[xorcist]

Why not use a sidechain instead? They can compress transactions at least as effective, and have more simple security properties.

The main drawback with sidechains are that they are hard to run decentralized in any credible sense. Basically just as hard as the blockchain in the first layer sense. They seem to be identical in this regard.

[fbrusch]

Sidechains have different security properties. You probably know xdai (https://www.xdaichain.com/), where you can transact tokens that "wrap" dais from Ethereum mainnet. The sidechain is secured by a proof of authority consensus, where you require a fraction of validators to behave honestly. If a certain number of validators collude, they can do nasty things, such as censoring transactions from a certain address, or keeping the chain from making progress. This is not possible in a rollup, either optimistic or zk, because any single user can always commit a batch or report fraud on L1, so you just need a single honest actor for things to work.

[simonebrunozzi]

As HN user timdaub stated earlier in the thread,

> in order to transact "off-chain", a user had to transfer some money into a bridge

I believe that this is the main problem with side chains.

[dboreham]

To me this is a side chain approach, but it depends on your definition of side chain.

[xorcist]

That is my understanding as well. At least the "optimistic" version as described seems like a standard sidechain.

The important part, who gets to publish this chain and if and how that can operate in a trustless manner, is not described here. That makes the ZK proof seem misplaced. If it is operated by a trusted third party, why bother?