Original author: Offchain Labs
Original link:
https://medium.com/offchainlabs/introducing-anytrust-chains-cheaper-faster-l2-chains-with-minimal-trust-assumptions-31def59eb8d7
Translation and proofreading: TinTinLand
In March 2022, Arbitrum announced the launch of AnyTrust Chain, an Arbitrum model of ultra-low-cost transactions with strong security guarantees. AnyTrust will run with Arbitrum One.
Arbitrum One, as a series of solutions for Optimistic Rollups, inherits the security of Ethereum and has lower cost and higher throughput than L1. However, in some blockchain areas, such as gaming projects, these applications require further reductions in costs or faster withdrawals. In response, Arbitrum launched AnyTrust Chains, allowing lower costs and fast withdrawals in exchange for minimal additional trust assumptions. The main advantage of AnyTrust compared to sidechains is that it is built on Ethereum, so AnyTrust requires much less trust. This will be elaborated on below.
Before analyzing AnyTrust in depth, the first thing to make clear is that Arbitrum One will remain a trustless Rollup as always and will continue to invest resources in improving the Arbitrum One protocol and ecosystem. For example, Arbitrum released a Nitro upgrade and upgraded Arbitrum One to Nitro. Arbitrum isn't moving away from trustless Rollup, it's just introducing an alternative.
Introduction to AnyTrust
How does AnyTrust work? AnyTrust Chains is run by a committee of nodes that uses minimal assumptions to determine how many committee members are honest. For example, there may be 20 committee members and it is assumed that at least 2 of them are honest. This is an easier trust assumption than traditional BFT sidechains, which require more than 2/3 of the members to tell the truth, or 14 out of 20 members. AnyTrust Chains reduces the trust requirement from 14 to 2 through the "fallback to rollup" feature, which is built on top of Ethereum.
Assuming trust is established and committee members are involved, users gain two major advantages. First, there is no need to record L2 transaction data on L1 because nodes can rely on the committee to provide the data when needed. Instead, since the committee commits to providing the data, it is secure by simply recording the hash of the transaction batch on L1, saving the cost of running a rollup. Secondly, withdrawals to L1 can be executed immediately once the committee guarantees it.
As long as 19 of the 20 committee members commit (by signing) that it's OK, it can be done safely. That is, if there are at least 2 honest members, and 19 out of 20 members have signed, then at least one honest member must have signed.
Back to Rollup
What if the committee doesn’t sign off on anything? What if a group of committee members collapses or refuses to cooperate? If this happens, the chain can still function by falling back to the standard rollup protocol. Data will be published on the L1 Ethereum chain, and withdrawals will have a delay period, just like on a standard rollup, until the committee resumes operations, and then the chain will seamlessly switch back to the cheaper and faster mode.
Why AnyTrust is secure
With 20 committee members, at least 2 of them are honest, anything signed by a quorum of 19 committee members, must be correct because there are at least 2 honest members, as long as 1 of them can The quorum is exceeded, so the quorum must contain 1 honest member. (In general, for N members and K assumed to be honest, an Arbitrum is any N+1-K member.) So if 1 quorum signs 1 pledge promising to provide data supporting a batch of transactions, we know The data is available to anyone who wants it, so it is safe to publish the hash of the data on the L1 chain.
Likewise, if Arbitrum signs a statement indicating that a particular state transition is correct, the state transition can be accepted without waiting for the challenge period, which allows withdrawals to L1 to be processed immediately. If there is no active quorum willing to sign the statement, neither situation will occur. But it doesn't matter, the chain can still run by using the original Arbitrum Rollup protocol, transaction data is published on Ethereum, and the new Rollup state is confirmed after the challenge period. Once arbitration is running again, the chain will seamlessly switch back to a more efficient and faster operating mode.
To summarize, in our example, if at least 2 members are honest, the chain will function properly. If 19 members are available and cooperate, it will operate at minimal cost. In the middle zone, the chain will run at the expense of Ethereum-based Rollup.
Conclusion
Are AnyTrust Chains a new idea? It is actually based on the original design of Arbitrum in Offchain Labs' 2018 academic paper. The paper describes a committee-based chain design that evolved into what are now called Optimistic Rollups, removing the committee part and improving it in other ways to create the current Arbitrum Rollup project.
Now reintroduced in parallel with Arbitrum One, AnyTrust Chain can enable lower costs and faster withdrawals for projects willing to make minimal trust assumptions.
This year is the first year of L2, and many Ethereum expansion plans are emerging one after another. TinTinLand will continue to pay attention to Ethereum's hot expansion plans, report on the progress of related projects, provide developers with the latest technical information and development opportunities, and jointly build a better Web3 world.