Network Bridges: How They Work and Why They Break Down Most Often

Blockchains do not communicate with each other natively: Bitcoin is unaware of Ethereum’s existence. A bridge serves as a workaround for this lack of communication, and its design explains why bridges hold the record for the most thefts.

The “lock-and-mint” mechanism

A classic bridge: you deposit an asset on the source network-it is locked in a smart contract or with a custodian-and a “wrapped” version (a receipt) is minted on the destination network. To reverse the process: burn the receipt-and retrieve the original from storage. Everything hinges on who verifies the “deposit occurred” event and how.

Why they fail

• Decoy vault: The bridge contract holds all users’ assets together-the ecosystem’s most valuable vault with a known address.
• Intermediary validators: For most bridges, the event is confirmed by a committee of N signatures. Steal the keys of the majority-you’ve stolen the vault (Ronin: 5 out of 9).
• Code running on two networks simultaneously: a double attack surface; a signature verification bug in Wormhole cost $320 million.
• The receipt takes on a life of its own: if the vault is robbed, “wrapped” tokens instantly lose their collateral-de-pegging for all holders, even those who didn’t know about the bridge.

Best practices: Use verified routes for bridging; do not hold “wrapped” assets long-term (native asset > receipt); for large amounts, use the networks’ canonical bridges. We’re tracking the timeline in this section.