Astar zkEVM
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About
Astar zkEVM is a Validium that leverages Polygon's CDK and zero-knowledge cryptography to enable off-chain transactions while maintaining EVM equivalence.
Badges
About
Astar zkEVM is a Validium that leverages Polygon's CDK and zero-knowledge cryptography to enable off-chain transactions while maintaining EVM equivalence.
Recategorisation
The project will be classified as "Other" due to its specific risks that set it apart from the standard classifications.
The project will move to Others because:
Consequence: projects without a sufficiently decentralized data availability committee rely on few entities to safely attest data availability on Ethereum. A small set of entities can collude with the proposer to finalize an unavailable state, which can cause loss of funds.
Learn more about the recategorisation here.
Astar zkEVM Launch
2024 Mar 6th
Astar Network launched Astar zkEVM, integrated with Polygon AggLayer.
Funds can be stolen if
Funds can be lost if
Funds can be frozen if
Users can be censored if
MEV can be extracted if
Sequencer failure
No mechanismThere is no mechanism to have transactions be included if the sequencer is down or censoring. Although the functionality exists in the code, it is currently disabled.
State validation
ZK proofs (ST, SN)STARKs and SNARKs are zero knowledge proofs that ensure state correctness. STARKs proofs are wrapped in SNARKs proofs for efficiency. SNARKs require a trusted setup.
Data availability
External (DAC)Proof construction relies fully on data that is NOT published onchain. There exists a Data Availability Committee (DAC) with a threshold of 3/5 that is tasked with protecting and supplying the data.
Exit window
NoneEven though there is a 10d Timelock for upgrades, forced transactions are disabled. Even if they were to be enabled, user withdrawals can be censored up to 15d.
Validity proofs ensure state correctness
Each update to the system state must be accompanied by a ZK proof that ensures that the new state was derived by correctly applying a series of valid user transactions to the previous state. These proofs are then verified on Ethereum by a smart contract.
Zero knowledge STARK and SNARK cryptography is used
Despite their production use zkSTARKs and zkSNARKs proof systems are still relatively new, complex and they rely on the proper implementation of the polynomial constraints used to check validity of the Execution Trace. In addition zkSNARKs require a trusted setup to operate.
Funds can be lost if the proof system is implemented incorrectly.
Data is not stored on chain
The transaction data is not recorded on the Ethereum main chain. Transaction data is stored off-chain and only the hashes are posted onchain by the Sequencer, after being signed by the DAC members.
Funds can be lost if the external data becomes unavailable (CRITICAL).
Set of parties responsible for signing and attesting to the availability of data.
There are no onchain assets at risk of being slashed in case of a data withholding attack, and the committee members are not publicly known.
There is no fraud detection mechanism in place. A data withholding attack can only be detected by nodes downloading the full data from the DA layer.
The committee does not meet basic security standards, either due to insufficient size, lack of member diversity, or poorly defined threshold parameters. The system lacks an effective DA bridge and it is reliant on the assumption of an honest sequencer, creating significant risks to data integrity and availability.
There is no delay in the upgradeability of the bridge. Users have no time to exit the system before the bridge implementation update is completed.
The relayer role is permissioned, and the DA bridge does not have a Security Council or a governance mechanism to propose new relayers. In case of relayer failure, the DA bridge will halt and be unable to recover without the intervention of a centralized entity.
Architecture
Polygon CDK validiums utilize a data availability solution that relies on a Data Availability Committee (DAC) to ensure data integrity and manage off-chain transaction data.
This architecture comprises the following components:
- Operator: A trusted entity that collects transactions, computes hash values for the transaction batch, and then requests and collects signatures from Committee members.
- Data Availability Committee (DAC): A group of nodes responsible for validating batch data against the hash values provided by the operator (sequencer), ensuring the data accurately represents the transactions.
- PolygonCommittee Contract: Contract responsible for managing the data committee members list. Each DAC node independently validates the batch data, ensuring it matches the received hash values. Upon successful validation, DAC members store the hash values locally and generate signatures endorsing the batch’s integrity. The sequencer collects these signatures and submits the transactions batch hash together with the aggregated signature on Ethereum. The PolygonCommittee contract is used during batch sequencing to verify that the signature posted by the sequencer was signed off by the DAC members stored in the contract.
DA Bridge Architecture
The DA commitments are posted to the destination chain through the sequencer inbox, using the inbox as a DA bridge. The DA commitment consists of a data availability message provided as transaction input, made up of a byte array containing the signatures and all the addresses of the committee in ascending order. The sequencer distributes the data and collects signatures from Committee members offchain. Only the DA message is posted by the sequencer to the destination chain inbox (the DA bridge). A separate contract, the PolygonCommittee contract, is used to manage the committee members list and verify the signatures before accepting the DA commitment.
No compression scheme yet.
The genesis state, whose corresponding root is accessible as Batch 0 root in the getRollupBatchNumToStateRoot method of PolygonRollupManager, is available here.
The trusted sequencer request signatures from DAC members off-chain, and posts hashed batches with signatures to the AstarValidium contract.
The system has a centralized sequencer
Only a trusted sequencer is allowed to submit transaction batches. A mechanism for users to submit their own batches is currently disabled.
MEV can be extracted if the operator exploits their centralized position and frontruns user transactions.
Funds can be frozen if the sequencer refuses to include an exit transaction (CRITICAL).
Users can't force any transaction
The mechanism for allowing users to submit their own transactions is currently disabled.
Users can be censored if the operator refuses to include their transactions.
Ethereum
Actors:
Its sole purpose and ability is to submit transaction batches. In case they are unavailable users cannot rely on the force batch mechanism because it is currently disabled.
The trusted proposer (called Aggregator) provides ZK proofs for all the supported systems. In case they are unavailable a mechanism for users to submit proofs on their own exists, but is behind a 5d delay for proving and a 5d delay for finalizing state proven in this way. These delays can only be lowered except during the emergency state.
A Multisig with 6 / 8 threshold. The Security Council is a multisig that can be used to trigger the emergency state which pauses bridge functionality, restricts advancing system state and removes the upgradeability delay.
Participants (8):
0xFe45…2e4b0xaF46…261D0xBDc2…FEFf0x4c16…88910x3ab9…D6220x49c1…0E860x9F7d…86A00x2188…1C28Used in:
Sole account allowed to submit forced transactions. If this address is the zero address, anyone can submit forced transactions.
A Multisig with 2 / 3 threshold. Admin of the PolygonRollupManager contract, can set core system parameters like timeouts and aggregator as well as deactivate emergency state. They can also upgrade the AstarValidium contracts, but are restricted by a 10d delay unless rollup is put in the Emergency State.
Used in:
A Multisig with 3 / 6 threshold. Admin of the AstarValidium contract, can set core system parameters like timeouts, sequencer, activate forced transactions, update the DA mode and upgrade the AstarValidiumDAC contract
Ethereum
Validium committee contract that allows the admin to setup the members of the committee and stores the required amount of signatures threshold.
Upgrade delay: None
The main contract of the Astar zkEVM. Contains sequenced transaction batch hashes and forced transaction logic.
Upgrade delay: None
Implementation used in:
An autogenerated contract that verifies ZK proofs in the PolygonRollupManager system.
Implementation used in:
It defines the rules of the system including core system parameters, permissioned actors as well as emergency procedures. The emergency state can be activated either by the Security Council, by proving a soundness error or by presenting a sequenced batch that has not been aggregated before a 7d timeout. This contract receives L2 state roots as well as ZK proofs.
Upgrade delay: None
Proxy used in:
The escrow contract for user funds. It is mirrored on the L2 side and can be used to transfer both ERC20 assets and arbitrary messages. To transfer funds a user initiated transaction on both sides is required. This contract can store any token.
Upgrade delay: None
Proxy used in:
Contract upgrades have to go through a 10d timelock unless the Emergency State is activated. It can also add rollup types that can be used to upgrade verifier contracts of existing systems. It is controlled by the ProxyAdminOwner.
Implementation used in:
Value Secured is calculated based on these smart contracts and tokens:
Proxy used in:
The current deployment carries some associated risks:
Funds can be stolen if a contract receives a malicious code upgrade. There is a 10d delay on code upgrades.