PlayBlock
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About
PlayBlock is an Orbit stack Layer 3 on Arbitrum Nova. It is built by the team behind Playnance, and is focused on gasless gaming and gambling.
Badges
About
PlayBlock is an Orbit stack Layer 3 on Arbitrum Nova. It is built by the team behind Playnance, and is focused on gasless gaming and gambling.
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 set of challengers rely on few entities to safely update the state. A small set of challengers can collude with the proposer to finalize an invalid state, which can cause loss of funds.
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.
Arbitrum NovaFunds can be stolen if
Funds can be lost if
Users can be censored if
MEV can be extracted if
| SEQUENCER FAILURE | STATE VALIDATION | DATA AVAILABILITY | EXIT WINDOW | PROPOSER FAILURE | |
| Arbitrum Nova L2 | Self sequence | Fraud proofs (INT) | External (DAC) | 2d | Self propose |
| PlayBlock L3 • Individual | Self sequence | Fraud proofs (INT) | External (DAC) | None | Self propose |
| PlayBlock L3 • Combined | Self sequence | Fraud proofs (INT) | External (DAC) | None | Self propose |
Sequencer failure
Self sequenceState validation
Fraud proofs (INT)No actor outside of the single Proposer can submit fraud proofs. Interactive proofs (INT) require multiple transactions over time to resolve. The challenge protocol can be subject to delay attacks. There is a 30m challenge period.
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 1/2 that is tasked with protecting and supplying the data.
Exit window
NoneThere is no window for users to exit in case of an unwanted regular upgrade since contracts are instantly upgradable.
Proposer failure
Self proposeAnyone can become a Proposer after 19d 2h of inactivity from the currently whitelisted Proposers.
Arbitrum NovaData is not stored on chain
Users transactions are not published onchain, but rather sent to external trusted parties, also known as committee members (DAC). Members of the DAC collectively produce a Data Availability Certificate (comprising BLS signatures from a quorum) guaranteeing that the data behind the new transaction batch will be available until the expiry period elapses (currently a minimum of two weeks). This signature is not verified by L1, however external Validators will skip the batch if BLS signature is not valid resulting. This will result in a fraud proof challenge if this batch is included in a consecutive state update. It is assumed that at least one honest DAC member that signed the batch will reveal tx data to the Validators if Sequencer decides to act maliciously and withhold the data. If the Sequencer cannot gather enough signatures from the DAC, it will “fall back to rollup” mode and by posting the full data directly to the L1 chain. The current DAC threshold is 1 out of 2.
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.
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
The DAC uses a data availability solution built on the AnyTrust protocol. It is composed of the following components:
- Sequencer Inbox: Main entry point for the Sequencer submitting transaction batches.
- Data Availability Committee (DAC): A group of members responsible for storing and providing data on demand.
- Data Availability Certificate (DACert): A commitment ensuring that data blobs are available without needing full data posting on the L1 chain.
Committee members run servers that support APIs for storing and retrieving data blobs. The Sequencer API allows the rollup Sequencer to submit data blobs for storage, while the REST API enables anyone to fetch data by hash. When the Sequencer produces a data batch, it sends the batch along with an expiration time to Committee members, who store it and sign it. Once enough signatures are collected, the Sequencer aggregates them into a valid DACert and posts it to the L1 chain inbox. If the Sequencer fails to collect enough signatures, it falls back to posting the full data to the L1 chain.
A DACert includes a hash of the data block, an expiration time, and proof that the required threshold of Committee members have signed off on the data. The proof consists of a hash of the Keyset used in signing, a bitmap indicating which members signed, and a BLS aggregated signature. L2 nodes reading from the sequencer inbox verify the certificate’s validity by checking the number of signers, the aggregated signature, and that the expiration time is at least two weeks ahead of the L2 timestamp. If the DACert is valid, it provides a proof that the corresponding data is available from honest committee members.
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 Data Availability Certificate (DACert), including a hash of the data block, an expiration time, and a proof that the required threshold of Committee members have signed off on the data. The sequencer distributes the data and collects signatures from Committee members offchain. Only the DACert is posted by the sequencer to the destination chain inbox (the DA bridge), achieving destination chain transaction ordering finality in a single onchain transaction.
Funds can be lost if a malicious committee attests to an invalid data availability certificate.
Funds can be lost if the bridge contract or its dependencies receive a malicious code upgrade. There is no delay on code upgrades.
Updates to the system state can be proposed and challenged by a set of whitelisted validators. If a state root passes the challenge period, it is optimistically considered correct and made actionable for withdrawals.
Whitelisted validators propose state roots as children of a previous state root. A state root can have multiple conflicting children. This structure forms a graph, and therefore, in the contracts, state roots are referred to as nodes. Each proposal requires a stake, currently set to 0.1 ETH, that can be slashed if the proposal is proven incorrect via a fraud proof. Stakes can be moved from one node to one of its children, either by calling stakeOnExistingNode or stakeOnNewNode. New nodes cannot be created faster than the minimum assertion period by the same validator, currently set to 15m. The oldest unconfirmed node can be confirmed if the challenge period has passed and there are no siblings, and rejected if the parent is not a confirmed node or if the challenge period has passed and no one is staked on it.
Funds can be stolen if none of the whitelisted verifiers checks the published state. Fraud proofs assume at least one honest and able validator (CRITICAL).
A challenge can be started between two siblings, i.e. two different state roots that share the same parent, by calling the startChallenge function. Validators cannot be in more than one challenge at the same time, meaning that the protocol operates with partial concurrency. Since each challenge lasts 30m, this implies that the protocol can be subject to delay attacks, where a malicious actor can delay withdrawals as long as they are willing to pay the cost of losing their stakes. If the protocol is delayed attacked, the new stake requirement increases exponentially for each challenge period of delay. Challenges are played via a bisection game, where asserter and challenger play together to find the first instruction of disagreement. Such instruction is then executed onchain in the WASM OneStepProver contract to determine the winner, who then gets half of the stake of the loser. As said before, a state root is rejected only when no one left is staked on it. The protocol does not enforces valid bisections, meaning that actors can propose correct initial claim and then provide incorrect midpoints.
Arbitrum NovaThe system has a centralized sequencer
While forcing transaction is open to anyone the system employs a privileged sequencer that has priority for submitting transaction batches and ordering transactions.
MEV can be extracted if the operator exploits their centralized position and frontruns user transactions.
Users can force any transaction
Because the state of the system is based on transactions submitted on the underlying host chain and anyone can submit their transactions there it allows the users to circumvent censorship by interacting with the smart contract on the host chain directly. After a delay of 1d in which a Sequencer has failed to include a transaction that was directly posted to the smart contract, it can be forcefully included by anyone on the host chain, which finalizes its ordering.
Arbitrum NovaRegular messaging
Tradeable Bridge Exit
When a user initiates a regular withdrawal a third party verifying the chain can offer to buy this withdrawal by paying the user on L1. The user will get the funds immediately, however the third party has to wait for the block to be finalized. This is implemented as a first party functionality inside Arbitrum’s token bridge.
Autonomous exit
Users can (eventually) exit the system by pushing the transaction on L1 and providing the corresponding state root. The only way to prevent such withdrawal is via an upgrade.
EVM compatible smart contracts are supported
Arbitrum One uses Nitro technology that allows running fraud proofs by executing EVM code on top of WASM.
Funds can be lost if there are mistakes in the highly complex Nitro and WASM one-step prover implementation.
Arbitrum Nova
Actors:
Central actors allowed to submit transaction batches to L1.
They can submit new state roots and challenge state roots. Some of the operators perform their duties through special purpose smart contracts.
This address has the Executor role and can upgrade the rollup contracts (via ProxyAdmin) without delay, potentially stealing all funds.
Arbitrum Nova
This contract can upgrade the implementations of the rollup proxies. The source code of this contract is not verified on Etherscan.
Main contract implementing Arbitrum One Rollup. Manages other Rollup components, list of Stakers and Validators. Entry point for Validators creating new Rollup Nodes (state commits) and Challengers submitting fraud proofs. The source code of this contract is not verified on Etherscan.
Contract managing Inboxes and Outboxes. It escrows the native token used for gas on the chain. This contract stores the following tokens: ETH.
Main entry point for the Sequencer submitting transaction batches. The source code of this contract is not verified on Etherscan.
Contract allowed to upgrade the system.
Contract that allows challenging invalid state roots. Can be called through the RollupProxy.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Contract used to perform the last step of a fraud proof.
Value Secured is calculated based on these smart contracts and tokens:
Contract managing Inboxes and Outboxes. It escrows ETH sent to L2.
Upgrade delay: No delay
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).
Funds can be stolen if the source code of unverified contracts contains malicious code (CRITICAL).