Q-FinGuard: A Real-Time Hybrid Quantum-Cryptographic Protocol for Secure Financial Transactions

Abstract

Real-time financial authorisation needs to maintain confidentiality and transaction integrity while meeting strict tail-latency targets, and the long-lived public-key assumption is increasingly vulnerable to store-now-decrypt-later collection and future quantum computing. Q-FinGuard is a deployable hybrid protocol proposed in this paper that transforms quantum key distribution (QKD) output into bounded-lifetime transaction keys and maintains service via post-quantum cryptographic continuity. The protocol divides the payment data plane from the software-defined key-control plane, maintains hardware-protected key pools at paired gateways, authenticates control messages with post-quantum signatures, and adjusts key consumption based on transaction risk and measured quantum-link health. A composable accounting model does not reuse keys and makes every authorisation decision conditional on freshness, available entropy, and a latency deadline. Experiments in a three-region emulation combine bursty payment traces with loss, denial-of-service, relay compromise and QKD outage scenarios. At an offered load of 120,000 transactions/s, Q-FinGuard adds 0.74ms to the median authorisation latency and 2.82ms to the 99th percentile; a 12-worker deployment supports 168,000 transactions/s. The adaptive policy gives 96.8% of the high-risk transactions a special quantum shares and uses 19% fewer QKD bits than fixed per-message allocation. Q-FinGuard also supports authenticated continuity during quantum-link impairment and rejects all injected replays outside the receive window. Based on the above data, it can be seen that quantum-derived keys can protect operational payment traffic without increasing the delay of the quantum channel.