BOB announced that it will be the first rollup project to use ZK proofs as fraud proofs by integrating RISC Zero's Kailua architecture
On July 25, BOB (Build on Bitcoin) announced a cooperation with zero-knowledge proof infrastructure RISCZero, which will become the first rollup project in the industry to use zero-knowledge proofs as fraud proofs by integrating Kailua, a hybrid architecture framework launched by RISC Zero. This will significantly save time and cost on existing setups and can reduce withdrawal times from the usual 7 days to 1 hour. This is a key step for BOB to implement Rollup Phases 1 and 2 on L2beat.
It is reported that Kailua is an OP stack extension built by RISC Zero using its verifiable computing layer Boundless network, which is a hybrid architecture (i.e., Hybrid Rollup) that can upgrade Optimistic Rollups to Hybrid ZK Rollups, which combines the advantages of Optimistic Rollups and ZK Rollups to achieve efficient blockchain settlement and dispute resolution. It attempts to balance high leaf swallowing, low cost, and high security by employing Optimistic Rollups to process transactions quickly by default and enabling ZK proofs in case of disputes or the need for quick settlement. In simple terms, it has the ability to integrate ZK rollup benefits for existing Optimistic Rollups.
One of the most important features is that it can shorten the settlement cycle from the original 7-day challenge period to a minimum of 1 hour, and for the Optimistic Rollup network that integrates Kailua, there is no need to worry about the continuous generation cost of ZK proofs because it is implemented on demand.
BOB is the first chain to use zero-knowledge proofs (ZK). This new approach offers the best of both worlds over Optimistic Rollups, which are slow to withdraw and expensive to anti-fraud, and ZK Rollups, which are expensive to run.
BOB perfectly combines efficiency (less expensive to submit proposals compared to validity rollups) and security (proving block correctness in case of fraud). Additionally, ZK proofs cost much less than on-chain binary games on the Optimism or Ink platforms (less than $100, compared to about $1 million for the latter).
Three advantages:
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Anyone can challenge the BOB sequencer's proposal with a margin as low as 0.5 ETH, without requiring hundreds of ETH like non-zero-knowledge fraud proofs.
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In the event of a challenge, the settlement of fraud proofs can be completed in just one transaction on Ethereum, so they can be finalized in minutes, compared to hours or days and multiple transactions for non-zero-knowledge versions.
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In the long run, BOB's withdrawal time can be significantly reduced because on-chain fraud solutions are fast and inexpensive. The initial estimated withdrawal time is 4 days, but after the system stabilizes, it can be shortened to a few hours.
Working principle:
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Kailua introduces its new self-developed error-proof game design to provide first-class security for rollup transaction ordering.
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BOB will use zero-knowledge proofs (ZK) fraud-proof proofs instead of multiple transactions in Optimism's binary game.
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Zero-knowledge proofs allow BOB to streamline the error-proofing mechanism to a single transaction on Ethereum rather than multiple transactions in a binary game.
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Specific process:
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For each checkpoint, the BOB sequencer (run by Conduit) will propose a new canonical chain for a specific height.
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Anyone can use the Kailua binary to make another proposal to dispute the canonical chain. Making a proposal requires a deposit of a deposit in ETH on Layer1. The initial setup is 0.5 ETH, which makes it easy for anyone to challenge and significantly lowers the barrier to entry for permissionless verification.
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When there are conflicting proposals at the same height, the challenger or validator (run by Conduit) will generate a zero-knowledge proof (using the Boundless algorithm) to solve the problem of the canonical chain. Since the structure of BOB depends on the order in which transactions are coded on Layer1, only one valid chain can exist. The wrong proposer or challenger's security deposit will be forfeited.
Alexei Zamyatin, co-founder of BOB and founding member of the BitVM Alliance, said: "With the launch of a fully functional proof system, BOB L2 will have full Ethereum security. This means that BOB will still be in the L2 layer of phase 0, while most other L2 layers will be moved to other categories on L2Beat. Phase 1 rollups are only subject to the launch of the Security Committee, which will be announced in the near future. Rollups in Phase 2 simply open the proposal process to anyone. ”
The RISC Zero team believes that Kailua upgraded Optimistic Rollup to use zero-knowledge proofs (ZK Fault Proofs) powered by RISC Zero zkVMs. The current market choice for rollup solutions is either Optimistic Rollup or ZK Rollup. Optimistic Rollup dominates the current market due to its low cost and high throughput, but requires a 7-day challenge window, which delays finality and limits interoperability. ZK rollups can provide fast finality, but generating ZK proofs for each block incur significant additional costs, and high-throughput rollups can cost millions of dollars or more.
Now that the third method is live on BOB, this is the solution powered by RISC Zero's Kailua architecture, which combines the advantages of both approaches: Optimistic ZK Rollups have both the low operating costs of the Optimistic Rollup system and the fast finality of ZK Rollups.