Arbitrum Nova is an AnyTrust chain that aims for ultra low transaction fees. Nova differs from Arbitrum One by not posting transaction data on chain, but to Data Availability Committee.
Funds can be stolen if
Funds can be lost if
Users can be censored if
MEV can be extracted if
After some period of time, the published state root is assumed to be correct. For a certain time period, usually one week one of the whitelisted actors can submit a fraud proof that shows that the state was incorrect.
Funds can be stolen if none of the whitelisted verifiers checks the published state. Fraud proofs assume at least one honest and able validator (CRITICAL).
Users transactions are not published on-chain, but rather sent to several well known and trusted parties, also known as committee members (DAC). New transaction batch needs a BLS signature with the required DAC quorum, for example 9/10. This signature is not verified by L1, however external Validators will skip the batch if BLS signature is not valid resulting. This will reslt in a fraud proof challenge if this batch is included in a consequitive state update. It is assumed that at least one honest DAC member that signed the batch will reveal tx data to the Validators if Sequencer decides to act maliciously and withhold the data.
Funds can be lost if the external data becomes unavailable (CRITICAL).
Users can be censored if the committee restricts their access to the external data.
While proposing blocks is open to anyone the system employs a privileged sequencer that has priority for submitting transaction batches and ordering transactions.
MEV can be extracted if the operator exploits their centralized position and frontruns user transactions.
The user initiates the withdrawal by submitting a transaction on L2. When the block containing that transaction is finalized the funds become available for withdrawal on L1. The process of block finalization usually takes several days to complete. Finally the user submits an L1 transaction to claim the funds. This transaction requires a merkle proof.
When a user initiates a regular withdrawal a third party verifying the chain can offer to buy this withdrawal by paying the user on L1. The user will get the funds immediately, however the third party has to wait for the block to be finalized. This is implemented as a first party functionality inside Arbitrum's token bridge.
The system consists of the following smart contracts:
This contract is an admin of most other contracts allowed to upgrade their implementations. It is owned by a 4-of-6 multisig.
Contract managing adjudication logic for EVM implementation in WASM used by the fraud proofs.
This is a different proxy admin for the three gateway contracts below. It is also owned by a 4-of-6 multisig.
Custom DAI Gateway, main entry point for users depositing DAI to L2 where "canonical" L2 DAI token managed by MakerDAO will be minted. Managed by MakerDAO.
DAI Vault for custom DAI Gateway managed by MakerDAO. This contract stores the following tokens: DAI.
The current deployment carries some associated risks:
Funds can be stolen if a contract receives a malicious code upgrade. There is no delay on code upgrades (CRITICAL).