X Layer
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X Layer is Validium by OKX with seamless integration with OKX products. It is powered by the Polygon CDK.
Badges
About
X Layer is Validium by OKX with seamless integration with OKX products. It is powered by the Polygon CDK.
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 2/2 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 on-chain by the Sequencer, after being signed by the DAC members.
Funds can be lost if the external data becomes unavailable (CRITICAL).
X Layer DACThe 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.
Regular exit
The system uses the following set of permissioned addresses:
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.
This is a Gnosis Safe 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.
Used in:
Those are the participants of the SecurityCouncil.
Sole account allowed to submit forced transactions. If this address is the zero address, anyone can submit forced transactions.
This is a Gnosis Safe 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 XLayerValidium contracts, but are restricted by a 10d delay unless rollup is put in the Emergency State.
Used in:
Those are the participants of the RollupManagerAdminMultisig.
Admin of the XLayerValidium contract, can set core system parameters like timeouts, sequencer, activate forced transactions and update the DA mode.
Owner of the XLayerValidiumDAC’s ProxyAdmin. Can upgrade the contract.
The system consists of the following smart contracts on the host chain (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: No delay
The main contract of the X Layer. 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 Locked 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.