Information-Theoretic Solutions for Seedless QRNG Bootstrapping and Hybrid PQC-QKD Key Combination

TL;DR

This paper introduces information-theoretic methods using universal hash functions to bootstrap seedless QRNGs and securely combine PQC and QKD keys, enhancing quantum network security.

Contribution

It proposes a novel seedless QRNG bootstrapping technique and a secure key combining method that maintains security even if parts are compromised, extending to hybrid PQC-QKD systems.

Findings

Bootstrapping seedless QRNGs using raw entropy sources is feasible.

The hash-based key combining method preserves security under partial compromise.

The framework extends to hybrid PQC-QKD systems, ensuring future-proof security.

Abstract

This paper considers two challenges faced by practical quantum networks: the bootstrapping of seedless Quantum Random Number Generators (QRNGs) and the resilient combination of Post-Quantum Cryptography (PQC) and Quantum Key Distribution (QKD) keys. These issues are addressed using universal hash functions as strong seeded extractors, with security foundations provided by the Quantum Leftover Hash Lemma (QLHL). First, the 'randomness loop' in QRNGs -- the requirement of an initial random seed to generate further randomness -- is resolved by proposing a bootstrapping method using raw data from two independent sources of entropy, given by seedless QRNG sources. Second, it is argued that strong seeded extractors are an alternative to XOR-based key combining that presents different characteristics. Unlike XORing, our method ensures that if the combined output and one initial key are compromised, the remaining key material retains quantifiable min-entropy and remains secure in exchange of longer keys. Furthermore, the proposed method allows to bind transcript information with key material in a natural way, providing a tool to replace computationally based combiners to extend ITS security of the initial key material to the final combined output. By modeling PQC keys as having HILL (Hastad, Impagliazzo, Levin and Luby) entropy, the framework is extended to hybrid PQC-QKD systems. This unified approach provides a mathematically rigorous and future-proof mechanism for both randomness generation and secure key management against quantum adversaries.