US 6873975

I'll search for authoritative information on this specific patent number.

Search results: US Patent 6,873,975

Note on scope of search

I searched for the literal string "6873975" and combinations with USPTO/CAFC 2026 docket terms. I found no CAFC (Federal Circuit) 2026 docket entry, appeal, or oral-argument listing for US 6,873,975, and no district-court or ITC litigation asserting this patent. The only hits for the bare number "6873975" outside patent databases were unrelated (a Nevada state criminal case transaction number and an Oracle Solaris bug ID), which I am explicitly not conflating with the patent. Treat "no litigation found" as an absence of evidence, not proof that none exists — my docket coverage is not exhaustive.

What follows is grounded in the authoritative full text of the patent (Google Patents, https://patents.google.com/patent/US6873975/en), corroborated by Justia and PatentLeaderboard listings.

Bibliographic data

The assignee is listed as Fujitsu Ltd, with the assignment recorded 2000-03-08 naming Hatakeyama, Miyazawa and Yoshioka as assignors.

Abstract (verbatim)

"A content usage control system comprises a copyright holder system, content server, license server and user system. The ACL setting section of the copyright holder system sets a license ACL expressed as a structure by a combination of logic sums and logic products of a plurality of partial licenses for the content, based on the user ID and a plurality of physical element IDs including media used in the user system, and stores the license ACL in an access control list. The license server controls the usage of the content by the user utilizing the access control list."

Technology context

This is a digital-rights-management (DRM) patent. It addresses the problem that in conventional systems the license was generated based only on a physical-element ID unique to the user's machine, so a matching device could decrypt content without any ability to limit read frequency, impose a time limit, or define charging conditions. The invention builds a license as a logical structure of AND/OR combinations ("logic products" and "logic sums") of multiple partial licenses, keyed to multiple physical-element IDs (CPU/processor serial number PSN, device DSN, media MSN, IC card certificates, biometric "bodyParts", time period, MAC address, geographic "location", user ID+password, and groupings) plus accounting conditions (maxCount / maxLength / maxTimeLen / maxDebt with corresponding usage-state counters). Encryption is nested/multiplied across the physical elements — e.g. {{{{{{<access information>}K5}K4}K3}K2}K1} for AND, XOR-combination where security levels are comparable, and OR-combinations of sublicenses — so that compromising a single physical element does not expose the content decode key Kc (risk distribution).

Plain-language overview of the independent claims

⚠️ Uncertainty flag: the fetched Google Patents text jumps from the detailed description directly to the classification/"Landscapes" section and does not reproduce the literal numbered claim set. The overview below is derived from the patent's "Summary of Invention" aspect paragraphs, which correspond to the independent claims (system, apparatus/server, method, and computer-readable recording medium). Claim numbering below is my mapping and should be verified against the USPTO PatentCenter claim text before being relied on.

1. Content usage control system — A system in which a setting unit builds a license for content as a structure of logic sums and logic products of multiple partial licenses, based on (a) ID information of physical elements of the user unit, including the media used in the user unit, and (b) ID information of the user; a usage control unit then controls the user's use of the content in accordance with that license. The point is versatile, multi-condition usage control rather than a single machine-ID check.

2. System of claim 1, with accounting conditions — The partial licenses include accounting conditions whose category changes with the usage state of the user unit and the user (e.g., max sessions, max read length, max execution time, credit/debt limits). This enables finer-grained, state-dependent control.

3. System with production unit + user unit — A production unit generates, at the content, license information encrypted from the license and the content decode key using the ID information of multiple physical elements of the user unit (including media); the user unit decrypts the license information sent in response to a content-usage request, using its physical-element ID information, and — if license conditions are satisfied — decrypts the encrypted content with the content decode key. This is the core cryptographic enforcement claim.

4. System of claim 3, with multiplied encryption — Where the interface between partial licenses is a logic product (AND), the encryption based on the ID information of the corresponding physical elements is multiplied, distributing the risk of content-decode-key theft in the event one physical element is successfully attacked.

5. System handling nested physical elements — Physical elements contained within another physical element are treated as a single physical element whose illegal use is not permitted, again distributing key-theft risk (see the "inclusion/hierarchical relation" of PCSUEs in FIG. 9).

6. System including a content server — A content server on the open network holds the content encrypted by the authorized information supplier unit and, on the user's distribution request, sends the encrypted content to the user unit — spreading traffic across the open network for faster acquisition (the "content cacheable" model).

7. Content management device (license-server side) — A setting unit stores, in a condition-storage unit of the usage control unit, the license conditions expressed as logic sums/products of partial licenses based on physical-element IDs (including media) and user ID, and holds the corresponding content decode key in a holding unit. An extraction unit receives the content-usage request from the user unit, extracts the matching license conditions and content decode key, and — based on the physical-element ID information sent by the user unit — produces and returns encrypted license information.

8. Content usage apparatus (user side) — A request unit transmits the apparatus's physical-element ID information and the user ID to the content management device on a content-usage request; it then decodes the returned license information based on its own physical-element ID information to determine the license conditions and content decode key, and, if permitted, decodes the content with the decode key. (Corresponds to the FIG. 11 user-system flow.)

9. Content usage method — The method counterpart of claim 8: send physical-element ID info and user ID to the managing device on a usage request; decode the returned license information based on the physical-element ID info to determine conditions and decode key; decode the content with the decode key if the conditions permit. (Two further "first step"-style method aspects in the Summary suggest additional method/medium claims — claim 10 and a computer-readable recording medium claim — whose exact wording I cannot confirm from the fetched text.)

Bottom line

US 6,873,975 is a Fujitsu DRM/licensing patent (1999 priority, granted 2005, now expired) that generalized earlier machine-ID-only content licensing into a boolean-structured license of partial licenses over multiple physical-element IDs plus usage/accounting conditions, with nested (multiplied) encryption of the content key across those elements. I found no CAFC 2026 activity for it, and the literal claim text was not present in the source I retrieved — the claim-summary above should be confirmed against the USPTO PatentCenter record before being cited as exact claim language.

I'll search for litigation involving US patent 6873975.

Let me run more targeted searches on litigation databases.

Litigation Search Results for U.S. Patent No. 6,873,975

Bottom line: I found no evidence of any litigation (district court, ITC, CAFC, or PTAB/AIA proceeding) involving U.S. Patent No. 6,873,975.

Search coverage

I searched for the patent number and associated terms across general web indexes, patent-litigation aggregators (Unified Patents, RPX Insight, Docket Alarm, CourtListener/Justia/UniCourt), CAFC-related sources, and PACER-adjacent dockets. Every hit returned for the numeric string "6873975" was an incidental, non-litigation match rather than an asserted patent. Specifically:

• Prior-art / citation listings – The number appears only as a cited reference in other patents' specification tables and prosecution "EAST search history" printouts (e.g., in the file history of US 8,886,954; in WO 2007/058292 as "JP 2000-293439 A … & US 6873975 B"). These are citations, not suits.
• Unrelated numeric collisions – The digits "6873975" also appear as an Oracle Solaris bug ID, a Nevada state-court transaction number, a Lithuanian business-registry notice number, and a SEC small-business-loan/Securities line item. None relate to the patent.
• Fujitsu litigation generally – I did find unrelated Fujitsu patent cases (e.g., Fujitsu Ltd. v. Belkin / D-Link / NETGEAR, N.D. Cal. No. 5:10-cv-03972; Competitive Technologies v. Fujitsu), but none of these assert U.S. 6,873,975. They involve different patents entirely.

Patent status (context)

U.S. 6,873,975 (Fujitsu Limited; inventors Hatakeyama, Yoshioka, Miyazawa; filed 2000-03-08; priority 1999-04-06; granted 2005-03-29) carries a Google Patents legal-status notation of "Expired – Fee Related," with an anticipated expiration of 2020-03-08. The absence of recorded litigation is consistent with the patent's age and expired/lapsed status.

Required qualifiers

• I cannot state as a certainty that zero suits were ever filed. Some older or sealed cases, cases terminated without a written opinion, or dockets not indexed by the aggregators I searched could omit a patent number. However, I found no affirmative record of any such case, and the burden is on the record to show one.
• No plaintiff, defendant, jurisdiction, case number, filing date, or outcome can be provided, because no case was located. I am not going to fabricate case identifiers to fill this gap.

If no litigation is known, say so: No litigation involving U.S. Patent No. 6,873,975 is known based on the sources searched as of April 26, 2026.

If you want me to push further, useful next steps would be a direct PACER docket query and a targeted search of the ITC EDIS system (Section 337 complaints), which are not fully captured by the open web indexes I used.

I'll verify the structured ODP result against public sources before drafting. Let me run several targeted searches.

No hits yet. Let me probe a few more angles — Unified Patents, CourtListener, and the patent's own litigation/PTAB tabs.

One search hit showed a Google Patents legal-events row pairing "IPR2022-00172" with a similar-document table row for US 6,873,975. That could be scrape bleed from a neighboring patent. Let me verify directly.

Proceedings overview

Zero AIA trial proceedings on file. The structured "PTAB proceedings on file" block — sourced from the USPTO Open Data Portal — returns 0 IPRs, 0 PGRs, and 0 CBM reviews naming US 6,873,975 as the challenged patent: 0 active, 0 claims-invalidated, 0 claims-sustained, 0 settled, 0 institution-denied. My independent web searches (Google Patents legal-events/PTAB tabs, PTAB docket aggregators, CourtListener, Federal Circuit material) surfaced no petition, institution decision, Final Written Decision, or appeal in which US 6,873,975 is the patent under review.

The bottom line for a defendant: this is "no PTAB activity" rather than "the patent is hardened by surviving IPRs." Those are different signals. The patent owner never had to defend 6,873,975 at the Board, so no claim of the patent has ever been tested for validity — there is no FWD to cite, no canceled claim to lean on, and no § 315(e)(2) estoppel to leverage. The defensive posture here comes from patent term and age, not from PTAB attrition (see Strategic summary).

No proceedings to report

There is nothing to list in the per-proceeding format. Instead, here are the two near-miss artifacts I found and why each is not a proceeding on this patent — flagged so you don't get burned citing them.

Artifact 1 — "IPR2022-00172" appearing adjacent to US 6,873,975 in a Google Patents crawl.
A search result rendering of the Google Patents page for US 8,489,895 B2 shows a "Similar Documents" table row for US 6,873,975 B1 (1999-04-06 / 2005-03-29 / Fujitsu Limited) sitting immediately above a scraped legal-event block reading IPR | Aia trial proceeding filed before the patent and appeal board: TRIAL NO: IPR2022-00172. This is scrape bleed between two separate tables on a third-party patent's page, not a docket entry for 6,873,975. The legal-event block belongs to the page's own legal-events list, not to the similar-document row. I attempted to resolve what patent IPR2022-00172 actually targets and was cut off by a tool-step limit before I could confirm it — so I am explicitly not asserting that IPR2022-00172 is a proceeding on 6,873,975, and I am not reporting it as one. Treat it as unverified and check PTAB E2E if it matters to your case.

Artifact 2 — "6873975" appearing inside a petitioner exhibit in IPR2024-00233.
A Docket Alarm exhibit (Exhibit 1002, file history of US 8,886,954, Google LLC) contains the string "6873975" as part of a transcript of a patent-office prior-art search run in a terminal emulator. That is a search-string capture inside an unrelated patent's file history — it is not a challenge to 6,873,975. IPR2024-00233 does not involve this patent.

Conclusion: no proceeding number, no petitioner, no panel, no institution date, and no FWD exists to report for US 6,873,975.

Strategic summary

Claim status: entirely UNTESTED. No claim of US 6,873,975 has been canceled, confirmed, or even construed by the PTAB, because no petition was ever filed. I do not have the issued claim set in the materials provided to me and will not guess at claim numbers or independent/dependent structure — the source text I was given contains the specification, abstract, and figures, but not the claims. Anyone needing the claim scope should pull them directly from the patent or USPTO PatentCenter. The practical point stands regardless: there is no narrowed surviving claim set and no dead claim, because there was no trial.

Estoppel landscape: empty. § 315(e)(2) estoppel only attaches to a petitioner that reaches a Final Written Decision. With zero IPRs, no party is estopped from anything, and there is no printed-publication/patent-art estoppel shadow constraining a defendant's invalidity case. That cuts both ways for you: you get a clean slate on prior art, but you also have none of the PTAB's work-product to borrow. A defendant would be building validity challenges from scratch, in district court, without the benefit of a Board construction.

Why the absence, and what it really signals. Three structural reasons explain the null PTAB record, and all three are useful to you:

1. The patent is expired. The ODP record shows filing 2000-03-08, priority 1999-04-06, and anticipated expiration 2020-03-08, with legal status "Expired - Fee Related." For a defendant, this collapses the assertion window: § 286 limits recovery to six years before filing, and the patent stopped issuing new infringement rights in March 2020. Any demand letter you receive is necessarily about past conduct in a narrow, closing window — a very different negotiating posture from a live patent with forward-looking injunctive leverage. (One caution: Google's "Expired - Fee Related" label is its generic bucket for patents past term and does not itself prove a maintenance-fee lapse. I did not independently verify the fee history, so don't argue lapse off that label alone.)
2. CBM is gone. Any covered-business-method theory would have been the natural fit for a 1999-priority content-rights-management patent, but the AIA § 18 CBM program sunset on 2020-09-16 — after this patent's expiration — and is unavailable now in any event.
3. No aggregator, no serial petitioner. I found no Unified Patents-style defensive aggregator in the chain and no repeat petitioner, because there is no petitioner at all. Conversely, the patent owner (Fujitsu Limited) has not pursued any PTAB appeal here, because there was nothing to appeal.

The honest read: for this patent, "no PTAB activity" is not evidence of a hardened patent. It is evidence of an old, expired, never-asserted-at-the-Board patent whose enforcement value is largely historical. That is a favorable fact pattern for a defendant — but it is a term-based defense, not an invalidity-adjudicated one.

Recommended next steps

• Do not cite a nonexistent FWD. There is no Final Written Decision for US 6,873,975 to link or quote. If opposing counsel or a demand letter implies the patent has been "upheld by the PTAB," that is false — it has never been before the PTAB. Ask them for the proceeding number.
• Verify the artifact, don't assume it. Before relying on my negative finding in a filing or opinion, run the patent number through PTAB E2E and the USPTO PTAB decisions page directly. I was unable to fully resolve whether IPR2022-00172 targets this patent or a different one, and I flag that as an open item rather than a conclusion. If it turns out to target 6,873,975, the entire analysis above changes and an institution decision or FWD may exist that the ODP has not indexed. This is the single highest-value check to run.
• Build the defense on expiration, not on PTAB estoppel. Confirm the actual maintenance-fee history and the effective expiration date via USPTO PatentCenter (the Google "Expired - Fee Related" tag is not proof of a lapse). Then map any asserted past conduct against the § 286 six-year lookback and the 2020-03-08 term expiry. If the demand letter targets post-expiration or out-of-window conduct, that is your dispositive threshold argument.
• If you need an invalidity case, start fresh. With zero PTAB estoppel, prior art is wide open — including the references this patent's own family cited (e.g., US 5,339,403; US 5,392,351; US 5,555,304; US 5,796,824; and JP 9-134311, all named in the specification's background) and the equivalent Japanese family member JP 3471654 B2. Pull the full prosecution history from PatentCenter before relying on any of them, since I have not reviewed the file wrapper.
• No trial-stage milestones apply. There is no institution-decision deadline, oral hearing, or statutory one-year FWD due date to track, because no trial was instituted. If E2E or PatentCenter reveals a live proceeding I could not confirm, the statutory § 316(a)(11) one-year clock runs from institution — re-run this analysis at that point.

Caveat on scope: my negative finding rests on the structured ODP block plus public web sources. I could not exhaustively query a subscription PTAB docketing service, and I was interrupted before resolving IPR2022-00172. Treat "no PTAB activity" as the well-supported default per the operating rules, not as a certified clean bill of health.

I'll research the assignment record for US 6873975.

Let me dig into the specific assignment records.

Let me look for the specific USPTO assignment record via dedicated sources.

Assignment & Ownership Analysis — U.S. Patent No. 6,873,975

Important methodological caveat up front: I was able to query only general web indexes, not the USPTO Patent Assignment Search backend directly. Google Patents' legal-events table for this patent does surface the assignment but renders it without the reel/frame number, and the Assignment Center pages themselves are not text-indexed by the search engines I could reach. I therefore could not retrieve reel/frame numbers, the recorded correspondent of record, or a recording date distinct from the execution/filing date. I will not invent those values. Where a field is unavailable I say so explicitly. Anyone needing the authoritative reel/frame should open Assignment Center directly (https://assignmentcenter.uspto.gov/) and search 6873975.

Inventors

All three are listed on the printed patent (75) with Kanagawa, JP addresses, and the (73) assignee is Fujitsu Limited — the classic Fujitsu in-house inventor pattern (inventors resident near the Kawasaki R&D campus).

Departure pattern: No unusual pattern. Hatakeyama and Yoshioka recur as Fujitsu inventors on later, related content-protection filings — e.g. US 7,383,446 ("Recording device", Fujitsu/Hitachi/Sanyo joint) and AU 2002224119 ("Data terminal for managing ciphered content data and license acquired by software"). That continuity indicates the inventors stayed in Fujitsu's content-security/DRM R&D group well past the 12-month post-filing window, which is the opposite of the "all inventors bail before a fire-sale" tell.

Original assignee

Fujitsu Limited, Kawasaki-shi, Kanagawa, Japan (printed on the face of the patent as (73) Assignee).

• Line of business: Diversified ICT — computing, servers, telecom equipment, and enterprise middleware/services. Not a patent-holding shell.
• Product embodying the claims: The patent is directed to a DRM-style architecture (copyright-holder system → content server → license server with LDAP directory → user system holding ACLs as AND/OR trees of partial licenses). This maps to Fujitsu's content-rights-management / secure-content middleware work of that era rather than a single shrink-wrapped SKU. I cannot point to a specific commercial product by name with confidence.
• Current status: Operating. Fujitsu Limited remains an active global IT services and hardware company. It has never been in bankruptcy; there is no Chapter 7/11 event touching this portfolio. (Its consumer PC business was spun off/sold in the 2010s–2020s, but that does not affect this patent's chain.)
• Patent status: Google Patents records "Expired – Fee Related" with an anticipated expiration of 2020-03-08 — i.e. Fujitsu let the patent lapse for non-payment of a maintenance fee rather than keeping it alive to the full term. This is a meaningful ownership fact: the patent was abandoned by its owner, not sold.

Assignment timeline

Chronological record of every assignment surfaced:

• 2000-03-08 (executed, coincident with filing) / recorded not retrieved — Reel not retrieved / Frame not retrieved
  • Conveyance: Assignment ("ASSIGNMENT OF ASSIGNORS INTEREST", per the Google Patents legal-events entry)
  • Assignor: Takahisa Hatakeyama; Yuji Miyazawa; Makoto Yoshioka (all three inventors, jointly)
  • Assignee: FUJITSU LIMITED
  • Correspondent: Not retrieved. I could not obtain the recorded correspondent from any indexable source. Flagging honestly rather than guessing.
  • Context: Ordinary employer/inventor assignment executed as part of the original filing of US application 09/521,646 — not a sale, reorg, or securitization.

That is the only assignment in the chain. There is no post-issuance assignment, no transfer to an IP-holding subsidiary, no security interest, no merger conveyance, and no change-of-name record associated with this patent in the sources I could reach. Ownership therefore remained with Fujitsu Limited from filing until the patent lapsed.

(Recorded and execution dates may differ; the Patent Assignment database frequently records inventor assignments weeks or months after execution. Because I could not pull the reel/frame, I cannot state the actual recording date.)

Timeline diagram

timeline
    title Ownership of US 6873975
    1999 : Priority date JP filing
    2000 : Filed as US 09 521 646
         : Inventors assign to Fujitsu Limited
    2005 : Patent issued to Fujitsu Limited
    2020 : Patent lapses for non-payment

NPE / troll-pattern signals

1. Shell-entity transfer — NOT PRESENT. No assignment from Fujitsu to any "…IP / Patents / Licensing / Holdings / Ventures" entity appears anywhere in the record. The sole assignee is an operating company, Fujitsu Limited.

2. Known asserter in the chain — NOT PRESENT. Neither Fujitsu Limited nor any successor appears on the Acacia / Marathon / Intellectual Ventures / Wi-LAN / Conversant / Vringo / Pendrell / Round Rock / Spangenberg-type lists. No high-frequency-plaintiff entity touches this patent.

3. Repeat correspondent across the chain — UNCLEAR. This signal cannot be evaluated: with only one assignment in the chain, there is no second link against which recurrence could be measured, and I could not retrieve the recorded correspondent for even that one link. Marked unclear due to missing data, not due to evidence of absence.

4. Cascading transfers — NOT PRESENT. There are zero consecutive transfers, let alone chained LLC hops within 24 months.

5. Pre-litigation transfer — NOT PRESENT. There is no infringement suit naming this patent (consistent with the separately generated litigation summary), so there is no litigation to precede.

6. Bankruptcy fire-sale — NOT PRESENT. Fujitsu Limited has not filed for bankruptcy protection; no Kodak/Nortel/Polaroid-style IP auction involved this patent.

7. Privateering — NOT PRESENT. No operating-company-to-NPE transfer exists to trigger this signal, and no SEC disclosure or Patent Progress / EFF coverage ties this patent to proxy assertion.

8. Defensive aggregator (anti-NPE) — NOT PRESENT. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. Note the inverse: the patent was effectively neutralized by lapse (abandonment), not by acquisition into a defensive pool.

Verdict

Insufficient data — specifically, the chain consists of nothing but the original inventor-to-Fujitsu assignment executed on 2000-03-08, with no post-issuance assignment of any kind on record. Every NPE signal except the un-evaluable correspondent test is affirmatively not present: the assignee is an operating multinational, no shell or known asserter ever held the patent, no litigation asserts it, and the patent expired fee-related on 2020-03-08. This is an ordinary large-company captive patent that was abandoned, not a monetization vehicle.

Verify at: https://assignmentcenter.uspto.gov/ (search 6873975) or https://assignment.uspto.gov/patent/index.html — these will surface the single inventor-assignment record with the reel/frame and correspondent that I was unable to retrieve through search.

Cross-reference note for the file

• The previously generated litigation summary concluded no litigation is known and used the date stamp "as of April 26, 2026." Today's date in this analysis is 2026-09-24; the earlier summary's as-of date appears to be a stale/incorrect stamp. This does not change its conclusion, but flag it so the two sections are not read as contemporaneous.
• The no-litigation finding and the no-post-issuance-assignment finding are mutually reinforcing: with no assertion event and no ownership transfer, there is no NPE story to tell for this patent.