Overview
At a high level, ZetaChain is a Proof of Stake (PoS) blockchain built on the Cosmos SDK and Tendermint PBFT consensus engine. As a result, ZetaChain enjoys fast block time (~5s) and instant finality (no confirmation needed, no re-organization allowed). The Tendermint PBFT consensus engine has shown to scale to ~300 nodes in production. With future upgrades with BLS threshold signatures the number can potentially increase to 1000+. The throughput of transactions on ZetaChain can potentially reach 100 TPS due to the efficient Tendermint consensus protocol.
The ZetaChain architecture consists of a distributed network of nodes, often referred to as validators. Validators act as decentralized observers that reach consensus on relevant external state and events, and can also update external chain state via distributed key signing. ZetaChain accomplishes these functions in a decentralized (without a single point of failure, trustless, permissionless), transparent, and efficient way.
Contained within each validator is the ZetaCore and ZetaClient. ZetaCore is responsible for producing the blockchain and maintaining the replicated state machine. ZetaClient is responsible for observing events on external chains and signing outbound transactions.
ZetaCore and ZetaClient are bundled together and run by node operators. Anyone can become a node operator to participate in validation provided that enough bonds are staked.
Validators
Validators are comprised of 3 different roles: Basic Validators, Observers, and TSS signer. Fees from transactions and rewards are distributed to Validators in return for their service of processing transactions and keeping the network secure. Observers and TSS Signers scale separately from Basic Validators due to varying security and bond requirements.
Basic Validators
ZetaChain uses the Tendermint consensus protocol which is a partially synchronous Byzantine Fault Tolerant (BFT) consensus algorithm. Each validator node can vote on block proposals with voting power proportional to the staking coins (ZETA) bonded/delegated. Each validator is identified by its consensus public key. Validators need to be online all the time, ready to participate in the constantly growing block production. In exchange for their service, validators will receive block rewards and transaction fees.
Observers
Another set of important participants for ZetaChain consensus are the observers who reach consensus on external chain events and states. The observers watch externally connected chains for certain relevant transactions/events/states at particular addresses via their full nodes of external chains. Observers will divide into two roles: sequencer and verifier. The sequencer discovers relevant external trans-actions/events/states and reports to verifiers; the verifiers verify and vote on ZetaChain to reach consensus. The system requires at least one sequencer and multiple verifiers. The sequencer does not need to be trusted, but at least one honest sequencer is needed for liveness.
TSS Signers
ZetaChain collectively holds standard ECDSA/EdDSA keys for authenticated interaction with external chains. The keys are distributed among multiple signers in such a way that only a super majority of them can sign on behalf of the ZetaChain. It's important to ensure that at no time is any single entity or small fraction of nodes able to sign messages on behalf of ZetaChain on external chains. The ZetaChain system uses bonded stakes and positive/negative incentives to ensure economic safety.