The dream of seamless and cost-effective cryptocurrency transactions using ZK-rollups is being hampered by a significant bottleneck: the high costs associated with proof generation. Users attempting to bridge funds from Ethereum (ETH) to ZK-rollups like zkSync are often facing fees that range from $0.15 to $0.50 instead of the expected minimal charges. This situation is frustrating, especially when considering that optimistic rollups typically offer lower fees, and the recent Dencun upgrade has drastically reduced data costs.
At the core of this issue lies the proof generation mechanism, which is not a victim of network congestion but rather the inherent inefficiencies of the proof process itself. Generating a zero-knowledge proof for a batch of transactions is an extremely resource-intensive task. It requires executing trillions of mathematical operations, particularly elliptic curve multiplications, on hardware that is not optimized for such tasks. According to L2Beat, approximately 60-70% of all fees on ZK-layer 2 solutions are consumed by this proving process, resulting in a centralized market of “prover farms” valued at an estimated $97 million.
This dependency creates a precarious centralization and security issue: over 90% of ZK-layer 2 solutions rely on a limited number of prover-as-a-service providers. This situation raises concerns about censorship, maximum extractable value (MEV) extraction, and potential outages, all of which undermine the principles of decentralization and broader adoption. The solution to this problem is twofold: the development of specialized hardware and the establishment of competitive open prover markets.
Currently, the ZK proving process can take anywhere from two to five minutes to generate a proof for a batch of transactions, leading to cloud computing costs ranging from $0.04 to $0.17. Under heavy network load, these costs can soar to over ten cents per transaction. The inefficiencies stem from the fact that GPUs, while excellent at parallel floating-point operations used in AI, are poorly suited for the operations required in zero-knowledge proofs, resulting in significant idle cycles during computation.
In a recent report, zkSync Era revealed that proving accounted for 65% of their total revenue of $2.3 million, translating to about $1.5 million going to centralized proving clusters. This high cost structure is a significant barrier, as it has resulted in a total value locked in leading ZK-layer 2s stagnating at $3.3 billion, in stark contrast to the over $40 billion captured by optimistic rollups.
Furthermore, optimistic rollups come with trade-offs such as the requirement for a seven-day withdrawal delay, which can be a hindrance for users in the fast-paced decentralized finance (DeFi) ecosystem. Therefore, the pathway to achieving truly scalable, affordable, and secure transactions lies not in avoiding proof generation but in innovating the process itself.
To resolve the current bottleneck, the industry needs to focus on developing domain-specific application-specific integrated circuits (ASICs) and creating open marketplaces for proving services. Recent advancements have demonstrated that specialized hardware can drastically outperform traditional GPUs, reducing proof generation time and energy consumption significantly.
Moreover, establishing an auction-based system for proving services would allow for greater decentralization and competition. This model would enable rollups to post jobs on Ethereum-based auctions where specialized rigs can bid to execute proofs, thereby reducing costs and enhancing efficiency.
As the need for cheaper proving costs becomes apparent, the potential for ZK-rollups to deliver sub-cent transaction fees at high throughput rates becomes increasingly feasible. This could unlock new possibilities for applications such as real-time gaming economies and innovative NFT marketplaces. By decentralizing the proving process and making it efficient, ZK-rollups can finally fulfill their promise as a viable scaling solution without compromising on security.
The battle for ZK adoption is fundamentally an engineering challenge, focused on improving the cost and decentralization of the proving process. The future of trustless transactions for millions hinges on overcoming these technical hurdles and establishing a robust marketplace for verifiable computation.
