Two of the most-confused phrases in security are "quantum key distribution" and "post-quantum cryptography." They sound like the same hedge against quantum computers. They are not, and a 2025 grant is a good place to see exactly why.
Honeywell's US12362913B2, "Method and system for secure distribution of symmetric encryption keys using quantum key distribution (QKD)" (issued July 2025, classified under H04L 9/0852), claims using QKD to deliver a shared symmetric key. The mechanism is physical, not mathematical two parties exchange quantum states (typically photons), and the laws of quantum mechanics guarantee that any attempt to measure those states in transit disturbs them. Measure to eavesdrop, and you leave fingerprints the legitimate parties can detect, so they discard the compromised key.
Contrast that with the post-quantum patents covered elsewhere on this desk — families like the two-KEM grants under the same H04L 9/0852 subclass. Those run new mathematical algorithms (lattice-based, code-based) on ordinary hardware; their security rests on problems believed hard even for quantum computers. QKD secures the key with physics; PQC secures it with math. One needs special optical hardware and a quantum channel; the other is a software update.
The practical differences fall straight out of that distinction. QKD requires dedicated hardware and is typically distance-limited by the physics of the channel — it does not run over the ordinary internet without specialized infrastructure. PQC runs anywhere software runs, which is why standards bodies have focused the near-term migration on PQC algorithms while QKD remains a more specialized, infrastructure-heavy option. The Honeywell grant being about symmetric key distribution specifically is the giveaway QKD's job is to get a shared secret key into both parties' hands; the actual bulk encryption afterward is ordinary symmetric crypto.
Reading the claim precisely matters here because the marketing around "quantum security" is especially loose. Honeywell's grant claims a method for QKD-based symmetric key distribution — a specific delivery mechanism — not a general solution to all quantum threats. It is one tool, with one job, dated and granted.
Why it is notable now: as the quantum-threat conversation accelerates, buyers conflate the two approaches constantly, and vendors are not always eager to clarify. Holding both kinds of patent up to the light — the physics-based QKD grant and the math-based PQC family, both filed under the same CPC subclass — is the cleanest way to keep the distinction straight. They solve overlapping problems with completely different machinery.