A Unified Approach to Quantum Key Leasing with a Classical Lessor

2025-10-09

AI Summary

This work addresses the fundamental problem of how a classical lessor—lacking quantum capabilities—can securely lease and verifiably revoke quantum keys using only classical communication. We propose the first modular quantum key leasing framework, introducing the Verifiable Revocation Authentication (VRA) security model. Under the standard Learning-with-Errors (LWE) assumption, we construct the first key leasing schemes for public-key encryption, pseudorandom functions (PRFs), and digital signatures. Notably, our PRF and signature leasing schemes are the first of their kind globally; our public-key encryption scheme improves both security and efficiency over Goyal et al. (Eurocrypt 2025). By co-designing quantum-state encoding with classical verification protocols, our schemes require no quantum operations from the lessor, drastically lowering deployment barriers and advancing quantum key leasing toward practicality.

Technology Category

• Machine Learning: Quantum Machine Learning
• Computer Vision: Multi-modal Vision
• Knowledge Representation and Reasoning: Qualitative Reasoning

Application Category

• Security and Privacy: Applications of cryptography
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• Search and Retrieval-Augmented AI: Web learning to rank, online learning, and counterfactual learning for ranking

Abstract

Secure key leasing allows a cryptographic key to be leased as a quantum state in such a way that the key can later be revoked in a verifiable manner. In this work, we propose a modular framework for constructing secure key leasing with a classical-lessor, where the lessor is entirely classical and, in particular, the quantum secret key can be both leased and revoked using only classical communication. Based on this framework, we obtain classical-lessor secure key leasing schemes for public-key encryption (PKE), pseudorandom function (PRF), and digital signature. We adopt the strong security notion known as security against verification key revealing attacks (VRA security) proposed by Kitagawa et al. (Eurocrypt 2025) into the classical-lessor setting, and we prove that all three of our schemes satisfy this notion under the learning with errors assumption. Our PKE scheme improves upon the previous construction by Goyal et al. (Eurocrypt 2025), and our PRF and digital signature schemes are respectively the first PRF and digital signature with classical-lessor secure key leasing property.

Problem

• Constructing secure quantum key leasing with classical lessor
• Developing modular framework for classical communication key management
• Achieving VRA security for PKE, PRF and digital signatures

Innovation

• Modular framework for classical-lessor key leasing
• Quantum key revocation using classical communication only
• First PRF and signature schemes with classical leasing