Clark v. DocuSign (24-1302): Federal Circuit Affirms Unpatentability of Secure Communication Patent
Patent owner Paul C. Clark appealed to the Federal Circuit seeking to overturn an invalidity finding against US9391957B2, covering a system and method for secure communication between domains. The court affirmed the unpatentability ruling in full, ending DocuSign’s exposure to the asserted patent after 574 days of appellate proceedings.
Federal Circuit shuts down Clark’s bid to revive secure-comms patent against DocuSign
Paul C. Clark, holder of US9391957B2 — a patent covering a system and method for secure communication between domains — initiated appellate proceedings (Case No. 24-1302) before the Court of Appeals for the Federal Circuit on 29 December 2023. The appeal contested an underlying determination that the patent’s claims were unpatentable, a verdict cause categorised as an invalidity or cancellation action. DocuSign, Co. was the prevailing respondent, represented by Fenwick & West, LLP.
On 25 July 2025, the Federal Circuit issued a summary order affirming the prior unpatentability ruling. The court’s ‘AFFIRMED’ disposition means it found no reversible legal error in the lower tribunal’s conclusion that Clark’s claims did not meet the statutory requirements for patentability. For Clark, the affirmance extinguishes his ability to enforce US9391957B2 against DocuSign at this level; for DocuSign, the ruling confirms it faces no live patent threat from this asset.
The case ran for 574 days from filing to closure — longer than the typical Federal Circuit appeal cycle, suggesting the panel may have required meaningful briefing before reaching its conclusion. The public record does not reveal the specific ground of unpatentability (e.g., obviousness under §103 or anticipation under §102) that was affirmed, nor whether any dependent claims survived. What remains certain is that the patent, as asserted, has been adjudicated unpatentable and the ruling is now final at the circuit level.
Filing to Unpatentable in 574 days
574 days — above the median Federal Circuit appeal duration of ~400 days
Federal Circuit affirms: what the unpatentability ruling means for both parties
‘Affirmed’ means the lower unpatentability finding stands as law
When the Federal Circuit issues an ‘AFFIRMED’ disposition, it is declaring that it found no reversible error in the decision below. The appellate court does not retry facts — it reviews legal conclusions de novo and factual findings for clear error. Here, the lower tribunal’s determination that US9391957B2’s claims are unpatentable has been validated at the highest available level short of the Supreme Court. The patent’s claims cannot now be enforced based on this record.
No reversible error foundClark’s US9391957B2 is judicially confirmed unpatentable
The affirmance is a terminal outcome for Clark’s patent rights in this dispute. US9391957B2 cannot be enforced against DocuSign, and the ruling signals significant enforceability risk against any other potential infringer. Clark’s remaining options are limited to a petition for certiorari to the Supreme Court — a high bar — or reexamination proceedings if distinct claim scope arguments exist. The commercial value of this patent has been materially diminished by the ruling.
Patent rights extinguishedDocuSign secures full clearance on the asserted patent claims
For DocuSign, the Federal Circuit’s affirmance delivers commercial certainty: the claims of US9391957B2 that were asserted against it have been confirmed unpatentable and pose no ongoing legal threat. Fenwick & West’s successful defence at the appellate level also raises the bar for any future assertion of related patent assets. DocuSign’s secure-communication and electronic agreement technology stack is no longer encumbered by this specific patent risk.
Full patent clearance confirmedUnpatentability affirmance strengthens sector freedom-to-operate
The Federal Circuit’s confirmation that claims covering secure inter-domain communication systems are unpatentable has broad implications for the digital transaction and e-signature sector. Competitors and adjacent technology providers — particularly those building secure document exchange or domain-bridging authentication systems — may now have stronger freedom-to-operate arguments in this space. The ruling also suggests the original claims lacked sufficient differentiation from prior art, a signal worth tracking for patent strategy teams.
FTO landscape improvedFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Paul C. Clark | Individual | Individual patent owner — holder of US9391957B2 covering secure inter-domain communicationSearch in Eureka ↗ |
| Defendant | DocuSign, Co. | Company | DocuSign, Co. — electronic agreement and digital transaction management platformSearch in Eureka ↗ |
| Plaintiff counsel | Frederick Ngosi Samuels | Attorney | Counsel for Paul C. ClarkSearch in Eureka ↗ |
| Plaintiff counsel | Maurice U. Cahn | Attorney | Counsel for Paul C. ClarkSearch in Eureka ↗ |
| Plaintiff law firm | Cahn & Samuels, LLP | Law Firm | Representing Paul C. ClarkSearch in Eureka ↗ |
| Defendant counsel | Jennifer Bush | Attorney | Counsel for DocuSign, Co.Search in Eureka ↗ |
| Defendant law firm | Fenwick & West, LLP | Law Firm | Representing DocuSign, Co.Search in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | Court of Appeals for the Federal CircuitSearch in Eureka ↗ |
Official order — verbatim text
The Federal Circuit’s terse ‘ORDERED AND ADJUDGED: AFFIRMED’ language is characteristic of a Rule 36 summary affirmance or a short merits panel opinion finding no reversible error. At the appellate level, legal conclusions on patentability — including obviousness and anticipation — are reviewed de novo, while underlying factual findings are reviewed for clear error. The court’s affirmance signals that Clark failed to identify a legal error sufficient to disturb the prior ruling on either standard. The unpatentability determination is now final at the circuit level.
US9391957B2 — System and method for secure communication between domains
US9391957B2 (application number US14/246447) covers a system and method for secure communication between domains — a technology area encompassing authenticated, encrypted messaging or data exchange across distinct network or organisational boundaries. Patents in this space typically claim novel session management, token-based authentication, or cryptographic handshake protocols designed to extend secure channels across domain perimeters. The application’s filing period aligns with a period of intense activity in federated identity and cross-domain security infrastructure.
For the digital transaction management and e-signature sector, secure inter-domain communication is a foundational technical requirement: platforms like DocuSign must authenticate and route documents across enterprise, government, and consumer network boundaries. A valid, enforceable patent in this space could constrain a broad range of SaaS, identity federation, and document exchange products. The Federal Circuit’s affirmance that US9391957B2’s claims are unpatentable removes one assertion vector, but the underlying technical problem — securing cross-domain data transfer — remains heavily contested IP territory.
Should you run an FTO against US9391957B2 and related secure-domain communication patents?
Any R&D or product team building systems that transmit, authenticate, or broker data across distinct network domains — including e-signature platforms, identity federation services, API gateway providers, and enterprise SSO vendors — should assess exposure to this patent family. Although the asserted claims have been confirmed unpatentable, continuation or divisional filings by the same inventor may claim overlapping or adjacent scope that has not been adjudicated. The risk does not end with this ruling.
PatSnap Eureka’s FTO Search Agent enables IP and product teams to map the full US9391957 patent family, identify related applications under US14/246447’s priority chain, and surface prior art combinations that have been validated through litigation. Eureka’s claim-level analysis can flag which elements of your cross-domain communication architecture warrant further clearance work — saving time before a new assertion surfaces.
Run a freedom-to-operate analysis on US9391957B2 to assess your product’s exposure
Run FTO in Eureka →Similar Federal Circuit cases: secure communication and domain authentication patents
Browse Federal Circuit appeals involving secure inter-domain communication, authentication, and digital transaction management patents with comparable patentability dispositions.
What this case signals for the secure communications IP landscape
The Federal Circuit’s affirmance in Clark v. DocuSign carries lessons for patent owners and technology companies in the secure inter-domain communication space.
Unpatentability affirmances at the Federal Circuit are rarely reversed
Once the Federal Circuit affirms an unpatentability finding, the practical path to reinstatement is effectively closed. Patent owners in the secure communications and digital transaction management sectors should treat this outcome as a signal to audit claim breadth and prior art exposure before assertion, not after. Affirmances on patentability grounds carry issue preclusion risk for related claims.
DocuSign’s Fenwick & West defence sets a procedural benchmark
The successful invalidation and subsequent appellate affirmance against an asserted secure-communication patent demonstrates that well-resourced prior art challenges can neutralise individual patent owner assertions. Companies facing similar suits in the document management and e-signature space should evaluate IPR or inter partes reexamination as a first-line strategy before or alongside district court defence.
Clark v DocuSign — key questions answered
The Federal Circuit affirmed the lower tribunal’s finding that US9391957B2 is unpatentable. The court found no reversible error in the patentability determination, ending Clark’s ability to enforce the patent against DocuSign at the appellate level. The case closed on 25 July 2025.
US9391957B2 (application US14/246447) is a United States patent covering a system and method for secure communication between domains. The patent addresses cross-domain network security — typically involving authenticated, encrypted data exchange or session management across distinct organisational or network boundaries. The claims were adjudicated unpatentable in this proceeding.
An ‘affirmed’ outcome from the Federal Circuit means the appellate court found no reversible legal error in the lower tribunal’s decision. For patentability appeals, the court reviews legal conclusions de novo and factual findings for clear error. Affirmance means the unpatentability finding stands as final law at the circuit level. The patent owner’s remaining recourse is a petition for certiorari to the Supreme Court.
The affirmance confirms the asserted claims of US9391957B2 are unpatentable, which typically has estoppel implications for re-assertion of those same claims. However, the ruling does not automatically extinguish any continuation, divisional, or related applications in the same priority family that may claim distinct scope. Third parties in the secure communications sector should conduct a family-level FTO review rather than relying solely on this ruling for clearance.
Paul C. Clark was represented by Cahn & Samuels, LLP, with attorneys Frederick Ngosi Samuels and Maurice U. Cahn on record. DocuSign, Co. was represented by Fenwick & West, LLP, with Jennifer Bush as the listed attorney. DocuSign’s successful defence at the Federal Circuit level affirmed the unpatentability of Clark’s US9391957B2.
PatSnap Eureka searches patents and litigation data to answer instantly.