Pause and Unpause the Bridge

Why do it?

The OptimismPortal is a bridge contract that makes it possible to send messages between your L1 and your L2 OP Stack chain. The OptimismPortal is pausable as a backup safety mechanism that allows a specific GUARDIAN address to temporarily halt deposits and withdrawals to mitigate security issues if necessary. An OP Stack chain does not have to specify a usable GUARDIAN address if it does not want to make the OptimismPortal contract pausable, it can specify an address such as zero.

Who can do it?

OptimismPortal (opens new window) has an immutable GUARDIAN. That address can call pause (opens new window) and unpause (opens new window).

Changing the guardian

The guardian created by the setup script is the admin account. This is sufficient for testing, but for a production system you would want the guardian to be a multisig with trusted security council.

The GUARDIAN variable is immutable, but the OptimismPortal contract sits behind a proxy, so the GUARDIAN can be modified by changing the OptimismPortal proxy to point to a new implementation contract. You do this using the L1 ProxyAdmin (opens new window) contract.