BOB announces integration of RISC Zero's Kailua architecture, becoming the first Rollup project to use ZK proofs as fraud proofs
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BOB announces integration of RISC Zero's Kailua architecture, becoming the first Rollup project to use ZK proofs as fraud proofs
This will significantly save time and cost for the existing setup, and reduce withdrawal times from the usual 7 days to just 1 hour. This is a key step for BOB achieving Rollup Stage 1 and Stage 2 on L2beat.
Navigating Web3 tides with focused insightsOn July 25, BOB (Build on Bitcoin) announced a partnership with zero-knowledge proof infrastructure provider RISCZero. By integrating Kailua, the hybrid architecture framework launched by RISCZero, BOB will become the first project in the industry to use zero-knowledge proofs as fraud proofs for Rollups. This will significantly reduce setup time and costs, and shorten withdrawal times from the typical 7 days to just 1 hour. This marks a key step for BOB toward achieving Rollup Stage 1 and Stage 2 on L2beat.
Kailua is an OP Stack extension built by RISC Zero using its verifiable computing layer, Boundless Network. It is a hybrid architecture—also known as Hybrid ZK Rollup—that upgrades Optimistic Rollups into Hybrid ZK Rollups by combining the advantages of both Optimistic Rollups and ZK Rollups, aiming to achieve efficient blockchain settlement and dispute resolution. It defaults to fast transaction processing via Optimistic Rollups and activates ZK proofs when disputes arise or rapid settlement is needed, thus balancing high throughput, low cost, and high security. In simple terms, it enables existing Optimistic Rollups to integrate the benefits of ZK Rollups.
The most significant feature is that settlement periods can be reduced from the original 7-day challenge window to as little as one hour. Additionally, Optimistic Rollup networks integrating Kailua do not need to worry about the continuous generation cost of ZK proofs, as Kailua’s design only engages them on-demand.
BOB is the first chain to utilize zero-knowledge proofs (ZK). Compared to slow withdrawals and expensive fraud detection mechanisms in Optimistic Rollups, as well as the high operational costs of ZK Rollups, this new approach combines the strengths of both.
BOB perfectly blends efficiency (lower proposal submission costs compared to validity rollups) and security (ability to prove block correctness in case of fraud). Moreover, ZK proofs are far cheaper than the on-chain bisection games currently used on platforms like Optimism or Ink—costing less than $100 versus approximately $1 million.
Three major advantages:
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Anyone can challenge a BOB sequencer proposal with a margin as low as 0.5 ETH, rather than requiring hundreds of ETH as in non-zero-knowledge fraud proofs.
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In the event of a challenge, fraud proof settlement requires only one transaction on Ethereum, finalizing within minutes—compared to hours or days and multiple transactions for non-zero-knowledge versions.
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In the long term, BOB's withdrawal times can be drastically shortened due to fast and low-cost on-chain fraud resolution. Initially estimated at 4 days, once the system stabilizes, withdrawal times could be reduced to just a few hours.
How it works:
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Kailua introduces a novel fault-dispute game design developed in-house, providing top-tier security for Rollup transaction ordering.
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BOB uses zero-knowledge proof (ZK) based fraud proofs instead of the multi-round transactions used in Optimism’s bisection game.
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Zero-knowledge proofs allow BOB to streamline its fault-proof mechanism into a single Ethereum transaction, rather than multiple rounds of transactions required in bisection games.
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Detailed process:
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For each checkpoint, the BOB sequencer (operated by Conduit) proposes a new canonical chain at a specific height.
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Anyone can submit an alternative proposal contesting the canonical chain using the Kailua binary. Submitting a proposal requires posting a bond in ETH on Layer 1. The initial setting is 0.5 ETH, making it easy for anyone to challenge and significantly lowering the barrier to permissionless validation.
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When conflicting proposals exist at the same height, the challenger or verifier (operated by Conduit) generates a zero-knowledge proof (using the Boundless algorithm) to resolve the issue with the canonical chain. Since BOB’s construction depends on the order of transaction encodings on Layer 1, only one valid chain can exist. The bonds of incorrect proposers or challengers will be slashed.
Alexei Zamyatin, co-founder of BOB and founding member of BitVM Alliance, said: “With the launch of a fully functional proof system, the BOB L2 will have full Ethereum-level security. This means BOB will remain in Stage 0 on the L2 layer, while most other L2s will move to different categories on L2Beat. Stage 1 Rollup depends only on launching a security council, which will be announced soon. Stage 2 Rollup simply requires opening the proposal process to everyone.”
The RISC Zero team believes Kailua upgrades Optimistic Rollups by enabling zero-knowledge fault proofs powered by RISC Zero’s zkVM. Currently, market choices for Rollup solutions are limited to either Optimistic Rollups or ZK Rollups. Due to low cost and high throughput, Optimistic Rollups dominate today’s market but require a 7-day challenge window, delaying finality and limiting interoperability. ZK Rollups offer fast finality, but generating ZK proofs for every block incurs substantial overhead—costs for high-throughput Rollups can reach millions of dollars or more.
Now, a third option has launched on BOB: a solution powered by RISC Zero’s Kailua architecture that combines the best of both worlds. Optimistic ZK Rollup offers both the low operating costs of Optimistic Rollup systems and the fast finality of ZK Rollups.
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