Paper 2026/506

Unclonable Encryption in the Haar Random Oracle Model

Abstract

We construct unclonable encryption (UE) in the Haar random oracle model, where all parties have query access to $U,U^\dagger,U^*,U^T$ for a Haar random unitary $U$. Our scheme satisfies the standard notion of unclonable indistinguishability security, supports reuse of the secret key, and can encrypt arbitrary-length messages. That is, we give the first evidence that (reusable) UE, which requires computational assumptions, exists in "microcrypt", a world where one-way functions may not exist. As one of our central technical contributions, we build on the recently introduced path recording framework to prove a natural "unitary reprogramming lemma", which may be of independent interest.

Note: Updated with full version of camera-ready for Crypto 2026. Minor typos corrected, some intuition added, and expanded discussion of related work.