The leaks · 43 / 86 · 3 min
Bridges
A bridge moves value from one chain to another by locking it in one place and issuing a stand-in in the other. The lock, and the people who run it, are the risk.
The lock, and the people who run it, are the risk. The chain you arrive on cannot save the lock.
A worked case
A bridge is used because the other chain is cheaper. The bridge's signers are compromised. The stand-in tokens still display a balance. The locked coins are gone. The cheaper fees were real. The bridge was the vault.
Where the money sits
During the move, and often after, the original asset is in a contract or with a custodian. You hold a claim on the other side. If the lock is drained, the claim can become worthless while the original is gone.
The check
Who operates it. How many signatures are needed. Whether you can verify the locked funds. A bridge is not the chain. It is a narrower door, and narrow doors get robbed.
Do not bridge an amount you cannot afford to wait on, or lose.
Ronin: the lock was nine keys, and five were enough
A bridge locks value on one chain and issues a stand-in on another. In March 2022 the Ronin bridge, used by the game Axie Infinity, was drained of about 173,600 ether and 25.5 million USDC, reported at about 625 million dollars. The bridge was controlled by a small set of validator keys. Attackers obtained enough of them to approve withdrawals. Sky Mavis, the company, halted the bridge. The US Treasury and the FBI later attributed the theft to the Lazarus Group, a North Korean state hacking operation. The coins on the far side had been a claim on that lock. The lock moved.
Wormhole, a month earlier, had lost more than 320 million dollars, and a trading firm refilled it. Nomad, in August 2022, was robbed by a crowd once one attacker showed that the checks were not checking. The Treasury's Tornado Cash notice lists bridge thefts as a source of stolen funds. The pattern is the product: a handful of signers, a large pile, a stand-in token that still has a ticker after the pile is gone.
This page does not describe how the keys were taken. Who holds the keys, and how many must agree, is the whole lesson. If you cannot name them, you are trusting a logo with a vault.
Read it yourself
These links are the record. They are not a recommendation, and they are not instructions. A news story or a court paper can still be wrong about a detail. The check does not change because a famous name is in the story.
Apply the check
Open a question. The line is about this topic. It is not a verdict that anything is safe.
The attacker, or the bridge's fee.
The bridge signers or the upgrade key.
Those signers. Your wallet on the far side holds a claim, not the original coin.
Check yourself
Is a bridged coin the same as the coin on its home chain?
No. It is a claim, and the lock can fail.
After this you can name who holds the locked funds before you send them across.