A hack, or hacking, is the process whereby a malicious third-party cybercriminal breaks into a computer system or network that they do not legally have access to. Hacks can be carried out to steal sensitive data, for monetary gain, or for other malicious intentions. The process of hacking can also be used for legitimate purposes by various enterprise, private, or government entities to stop cybercriminals from carrying out online criminal activity.

A hackathon is a competitive and time-sensitive event held by a firm, consortium, or related entity (for example in the technology, FinTech, or blockchain industries). In these events, software engineers compete to produce working applications, software programs, or even entire computer networks. Hackathons often provide several distinct prize categories for winning participants, and tend to have a specific focus — such as on programming languages used, operating system type serviced, or the specific demographic of programmers involved. The name Hackathon is a portmanteau of hacking and marathon.

Computer hackers are often malicious actors who use their programming skills and technical expertise to break into computer systems or networks to steal, destroy, or modify data. Hackers are often employed by governments, large enterprises, or other organizations for varying purposes such as law enforcement agencies in order to retrieve information that could lead to the arrest and conviction of criminals.

A halving is when the reward allocated to miners for mining new blocks is reduced by 50%. Halving events usually occur at fixed intervals. For example, Bitcoin's block reward is halved every 210,000 blocks, and happens about every four years.

Decentralized applications (dApps) which are built on the Holochain blockchain platform are referred to as hApps. Holochain is a completely distributed open-source network that allows anyone to create hApps. Many hApps are developed to help users better manage their personal data by employing strong privacy and security parameters. Elemental Chat (a secure P2P messaging hApp) and HoloVault (an integrated dashboard that allows users to manage how their data is being used) are two examples of hApps.

Hard cap has two separate definitions related to blockchain. Firstly, a hard cap indicates the absolute maximum supply of a cryptocurrency that can ever be created. For example, Bitcoin has a hard-capped supply of 21 million bitcoin (BTC). The second meaning indicates the maximum amount of a currency that will be offered to investors during an Initial Coin Offering (ICO) or funding round. For example, a new blockchain project raising funds may impose a hard cap of 100 million tokens to be initially sold, meaning that only 100 million tokens can be sold during the ICO.

A hard fork is a software update that is not backwards compatible. In the context of blockchain technology, a hard fork happens when new rules have been introduced into the blockchain code that are not compatible with the rules of the blockchain's previous code. If network nodes do not update their software, they are unable to communicate with nodes that have updated their software. This sometimes results in the blockchain splitting into two networks — one which operates with the old rules and one which operates with the new, updated rules. For example, Bitcoin Cash emerged after a hard fork of the Bitcoin blockchain.

A hard peg is a specific type of exchange rate model that is applied to a currency in order to maintain its value relative to a reserve currency or basket of currencies. As they relate to blockchain, a hard peg is usually applied to stablecoins to maintain their peg to a fiat currency like the U.S. dollar, and typically do not allow for much flexibility to deal with economic shocks and fluctuations.

A hardware wallet is a non-custodial wallet and is considered a secure way to personally store crypto. Typically looking like a USB stick, a hardware wallet is usually offline but connects via USB or bluetooth to an online device when making transactions. Although technically connected to the internet at times, it’s still considered a cold — or offline — wallet as transactions are signed “in-device.” This means the transaction has been signed offline prior to being broadcast to the blockchain via the internet. Due to this security feature, malware is unable to sign these transactions — or view your keys.

Hashed Timelock Contracts (HTCL) are smart contracts that facilitate atomic swap transactions. These smart contracts function as a "virtual lockbox" that requires a HashLock and TimeLock Key to unlock funds during an exchange.

Hashes per second (h/s) is the measurement used to determine the hash rate on a blockchain network. This measurement calculates the number of double SHA-256 computations performed on the Bitcoin blockchain network per second to facilitate cryptocurrency mining. The hash rate is integral to determining how fast a blockchain can carry out mining and transactions on the network.

Hash functions are algorithms that take data of any size and convert it into a fixed-length hexadecimal number, or hash. Hash functions are one-way functions and cannot be inverted to reveal the data input to create the hash. The Bitcoin blockchain utilizes the SHA-256 hash algorithm in its transaction validation process.

Hashing is the process of taking an input of any size and using a mathematical function called a hash function to create an output of fixed size. Hash functions are considered one-way functions. Unlike encryption, which is intended to conceal data as it moves over a network or is stored on a device, hashing is primarily used to verify the authenticity of data. Hashing also serves an important security function in protecting network components such as passwords and sensitive information that can be stored as hashes — the outputs of hash functions.

During an atomic swap, the HashLock Key will only distribute exchanged cryptocurrency when both parties have signed off on their respective transactions.

The hash rate is the unit of measure for the computing power of a Proof-of-Work consensus mechanism. The hash rate is valued in terahashes per second (TH/s), and increases or decreases according to the number of miners operating on the network.

Haskell is a programming language suitable for a variety of applications in financial services and hardware design. Cardano is programmed in Haskell.

Head and shoulders technical formations visually consist of a left shoulder, a head, a right shoulder, as well as a neckline (which is drawn across the bottom of the formation). These formations are created by rising and dropping prices that form two smaller "shoulders" surrounding a larger "head" in the center. Head and shoulders typically occur when an asset is close to a reversal in price. With an inverse head and shoulders formation, the opposite occurs once the pattern has been defined, with the end result often being an increase in price.

A hedge is when an investment in a security or asset is made with the intention of offsetting potential risks or losses elsewhere in an investment portfolio.

Hedge contracts are specialized smart contracts utilized by the Hegic protocol that enable the on-chain trading and execution of options contracts. Like traditional options contracts, hedge contracts come in the form of both call and put options.

A hedge fund is a pooled investment fund that uses complex combinations of investment strategies and techniques to increase its performance. Hedge funds have a relatively low barrier for entry compared to other types of funds, but are still typically reserved for accredited institutional investors and high net-worth individuals (HNWIs). Hedge funds can be expensive to gain entry to compared to traditional investments, but tend to exhibit higher returns than market averages globally.

A Heimdall Node is a PoS validator node that is integrated with Polygon’s staking contract system on Ethereum to enable Polygon’s Proof of Stake (PoS) consensus mechanism. This capability was realized by building on top of the Tendermint consensus engine with modifications to the signature scheme and specific data structures. Heimdall Nodes oversee block validation, block producer committee selection, and checkpointing of Polygon’s sidechain blocks to the Ethereum network. The Heimdall layer aggregates blocks produced by Bor Nodes into a Merkle tree and publishes the Merkle root sequentially to the Polygon root chain (one of any number of side chains that Polygon creates).

Within the fields of mathematics and computing, the hexadecimal numerical system or “hex” system is a positional numerical system that represents numbers utilizing a radix base of 16. Instead of using the common methodology of representing numbers using 10 symbols, hexadecimal makes use of 16. Typically, the symbols “0”-“9” represent values 0-9, while “A”-“F” represent the values 10-15. Hexadecimal numerals are generally used by computer system designers and software engineers to provide a human-friendly representation of binary-coded values to allow for simple readability.

A hidden cap is a blockchain-focused fundraising strategy where the fundraising goal’s upper limit is kept secret and known only to the blockchain team. Used on some Initial Coin Offerings (ICOs) and similar equity offerings, proponents claim that hidden caps benefit smaller investors. This is because bigger investors generally want the transparency of knowing the total amount or supply of an asset before they are willing to make a substantial capital investment. This typically discourages large investments as a hidden cap affects investment allocation decision-making. Critics counter that hidden caps go against the blockchain ethos of transparency, verifiability, and trustlessness.

A hierarchical-deterministic wallet is a cryptocurrency wallet that generates new cryptographic key pairs or addresses from a master key pair each time funds are received. This technique is intended to enhance the privacy of the wallet by distributing the total balance of a user's cryptocurrency holdings across several addresses. This feature also increases the security of the wallet by distributing private keys, while all previously used addresses remain usable and within the user's control.

The high, or highest price, is one of four main data points used for day trading on the stock market. The other three are called opening price, low, and close — and all four are collectively known as OHLC. The high is generally classified as the highest price obtained during the last 24-hour trading period since the markets opened. Cryptocurrency markets are open 24 hours a day, every day of the year unlike the traditional stock market, which is closed for trading on weekends.

High-frequency trading is an automated market trading method that utilizes algorithms to rapidly buy and sell a large quantity of orders.

A high-level programming language is a programming language that possesses high levels of abstraction and is designed to be less complex and more efficient than low-level languages. High-level programming languages are characterized as highly readable (they are usually based on English), extremely portable for use with numerous platform types, and easier to debug and maintain compared to their low-level counterparts. High-level programming languages are also highly executable, and typically require a compiler to translate into a machine-readable format. Most widespread programming languages are considered high-level, with examples being JavaScript, C++, Python, Java, C#, and WebAssembly (WASM).

A high-net-worth individual (HNWI) is an individual that possesses liquid assets above a certain amount, generally at least $1 million. These assets could include stocks, bonds, and commodities, among others.

A junk bond is a bond that holds a high risk of default. Junk bonds are also referred to as 'high-yield,' because investors receive high interest rates in return for taking on increased risk.

A HMAC-based One-Time Password (HOTP) is a password that makes use of a one-time password (OTP) algorithm leveraging Hash-Based Message Authentication Code (HMAC). HOTPs, like Time-based One-Time Passwords (TOTPs), are used as a security measure for specialized authentication methods such as two-factor authentication (2FA). The HOTP mechanism uses a hash-generated one-time password that allows users to securely log in to various websites often through their mobile phone using an authentication application.

"Hodl" is a slang expression that refers to the holding of cryptocurrency assets, as opposed to liquidation. The term was derived from a post on Bitcointalk in which the poster misspelled 'hold,' and subsequently became a meme.

Homestead was an upgrade of the Ethereum network that took place during March 2016, after the initial Frontier phase of the Ethereum network was determined to be stable enough for the launch of Homestead. Homestead provided much of the same beta testing-level experience as Frontier, alongside a command line interface, more stability, and a few additional features.

An Honest Geppetto attack refers to a computer network attack in which a hacker runs a large number of nodes for a long period of time in order to gain trust of the other nodes in a given network. When this has been achieved, the attacker abruptly takes the nodes offline with the goal of disrupting the entire network. The best way to prevent an Honest Geppetto attack is to build a large network that makes the attack ineffective.

HoneyBadger BFT (HBBFT) is an asynchronous Byzantine Fault Tolerant (aBFT) network consensus mechanism that is designed to handle potentially thousands of transactions per second (TPS) and scale over a wide area network. As an asynchronous method of BFT consensus, HBBFT does not rely on assumptions about time to achieve network consensus, which is beneficial in an environment where network nodes are operating under widely different conditions and connection speeds.

Horizontal Relay-Routed Message Passing (HRMP) is a solution built for the Kusama and Polkadot networks that helps parachains communicate and share data with each other. HRMP is eventually slated to be replaced by the more advanced — but (as of early 2021) not yet complete — Cross-Chain Message Passing (XCMP) technology. HRMP is more computationally demanding compared to XCMP because it stores all messages in Polkadot’s Relay Chain. HRMP and XCMP are designed to help facilitate cross-chain communication and the transfer of assets and other data from one blockchain protocol to another.

Horizontal scalability is a means of increasing the transactional capacity of a blockchain network by adding more nodes to the network or optimizing systems, rather than altering the protocol via code.

A hostage byte attack is a theoretical vulnerability in the STORJ network in which malicious storage nodes might extort payment from users by refusing to transfer pieces of data.

The term hot wallet refers to a cryptocurrency wallet that is connected to the internet. The wallet's assets are therefore held online, as opposed to a cold wallet, which is held in an offline environment.

Hotspots are devices that operate on the Helium Network both as specialized network nodes and as wireless internet hotspots. Helium Hotspots are manufactured by multiple vendors and are designed to be easily deployable solutions to participate in the Helium Network and earn rewards for providing internet coverage to various devices on the network.

The Howey Test is a series of four conditions that the U.S. Securities and Exchange Commission (SEC) uses to determine whether a financial transaction is considered to have involved the purchase of a security. The conditions are:

1) The transaction involves an investment of money

2) There is an expectation of profits from the investment

3) The investment of money is in a common enterprise

4) Any profit comes from the efforts of a promoter or third party

-If a transaction passes all four conditions of the Howey Test, it is legally considered to involve the purchase of a security.

Human-readable agreements are agreements that are written in human-interpretable language (i.e. English) instead of code. This mechanism is important because it helps allow the technical architecture of a computerized system to be better understood by humans.

A version of wrapped bitcoin launched by Huobi Global, the hBTC (or HBTC) crypto protocol generates an ERC-20 representation of bitcoin (BTC). Backed 1:1 by BTC, hBTC is custodied by Huobi.

Huobi is a cryptocurrency exchange that was founded in 2013 by CEO Leon Li. Huobi provides services for both retail and institutional investors. It has a version of wrapped Bitcoin called Huobi BTC (hBTC), and has also built its own blockchain called the Huobi Eco Chain.

The Huobi Ecochain blockchain is the proprietary blockchain created by the Huobi Group and its main underlying cryptocurrency exchange Huobi Global. It is characterized by its cost-efficiency, extremely fast transaction times, and Ethereum Virtual Machine (EVM)-compatible architecture allowing developers to deploy Solidity-based smart contracts on the protocol. Huobi Ecochain is designed mainly to transfer tokenized assets between different decentralized applications (dApps) and the various services offered by its region-specific Huobi exchange platforms. Huobi Ecochain provides the technical infrastructure needed to operate various centralized finance (CeFi) and decentralized finance (DeFi) systems for both retail and institutional investors across the globe.

A hybrid blockchain network combines elements of both private and public blockchains. The hybrid aspect of the network's architecture most often includes a main public chain, in addition to private side-chains of various purposes that link back to the main chain and public access.

Hybrid exponential minting is a method for minting coins utilized by the Filecoin network. In this model, 30% of rewards are distributed according to an exponential decay model, in which block rewards are greatest at the protocol's inception and decrease over time. 70% of rewards are distributed in proportion with the growth of the total storage capacity of the network. This model was developed to ensure the long-term viability of the Filecoin network because it rewards miners throughout the entire lifecycle of the network, in proportion to the utility they provide to the network.

Hybrid smart contract is a term employed by the Chainlink protocol, referring to augmented smart contracts that combine both on-chain and off-chain elements. An example of a hybrid smart contract could be a decentralized finance (DeFi) application that relies on external Chainlink price feeds — combining off-chain data into the structure of the on-chain smart contract. Hybrid smart contracts are envisioned to expand the applicability of smart contract technology to broader real-world use cases.

Hyperinflation describes severe, and often rapid price increases in an economy resulting from surplus money supply. Political instability, a weak economy, and loss of confidence in the financial system can cause hyperinflation, which can be highly destabilizing to a national currency and economy.

The Hyperledger project is an open-source umbrella project for blockchain that first came to fruition in December of 2015 via the Linux Foundation. Hyperledger has received considerable contributions from large-scale global enterprises such as IBM, Intel, and JP Morgan to support the collaborative development and ongoing research of distributed ledger technology and blockchain. The mission of the project is to develop multi-industry collaboration for the development of blockchain to improve the performance and reliability of distributed ledger systems to support global business transactions. The Hyperledger project consists of four main blockchain network protocols — Hyperledger Fabric, Hyperledger Sawtooth, Hyperledger Besu, and Hyperledger Iroha.

Hyperledger Fabric is a permissioned blockchain protocol that was initially designed by IBM and other constituents built to provide a modular framework enabling precise delineation of node infrastructure, smart contract execution (known as “chaincode”), configurable consensus, and blockchain-agnostic membership services. Hyperledger Fabric is composed of Peer Nodes, Orderer Nodes, and Membership Service Providers (MSPs) which typically make use of a Certificate Authority responsible for authenticating Hyperledger member identities and role types. Hyperledger uses JavaScript, Go, Java, and other languages. It is capable of using multiple consensus methodologies, but is generally used with Practical Byzantine Fault Tolerance (pBFT).

Hypertext Transfer Protocol (HTTP) is an application layer protocol that allows hypermedia data like HTML to operate online. HTTP is one of the main foundational layers of the internet and allows web pages, hyperlinks, hypertext, data, and more to communicate with different types of web servers that are needed to display information to users via a user interface (UI) or screen. HTTP not only interacts with HTML, but also with other web-based systems such as JavaScript, cascading style sheets (CSSs), application programming interfaces (APIs), and the Transmission Control Protocol (TCP) and Internet Protocol (IP) layers of the internet.