TQKD: A More Efficient QKD Network Based on Homomorphic Encryption Technology

Quantum key distribution (QKD) provides unconditional security but relies on repeaters to extend coverage, thereby introducing repeater trust risks—compromised repeaters may leak keys. Brakerski/Fan-Vercauteren scheme (BFV)-based QKD addresses this issue through key encryption and quantum attack resistance. However, Fast Fully Homomorphic Encryption over the Torus (TFHE) outperforms BFV in encryption/decryption speed for single-qubit homomorphic XOR operations, which is critical for the real-time requirements of QKD. We propose TFHE-based QKD (TQKD), a quantum key distribution protocol based on public-key TFHE. During key forwarding, it leverages the “usable-but-unobservable” property of homomorphic encryption to prevent key exposure. A reduction proof verifies the scheme’s Indistinguishability under Chosen-Plaintext Attack (IND-CPA) security. To validate TQKD’s computational speed advantage, we developed code using the Open-Source Fully Homomorphic Encryption Library (OpenFHE) platform and designed single-pass and multi-hop relay experiments. We compared the computational efficiency of TQKD against QKD schemes based on similar homomorphic encryption algorithms, Brakerski-Gentry-Vaikuntanathan scheme (BGV) and BFV. Results demonstrate that our scheme achieves faster key encryption/decryption speeds in both scenarios, significantly reducing processing time compared to similar algorithms. Furthermore, while enhancing the scalability of quantum key distribution networks, the added computational overhead is negligible, indicating higher practical value.