Cross-Chain Bridge Security Fundamentals
HasFocus Research · 2026
Abstract
An educational guide to the security challenges in cross-chain bridge design. We cover validator management, message verification, token accounting, and operational security -- the four pillars of bridge security.
1. Why Bridges Are High-Risk
Cross-chain bridges hold large amounts of locked assets and operate across trust boundaries. The bridge contract on each chain must independently verify the validity of messages from other chains, typically relying on a validator committee. A single flaw in verification logic or validator key management can lead to total loss of locked funds.
2. Validator Security
Validator key compromise is the most common bridge attack vector. Best practices include HSM-backed key storage, geographic distribution, threshold signatures instead of multi-sig, automatic key rotation, and anomaly detection on signing patterns. The validator threshold must be calculated carefully -- off-by-one errors in integer division can reduce security guarantees.
3. Token Accounting
Bridges must handle fee-on-transfer tokens, rebasing tokens, and tokens with non-standard ERC-20 behavior. Balance-before/after checks are essential for all transfers. Per-chain accounting with regular cross-chain reconciliation prevents insolvency. Circuit breakers that halt the bridge when accounting drift exceeds a threshold provide a last line of defense.
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