Ethereum co-founder Vitalik Buterin has publicly identified the modular exponentiation (modexp) precompile as the most “ZK-EVM-unfriendly” component of the Ethereum Virtual Machine (EVM), describing it as being up to 50 times more complex than average blocks when used inside zero-knowledge proof systems. He suggested that the solution lies in submitting a new Ethereum Improvement Proposal (EIP) that replaces the precompile with computationally equivalent EVM-native code—despite a likely increase in gas costs. In his remarks, Buterin noted that modexp is primarily used today for RSA encryption and signing, and these functions could instead be handled more efficiently via SNARK-based methods.
What was said
In a technical discussion (conference panel and online threads) Buterin called out the modexp precompile (often referred to by its EVM opcode ID) as a key bottleneck for zero-knowledge roll-up (ZK-EVM) adoption. He claimed that when a prover circuit includes modexp operations, the arithmetic complexity grows by a factor of around 50 compared to typical operations.
He proposed the following measures:
- Drafting a new EIP that deprecates or removes the modexp precompile, replacing it with a direct EVM code implementation that yields the same computational result.
- Accepting higher per-transaction gas cost in favour of better compatibility with zero-knowledge proof systems and improved prover performance.
- Encouraging protocols that rely on RSA encryption/signing (via modexp) to migrate toward SNARK-based alternatives (e.g., proving statements via succinct proofs rather than costly modexp on‐chain).
While the exact EIP number and text were not yet published publicly at the time of Buterin’s comments, the call has sparked discussion among core-devs and ZK-roll-up teams.
Why this matters
- ZK-EVM scalability: Zero-knowledge roll-ups are widely regarded as one of the most promising scaling paths for Ethereum. Components that impose large prover or verification overheads—such as modexp—slow down adoption of ZK-EVM chains or increase their costs.
- Protocol design trade-offs: Buterin’s proposal signals that Ethereum may accept higher immediate gas costs in favour of long-term proof-friendliness and ecosystem sustainability. This reflects a shift in priorities from raw gas-optimisation toward ZK-optimal code paths.
- Cryptographic paradigm shift: By pointing out that RSA-based operations (via modexp) can be replaced with zk-friendly alternatives (e.g., SNARKs), the remarks highlight an ongoing cryptographic transition in decentralized systems.
- Developer and proposer ecosystem: The call for a new EIP means core-developers, layer-2 roll-up teams and ecosystem tooling vendors must plan for coordination, migration paths, and compatibility concerns if modexp is phased out or changed.
Technical background
- The modexp precompile (often referenced as precompiled contract address 0x05 in Ethereum) implements modular exponentiation, a basic building block for RSA encryption, digital signatures and other cryptographic protocols.
- Precompiles in Ethereum are special contracts implemented in native code for efficiency (e.g., EC mul, SHA-256, etc.). However, they often pose challenges for ZK-proof systems because they rely on specialised arithmetic that is hard to replicate efficiently inside ZK circuits.
- ZK-EVMs aim to replicate EVM semantics inside zero-knowledge proof systems so that roll-up blocks can be verified succinctly on‐chain. When operations like modexp dominate prover cost or circuit size, the cost and latency of roll-up proofs increase significantly.
- By converting modexp to equivalent EVM code (that is ZK-friendly because it uses standard arithmetic or logical operations), the ecosystem can achieve better prover efficiency, even if on‐chain costs rise.
Challenges & Considerations
- Gas cost increase: Buterin acknowledges that replacing the precompile with EVM code will raise gas costs for transactions that rely heavily on modular exponentiation. Protocols dependent on RSA will need to evaluate cost‐benefit trade-offs.
- Migration complexity: Projects using modexp (e.g., cross-chain bridges, encryption suites, signature schemes) will need to migrate to the new EIP standard, adjust contracts, and coordinate network upgrades.
- Backward compatibility: To avoid disruption, the transition needs careful planning: whether old contracts remain valid, how roll-up systems handle mixed blocks, and how nodes upgrade.
- Proof ecosystem readiness: While SNARK-based substitutes are promising, toolchain maturity, auditor readiness and developer familiarity vary. Some ecosystems may take time to adopt the alternatives.
- Consensus & governance: Changing or removing a precompile is a non-trivial change in Ethereum’s protocol. The EIP must go through discussion, testing, client implementation, and network consensus—any broken assumption could cause broader impact.
What to Watch
- Publication of the EIP draft that Buterin referenced: its number, summary, rationale and proposed gas cost changes.
- Core-dev meeting minutes or Ethereum Foundation blog posts discussing modexp deprecation, ZK-EVM alignment, and protocol timelines.
- Layer-2 roll-up teams’ responses — how ZK-EVM infra (e.g., Matter Labs, Scroll, Polygon Zero) incorporate or encourage transition away from modexp.
- Ecosystem impact: Contracts using RSA or modexp—how many will need refactoring, what the migration cost is, and whether few protocols resist the change.
- Gas price movement: After implementation, transactions using modular exponentiation will cost more; monitoring gas implications will be critical for impacted protocols.
Bottom Line
Vitalik Buterin’s remarks on the modexp precompile position it as a significant bottleneck to ZK-EVM scalability and signal a potential paradigm shift in Ethereum’s cryptographic architecture. By favouring ZK-proof friendliness over short‐term gas optimisation, the ecosystem may open the door to more efficient layer-2 proof systems and broader adoption of zero-knowledge roll-ups. The execution risk is non-trivial—requiring protocol upgrades, ecosystem coordination and migration support—but the long-term impact on Ethereum’s scalability and cryptography could be substantial.
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