Reports
Digital Quantum Key Distribution: Closing the Gap That PQC Alone Can’t Close
Post-quantum cryptography (PQC) migration is now firmly on the agenda for most UK IT security teams, driven by NIST’s finalised algorithms and, increasingly, by the UK’s Cyber Assessment Framework and NCSC guidance on cryptographic agility. What’s discussed less often is a more specific and, in some respects, more immediate problem: even where PQC algorithms are correctly implemented, the key exchange itself is usually still negotiated in-band, over the same channel as the data it’s meant to protect.
That distinction matters, because any key exchange carried in-band, whether via IKEv2 for IPSec, MKA for MACSec, or standard TLS handshakes, can be intercepted and stored today by an adversary, even if it can’t currently be decrypted. This is the basis of Harvest-Now, Decrypt-Later (HNDL) attacks: encrypted traffic is captured now, on the expectation that sufficient quantum computing capability will eventually allow the key material to be recovered. Deloitte’s 2022 polling found that just over half of organisations considering quantum computing believed they were already exposed to this risk. Upgrading to PQC algorithms narrows the mathematical attack surface, but if the key exchange mechanism itself remains in-band, the exposure has not been removed, only pushed further out. Should a PQC algorithm later prove weaker than assumed, a real possibility this early in its adoption, all the traffic harvested under it becomes retrospectively vulnerable.
This guide, produced by Quantropi, sets out an alternative approach: Digital Quantum Key Distribution (D-QKD), delivered through the QiSpace platform. Rather than negotiating keys within the same channel as the data, D-QKD delivers keys out-of-band, so there is no key exchange for an adversary to intercept alongside the traffic it protects. The guide is explicit that this is a software-only deployment: no specialised endpoint hardware, no dedicated optical fibre, and no distance limitation, in contrast to photonic QKD implementations, which the guide notes have been advised against by French, German, Dutch and Swedish national security agencies on security and practicality grounds. D-QKD instead runs over standard IP infrastructure and integrates with existing IPSec, MACSec and OTNSec deployments, using the ETSI-014 and SKIP interface standards and following NSA guidance on the secure implementation of pre-shared keys over digital networks.
For UK IT and security leaders evaluating this space, three things in the guide are worth particular attention. First, the entropy behind the keys: D-QKD is powered by Quantropi’s multisource Quantum Random Number Generator (QRNG) portfolio, addressing a well-documented weakness in conventional key generation, poor-quality randomness has been directly linked to compromised RSA certificates in prior research. Second, the performance evidence: in independent benchmarking at the Deutsche Telekom Open QKD Lab, QiSpace supported concurrent AES-256 sessions at a scale reported to be several orders of magnitude higher than the photonic QKD alternatives it was tested against, while its output passed standard NIST, ENT and Dieharder randomness testing. Third, the deployment track record: the guide references live use in a NATO transatlantic quantum-safe network connection and a Nokia fibre network integration, alongside stated compatibility with infrastructure from Palo Alto Networks, Cisco, Fortinet, Ciena and Ribbon.
We’re including this guide in our resource library because it addresses a question we increasingly hear from customers who have already started, or are planning, their PQC migration: does upgrading the algorithm actually close the HNDL exposure, or does it just relocate it? D-QKD offers one answer, built on removing in-band key exchange entirely, and this guide sets out the reasoning, the standards basis and the evidence behind it in enough depth to support your own evaluation.
As ever, the right approach depends on your existing network architecture, vendor estate and risk tolerance. If you’d like to talk through how D-QKD might fit alongside your current PQC roadmap, or want an independent view before engaging directly with Quantropi, Covenco’s team is happy to help.