Scroll
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Description
Scroll is rollup that extends Ethereum’s capabilities through zero knowledge tech and EVM compatibility.
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Risk analysis
State validation
ZK proofs (SN)zkSNARKS are zero knowledge proofs that ensure state correctness, but require trusted setup.
Data availability
On chainAll of the data needed for proof construction is published on chain.
Upgradeability
YesThe code that secures the system can be changed arbitrarily and without notice.
Sequencer failure
No mechanismThere is no mechanism to have transactions be included if the sequencer is down or censoring.
Proposer failure
Cannot withdrawOnly the whitelisted proposers can publish state roots on L1, so in the event of failure the withdrawals are frozen.
Rollup stage
Scroll is a 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.
All transaction data is recorded on chain
All executed transactions are submitted to an on chain smart contract. The execution of the rollup is based entirely on the submitted transactions, so anyone monitoring the contract can know the correct state of the rollup chain.
State derivation
The node software to reconstruct the state is available here. Note that it uses the L2 p2p network to fetch blocks, and not the L1 network. The ability to check consistency with L1 data is in the works.
The rollup does not use compression.
The genesis file can be found here, which contains two prefunded addresses and five predeployed contracts.
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.
MEV can be extracted if the operator exploits their centralized position and frontruns user transactions.
Users can't force any transaction
There is no general mechanism to force the sequencer to include the transaction.
Users can be censored if the operator refuses to include their transactions.
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.
Funds can be frozen if the operator censors withdrawal transaction.
Permissions
The system uses the following set of permissioned addresses:
Currently also designated as the Security Council. Can upgrade proxies and the verifier without delay and propose transactions within Timelocks. It can also revert non finalized batches, remove sequencers and provers and pause contracts. This is a Gnosis Safe with 4 / 5 threshold.
Those are the participants of the ScrollMultisig.
Can execute timelock transactions. This is a Gnosis Safe with 1 / 5 threshold.
Those are the participants of the ExecutorMultisig.
Can revert batches, remove sequencers and provers, and pause contracts. This is a Gnosis Safe with 2 / 5 threshold.
Those are the participants of the EmergencyMultisig.
Actors allowed to commit transaction batches.
Actors allowed to prove transaction batches and publish state root updates.
Smart contracts
The system consists of the following smart contracts:
The main contract of the Scroll chain. Allows to post transaction data and state roots, along with proofs. Sequencing and proposing are behind a whitelist. L1 -> L2 message processing on L2 is not enforced.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to send L1 -> L2 and relay messages from L2. It allows to replay failed messages and to drop skipped messages. L1 -> L2 messages sent using this contract pay for L2 gas on L1 and will have the aliased address of this contract as the sender. This contract stores the following tokens: ETH.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contains the array of queued L1 -> L2 messages, either appended using the L1ScrollMessenger or the EnforcedTxGateway. The latter contract, which would allow users to send L2 messages from L1 with their own address as the sender, is not enabled yet.
Contract used to relay the L2 basefee on L1 in a trusted way using a whitelist. It is also used to store and update values related to intrinsic gas cost calculations.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to store whitelists for the L2GasPriceOracle contract.
Owner of all contracts in the system. It implements an extension of AccessControl that manages roles and functions allowed to be called by each role.
14d timelock. Admin of the ScrollOwner contract, meaning it can assign and revoke roles. The ScrollMultisig can propose and cancel transactions, and the ExecutorMultisig can execute them.
7d timelock. Can update the verifier and manage the USDC gateway bridge. The ScrollMultisig can propose and cancel transactions, and the ExecutorMultisig can execute them.
1d timelock. Can add new sequencers and provers, update the gas oracle and permissions to update its values, the max gas limit, and gateways token mappings. The ScrollMultisig can propose and cancel transactions, and the ExecutorMultisig can execute them.
Contract used to update the verifier and keep track of current and old versions.
Current verifier, used to prepare data for the PlonkVerifier.
Contract used to bridge ETH from L1 to L2.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to bridge WETH from L1 to L2.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to bridge ERC20 tokens from L1 to L2. It uses a fixed token list. This contract can store any token.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to bridge ERC20 tokens from L1 to L2. It allows to change the token mappings. This contract can store any token.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to bridge USDC tokens from L1 to L2. This contract stores the following tokens: USDC.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to bridge ERC721 tokens from L1 to L2.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Contract used to bridge ERC1155 tokens from L1 to L2.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Main entry point for depositing ETH and ERC20 tokens, which are then forwarded to the correct gateway.
Can be upgraded by: ScrollMultisig
Upgrade delay: None
Multisig used to store fees collected from gateways to pay for L1 -> L2 message execution.
Contracts to force L1 -> L2 messages with the proper sender. Currently not enabled.
Can be upgraded by: ScrollMultisig
Upgrade delay: None