TLDR: The optimistic rollup ecosystem needs fraud prover light clients for the “1/N honest participants” assumption to be meaningful.

We demonstrate that the Optimism sequencer can be circumvented on mainnet, but show that there’s currently no way for end users to conduct Fraud Proofs on either Arbitrum or Optimsim.


The switch to layer two is one where it’s very important for the ecosystem to try and maintain and even improve its decentralization [...], and so we need light clients that can poke into optimism and poke into arbitrum and poke into starknet. And that’s something where there’s been a little bit of theoretical think-y work on, but it’s the sort of thing that I think there is a lot of room for people to slot themselves in and really try to improve that ecosystem a lot…

-Vitalik Buterin, ‘22

Ethereum scaling solutions have once again found themselves in the spotlight. Most of this rollup-centric-worldview type thinking is centered around computational complexity analysis, trust assumptions, and system-wide game-theoretic outcomes.

But at the end of the day, usage isn’t driven by people reading arxiv papers and codebases for years, trying to come up with objective frameworks to think about what’s “best.”

It’s driven by users who ask:

How good is the system? Is it easy to use? Deep liquidity? Rich Ecosystem?

Am I comfortable depositing my money? What’s the probability I get rugged?

The ZK camp of people have chosen to answer these questions by building a polynomial black-box (at least for people without a high level of mathematical sophistication) which theoretically minimizes trust assumptions and gives an extraordinary level of scalability at the cost of system complexity and development time.

The optimistic camp says “if we just make a weak trust assumption (1/N honest participants), then we get all that scalability with only a fraction of the complexity!”

This 1/N assumption warrants further investigation: what does it actually look like in practice? Is it as accessible as it’s claimed to be?