zkBNB Architecture

zkBNB is a zero-knowledge scalability solution, or L2, which focuses on straightforward token operations and built-in marketplaces for Gaming and Social use cases. It serves as a scalability solution for the BNB Smart Chain by bundling multiple transactions into a single transaction, reducing costs for on-chain transactions. The Zero Knowledge proof system used in zkBNB ensures a much faster finality time of the L2 transactions, that helps improve the user experience. zkBNB is essentially built on the zk-Rollup architecture.

zk-Rollup Architecture

• committer. Committer executes transactions and produce consecutive blocks.
• monitor. Monitor tracks events on BSC, and translates them into transactions on zkBNB.
• witness. Witness re-executes the transactions within the block and generates witness materials.
• prover. Prover generates cryptographic proof based on the witness materials.
• sender. The sender rollups the compressed l2 blocks to L1, and submit proof to verify it.
• api server. The api server is the access endpoints for most users, it provides rich data, including digital assets, blocks, transactions, gas fees.
• recovery. A tool to recover the sparse merkle tree in kv-rocks based on the state world in postgresql.

Maximum throughput

Pending benchmark…

Data Availability

zkBNB publish state data for every transaction processed off-chain to BSC. With this data, it is possible for individuals or businesses to reproduce the rollup’s state and validate the chain themselves. BSC makes this data available to all participants of the network as calldata.

zkBNB don’t need to publish much transaction data on-chain because validity proofs already verify the authenticity of state transitions. Nevertheless, storing data on-chain is still important because it allows permissionless, independent verification of the L2 chain’s state which in turn allows anyone to submit batches of transactions, preventing malicious committer from censoring or freezing the chain.

zkBNB will provide a default client to replay all state on Layer2 based on these call data.

Transaction Finality

BSC acts as a settlement layer for zkBNB: L2 transactions are finalized only if the L1 contract accepts the validity proof and execute the txs. This eliminates the risk of malicious operators corrupting the chain (e.g., stealing rollup funds) since every transaction must be approved on Mainnet. Also, BSC guarantees that user operations cannot be reversed once finalized on L1.

zkBNB provides relative fast finality speed within 10 minutes.

Instant confirmation ZkBS

Even though time to finality is about 10 minutes, it does not affect the usability of the network. The state transition happens immediately once the block been proposed on zkBNB. The rollup operations are totally transparent to most users, users can make further transfers without waiting.

Censorship resistance

Committer will execute transactions, produce batches. While this ensures efficiency, it increases the risk of censorship :malicious zk-rollup committer can censor users by refusing to include their transactions in batches.

As a security measure, zkBNB allow users to submit transactions directly to the rollup contract on Mainnet if they think they are being censored by the operator. This allows users to force an exit from the zk-rollup to BSC without having to rely on the commiter’s permission.