Stateful hash-based signature schemes, principally XMSS and LMS, build digital signatures from hash functions rather than number-theoretic problems like RSA or elliptic curves, which makes them resistant to attacks from a sufficiently large quantum computer. Because both schemes have been standardised and recommended by NIST, implementers are now filing patents on the practical problems around them — state management so a private key is never reused, accelerator hardware to make hashing fast enough for production, and integration into existing transaction and authentication systems. The patent record in this dataset is concentrated in those implementation layers rather than in the core cryptographic math, which is largely public and standardised.

The dataset's ranking covers 51 companies, and the field is top-heavy: the leading assignee holds 59 of the 186 records in scope, and the five leading assignees together hold 60.8% of all records. The mix of leaders spans chipmakers, defence and national-security research organisations, and financial infrastructure firms, reflecting the range of industries that need quantum-resistant signing at scale. Beyond the leading ten assignees, who together hold 75.3% of records, filing activity thins quickly into a long tail of single- or few-filing entrants.

No — filing peaked at 28 records in 2020 and has since declined, falling to 17 by 2024, a -19% move over that three-year span. That said, publication lags filing by roughly 18 months, so figures for 2025 and 2026 are still incomplete and should not be read as confirming a continued drop. The honest read is that the field grew quickly around the standardisation period and has since settled into a lower, steadier filing rate rather than accelerating further.

The large majority of records, 89.2% of the 186 in scope, fall under H04L (digital information transmission), reflecting the signatures' role in securing communications and transactions. G06F (electric digital data processing) covers 46.2% of records, and G06N (computing based on AI models) covers a notable 21.5%, which points to growing use of these signatures for verifying data and model integrity rather than purely for message authentication. Because records can carry multiple IPC codes, these percentages are each measured against the full 186-record set and add up to more than 100%.

The clearest gaps sit adjacent to the dense H04L/G06F core: state-synchronisation for LMS and XMSS keys across distributed or multi-node systems, hash-accelerator designs sized for constrained IoT devices, and hybrid schemes that manage the transition period where classical and hash-based signatures must coexist. These branches show much lighter coverage than the core signing-and-verification claims held by the leading assignees, making them a more realistic entry point for new filers than competing directly on the crowded core claims.