A blockchain oracle is a third-party service for smart contracts. Oracles provide trusted information based on the outside-world sources to the on-blockchain smart contracts. An oracle typically encapsulates the real-world complexity outside of the blockchain. This provides different engineering advantages, chiefly that critical errors and potential points of failure are easier to mitigate off-chain than on-chain. [1]
For example, in a contract to automatically purchase bitcoins at a predetermined price, the fulfillment condition is based on the current exchange rate for the bitcoin; an off-chain oracle can constantly monitor the price to provide the triggering condition to the contract. [2]
Kustov and Selanteva list the following types of oracles: [2]
If an oracle relies on a single source of truth (centralized), that can lead to issues: the data source can be hacked in a man-in-the-middle attack, or altered by its owner, in order to sway smart contracts. Decentralized oracles (consensus oracles) increase the reliability of the information provided to smart contracts by querying multiple data sources, thus distributing trust between participants. However, this does not achieve trustlessness, since oracles are not part of the main blockchain consensus, and thus not part of the security mechanisms of public blockchains. [3]
A smart contract is a computer program or a transaction protocol that is intended to automatically execute, control or document events and actions according to the terms of a contract or an agreement. The objectives of smart contracts are the reduction of need for trusted intermediators, arbitration costs, and fraud losses, as well as the reduction of malicious and accidental exceptions. Smart contracts are commonly associated with cryptocurrencies, and the smart contracts introduced by Ethereum are generally considered a fundamental building block for decentralized finance (DeFi) and non-fungible token (NFT) applications.
Trusted timestamping is the process of securely keeping track of the creation and modification time of a document. Security here means that no one—not even the owner of the document—should be able to change it once it has been recorded provided that the timestamper's integrity is never compromised.
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.
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.
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 decentralized autonomous organization (DAO), sometimes called a decentralized autonomous corporation (DAC), is an organization managed in whole or in part by decentralized computer program, with voting and finances handled through a blockchain. In general terms, DAOs are member-owned communities without centralized leadership. The precise legal status of this type of business organization is unclear.
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.
Hyperledger is an umbrella project of open source blockchains and related tools that the Linux Foundation started in December 2015. IBM, Intel, and SAP Ariba have contributed to support the collaborative development of blockchain-based distributed ledgers. It was renamed the Hyperledger Foundation in October 2021.
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).
The Lightning Network (LN) is a payment protocol built on the bitcoin blockchain. It is intended to enable fast transactions among participating nodes and has been proposed as a solution to the bitcoin scalability problem.
A cryptocurrency wallet is a device, physical medium, program or an online service which stores the public and/or private keys for cryptocurrency transactions. In addition to this basic function of storing the keys, a cryptocurrency wallet more often offers the functionality of encrypting and/or signing information. Signing can for example result in executing a smart contract, a cryptocurrency transaction, identification, or legally signing a 'document'.
Polkadot is a decentralized, nominated proof-of-stake blockchain with smart contract functionality. The cryptocurrency native to the blockchain is the DOT.
Distributed ledger technology law is not yet defined and recognized but an emerging field of law due to the recent dissemination of distributed ledger technology application in business and governance environment. Those smart contracts which were created through interaction of lawyers and developers and are intended to also be enforceable legal contracts are called smart legal contracts.
A stablecoin is a type of cryptocurrency where the value of the digital asset is supposed to be pegged to a reference asset, which is either fiat money, exchange-traded commodities, or another cryptocurrency.
A blockchain is a shared database that records transactions between two parties in an immutable ledger. Blockchain documents and confirms pseudonymous ownership of all transactions in a verifiable and sustainable way. After a transaction is validated and cryptographically verified by other participants or nodes in the network, it is made into a "block" on the blockchain. A block contains information about the time the transaction occurred, previous transactions, and details about the transaction. Once recorded as a block, transactions are ordered chronologically and cannot be altered. This technology rose to popularity after the creation of Bitcoin, the first application of blockchain technology, which has since catalyzed other cryptocurrencies and applications.
Decentralized finance provides financial instruments and services through smart contracts on a programmable, permissionless blockchain. This approach reduces the need for intermediaries such as brokerages, exchanges, or banks. DeFi platforms enable users to lend or borrow funds, speculate on asset price movements using derivatives, trade cryptocurrencies, insure against risks, and earn interest in savings-like accounts. The DeFi ecosystem is built on a layered architecture and highly composable building blocks. While some applications offer high interest rates, they carry high risks. Coding errors and hacks are a common challenge in DeFi.
Chainlink is a decentralized blockchain oracle network. Chainlink's token is on Ethereum. The network is intended to be used to facilitate the transfer of tamper-proof data from off-chain sources to on-chain smart contracts.
ICON is a decentralized, open-source blockchain with smart contract functionality. ICX is the native cryptocurrency of the platform.
Colored Coins is an open-source protocol that allows users to represent and manipulate immutable digital resources on top of Bitcoin transactions. They are a class of methods for representing and maintaining real-world assets on the Bitcoin blockchain, which may be used to establish asset ownership. Colored coins are bitcoins with a mark on them that specifies what they may be used for. Colored coins have also been considered a precursor to NFTs.