Arbitrum Nova
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Arbitrum Nova is an AnyTrust Optimium, differing from Arbitrum One by not posting transaction data onchain.
$46.79 M
6.44%
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About
Arbitrum Nova is an AnyTrust Optimium, differing from Arbitrum One by not posting transaction data onchain.
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Mainnet for everyone
2022 Aug 9th
Whitelist got removed, there are no restrictions on who can transact with the network.
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),
- a contract receives a malicious code upgrade. There is a 12d 8h delay on code upgrades,
- a contract receives a malicious code upgrade. There is no delay on code upgrades (CRITICAL).
Funds can be lost if
Users can be censored if
MEV can be extracted if
State validation
Fraud proofs (INT)Fraud proofs allow 13 WHITELISTED actors watching the chain to prove that the state is incorrect. Interactive proofs (INT) require multiple transactions over time to resolve. There is a 6d 8h challenge period.
Data availability
External (DAC)Proof construction relies fully on data that is NOT published on chain. There exists a Data Availability Committee (DAC) with a threshold of 5/6 that is tasked with protecting and supplying the data.
Exit window
2dUpgrades are initiated on L2 and have to go first through a 3d delay. Since there is a 1d to force a tx, users have only 2d to exit. If users post a tx after that time, they would need to self propose a root with a 6d 8h delay and then wait for the 6d 8h challenge window, while the upgrade would be confirmed just after the 6d 8h challenge window and the 3d L1 timelock.
Sequencer failure
Self sequenceProposer failure
Self proposeAnyone can become a Proposer after 6d 8h of inactivity from the currently whitelisted Proposers.
Fraud proofs ensure state correctness
After some period of time, the published state root is assumed to be correct. For a certain time period, one of the whitelisted actors can submit a fraud proof that shows that the state was incorrect. The challenge protocol can be subject to delay attacks.
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).
Data is not stored on chain
Users transactions are not published on-chain, but rather sent to external trusted parties, also known as committee members (DAC). Members of the DAC collectively produce a Data Availability Certificate (comprising BLS signatures from a quorum) guaranteeing that the data behind the new transaction batch will be available until the expiry period elapses (currently a minimum of two weeks). This signature is not verified by L1, however external Validators will skip the batch if BLS signature is not valid resulting. This will result in a fraud proof challenge if this batch is included in a consecutive 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. If the Sequencer cannot gather enough signatures from the DAC, it will “fall back to rollup” mode and by posting the full data directly to the L1 chain. The current DAC threshold is 5 out of 6.
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.
The system has a centralized sequencer
While forcing transaction 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.
Users can force any transaction
Because the state of the system is based on transactions submitted on-chain and anyone can submit their transactions there it allows the users to circumvent censorship by interacting with the smart contract directly. Anyone can become a Proposer after approximately 6d 8h (45818 blocks) of inactivity from the currently whitelisted Proposers.
Regular exit
The user initiates the withdrawal by submitting a regular transaction on this chain. 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.
Tradeable Bridge Exit
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.
Autonomous exit
Users can (eventually) exit the system by pushing the transaction on L1 and providing the corresponding state root. The only way to prevent such withdrawal is via an upgrade.
EVM compatible smart contracts are supported
Arbitrum One uses Nitro technology that allows running fraud proofs by executing EVM code on top of WASM.
Funds can be lost if there are mistakes in the highly complex Nitro and WASM one-step prover implementation.
Arbitrum DAO is in charge of upgrades
Arbitrum DAO allows $ARB token holders to propose and vote on changes to the organization and the technologies it governs. The governance smart contracts are implemented on Arbitrum One rollup chain. The DAO can upgrade the Arbitrum One contracts on L2 with 3d delay and - using L2 --> L1 Governance Relay, update contracts on L1 with additional 3d delay + 6d 8h delay for all L2 --> L1 messages (in total a delay of 12d 8h). The Security Council can upgrade the contracts without any delay. It can also cancel any upgrades initiated by the DAO.
Funds can be stolen if a contract receives a malicious code upgrade. There is a 12d 8h delay on code upgrades.
The system uses the following set of permissioned addresses:
Central actors allowed to submit transaction batches to L1.
They can submit new state roots and challenge state roots. Some of the operators perform their duties through special purpose smart contracts.
The admin of all contracts in the system, capable of issuing upgrades without notice and delay. This allows it to censor transactions, upgrade bridge implementation potentially gaining access to all funds stored in a bridge and change the sequencer or any other system component (unlimited upgrade power). It is also the admin of the special purpose smart contracts used by validators. This is a Gnosis Safe with 9 / 12 threshold. It uses the following modules: UpgradeExecutor.
Those are the participants of the SecurityCouncil.
It can update whether an address is authorized to be a batch poster at the sequencer inbox. The UpgradeExecutor retains the ability to update the batch poster manager (along with any batch posters). This is a Gnosis Safe with 4 / 6 threshold.
Those are the participants of the BatchPosterManagerMultisig.
![A diagram of the smart contract architecture](/images/architecture/nova.png)
The system consists of the following smart contracts on the host chain (Ethereum):
Main contract implementing Arbitrum One Rollup. Manages other Rollup components, list of Stakers and Validators. Entry point for Validators creating new Rollup Nodes (state commits) and Challengers submitting fraud proofs.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Contract managing Inboxes and Outboxes. It escrows ETH sent to L2. This contract stores the following tokens: ETH.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Upgrade delay: 12d 8h or 0 if overridden by Security Council
This contract can upgrade the system’s contracts. The upgrades can be done either by the Security Council or by the L1ArbitrumTimelock.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Timelock contract for Arbitrum DAO Governance. It gives the DAO participants the ability to upgrade the system. Only the L2 counterpart of this contract can execute the upgrades.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Router managing token <–> gateway mapping.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Contract that allows challenging invalid state roots. Can be called through the RollupProxy.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Value Locked is calculated based on these smart contracts and tokens:
Main entry point for users depositing ERC20 tokens. Upon depositing, on L2 a generic, “wrapped” token will be minted.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Main entry point for users depositing ERC20 tokens that require minting a custom token on the L2.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
Contract managing Inboxes and Outboxes. It escrows ETH sent to L2.
Upgrade delay: No delay
DAI Vault for custom DAI Gateway. Fully controlled by MakerDAO governance.
Upgrade delay: 12d 8h or 0 if overridden by Security Council
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).