Glossary
The vocabulary of blockchain validation, in plain words.
- Validator
- A participant entitled to propose and vote on blocks, with stake at risk.
- Full node
- A computer that checks every block and transaction against the rules for itself.
- Consensus
- Agreement among many computers on one history.
- Byzantine fault
- A failure in which a participant behaves arbitrarily, including lying differently to different peers.
- Safety and liveness
- Nothing bad happens (no two conflicting blocks are final) / something good eventually happens (the chain keeps growing).
- Stake
- Capital locked as a condition of validating, and forfeit in part for provable misbehaviour.
- Sybil attack
- Gaining influence by creating many fake identities.
- Proposer
- The validator chosen to build the next block.
- Attestation
- A validator’s signed vote for a block.
- Committee
- The subset of validators assigned to vote at a particular moment.
- Slot and epoch
- A fixed interval in which one block may be proposed / a fixed number of slots. On Ethereum: 12 seconds, and 32 slots.
- Fork
- Two competing versions of recent history.
- Fork-choice rule
- The rule by which a node picks which fork to follow.
- Finality
- The point after which a block cannot be reversed without a large, provable penalty.
- Equivocation
- Signing two conflicting messages for the same slot.
- Slashing
- Destruction of part of a validator’s stake for provable misbehaviour, usually with removal from the set.
- Inactivity penalty
- A gradual loss of stake by validators that stay offline while the chain is failing to finalise.
- Delegation
- Assigning one’s stake to a validator run by someone else.
- Unbonding period
- The delay between asking to withdraw stake and receiving it, during which it can still be slashed.
- Long-range attack
- Rewriting history from far back using keys that once held stake and no longer have anything to lose.
- Weak subjectivity
- The need for a node that has been offline for long to obtain a recent trusted checkpoint.
- Nothing at stake
- The problem that, without penalties, voting on every fork is free.
- Verifiable random function
- A function whose output looks random but comes with a proof that it was computed correctly.
- Signature aggregation
- Combining many signatures into one short signature that verifies them all.
- Client diversity
- Validators running independently written software, so that one bug cannot stop or split the chain.
- Distributed validator
- One validator whose signing key is split among several machines, none of which can sign alone.
- Maximal extractable value
- What a proposer can gain by choosing, ordering or excluding transactions in its block.