Secure Composition of Quantum Key Distribution and Symmetric Key Encryption
Kunal Dey, Reihaneh Safavi–Naini · 2025
Quantum key distribution (QKD) allows Alice and Bob to share a secret key with proven information-theoretic security. Composability-based security proofs for QKD ensure that using the established key to encrypt a message using a one-time-pad encryption system, will result in information-theoretic secrecy for the communication. In this paper, we consider the problem of using a QKD established key with a secure symmetrickey based encryption system with computational security, and use an extension of the framework of hybrid encryption to prove security of the composition. We use an extension of the original framework of hybrid encryption to correlated randomness setting (Sharifian et al. in ISIT 2021) and propose a quantum-enabled Key Encapsulation Mechanism (qKEM) that is used to construct a quantum-enabled hybrid encryption ($q H E$) system, and prove a composition theorem for the security of the qHE. We construct a qKEM with proven security using an existing QKD (Portmann et al. in Rev. of Mod. Physics 2022). Using this qKEM with a secure Data Encapsulation Mechanism (DEM), that can be constructed using a one-time symmetric key encryption scheme, results in an efficient encryption scheme for unrestricted length messages with proved security against an adversary with access to (efficient) quantum computations. Thus a key-efficient post-quantum secure encryption with proved security and without using any computational assumptions.