Why the 'Circuit as a Service' Model Threatens Decentralization

The centralization trap is the inevitable outcome of outsourcing critical state validation. Protocols like zkSync Era and Polygon zkEVM rely on centralized sequencers to batch and prove transactions, creating a single point of failure and censorship.

Decentralization is not a feature you add later; it is the foundational security model. The current CaaS landscape mirrors the early cloud wars, where convenience trumped sovereignty, leading to the dominance of AWS and Google Cloud.

The validator dilemma emerges when proving is commoditized. A service like Axiom or Herodotus provides proofs, but the circuit logic and data sourcing remain opaque black boxes controlled by a single entity.

Evidence: Over 95% of Arbitrum transactions are ordered by its single, permissioned sequencer. This is the CaaS future: scalable chains with centralized trust roots.

Centralized Proving Power is the primary failure mode. The model outsources proof generation to a single, opaque entity, creating a single point of failure and censorship. This directly contradicts the trust-minimized settlement that zk-rollups like zkSync and StarkNet are designed to achieve.

Economic Capture is Inevitable. The service provider controls the proving key, becoming a mandatory tollgate for all state transitions. This replicates the extractive model of sequencer centralization seen in early Optimism, but at a more fundamental cryptographic layer.

The Verifier's Dilemma emerges. While the on-chain verifier contract is decentralized, its sole job is to check a proof from a single source. If the proving service is compromised, the entire chain's validity is falsified, rendering decentralized verification moot.

Evidence: The StarkEx prover runs on centralized AWS instances. While the STARK proofs are sound, the proving infrastructure is a centralized black box, creating a systemic risk that the decentralized L1 cannot audit or mitigate.

Centralized State Management is the primary vector for capture. A service provider controlling the prover network and sequencer centralizes the most valuable assets: execution state and transaction ordering. This replicates the client-server model, making the network's liveness and correctness dependent on a single entity's infrastructure.

Economic Capture Follows Technical Control. The service provider becomes the gatekeeper for fee extraction, dictating pricing for proving and sequencing. This creates a classic platform risk, where applications built on the Circuit are subject to rent-seeking, mirroring the issues seen with centralized cloud providers like AWS in Web2.

The Verifier's Dilemma emerges. With a black-box proving service, the blockchain's verifiers (e.g., L1 validators) must trust the provider's attestations. This breaks the trust-minimized security model, reducing the role of the base layer to a passive data availability layer, similar to early critiques of Optimism's initial single sequencer.

Evidence: The rapid consolidation in the ZK-rollup prover market demonstrates this risk. Entities like RiscZero and Succinct aim to become the default proving backends, creating protocol-level vendor lock-in. The value accrues to the service, not the decentralized network.

Centralized compute is systemic risk. The 'Circuit as a Service' model outsources the proving layer to a few centralized operators like Brevis or Axiom. This reintroduces a single point of failure for the entire validity system, replicating the trust model of cloud providers like AWS.

Decentralized sequencing is the bottleneck. The real scaling constraint is not proving speed, but decentralized sequencing. Projects like Espresso and Astria are solving this, while centralized proving services bypass the harder problem for a temporary fix.

The precedent is dangerous. This mirrors the early days of rollups where centralized sequencers became entrenched. The proving layer is more critical; centralizing it creates a harder-to-dislodge dependency, as seen with early Infura reliance.

Evidence: Ethereum's roadmap prioritizes decentralized proving via PBS and peerDAS. The ecosystem's long-term health depends on solving decentralization first, not outsourcing it for short-term throughput gains.

The trust trap is a regression to pre-blockchain architecture. When a protocol like Polygon zkEVM or zkSync relies on a single, opaque service for its ZK circuit generation, it creates a critical dependency. The entire system's security and liveness depend on that service's honesty and uptime.

Centralized proving services become the new validators. This model mirrors the trusted setup ceremonies of early ZK projects, but as a persistent operational requirement. The service provider controls the proving key, creating a single point of censorship and a lucrative target for attacks or regulatory capture.

The counter-intuitive insight is that decentralization must extend beyond consensus to the prover network. A decentralized prover marketplace, akin to EigenLayer's restaking model for distributed security, is the necessary evolution. This prevents any single entity from controlling the proving bottleneck for major L2s.

Evidence: The Ethereum roadmap explicitly prioritizes enshrined ZK-EVMs and decentralized proving. This architectural direction, championed by Vitalik Buterin, rejects the 'Circuit-as-a-Service' model as a long-term solution, treating it as a temporary bootstrap mechanism.