Paper 2026/2709

Private Accounts Without $O(N)$ Work Through a Hybrid State Model

Abstract

Privacy-preserving smart contracts face a scalability problem. In account-balance-vector designs, hiding which accounts changed requires that every transaction perform an indistinguishable update over the global state, so validators pay work linear in the number of accounts for every private transfer. UTXO systems avoid this by validating local spends, but do not provide the same account-style programming model. We argue that the usual "account vs.~UTXO" framing conflates state representation and execution model, two choices that can be made separately. Miden, an Ethereum Layer 2, separates them. It uses persistent accounts for programmability, asynchronous notes for value transfer, and client-side proving for execution. Validators verify proofs and update commitments without re-executing transactions or accessing uninvolved state. The result is an account-based platform with private transfers and private computation, while keeping validator work per transaction logarithmic in the number of accounts.