Paper 2025/2139

Scalable Private World Computer via Root iO: Application-Agnostic iO and Our Roadmap for Making It Practical

Abstract

Ethereum has established itself as a world computer, enabling general-purpose, decentralized, and verifiable computation via smart contracts on a globally replicated state. However, because all computations and state are public by default, it is fundamentally unsuitable for confidential smart contracts that jointly process private data from multiple users. This motivates the notion of a private world computer: an ideal future form of Ethereum that preserves its integrity and availability guarantees while supporting such confidential smart contracts. Prior constructions based on implementable cryptographic primitives such as fully homomorphic encryption (FHE) inevitably rely on committees that hold secret shares and perform computations using those shares, a capability that is not provided by today's Ethereum validators. We cannot simply modify the Ethereum protocol so as to shift the committee’s role onto the Ethereum validators, because the computational and communication costs borne by the committee grow with the demand for confidential smart contracts, forcing higher hardware requirements for participation, undermining decentralization, and increasing the risk of malicious collusion. Hence, there remains a fundamental trade-off between committee decentralization and scalability for confidential smart contracts. In this position paper, we make two contributions toward a scalable private world computer. First, we show how indistinguishability/ideal obfuscation (iO), combined with FHE and succinct non-interactive arguments of knowledge (SNARK), yields a private world computer that, after a one-time obfuscation process, introduces no additional ongoing trust assumptions beyond Ethereum’s validators, incurring no additional overhead for validators to process confidential smart contracts compared to public smart contracts. In this design, a single application-agnostic obfuscated circuit, called root iO, suffices to realize arbitrary confidential smart contracts. The outputs of root iO can be verified on-chain at a cost comparable to signature verification, and the obfuscation process can be distributed among multiple parties while remaining secure as long as at least one party is honest. As the second contribution, we outline our roadmap toward a practical implementation of root iO. Assuming that the underlying assumptions of our lattice-based iO construction remain secure, the remaining missing pieces are technically concrete: namely, practical implementations of verifiable FHE and of homomorphic evaluation of a pseudorandom function (PRF) and SNARK verification over key-homomorphic encodings, which together would allow us to implement root iO without incurring prohibitive overhead.