Arbitrum AnyTrust: off-chain data committees with minimal trust
Thread410 words
Explains how AnyTrust chains post only data hashes to Ethereum while a data availability committee holds the data, with a fallback to rollup mode if the quorum fails, trading some security for lower fees.
Key claims
With a 20-node committee and a quorum of 19, the chain is safe if just 2 members are honest
Fallback to rollup mode kicks in when no quorum signs
Withdrawals to L1 can be immediate once the committee vouches for state
0/ @arbitrum's #AnyTrust is an $ETH L2 scaling solution that enables fast & cheap L2 chains with minimal trust assumptions
A 🧵 on how it works (0/10) ⚡️👇
#L222
@arbitrum 1/ On a high level, AnyTrust chains are a cheaper but less secure version of the #Arbitrum rollup. The idea is that not all the tx data will be stored on the $ETH L1 but rather off-chain by a data committee
@arbitrum 2/ By minimizing the amount of data submitted to the $ETH L1, #AnyTrust saves gas which results in lower tx fees. What is interesting about AnyTrust is the low trust assumptions
@arbitrum 3/ Assuming a data committee size of 20 nodes and a quorum of 19, an #AnyTrust L2 is safe as long as at least 2 out of 20 nodes are honest. These are much lower trust assumption than the ones behind conventional BFT chains which require more than 2/3 of nodes to be honest
@arbitrum 4/ This is true as there are at least two honest members and only one member can be outside of the quorum
@arbitrum 5/ Hence, if a quorum signs a promise to provide the data backing a batch of tx, it’s safe that that the tx data will be available and consequently it’s safe to only post the hash of the tx data on the L1, rather than the full data
@arbitrum 6/ But what happens if there are not enough nodes available to reach the necessary quorum? Well, if there no active quorum that is willing to sign statements, then the “fallback to rollup” mechanis, kicks in
@arbitrum 7/ That means that tx data is posted on Ethereum (as normal #Arbitrum rollup data is), and new rollup states are confirmed after a challenge period
@arbitrum 8/ In conclusion, #AnyTrust achieves significant scaling advantages because there’s no need to record L2 tx data on the L1 chain (similar to Metis)
@arbitrum 9/ #AnyTrust nodes rely on the committee to provide tx data if needed. So instead of having all the tx data stored on L1, only the hash of a batch of tx is recorded on the L1, saving a lot of gas and mitigating the main cost factor for running a rollup system
@arbitrum 10/ An additional benefit is immediate withdrawals to L1, as soon as the committee vouches for the validity of the state
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