Union Basics: A Cross-Chain Bridge with Minimal Trust Elements - Connect all blockchains like IBC with ZK! (Before diving into the @union_build hype that many are joining, it would be good to read about what this project is and what technology it involves.) We usually use a "bridge" when transferring assets to another chain. Cross-chain bridges, which are technologies for transferring assets or messages between chains, are essential in today's blockchain infrastructure, but they mostly operate based on trust, meaning you have to trust someone. Today, I will explain Union, a protocol designed to minimize trust in cross-chain messaging. Union allows communication between chains without trusting people, instead relying on ZK proofs, which means you can trust mathematics. Traditional bridges require you to trust the operators running the bridge or the oracle providers. However, in the case of Union, this trust element is converted to be based on ZK proofs. Let me explain how Union actually works with a simple example. Scenario: Sending USDT tokens from BSC to Ethereum 1. The Union chain receives the root of the block state for each chain, which validators sign and record. (The Union chain is a self-developed L1 chain based on CometBLS, an improvement of Tendermint.) 2. The Prover references the state root of BSC recorded on the Union chain and finds the USDT token transfer event (burn or lock) on the actual BSC blockchain. Using this, it generates a ZK proof to demonstrate that the event exists within the Merkle tree. 3. This proof is submitted to Ethereum, where the ZK proof verification smart contract installed on Ethereum mathematically verifies the proof. 4. Once verification is complete, the transfer is finalized on Ethereum (mint or release). While traditional bridges operate by having bridge operators observe the state of each chain and execute token lock & mint through MPC or multi-signature, Union operates all processes based on mathematical proof (ZKP). Even if the Prover generates an incorrect proof, the transfer will fail due to verification failure. This verification is performed solely by the smart contract on the chain, making it fundamentally impossible for the verifier and Prover to collude or deceive. Currently, Union supports testnet communication with EVM and Cosmos-based chains like Ethereum, BSC, Sei, and Osmosis, and integration testing is also underway with Babylon (an L2 based on Bitcoin security) in the Bitcoin ecosystem. In the current landscape where various blockchains coexist, cross-chain messaging and bridges that connect different chains are crucial infrastructure. Union aims to redefine the trust structure between blockchains based on ZK and become a new standard for cross-chain messaging. It seeks to overcome the limitations of existing bridges by removing the trust element through mathematical proof (ZKP) instead of relying on trusting someone.