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Glossary
#
51% attack
A type of attack on a decentralized network where a group gains control of the majority of nodes. This would allow them to defraud the blockchain by reversing transactions and double spending ether and other tokens.
A
account
An object containing an address, balance, nonce, and optional storage and code. An account can be a contract account or an externally owned account (EOA).
Ethereum Accounts
address
Most generally, this represents an EOA or contract that can receive (destination address) or send (source address) transactions on the blockchain. More specifically, it is the rightmost 160 bits of a Keccak hash of an ECDSA public key.
application binary interface (ABI)
The standard way to interact with contracts in the Ethereum ecosystem, both from outside the blockchain and for contract-to-contract interactions.
ABI
assert
In Solidity, assert(false) compiles to 0xfe, an invalid opcode, which uses up all remaining gas and reverts all changes. When an assert() statement fails, something very wrong and unexpected is happening, and you will need to fix your code. You should use assert() to avoid conditions that should never, ever occur.
Security
attestation
A validator vote for a Beacon Chain or shard block. Validators must attest to blocks, signaling that they agree with the state proposed by the block.
B
Beacon Chain
An Eth2 upgrade that will become the coordinator for the Ethereum network. It introduces proof-of-stake and validators to Ethereum. It will eventually be merged with Mainnet.
Beacon Chain
big-endian
A positional number representation where the most significant digit is first in memory. The opposite of little-endian, where the least significant digit is first.
block
A collection of required information (a block header) about the comprised transactions, and a set of other block headers known as ommers. Blocks are added to the Ethereum network by miners.
Blocks
blockchain
In Ethereum, a sequence of blocks validated by the proof-of-work system, each linking to its predecessor all the way to the genesis block. There is no block size limit; it instead uses varying gas limits.
What is a Blockchain?
bytecode
An abstract instruction set designed for efficient execution by a software interpreter or a virtual machine. Unlike human-readable source code, bytecode is expressed in numeric format.
Byzantium fork
The first of two hard forks for the Metropolis development stage. It included EIP-649 Metropolis Difficulty Bomb Delay and Block Reward Reduction, where the Ice Age was delayed by 1 year and the block reward was reduced from 5 to 3 ether.
C
compiling
Converting code written in a high-level programming language (e.g., Solidity) into a lower-level language (e.g., EVM bytecode).
Compiling Smart Contracts
committee
A group of at least 128 validators assigned to beacon and shard blocks at random by the Beacon Chain.
consensus
When numerous nodes (usually most nodes on the network) all have the same blocks in their locally validated best blockchain. Not to be confused with consensus rules.
consensus rules
The block validation rules that full nodes follow to stay in consensus with other nodes. Not to be confused with consensus.
Constantinople fork
The second part of the Metropolis stage, originally planned for mid-2018. Expected to include a switch to a hybrid proof-of-work/proof-of-stake consensus algorithm, among other changes.
contract account
An account containing code that executes whenever it receives a transaction from another account (EOA or contract).
contract creation transaction
A special transaction, with the zero address as the recipient, that is used to register a contract and record it on the Ethereum blockchain.
crosslink
A crosslink provides a summary of a shard's state. It's how shard chains will communicate with one another via the Beacon Chain in the sharded proof-of-stake system.
Proof-of-stake
D
Decentralized Autonomous Organization (DAO)
A company or other organization that operates without hierarchical management. DAO may also refer to a contract named "The DAO" launched on April 30, 2016, which was then hacked in June 2016; this ultimately motivated a hard fork (codenamed DAO) at block 1,192,000, which reversed the hacked DAO contract and caused Ethereum and Ethereum Classic to split into two competing systems.
Decentralized Autonomous Organizations (DAOs)
Dapp
Decentralized application. At a minimum, it is a smart contract and a web user interface. More broadly, a Dapp is a web application that is built on top of open, decentralized, peer-to-peer infrastructure services. In addition, many Dapps include decentralized storage and/or a message protocol and platform.
Introduction to Dapps
decentralized exchange (DEX)
A type of dapp that lets you swap tokens with peers on the network. You need ether to use one (to pay transactions fees) but they are not subject to geographical restrictions like centralized exchanges – anyone can participate.
Decentalized exchanges
deed
DeFi
Short for "decentralized finance," a broad category of dapps aiming to provide financial services backed by the blockchain, without any intermediaries, so anyone with an internet connection can participate.
Decentralized Finance (DeFi)
difficulty
A network-wide setting that controls how much computation is required to produce a proof-of-work.
difficulty bomb
Planned exponential increase in proof-of-work difficulty setting designed to motivate the transition to proof-of-stake, reducing the chances of a fork
digital signature
A short string of data a user produces for a document using a private key such that anyone with the corresponding public key, the signature, and the document can verify that (1) the document was "signed" by the owner of that particular private key, and (2) the document was not changed after it was signed.
E
elliptic curve digital signature algorithm (ECDSA)
A cryptographic algorithm used by Ethereum to ensure that funds can only be spent by their owners. It's the preferred method for creating public and private keys. Relevant for account address generation and transaction verification.
epoch
A period of 32 slots (6.4 minutes) in the Beacon Chain-coordinated system. Validator committees are shuffled every epoch for security reasons. There's an opportunity at each epoch for the chain to be finalized.
Proof-of-stake
Ethereum Improvement Proposal (EIP)
A design document providing information to the Ethereum community, describing a proposed new feature or its processes or environment (see ERC).
Introduction to EIPs
Ethereum Name Service (ENS)
The ENS registry is a single central contract that provides a mapping from domain names to owners and resolvers, as described in EIP 137.
entropy
In the context of cryptography, lack of predictability or level of randomness. When generating secret information, such as private keys, algorithms usually rely on a source of high entropy to ensure the output is unpredictable.
externally owned account (EOA)
An account created by or for human users of the Ethereum network.
Ethereum Request for Comments (ERC)
A label given to some EIPs that attempt to define a specific standard of Ethereum usage.
Introduction to EIPs
Ethash
A proof-of-work algorithm for Ethereum 1.0.
ether
The native cryptocurrency used by the Ethereum ecosystem, which covers gas costs when executing transactions. Also writen as ETH or its symbol Ξ, the Greek uppercase Xi character.
Currency for our digital future
events
Allows the use of EVM logging facilities. Dapps can listen for events and use them to trigger JavaScript callbacks in the user interface.
Events and Logs
Ethereum Virtual Machine (EVM)
A stack-based virtual machine that executes bytecode. In Ethereum, the execution model specifies how the system state is altered given a series of bytecode instructions and a small tuple of environmental data. This is specified through a formal model of a virtual state machine.
Ethereum Virtual Machine
EVM assembly language
A human-readable form of EVM bytecode.
F
fallback function
A default function called in the absence of data or a declared function name.
faucet
A service carried out via smart contract that dispenses funds in the form of free test ether that can be used on a testnet.
Testnet Faucets
finality
Finality is the guarantee that a set of transactions before a given time will not change and can't be reverted.
Proof-of-work finality
Proof-of-stake finality
finney
A denomination of ether. 1 finney = 1015 wei. 103 finney = 1 ether.
fork
A change in protocol causing the creation of an alternative chain, or a temporal divergence in two potential block paths during mining.
fraud proof
A security model for certain layer 2 solutions where, to increase speed, transactions are rolled up into batches and submitted to Ethereum in a single transaction. They are assumed valid but can be challenged if fraud is suspected. A fraud proof will then run the transaction to see if fraud took place. This method increases the amount of transactions possible while maintaining security. Some rollups use validity proofs.
Optimistic rollups
frontier
The initial test development stage of Ethereum, which lasted from July 2015 to March 2016.
G
gas
A virtual fuel used in Ethereum to execute smart contracts. The EVM uses an accounting mechanism to measure the consumption of gas and limit the consumption of computing resources (see Turing complete).
Gas and Fees
gas limit
The maximum amount of gas a transaction or block may consume.
genesis block
The first block in a blockchain, used to initialize a particular network and its cryptocurrency.
geth
Go Ethereum. One of the most prominent implementations of the Ethereum protocol, written in Go.
Read more at geth.ethereum.org
gwei
Short for gigawei, a denomination of ether, commonly utilized to price gas. 1 gwei = 109 wei. 109 gwei = 1 ether.
H
hard fork
A permanent divergence in the blockchain; also known as a hard-forking change. One commonly occurs when nonupgraded nodes can't validate blocks created by upgraded nodes that follow newer consensus rules. Not to be confused with a fork, soft fork, software fork, or Git fork.
hash
A fixed-length fingerprint of variable-size input, produced by a hash function. (See keccak-256)
HD wallet
A wallet using the hierarchical deterministic (HD) key creation and transfer protocol.
HD wallet seed
A value used to generate the master private key and master chain code for an HD wallet. The wallet seed can be represented by mnemonic words, making it easier for humans to copy, back up, and restore private keys.
homestead
The second development stage of Ethereum, launched in March 2016 at block 1,150,000.
I
index
A network structure meant to optimize the querying of information from across the blockchain by providing an efficient path to its storage source.
Inter-exchange Client Address Protocol (ICAP)
An Ethereum address encoding that is partly compatible with the International Bank Account Number (IBAN) encoding, offering a versatile, checksummed, and interoperable encoding for Ethereum addresses. ICAP addresses use a new IBAN pseudo-country code- XE, standing for "eXtended Ethereum," as used in nonjurisdictional currencies (e.g., XBT, XRP, XCP).
Ice Age
A hard fork of Ethereum at block 200,000 to introduce an exponential difficulty increase (aka difficulty bomb), motivating a transition to proof-of-stake.
integrated development environment (IDE)
A user interface that typically combines a code editor, compiler, runtime, and debugger.
Integrated Development Environments
immutable deployed code problem
Once a contract's (or library's) code is deployed, it becomes immutable. Standard software development practices rely on being able to fix possible bugs and add new features, so this represents a challenge for smart contract development.
Deploying Smart Contracts
internal transaction
A transaction sent from a contract account to another contract account or an EOA (see message).
K
key derivation function (KDF)
Also known as a "password stretching algorithm," it is used by keystore formats to protect against brute-force, dictionary, and rainbow table attacks on passphrase encryption, by repeatedly hashing the passphrase.
Security
keccak-256
Cryptographic hash function used in Ethereum. Keccak-256 was standardized as SHA-3.
keystore file
A JSON-encoded file that contains a single (randomly generated) private key, encrypted by a passphrase for extra security.
L
layer 2
An area of development focused on layering improvements on top of the Ethereum protocol. These improvements are related to transaction speeds, cheaper transaction fees, and transaction privacy.
Layer 2
LevelDB
An open source on-disk key-value store, implemented as a lightweight, single-purpose library, with bindings to many platforms.
library
A special type of contract that has no payable functions, no fallback function, and no data storage. Therefore, it cannot receive or hold ether, or store data. A library serves as previously deployed code that other contracts can call for read-only computation.
Smart Contract Libraries
lightweight client
An Ethereum client that does not store a local copy of the blockchain, or validate blocks and transactions. It offers the functions of a wallet and can create and broadcast transactions.
M
Mainnet
Short for "main network," this is the main public Ethereum blockchain. Real ETH, real value, and real consequences. Also known as layer 1 when discussing layer 2 scaling solutions. (Also, see testnet)
Merkle Patricia trie
A data structure used in Ethereum to efficiently store key-value pairs.
message
An internal transaction that is never serialized and only sent within the EVM.
message call
The act of passing a message from one account to another. If the destination account is associated with EVM code, then the VM will be started with the state of that object and the message acted upon.
Metropolis
The third development stage of Ethereum, launched in October 2017.
miner
A network node that finds valid proof-of-work for new blocks, by repeated pass hashing (see Ethash).
Mining
N
network
Referring to the Ethereum network, a peer-to-peer network that propagates transactions and blocks to every Ethereum node (network participant).
Networks
non-fungible token (NFT)
Also known as a "deed," this is a token standard introduced by the ERC-721 proposal. NFTs can be tracked and traded, but each token is unique and distinct; they are not interchangeable like ETH and ERC-20 tokens. NFTs can represent ownership of digital or physical assets.
Non-Fungible Tokens (NFTs)
ERC-721 Non-Fungible Token Standard
node
A software client that participates in the network.
Nodes and Clients
Nodes and Clients
nonce
In cryptography, a value that can only be used once. There are two types of nonce used in Ethereum- an account nonce is a transaction counter in each account, which is used to prevent replay attacks; a proof-of-work nonce is the random value in a block that was used to satisfy the proof-of-work.
O
ommer (uncle) block
When a miner finds a valid block, another miner may have published a competing block which is added to the tip of the blockchain first. This valid, but stale, block can be included by newer blocks as ommers and receive a partial block reward. The term "ommer" is the preferred gender-neutral term for the sibling of a parent block, but this is also sometimes referred to as an "uncle".
Optimistic rollup
A rollup of transactions that use fraud proofs to offer increased layer 2 transaction throughput while using the security provided by Mainnet (layer 1). Unlike Plasma, a similar layer 2 solution, Optimistic rollups can handle more complex transaction types – anything possible in the EVM. They do have latency issues compared to Zero-knowledge rollups because a transaction can be challenged via the fraud proof.
Optimistic Rollups
P
parity
One of the most prominent interoperable implementations of the Ethereum client software.
Plasma
An off-chain scaling solution that uses fraud proofs, like Optimistic rollups. Plasma is limited to simple transactions like basic token transfers and swaps.
Plasma
private key (secret key)
A secret number that allows Ethereum users to prove ownership of an account or contracts, by producing a digital signature (see public key, address, ECDSA).
proof of stake (PoS)
A method by which a cryptocurrency blockchain protocol aims to achieve distributed consensus. PoS asks users to prove ownership of a certain amount of cryptocurrency (their "stake" in the network) in order to be able to participate in the validation of transactions.
Proof of stake
proof of work (PoW)
A piece of data (the proof) that requires significant computation to find. In Ethereum, miners must find a numeric solution to the Ethash algorithm that meets a network-wide difficulty target.
Proof of work
public key
A number, derived via a one-way function from a private key, which can be shared publicly and used by anyone to verify a digital signature made with the corresponding private key.
R
receipt
Data returned by an Ethereum client to represent the result of a particular transaction, including a hash of the transaction, its block number, the amount of gas used, and, in case of deployment of a smart contract, the address of the contract.
re-entrancy attack
An attack that consists of an attacker contract calling a victim contract function in such a way that during execution the victim calls the attacker contract again, recursively. This can result, for example, in the theft of funds by skipping parts of the victim contract that update balances or count withdrawal amounts.
Re-entrancy
reward
An amount of ether included in each new block as a reward by the network to the miner who found the proof-of-work solution.
Recursive Length Prefix (RLP)
An encoding standard designed by the Ethereum developers to encode and serialize objects (data structures) of arbitrary complexity and length.
rollups
A type of layer 2 scaling solution that batches multiple transactions and submits them to the Ethereum main chain in a single transaction. This allows for reductions in gas costs and increases in transaction throughput. There are Optimistic and Zero-knowledge rollups which use different security methods to offer these scalability gains.
Rollups
S
Serenity
The fourth and final development stage of Ethereum, otherwise known as Ethereum 2.0.
Ethereum 2.0 (Eth2)
Secure Hash Algorithm (SHA)
A family of cryptographic hash functions published by the National Institute of Standards and Technology (NIST).
shard / shard chain
A proof-of-stake chain that is coordinated by the Beacon Chain and secured by validators. There will be 64 added to the network as part of the Eth2 shard chain upgrade. Shard chains will offer increased transaction throughput for Ethereum by providing additional data to layer 2 solutions like optimistic rollups and ZK-rollups.
Shard chains
sidechain
A scaling solution that uses a separate chain with different, often faster, consensus rules. A bridge is needed to connect these sidechains to Mainnet. Rollups also use sidechains, but they operate in collaboration with Mainnet instead.
Sidechains
singleton
A computer programming term that describes an object of which only a single instance can exist.
slot
A period of time (12 seconds) in which a new Beacon Chain and shard chain block can be proposed by a validator in the proof-of-stake system. A slot may be empty. 32 slots make up an epoch.
Proof-of-stake
smart contract
A program that executes on the Ethereum computing infrastructure.
Introduction to Smart Contracts
Solidity
A procedural (imperative) programming language with syntax that is similar to JavaScript, C++, or Java. The most popular and most frequently used language for Ethereum smart contracts. Created by Dr. Gavin Wood.
Solidity
Solidity inline assembly
EVM assembly language in a Solidity program. Solidity's support for inline assembly makes it easier to write certain operations.
Spurious Dragon
A hard fork of the Ethereum blockchain, which occurred at block 2,675,000 to address more denial-of-service attack vectors and clear state (see Tangerine Whistle). Also, a replay attack protection mechanism (see nonce).
stablecoin
An ERC-20 token with a value pegged to another asset's value. There are stablecoins backed by fiat currency like dollars, precious metals like gold, and other cryptocurrencies like Bitcoin.
ETH isn't the only crypto on Ethereum
staking
Depositing a quantity of ether (your stake) to become a validator and secure the network. A validator checks transactions and proposes blocks under a proof-of-stake consensus model. Staking gives you an economic incentive to act in the best interests of the network. You'll get rewards for carrying out your validator duties, but lose varying amounts of ETH if you don't.
Stake your ETH to become an Ethereum validator
state channels
A layer 2 solution where a channel is set up between participants, where they can transact freely and cheaply. Only a transaction to set up the channel and close the channel is sent to Mainnet. This allows for very high transaction throughput, but does rely on knowing number of participants up front and locking up of funds.
State channels
szabo
A denomination of ether. 1 szabo = 1012 wei, 106 szabo = 1 ether.
T
Tangerine Whistle
A hard fork of the Ethereum blockchain, which occurred at block 2,463,000 to change the gas calculation for certain I/O-intensive operations and to clear the accumulated state from a denial-of-service attack, which exploited the low gas cost of those operations.
testnet
Short for "test network," a network used to simulate the behavior of the main Ethereum network (see Mainnet).
Testnets
token standard
Introduced by ERC-20 proposal, this provides a standardized smart contract structure for fungible tokens. Tokens from the same contract can be tracked, traded, and are interchangeable, unlike NFTs.
ERC-20 Token Standard
transaction
Data committed to the Ethereum Blockchain signed by an originating account, targeting a specific address. The transaction contains metadata such as the gas limit for that transaction.
Transactions
transaction fee
A fee you need to pay whenever you use the Ethereum network. Examples include sending funds from your wallet or a dapp interaction, like swapping tokens or buying a collectible. You can think of this like a service charge. This fee will change based on how busy the network is. This is because miners, the people responsible for processing your transaction, are likely to prioritise transactions with higher fees – so congestion forces the price up.
At a technical level, your transaction fee relates to how much gas your transaction requires.
Reducing transaction fees is a subject of intense interest right now. See Layer 2
Turing complete
A concept named after English mathematician and computer scientist Alan Turing- a system of data-manipulation rules (such as a computer's instruction set, a programming language, or a cellular automaton) is said to be "Turing complete" or "computationally universal" if it can be used to simulate any Turing machine.
V
validator
A node in a proof-of-stake system responsible for storing data, processing transactions, and adding new blocks to the blockchain. To active validator software, you need to be able to stake 32 ETH.
Proof of stake
Staking in Ethereum
Validity proof
A security model for certain layer 2 solutions where, to increase speed, transactions are rolled up into batches and submitted to Ethereum in a single transaction. The transaction computation is done off-chain and then supplied to the main chain with a proof of their validity. This method increases the amount of transactions possible while maintaining security. Some rollups use fraud proofs.
Zero-knowledge rollups
Validium
An off-chain solution that uses validity proofs to improve transaction throughput. Unlike Zero-knowledge rollups, Validium data isn't stored on layer 1 Mainnet.
Validium
Vyper
A high-level programming language with Python-like syntax. Intended to get closer to a pure functional language. Created by Vitalik Buterin.
Vyper
W
wallet
Software that holds private keys. Used to access and control Ethereum accounts and interact with smart contracts. Keys need not be stored in a wallet, and can instead be retrieved from offline storage (i.e. a memory card or paper) for improved security. Despite the name, wallets never store the actual coins or tokens.
Ethereum Wallets
Web3
The third version of the web. First proposed by Dr. Gavin Wood, Web3 represents a new vision and focus for web applications- from centrally owned and managed applications, to applications built on decentralized protocols (see Dapp).
Web2 vs Web3
wei
The smallest denomination of ether. 1018 wei = 1 ether.
Z
zero address
A special Ethereum address, composed entirely of zeros, that is specified as the destination address of a contract creation transaction.
Zero-knowledge rollup
A rollup of transactions that use validity proofs to offer increased layer 2 transaction throughput while using the security provided by Mainnet (layer 1). Although they can't handle complex transaction types, like Optimistic rollups, they don't have latency issues because transactions are provably valid when submitted.
Zero-knowledge Rollups
Sources
Provided in part by Mastering Ethereum by Andreas M. Antonopoulos, Gavin Wood under CC-BY-SA
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