Cross-chain Bridge Overview: Hub Connecting the Multi-chain World
As blockchain technology evolves, we are entering a multi-chain ecosystem composed of numerous Layer-1 blockchains such as Ethereum, Solana, Avalanche, and BNB Chain. However, these blockchains are often designed to be independent, unable to communicate directly or transfer assets between each other. Cross-chain bridges are precisely created to solve this interoperability challenge, allowing assets, information, and data to be transferred between otherwise incompatible blockchains, serving as critical infrastructure for realizing the Web3 vision.
The emergence of cross-chain bridges enables users to flexibly integrate or transfer their digital assets when participating in various activities such as DeFi, NFTs, and GameFi on different chains, meeting the growing demand for cross-chain functionality.
Main Types of Cross-chain Bridges
Based on trust assumptions and transfer methods, cross-chain bridges can be categorized into several types:
- Classification by Trust Assumption:
- Trusted Cross-chain Bridges: Typically rely on centralized entities or a small number of validators, such as cross-chain services provided by some CEXs.
- Trustless Bridges: Rely on smart contracts and cryptographic mechanisms, offering a higher degree of decentralization and reducing reliance on a single entity.
- Classification by Transfer Method:
- Lock & Mint: Native assets are locked on the source chain, and an equivalent amount of wrapped assets (e.g., WBTC) are minted on the target chain.
- Burn & Mint: Assets are burned on the source chain, and an equivalent amount of assets are minted on the target chain.
- Liquidity Pool: Liquidity pools are set up on both the source and target chains, and users complete cross-chain transfers through swaps.
- Atomic Swap: Asset exchanges are achieved through self-executing smart contracts, offering a high degree of trustlessness.
- Third-party Network/Relay Chain: Relies on external validators or relay networks for cross-chain verification and asset transfer.
Major Cross-chain Bridge Projects and Related Tokens
There are various types of cross-chain bridges in the market; some are official solutions for specific blockchains, while others are general protocols supporting multiple chains.
Official Cross-chain Bridges (Usually without independent tokens)
These bridges primarily serve specific blockchain ecosystems and typically do not issue independent tokens, but they support cross-chain transfers of native or wrapped assets:
- Polygon Bridge (PoS Bridge): Primarily used for asset transfers between Ethereum and Polygon networks.
- Arbitrum Bridge: The official bridge for Arbitrum, an Ethereum Layer 2 scaling protocol, supporting ETH and ERC-20 assets. Withdrawals from Arbitrum to Layer 1 typically require a 7-day challenge period.
- Optimism Gateway: The official bridge for Optimism, an Ethereum Layer 2 scaling solution, supporting mainstream ERC-20 assets like ETH, DAI, LINK, and UNI.
- Avalanche Bridge (AB): Avalanche's official bridge, supporting the transfer of ERC-20 standard assets between Ethereum and Avalanche.
- BNB Chain Bridge: Supports multiple networks including Ethereum, Solana, BNB Chain, and Tron.
- zkSync Era Bridge: zkSync's official bridge, withdrawals also have a challenge period.
- Rainbow Bridge (NEAR): Connects Ethereum and NEAR Protocol, supporting cross-chain transfers of ERC-20 assets and NFTs.
Third-party/General Cross-chain Bridges (Usually with independent tokens)
These projects aim to provide broader cross-chain interoperability and often have their own governance or utility tokens:
- Multichain (formerly Anyswap): Was a Web3 routing protocol, supporting nearly 40 chains and over 1000 tokens. The project ceased operations in 2023.
- Synapse Protocol (SYN): As a cross-chain liquidity protocol, it allows users to bridge assets between chains such as Ethereum, Arbitrum, Avalanche, BNB Chain, Optimism, and Polygon. Its token is SYN. According to March 2023 data, its Total Value Locked (TVL) was approximately $204 million.
- Celer cBridge (CELR): Utilizes the Celer State Guardian Network to enable cross-chain liquidity, supporting numerous blockchain networks including Ethereum, Astar, BNB Chain, Avalanche, Polygon, and Arbitrum. Its governance token is CELR.
- Wormhole: An interoperability protocol connecting Layer-1 blockchains like Ethereum and Solana. The project suffered an attack on February 3, 2022, losing approximately $326 million in ETH, which was later replenished by Jump Crypto.
- Hop Protocol (HOP): Focuses on fast cross-chain bridging of common tokens between Rollups, achieving rapid transfers without waiting for challenge periods by introducing market makers (Bonders) to provide liquidity on the target chain. Its token is HOP.
- Stargate (STG / ZRO): Built on the LayerZero V2 messaging layer, it provides unified liquidity, enabling native asset delivery and instant finality. Its native token is STG, and it plans to merge with LayerZero into the ZRO token by the end of 2025. According to April 2022 data, the protocol once had a stablecoin TVL as high as $360 million.
- Connext: An Ethereum Layer 2 interoperability protocol, formerly known as xPollinate, whose main function is to facilitate asset transfers across blockchains and Rollups, relying on AMM for liquidity pricing.
- RelayChain (RELAY): A cross-chain bridge aggregator designed to aggregate the most efficient cross-chain bridges. Its token is RELAY. According to March 2023 data, its TVL was approximately $77 million.
- Orbiter Finance: Focuses on cross-chain transfers between Layer 2s, known for its speed, with transactions completing in minutes without waiting for challenge periods. Supports Arbitrum, Optimism, zkSync, StarkNet, and others.
- Rango Exchange: A cross-chain aggregator capable of scanning over 120 liquidity sources across 73+ chains, integrating multi-step paths, and supporting non-EVM chains like Bitcoin, Solana, Cosmos, and TON. The platform has processed over 4.8 million transactions with a volume exceeding $4 billion.
- PancakeSwap Bridge (CAKE): Built on Axelar, it supports mainstream chains such as BNB Chain, ETH, Arb, OP, BASE, and Polygon, and facilitates cross-chain conversion between different tokens. Its governance token is CAKE.
- WBTC: Wrapped Bitcoin is an anchored coin of Bitcoin on Ethereum, pegged 1:1 to Bitcoin, aiming to bring Bitcoin's liquidity into the Ethereum DeFi ecosystem. Bitgo announced on August 4, 2026, its selection of Chainlink CCIP as the exclusive cross-chain infrastructure provider for WBTC, replacing LayerZero, to enhance security. Users can view WBTC's real-time price and related information on market platforms like Svmuu.
Challenges and Risks of Cross-chain Bridges
While cross-chain bridges offer immense value for multi-chain interoperability, their security remains a core challenge. As cross-chain bridges often manage vast amounts of user assets, they have become the most favored targets for Web3 hackers.
Common Security Vulnerabilities and Historical Incidents
- Smart Contract Risk: Code vulnerabilities can lead to fund loss.
- Private Key Compromise: Theft of multi-signature wallet private keys, such as the Harmony Horizon incident.
- Technical Risks: Software failures, human errors, malicious attacks, etc.
- Configuration Errors: Improper permission or parameter settings.
- Custody Risk: Centralized cross-chain bridge operators may act maliciously or be attacked.
Historically, multiple major security incidents have been related to cross-chain bridges:
- Poly Network: Stolen $610 million in August 2021, later returned by the hacker.
- Ronin Bridge: Stolen $620 million in March 2022, due to social engineering attacks leading to validator compromise.
- Wormhole: Stolen $326 million in February 2022, later compensated by Jump Crypto.
- Harmony Horizon: Stolen nearly $100 million in June 2022, suspected due to private key compromise.
- Nomad: Stolen $190 million in August 2022, due to a low-level code error.
- BNB Chain Cross-chain Bridge: Suffered an attack of over $500 million in October 2022.
Ethereum founder Vitalik Buterin once pointed out that the future will be "multi-chain" rather than "cross-chain," because bridges spanning multiple "sovereign zones" have fundamental security limitations. The general industry consensus is that users should prioritize projects with strong backgrounds, ample capital, and audit reports when choosing cross-chain bridges to mitigate risks.
Future Development Trends
Cross-chain bridge technology continues to evolve, with future development trends including:
- Aggregators: Cross-chain aggregators (e.g., Li.Finance, Rango Exchange, RelayChain) enhance user experience by optimizing routing, comparing fees, and speed.
- NFT Cross-chain: With the maturation of the NFT market, the demand for NFT cross-chain transfers is increasing, despite being more challenging to implement than fungible tokens.
- Liquidity Pool and DeFi Integration: Cross-chain bridge liquidity pools will be more deeply involved in DeFi activities, improving capital utilization and attracting liquidity through staking rewards.
- Focus on Specific Ecosystems: More cross-chain bridges will emerge focusing on Layer 2 or non-EVM chains, offering more optimized solutions.
- Higher Security and Generality: Cross-chain bridges will evolve towards higher security, lower costs, and more generalized information transfer to meet increasingly complex cross-chain demands.
- Coexistence of Multiple Bridges: The market may see a coexistence of multiple bridges rather than a single monopoly, giving users more choices.
