Quantum Impossibility Results Extend Classical Barriers for Simulation-Secure Functional Encryption

Global: Quantum Impossibility Results Extend Classical Barriers for Simulation-Secure Functional Encryption

Researchers have demonstrated that the long‑standing impossibility of simulation‑secure functional encryption (FE) in the classical setting also applies in the quantum regime. The findings were posted to arXiv in January 2026 and address an open question about whether quantum techniques could circumvent classical security barriers.

Background

Functional encryption enables fine‑grained access to encrypted data, but the strongest security notion—simulation security—has been proven unattainable classically. Those classical impossibility proofs rely on arguments that are inherently non‑quantum, leaving uncertainty about the quantum case.

Unconditional Impossibility

The new work shows that when an adversary is allowed to issue an unbounded number of challenge messages, an unconditional impossibility result holds, mirroring the classical barrier. This demonstrates that even unlimited quantum resources cannot achieve simulation‑secure FE under these conditions.

Key‑Dependent Impossibility

In scenarios where an adversary may obtain many functional keys, prior classical results required the assumption that pseudorandom functions exist. The authors strengthen this by proving impossibility under the potentially weaker assumption of pseudorandom quantum states, thereby tightening the security landscape.

Alternative Approach via Public‑Key Encryption

The paper also establishes a separate impossibility result based on the existence of public‑key encryption. Because public‑key encryption does not currently imply pseudorandom quantum states, this provides independent evidence supporting the overall barrier.

Technical Contribution: Incompressibility Property

As part of the analysis, the authors introduce a novel incompressibility property for pseudorandom states. This property may be of independent interest for future studies in quantum cryptography and complexity theory.

Implications for Quantum Cryptography

Collectively, the results suggest that achieving simulation‑secure functional encryption is unlikely, even with quantum capabilities. Researchers in quantum cryptography will need to explore alternative security models or relaxations if functional encryption is to remain viable.

This report is based on information from arXiv, licensed under Academic Preprint / Open Access. Based on the abstract of the research paper. Full text available via ArXiv.