Bridges

What are Bridges?

Blockchain bridges are protocols that connect separate blockchain networks, enabling the transfer of assets, data, and messages between them. Since blockchains are isolated systems that can’t natively communicate, bridges provide the critical infrastructure for multi-chain ecosystems.

Bridges have enabled billions of dollars to flow across chains, but have also been responsible for some of crypto’s largest hacks—making bridge security one of the industry’s most important challenges.

How Bridges Work

The Basic Problem

Blockchains can’t directly verify other chains:

• Ethereum doesn’t know Bitcoin’s state
• Solana can’t read Ethereum contracts
• Each chain is its own universe
• Yet users want assets everywhere

Lock and Mint

Most common mechanism:

1. User locks assets on source chain
2. Bridge verifies the lock
3. Equivalent assets minted on destination
4. Reverse to return to original chain

The “wrapped” asset represents a claim on the locked original.

Verification Methods

How bridges confirm cross-chain events:

Trusted Third Party:

• Centralized bridge operators
• Fast and simple
• Requires trusting operator
• Single point of failure

Multi-Sig/MPC:

• Multiple parties must agree
• Better than single operator
• Still requires trusting signers
• Most bridges use this

Light Client:

• Verifies chain state cryptographically
• Trustless but complex
• Expensive on some chains
• Ideal security model

Optimistic:

• Assume valid, challenge if not
• Similar to optimistic rollups
• Delay for challenge period
• Good security trade-off

Bridge Types

Trusted Bridges

Rely on external parties:

• Centralized exchanges (implicit bridges)
• Custodial bridges
• Multi-sig committees
• Fast but trust-requiring

Trustless Bridges

Cryptographic verification:

• Light client verification
• ZK proof-based
• Native chain verification
• Slower but more secure

Canonical vs. Third-Party

Canonical: Official L1↔L2 bridges

• Built by L2 teams
• Inherit L2 security
• Usually slower (withdrawal delays)

Third-Party: Independent bridges

• Faster withdrawals
• Additional trust assumptions
• May pool liquidity
• Compete on speed/fees

Security Considerations

Attack Vectors

Bridges are attractive targets:

• Concentrated value (locked assets)
• Complex multi-chain logic
• Novel cryptography
• High-value exploits possible

Common attack types:

• Private key compromise
• Smart contract vulnerabilities
• Validator collusion
• Oracle manipulation

Notable Bridge Hacks

Bridge	Amount	Year	Cause
Ronin	$625M	2022	Key compromise
Wormhole	$320M	2022	Contract bug
Nomad	$190M	2022	Contract bug
Harmony	$100M	2022	Key compromise

Security Best Practices

For bridge users:

• Use canonical bridges when possible
• Check bridge audit status
• Consider insurance options
• Don’t bridge more than necessary

Bridge Ecosystem

Major Bridges

Cross-Chain Messaging:

• LayerZero
• Chainlink CCIP
• Axelar
• Wormhole

Asset Bridges:

• Across Protocol
• Stargate
• Hop Protocol
• Synapse

L2 Bridges:

• Arbitrum Bridge
• Optimism Bridge
• zkSync Bridge
• StarkNet Bridge

Bridge Aggregators

Services comparing bridges:

• Find best rates
• Compare speeds
• Aggregate liquidity
• Improve UX

Technical Approaches

Hash Time-Locked Contracts (HTLCs)

Atomic swap mechanism:

• Cryptographic locks
• Time-limited windows
• Trustless but limited
• Used for simple transfers

Relayer Networks

Message passing:

• Relayers transmit proofs
• Decentralized operation
• Economic incentives
• Powers many bridges

Optimistic Verification

Dispute-based:

• Assume messages valid
• Fraud proofs if challenged
• Time delay required
• Good security/efficiency balance

Bridge UX Challenges

Complexity

User experience issues:

• Multiple transactions required
• Gas on multiple chains
• Waiting periods
• Confusing interfaces

Fragmentation

Asset proliferation:

• Multiple wrapped versions
• Liquidity split
• Which wrapped ETH is “real”?
• Confusion and inefficiency

Fees

Cost considerations:

• Bridge protocol fees
• Gas on both chains
• Slippage on liquidity
• Can be expensive

The Future of Bridges

Improved Security

Research directions:

• ZK-proof verification
• Distributed validator sets
• Economic security models
• Formal verification

Better Interoperability

Standards emerging:

• Cross-chain messaging standards
• Intent-based bridges
• Chain abstraction
• Unified interfaces

Native Integration

Long-term vision:

• Bridges built into protocols
• Seamless cross-chain UX
• Users don’t notice chains
• “One blockchain” experience

Conclusion

Bridges are essential infrastructure for the multi-chain world, enabling the flow of assets and information across isolated blockchain networks. However, their security record highlights the difficulty of cross-chain verification—bridge design involves fundamental trade-offs between trust, security, speed, and cost. Users should understand these trade-offs and approach bridges with appropriate caution.