Canvas Connect
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Canvas Connect is a Layer 2 solution based on StarkEx technology, specifically designed to provide centralized investment and trading services to financial institutions.
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Risk Analysis
State validation
ZK proofs (ST)ZK-STARKS are zero knowledge proofs that ensure state correctness.
Data availability
External (DAC)Proof construction relies fully on data that is NOT published on chain. There exists a data availability committee (DAC) that is tasked with protecting and supplying the data.
Upgradeability
YesThe code that secures the system can be changed arbitrarily and without notice.
Sequencer failure
Force via L1Users can force the sequencer to include a withdrawal transaction by submitting a request through L1. If the sequencer censors or is down for for more than 7d, users can use the exit hatch to withdraw their funds.
Proposer failure
Use escape hatchUsers are able to trustlessly exit by submitting a Merkle proof of funds. NFTs will be minted on L1 to exit.
Technology
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. The system state is represented using Merkle roots.
Zero knowledge STARK cryptography is used
Despite their production use ZK-STARKs 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.
Funds can be lost if the proof system is implemented incorrectly.
Data is not stored on chain
The balances of the users are not published on-chain, but rather sent to several well known and trusted parties, also known as committee members. A state update is valid and accepted on-chain only if at least a quorum of the committee members sign a state update.
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.
Operator
The system has a centralized operator
The operator is the only entity that can propose blocks. A live and trustworthy operator is vital to the health of the system. Typically, the Operator is the hot wallet of the StarkEx service submitting state updates for which proofs have been already submitted and verified.
MEV can be extracted if the operator exploits their centralized position and frontruns user transactions.
Users can force exit the system
Force exit allows the users to escape censorship by withdrawing their funds. The system allows users to force the withdrawal of funds by submitting a request directly to the contract on-chain. The request must be served within a defined time period. If this does not happen, the system will halt regular operation and permit trustless withdrawal of funds.
Users can be censored if the operator refuses to include their transactions. However, there exists a mechanism to independently exit the system.
Withdrawals
Regular exit
The user initiates the withdrawal by submitting a regular transaction on this chain. When the block containing that transaction is proven the funds become available for withdrawal on L1. Finally the user submits an L1 transaction to claim the funds. This transaction does not require a merkle proof. When withdrawing NFTs they are minted on L1.
Forced exit
If the user experiences censorship from the operator with regular exit they can submit their withdrawal requests directly on L1. The system is then obliged to service this request. Once the force operation is submitted and if the request is serviced, the operation follows the flow of a regular exit.
Emergency exit
If enough time passes and the forced exit is still ignored the user can put the system into a frozen state, disallowing further state updates. In that case everybody can withdraw by submitting a merkle proof of their funds with their L1 transaction.
Permissions
The system uses the following set of permissioned addresses:
Can upgrade implementation of the system, potentially gaining access to all funds stored in the bridge. Currently there is no delay before the upgrade, so the users will not have time to migrate.
Validity proof must be signed by at least 1 of these addresses to approve state update.
Can upgrade implementation of SHARP Verifier, potentially with code approving fraudulent state. Currently there is 28d delay before the upgrade.
SHARP Verifier Governor. This is a Gnosis Safe with 2 / 3 threshold.
Those are the participants of the SHARPVerifierGovernorMultisig.
Allowed to update state of the system. When Operator is down the state cannot be updated.
Smart Contracts
The system consists of the following smart contracts:
This contract stores the following tokens: ETH, USDC.
Data Availability Committee (DAC) contract verifying data availability claim from DAC Members (via multisig check).
CallProxy for GpsStatementVerifier.
Starkware SHARP verifier used collectively by Starknet, Sorare, ImmutableX, Apex, Myria, rhino.fi and Canvas Connect. It receives STARK proofs from the Prover attesting to the integrity of the Execution Trace of these Programs including correctly computed state root which is part of the Program Output.
Part of STARK Verifier.
Part of STARK Verifier.
MemoryPageFactRegistry is one of the many contracts used by SHARP verifier. This one is important as it registers all necessary on-chain data.
Part of STARK Verifier.
Value Locked is calculated based on these smart contracts and tokens:
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).
