maurelian
@maurelian.eth
We know that Superchain interoperability is hard to explain, but we're too close to the problem to know why. We would greatly appreciate you taking the time to read this, and tag @zain to complain about what's unclear to you. https://docs.optimism.io/stack/protocol/interop/explainer
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GIGAMΞSH
@gigamesh
Mostly makes sense but confused by this part. I thought L2 txs are only truly secured on L1 after the week long fault proof window?
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zain
@zain
This is a confusing topic: Transaction finalization on the rollup. Rollups derive their security from Ethereum. What that means is the L2 blockchain can be derived from data posted on Ethereum. Finality is when the data is posted to the DA layer (L1). The settlement layer. This is the mechanism that Ethereum uses to establish a view of the state on an OP Stack chain. Rollup nodes post and watch Ethereum. Ethereum, the protocol has no concept of the L2. It has these OP Stack smart contracts on it, but it doesn't care. It just processes transactions based on its consensus rules. If the L2 wants to post a L2-->L1 message (usually a withdrawal) it's the L2s responsibility to prove that its state is valid. This is how you make withdrawals. So, if I want to ensure the state of the source chain is final, all I have to do is wait for tx finalization. This is similar to why CCTP relies on 65 L1 blocks for L2s: https://developers.circle.com/stablecoins/docs/required-block-confirmations
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soyboy
@soyboy
The L2 txs are secured on the L1 when the sequencer posts the L2 transaction batches onto Etherem. The sequencer and all of the nodes on the L2 must follow consensus rules, so there isn't a way to make an invalid transaction because all the nodes on the network just throw it out. The same way its handled on Ethereum, Bitcoin, etc. Like @zain mentioned, this challenge window is very specific to ensuring the withdrawals from the L2 to Ethereum are valid. Essentially the L2 txs and the L1 deposit txs into the L2 are easy to verify because the L2 is aware of both the L2 network state and L1 deposits into the L2 network state. The tricky part is proving to the L1, that the L2 state is correct. Thats where the Optimistic rollups and ZKPs come in to solve the L2 --> L1 message passing direction.
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