Reading L2 state from L1.

[Bapi-Reddy]

Is there a way to verify L2 contract state at specific block on L1 using merkle proofs of some form. Can the state tries from State Commitment Chain be helpful in some form. The idea is if there is a decentralized way to verify state of L2 contracts on L1 it increases the support cross chain oracles which can be used for enabling crossh-chain defi apps.

[norswap]

It's easy to prove against the latest L1 block that L2 build upon via the L1 attributes contract:

• https://github.com/ethereum-optimism/optimistic-specs/blob/main/specs/deposits.md#l1-attributes-predeployed-contract
• https://github.com/ethereum-optimism/optimistic-specs/blob/main/packages/contracts/contracts/L2/L1Block.sol

It's theoretically possible this use the blockhash there to also build a proof for a specific L1 block (via the parent hash), but the proof gets too long fairly quickly.

The solution there would be store a Merkle root of a trie that stores the block height → blockhash mapping for L1 blocks. This is something we've discussed, and I think this is something we want to do (as you say, there are quite some use cases). Feel free to open an issue to track this :)

[Bapi-Reddy]

I think you understood my question incorrectly. I want to verify the state of L2 contract on L1. So its the other away around. Where a I want to check if merkle proof for l2 contract variable on latest committed block is valid on L1.

[trianglesphere]

You would use the L2 Output Oracle contract (this is how withdrawals are done) on L1.

[Bapi-Reddy]

I see its still in proposal stage here:https://github.com/ethereum-optimism/optimistic-specs/blob/main/packages/contracts/contracts/L1/L2OutputOracle.sol
or is it live now ? . Are there any code examples showing its usage ?

[trianglesphere]

This repo is not yet live. That's the correct contract accessing the state for bedrock. You can see withdrawals being verified here: https://github.com/ethereum-optimism/optimistic-specs/blob/main/packages/integration-tests/test/000_withdrawals.spec.ts
You could look at withdrawalRelay.sol for an example of performing the verification of some L2 state on L1. FYI these contract's are still pre-production.

It's probably a similar process for the current State Commitment Chain