base, whilst the native cryptocurrency of this layer is called CKB. This foundational layer uses a proof-of-work consensus model. Smart contracts and decentralized applications can be deployed on any layer.
