Glossary

Gaining more than half of the computing power (or stake) that publishes blocks, so as to outpace everyone else and replace recent blocks. Expensive rather than technically hard.

Explained in The limits.

A short string worked out from a public key with a hash, used to send and receive on a blockchain. It is not secret.

Explained in Keys and signatures.

Cryptography with a pair of keys: a private key kept secret, and a public key given to others. Data signed with the private key can be checked by anyone with the public key.

Explained in Keys and signatures.

On Ethereum, the lowest price per unit of gas a transaction must pay to be included in a block. It is set by the network, rises or falls from block to block, and is burned rather than paid to anyone.

A batch of transactions added to a blockchain at one time, with a header that describes it.

Explained in A blockchain in one page.

A website that shows a blockchain's data: its blocks, transactions, accounts and other activity. The checks on this site link to one for each chain they read; it is not an official register.

The part of a block that describes it: usually a timestamp, a hash of the block's transactions, the hash of the previous block's header, and a nonce.

Explained in A blockchain in one page.

What a publisher receives, usually in the network's own coin, for adding a block.

A shared record of signed transactions, kept by many computers and grouped into blocks. Each block is linked to the one before, so a change to an old block shows.

Explained in A blockchain in one page.

The rule a network uses to agree which block comes next and which copy of the record is the right one.

Explained in How the computers agree.

A group of organisations that run a permissioned blockchain together.

Explained in Public and private blockchains.

On Ethereum, the address a smart contract lives at. It is worked out when the contract is put on the chain.

Explained in Smart contracts.

A digital unit sent from one user of a blockchain to another, with a digital signature. New units are often created as the reward for publishing a block.

Anything purely digital, or a digital record standing for something physical, that can be transferred.

Proof, made with a private key, that a message came from that key's holder and has not been changed since. Anyone with the public key can check it.

Explained in Keys and signatures.

A record of transactions kept by many computers, with no central copy. A blockchain is one kind.

Explained in A blockchain in one page.

Spending the same digital money more than once. Most blockchains are designed to stop it.

Explained in How the computers agree.

A common method of making and checking digital signatures, used in many blockchains.

Explained in Keys and signatures.

On Ethereum, a period of 32 slots.

Explained in How the computers agree.

A standard for interchangeable tokens on Ethereum: a smart contract that offers its set of functions can be called an ERC-20 token contract.

Explained in Smart contracts.

Ethereum's own currency. Fees on Ethereum are paid in it.

A record a smart contract writes when a transaction runs it, kept in the transaction's receipt. An ERC-20 token writes a Transfer record each time tokens move.

On Ethereum, a block that cannot be changed without a large amount of staked ETH being destroyed. A node can say which is the latest finalised block; newer blocks are still waiting for that.

A change to a blockchain's software, usually to how blocks are agreed. It may be one older software can still follow (a soft fork) or one it cannot (a hard fork).

Explained in Public and private blockchains.

A computer on the network that keeps the whole record, passes it on, and checks that new blocks follow the rules.

Explained in A blockchain in one page.

On Ethereum, the measure of how much computing a transaction needs. The fee is worked out from it and paid in ETH.

Explained in Smart contracts.

The first block of a blockchain. It records the starting state that everyone joining agrees to.

Explained in A blockchain in one page.

Small units of ETH. One gwei is a billionth of an ETH, and one wei is a billionth of a gwei, the smallest unit there is. Gas prices are usually given in gwei.

A change to a blockchain's software that older versions cannot follow. Nodes that do not update can no longer deal with those that do.

Explained in Public and private blockchains.

The fixed-length fingerprint a hash function gives for a piece of data.

Explained in Hashes: a fingerprint for any data.

A function that turns data of any length into a fingerprint of fixed length. For a cryptographic one, you cannot run it backwards or find two inputs with the same output.

Explained in Hashes: a fingerprint for any data.

How many hashes a computer, or a whole network, works out each second.

Explained in How the computers agree.

Data that can only be written, never changed or deleted. NIST notes blockchains are not strictly immutable: they are tamper evident and tamper resistant.

Explained in The limits.

A hash function from the Keccak family, which won NIST's competition for the SHA-3 standard. Ethereum uses it to make addresses.

Explained in Hashes: a fingerprint for any data.

A blockchain that runs on top of another one and publishes its transactions to it. Base's own documents call Base a layer 2 and Ethereum its layer 1.

A record of transactions.

Explained in A blockchain in one page.

A computer on the network that does not keep a full copy of the record and passes its transactions to full nodes.

The queue where new transactions wait to be put into a block.

Explained in A blockchain in one page.

Ethereum's switch from proof of work to proof of stake, on 15 Sep 2022.

Explained in How the computers agree.

A way of hashing many items into one: hash them in pairs, then hash those hashes in pairs, until one hash, the root, stands for them all.

Explained in Hashes: a fingerprint for any data.

Solving the puzzle in proof of work, to win the right to publish the next block.

Explained in How the computers agree.

One computer on a blockchain network.

Explained in A blockchain in one page.

A number used once. In proof of work, publishers change it again and again until the block's hash meets the target.

Explained in How the computers agree.

A service that brings outside information to a smart contract. The contract can only be as right as that information.

Explained in The limits.

A block left out of the main chain after the network briefly split. Its transactions go back into the queue.

Explained in How the computers agree.

A network where every computer can talk to the others directly, with no central point, so losing any one does not stop the rest.

A blockchain where users and publishers must be given permission, usually by an administrator or a consortium.

Explained in Public and private blockchains.

A blockchain anyone can join, read, send to and publish blocks on, with no administrator setting who may.

Explained in Public and private blockchains.

The secret half of a key pair. It signs transactions; whoever holds it controls what it holds.

Explained in Keys and signatures.

A consensus model for permissioned networks where publishers are known by name and stake their reputation.

Explained in How the computers agree.

A consensus model where participants lock up some of the network's coin, and the more they lock up, the more likely they are to be picked to add a block.

Explained in How the computers agree.

A consensus model where publishers compete to solve a puzzle that is hard to solve and easy to check, by spending computing power.

Explained in How the computers agree.

A smart contract at a fixed address that passes every call on to another contract, so the code behind it can be swapped. Whoever can swap it can change the whole contract.

Explained in Smart contracts.

Not named, but not anonymous either: the user's name is not on the record, but their address and every transaction to and from it are.

Explained in Keys and signatures.

The half of a key pair that can be shared. It checks signatures made with the private key, and addresses are worked out from it.

Explained in Keys and signatures.

A full node that also creates and publishes new blocks.

Explained in How the computers agree.

A consensus model for permissioned networks where members take turns to add blocks.

Explained in How the computers agree.

A hash function that gives a 256-bit fingerprint, usually written as 64 hexadecimal characters. Bitcoin uses it, and so does this site's receipt.

Explained in Hashes: a fingerprint for any data.

On Ethereum, destroying part of a validator's stake when it breaks the rules.

Explained in How the computers agree.

On Ethereum, a 12-second turn in which one validator may propose a block.

Explained in How the computers agree.

Code and data placed on a blockchain, which every node runs the same way, with the result added to the record.

Explained in Smart contracts.

A change to a blockchain's software that older versions can still follow.

Explained in Public and private blockchains.

Coin locked up by a participant in proof of stake. While staked, it generally cannot be spent.

Explained in How the computers agree.

Making many fake identities to gain influence over a network. Proof of work and proof of stake make influence cost something real instead.

Explained in How the computers agree.

Built so that a change to the data is easy to see.

Explained in A blockchain in one page.

Built so that changing the data is hard, costly, or both.

Explained in A blockchain in one page.

Proof that data existed by a certain time. The Bitcoin paper describes a timestamp server: hash the data and publish the hash widely, each timestamp including the one before.

Explained in Hashes: a fingerprint for any data.

A unit kept track of by a smart contract, which records who holds how many. Tokens can stand for almost anything, from game points to a share in a company.

Explained in Smart contracts.

A record of an event on a blockchain, such as a transfer between users or the creation of new units.

Explained in A blockchain in one page.

What a user pays to have a transaction put into a block. It goes to the block's publisher.

What a node returns about a transaction once it is in a block: whether it succeeded or failed, the gas it used, and the event logs it wrote. Not the same as the receipt at the end of a check on this site.

A system or programming language that can run any algorithm, however complex.

On Ethereum, a participant who has deposited 32 ETH to take part in proposing and checking blocks.

Explained in How the computers agree.

Software that stores keys and addresses and uses them to make transactions.

Explained in Keys and signatures.