Users 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.

State validation

ZK proofs (ST)

STARKs are zero knowledge proofs that ensure state correctness.

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 5/7 that is tasked with protecting and supplying the data.

Exit window

None

There is no window for users to exit in case of an unwanted regular upgrade since contracts are instantly upgradable.

Proposer failure

Use escape hatch

Users 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.

Enforcing Consistency on the On-Chain State - StarkEx documentation

Zero knowledge STARK cryptography is used

Despite their production use zkSTARKs 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.

STARK Core Engine Deep Dive

Data is not stored on chain

The balances of the users are not published on-chain, but rather sent to external 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.

Operator - StarkEx documentation

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.

Censorship Prevention - StarkEx documentation

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.

Withdrawal - StarkEx documentation

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 the enough time deadline 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:

Governor 0x9C41…EC91

Can upgrade implementation of the system, potentially gaining access to all funds stored in the bridge. Currently there is 14d delay before the upgrade.

Data Availability Committee (7) 0x1FfB…58d1 0x24Ee…D54b 0x48AF…B949 0x51Ab…ff2E 0xAfC4…5d17 0xB71F…FF61 0xfF50…C537

Validity proof must be signed by at least 5 of these addresses to approve state update.

SHARP Verifier Governors (2) 0x3DE5…F5C6 SHARPVerifierGovernorMultisig

Can upgrade implementation of SHARP Verifier, potentially with code approving fraudulent state. Currently there is 0s delay before the upgrade.

SHARPVerifierGovernorMultisig SHARP Verifier Governors

This is a Gnosis Safe with 2 / 4 threshold. SHARP Verifier Governor.

Used in:

SHARPVerifierGovernorMultisig participants (4) 0x0405…8488 0x5923…8558 0xebc8…fD7F 0x955B…2Fec

Those are the participants of the SHARPVerifierGovernorMultisig.

Operators 0x9B7f…927e

Allowed to update the state. When the Operator is down the state cannot be updated.

Smart contracts

A diagram of the smart contract architecture

The system consists of the following smart contracts on the host chain (Ethereum):

StarkExchange 0x5FDC…27e9 Implementation #1 (Upgradable)Implementation #2 (Upgradable)Implementation #3 (Upgradable)Implementation #4 (Upgradable)Implementation #5 (Upgradable)Implementation #6 (Upgradable)Implementation #7 (Upgradable)Admin

This contract stores the following tokens: ETH, IMX, USDC, OMI.

Implementation used in:

Committee 0x16BA…A295

Data Availability Committee (DAC) contract verifying data availability claim from DAC Members (via multisig check).

SHARPVerifierProxy 0x4731…Db60 Implementation (Upgradable)Admin (1)Admin (2)

CallProxy for GpsStatementVerifier.

Proxy used in:

SHARPVerifier 0x9fb7…1942

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.

Implementation used in: