Paper 2026/1131

Public Key Encryption Secure Against Quantum Leakage

Abstract

Side-channel attacks are a relevant threat to many modern cryptographic schemes and often have fatal consequences such as revealing partial information about secret keys. While leakage-resilient cryptography aims to solve this problem, existing works focus exclusively on showing security against classical leakage. Moreover, recent public key encryption (PKE) schemes utilizing quantum secret keys achieve security against unbounded classical leakage, but offer no guarantees on any amount of quantum leakage. Since security guarantees on classical side information do not necessarily translate to guarantees on quantum side information, showing PKE schemes that are secure in the presence of quantum leakage remains open. In this work, we address this problem by extending the definition of leakage resilience for PKE in the bounded-leakage model to allow for quantum leakage. We provide the following two constructions: - PKE with Quantum Secret Keys: We construct a PKE scheme that tolerates unbounded classical leakage alongside bounded, constant-rate ($\lambda <0.057$) quantum leakage. Our construction assumes the existence of polynomially secure post-quantum indistinguishability obfuscation (iO) as well as one-way functions (OWFs). - PKE with Classical Secret Keys: We construct a classical PKE scheme that is secure against bounded quantum leakage. Our construction offers a tradeoff between the achievable leakage rate and the underlying cryptographic assumptions. Assuming the hardness of the learning with errors problem (LWE) we obtain an optimal leakage rate of $\lambda \leq 1-o(1)$. Alternatively, assuming only post-quantum PKE, we obtain a leakge rate of $\lambda\leq \frac{1}{poly(n)}$.