ZetaChain: A Blockchain with Native Cross-chain Smart Contracts

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This whitepaper proposes ZetaChain, a blockchain with generic omnichain smart
contract support that connects both smart contract blockchains such as Ethereum,
Ethereum L2 rollups, Solana, Terra, and Algorand, and even non smart contract
blockchains such as Bitcoin and Dogecoin. ZetaChain consists of a Proof-of-Stake
blockchain and observers and signers for external blockchains. The observers scan
external chains for relevant events, transactions, and states at a point in time, and
reach consensus on observation on ZetaChains blockchain. The signers collectively
possess a single Threshold Signature Scheme (TSS) key that is able to send authenticated messages to external chains and hold assets like normal accounts/addresses
on external chains. Smart contracts on ZetaChain support arbitrary logic that executes conditionally on external chain events, and can directly update external chain
states via its TSS signed transactions. ZetaChain thereby enables omnichain dApps
that interact with different blockchains natively and directly without wrapping or
bridging any assets.