Jemiiah / worldcoin-scroll-bridge

worldcoin-scroll-bridge

Docs copied from: worldcoin/world-id-state-bridge#112

Build your own state bridge

Intro

The point of the state bridge contracts in world-id-state-bridge is to have two contracts, one deployed on Ethereum mainnet and the other one on a target L2. The mainnet contract (e.g. OpStateBridge) has a public function which will fetch the latest root of the World ID merkle tree using the WorldIDIdentityManagerImplV1 method named latestRoot() and then will use the native L1<>L2 messaging layer to send a message to the target L2 contract (e.g. OpWorldID). The messaging layer of the L2 will forward the message to the target contract by calling the corresponding method on the L2 contract with the specified payload from the L1.

[!NOTE] The current implementation of WorldID will only work for EVM-compatible networks as mentioned in the Supported networks and Future integrations sections. If you are an EVM-compatible rollup you also need to support the pairing cryptography and keccak256 precompiles. The root of the World ID Identity Manager tree is the only public state that you need to send to the L2 in order to verify Semaphore proofs (proofs of inclusion in the World ID merkle tree). As long as you have the root and a World ID implementation on your network, you can deploy World ID on it.

Requirements

• service to sync the World ID merkle tree (currently only done by signup-sequencer)
• EVM support on the L2 (pairing cryptography and keccak256 precompile support needed)
  • or a custom implementation of World ID for your execution environment (see Future integrations)
• native L1<>L2 data messaging layer (e.g. Optimism cross domain messenger, Arbitrum, etc)
• relayer service that periodically calls propagateRoot() as a cron job (e.g. state-bridge-relay)
• deployment scripts
• audits (World ID contracts, both world-id-contracts and world-id-state-bridge are audited by Nethermind (1, 2))

Specification

If you want to build your own state bridge, you can use the OpStateBridge contract as a template. The contract has two main methods, namely propagateRoot() (fetches the latest root from the Orb/Phone World ID IdentityManager contract and propagates it to the target L2 contract using the native L1->L2 messaging layer) and setRootHistoryExpiry() (sets how long you want a propagated root to be valid for inclusion proofs) which you will need to implement. Most native bridges will have a messenger/relayer contract and a generic interface you can use to call a function on a target contract on the L2 with your desired calldata (which is the message). Another requirement for this system to work is to only allow the contract on L1 to be able to call this function on the L2, otherwise anyone would be able to insert arbitrary merkle tree roots into the L2 contract. On the OpWorldID contract we used a contract named CrossDomainOwnable3 which implements this functionality (checks that L1 sender is a given sender).

[!NOTE] If you want to support World ID on an OP-stack network it is very easy as we have already implemented it for Optimism, the only change you need to make is within the deploy scripts where you need to set the crossDomainMessengerAddress to the your own network's cross domain messenger address on Ethereum L1 (whether mainnet or testnet).