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 first implemented in Hashcash 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 the unauthorized production and spending of money, either digital or conventional. It represents a monetary design problem: a good money is verifiably scarce, and where a unit of value can be spent more than once, the monetary property of scarcity is challenged. 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.
Namecoin is a cryptocurrency originally forked from bitcoin software. It uses proof-of-work algorithm. Like bitcoin, it is limited to 21 million coins.
Litecoin is a decentralized peer-to-peer cryptocurrency and open-source software project released under the MIT/X11 license. Inspired by Bitcoin, Litecoin was among the earliest altcoins, starting in October 2011. In technical details, the Litecoin main chain shares a slightly modified Bitcoin codebase. The practical effects of those codebase differences are lower transaction fees, faster transaction confirmations, and faster mining difficulty retargeting. Due to its underlying similarities to Bitcoin, Litecoin has historically been referred to as the "silver to Bitcoin's gold." In 2022, Litecoin added optional privacy features via soft fork through the MWEB upgrade.
The bitcoin protocol is the set of rules that govern the functioning of bitcoin. Its key components and principles are: a peer-to-peer decentralized network with no central oversight; the blockchain technology, a public ledger that records all bitcoin transactions; mining and proof of work, the process to create new bitcoins and verify transactions; and cryptographic security.
Zerocoin is a privacy protocol proposed in 2013 by Johns Hopkins University professor Matthew D. Green and his graduate students, Ian Miers and Christina Garman. It was designed as an extension to the Bitcoin protocol that would improve Bitcoin transactions' anonymity by having coin-mixing capabilities natively built into the protocol. Zerocoin is not currently compatible with Bitcoin.
Vertcoin is an open-source cryptocurrency created in early 2014, that focuses on decentralization. Vertcoin uses a proof-of-work mechanism to issue new coins and incentivize miners to secure the network and validate transactions. Vertcoin is designed to be mined via graphics cards instead of through ASICs.
Dash is an open source cryptocurrency. It is an altcoin that was forked from the Bitcoin protocol. It is also a decentralized autonomous organization (DAO) run by a subset of its users. It was previously known as Xcoin and Darkcoin.
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.
Monero is a cryptocurrency which uses a blockchain with privacy-enhancing technologies to obfuscate transactions to achieve anonymity and fungibility. Observers cannot decipher addresses trading Monero, transaction amounts, address balances, or transaction histories.
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).
Zcash is a privacy-focused cryptocurrency which is based on Bitcoin's codebase. It shares many similarities, such as a fixed total supply of 21 million units.
Firo, formerly known as Zcoin, is a cryptocurrency aimed at using cryptography to provide better privacy for its users compared to other cryptocurrencies such as Bitcoin.
Bitcoin Cash is a cryptocurrency that is a fork of bitcoin. Launched in 2017, Bitcoin Cash is considered an altcoin or spin-off of bitcoin. In November 2018, Bitcoin Cash further split into two separate cryptocurrencies: Bitcoin Cash (BCH) and Bitcoin Satoshi Vision (BSV).
Verge Currency is a decentralized open-source cryptocurrency which offers various levels of private transactions. It does this by obfuscating the IP addresses of users with Tor and by leveraging stealth transactions making it difficult to determine the geolocation of its users.
Cryptocurrency and crime describe notable examples of cybercrime related to theft of cryptocurrencies and some methods or security vulnerabilities commonly exploited. Cryptojacking is a form of cybercrime specific to cryptocurrencies that have been used on websites to hijack a victim's resources and use them for hashing and mining cryptocurrency.
Equihash is a memory-hard Proof-of-work algorithm introduced by the University of Luxembourg's Interdisciplinary Centre for Security, Reliability and Trust (SnT) at the 2016 Network and Distributed System Security Symposium. The algorithm is based on a generalization of the Birthday problem which finds colliding hash values. It has severe time-space trade-offs but concedes vulnerability to unforeseen parallel optimizations. It was designed such that parallel implementations are bottle-necked by memory bandwidth in an attempt to worsen the cost-performance trade-offs of designing custom ASIC implementations. ASIC resistance in Equihash is based on the assumption that commercially-sold hardware already has quite high memory bandwidth, so improvements made by custom hardware may not be worth the development cost.
Cryptojacking is the act of exploiting a computer to mine cryptocurrencies, often through websites, against the user's will or while the user is unaware. One notable piece of software used for cryptojacking was Coinhive, which was used in over two-thirds of cryptojacks before its March 2019 shutdown. The cryptocurrencies mined the most often are privacy coins—coins with hidden transaction histories—such as Monero and Zcash.
Nervos Network is a proof-of-work blockchain platform which consists of multiple blockchain layers that are designed for different functions. The native cryptocurrency of this layer is called CKB. Smart contracts and decentralized applications can be deployed on the Nervos blockchain. The Nervos Network was founded in 2018.
