Introduction
When evaluating small chains connected to larger blockchain networks, one critical question emerges: "How much damage could a 51% attack on the small chain cause?" This concern highlights the importance of shared security—a concept that determines whether assets on a smaller chain are as secure as those on the main chain.
Security Models Compared
1. Independent L1 Chains
- Risk: Attackers can steal all assets.
- Why? No validation occurs on the larger chain, enabling unrestricted theft.
2. Sidechains
- Risk: Similar to independent L1s, but slightly safer because block headers are published on the main chain (e.g., Ethereum). This prevents theft via main-chain 51% attacks but not sidechain-specific attacks.
3. Rollups
- Risk: Attackers can delay transactions but cannot steal assets.
- Safety Mechanism: On-chain fraud proofs or data availability proofs validate withdrawals.
Special Cases:
- Plasma: Delays transactions but prevents theft.
- Validium: Locks assets permanently but doesn’t allow theft (e.g., Starkware’s ImmutableX). Offers a middle ground between rollups and sidechains.
What Is Shared Security?
Shared security means assets on smaller chains (e.g., rollups) are as secure as those on the main chain. Key points:
- Rollups and plasma inherit main-chain security.
- Independent L1s and sidechains are less secure.
- Validiums offer intermediate security.
Vitalik’s Insight:
"Your transaction’s security depends on whether the activity and asset issuance occur within the same shared security zone—a region where all chains (e.g., rollups) are ultimately secured by the same main chain."
Why Cross-Chain Bridges Are Risky
- 51% Attacks: If a main chain (e.g., Ethereum) is attacked, bridged assets on other chains (e.g., Solana-WETH) become vulnerable. Attackers can deposit and reverse transactions, causing losses.
- Native Assets Are Safer: Holding Ethereum-native assets on Ethereum L2s (e.g., Arbitrum) is safer than holding them on foreign chains (e.g., Solana).
Example:
If Ethereum suffers a 51% attack:
- Arbitrum/Optimism transactions roll back synchronously.
- But cross-chain bridges (e.g., Ethereum ↔ Avalanche) expose users to systemic risks.
FAQs
1. What’s the safest small-chain model?
Rollups—they inherit main-chain security and prevent theft.
2. Can validiums be trusted?
They’re less secure than rollups but safer than sidechains. Ideal for scalability-focused use cases.
3. Why avoid cross-chain bridges?
They magnify risks: more activity = higher attack incentives.
4. Does shared security apply to PoW chains like BSV?
No—BSV’s large, unverifiable blocks make it inherently vulnerable to 51% attacks.
Conclusion
Shared security ensures smaller chains (like rollups) leverage main-chain safety. Avoid bridges and prioritize native assets within the same security zone. 👉 Explore secure L2 solutions
Key Takeaways:
- Rollups > Validiums > Sidechains > Independent L1s.
- Cross-chain bridges introduce unnecessary risks.
- Always verify a chain’s security model before transacting.