US 5412730

Here is a concise summary of US Patent 5,412,730.

Title: Encrypted data transmission system employing means for randomly altering the encryption keys

Assignee: The original assignee was Telequip Corp. The current assignee is TQP DEVELOPMENT LLC.

Inventors: Michael F. Jones

Filing Date: April 23, 1992

Issue Date: May 2, 1995

Abstract: The patent describes a modem designed for transmitting encrypted data over standard voice-grade telephone lines. The system uses a combination of a microprocessor, a serial communications controller, and a modulator/demodulator. To secure the data, pseudo-random number generators are used at both the sending and receiving ends to create identical sequences of encryption keys. An initial "seed" value is provided to both stations to synchronize the key generation. The encryption keys are changed based on predetermined characteristics of the data being transmitted, ensuring that only the intended transmitter and receiver can know the common encryption key after the transmission has started.

Plain-Language Overview of Independent Claims:

Claim 1: This claim outlines a method for securely transmitting a sequence of data blocks over a communication link. The core idea is to provide both the transmitter and receiver with a secret starting value, or "seed." This seed is used by both ends to independently generate the same sequence of random encryption keys. A new key is generated at the transmitter based on specific characteristics of the data being sent. The data is then encrypted with these keys before being sent. The receiver, using the same seed and monitoring the same data characteristics, generates the identical sequence of keys to decrypt the incoming data. This process happens in a synchronized manner, allowing for secure communication.

Claim 6: This claim describes the receiving end of the secure communication system. It details a method for a receiver to decrypt data that has been encrypted using a sequence of changing keys. The receiver is initially provided with the same secret "seed" value as the transmitter. It then generates a sequence of pseudo-random decryption keys based on this seed. As it receives the encrypted data, it monitors for a predetermined characteristic within that data. When this characteristic is detected, the receiver switches to the next key in its generated sequence to continue decrypting the data.

Claim 8: This claim focuses on a modem specifically designed to carry out the secure data transmission method. The modem includes a standard modulator/demodulator for sending and receiving signals over a communication channel. Crucially, it contains a programmable processor. This processor is responsible for generating a sequence of pseudo-random encryption keys starting from a pre-shared "seed" value. It then encrypts the outgoing data using these keys, with the timing of the key changes being dependent on the data itself.

Claim 9: This claim describes a secure communication network that utilizes the method of changing encryption keys. The network has a central control station and multiple remote terminals. The central station securely provides each terminal with the necessary encryption keys to communicate with other authorized terminals. This allows the central control to manage which terminals can securely communicate with each other, and it can update these permissions as needed.

A search of the CAFC (Court of Appeals for the Federal Circuit) dockets for 2026 for cases involving patent 5,412,730 yielded no results. However, it's important to note that this patent has been the subject of extensive litigation in the past.

Litigation History for U.S. Patent No. 5,412,730

U.S. Patent No. 5,412,730, currently assigned to TQP Development, LLC, has been the subject of an extensive and notable litigation campaign. TQP Development, LLC, a patent assertion entity, has filed a very large number of infringement lawsuits against a wide array of companies across numerous industries. The majority of these cases were filed in the U.S. District Court for the Eastern District of Texas, a venue historically known for patent litigation.

Below is a representative list of known litigation involving this patent. Given the high volume of cases (numbering in the hundreds), this list is not exhaustive but illustrates the scope of the litigation campaign.

District Court Litigation

A significant wave of litigation was initiated by TQP Development, LLC between 2012 and 2014.

Plaintiff(s)	Defendant(s)	Jurisdiction	Case Number	Filing Date	Outcome / Status
TQP Development, LLC	Adobe Systems, Inc.	Texas Eastern District Court	2:12-cv-00570	Aug 31, 2012	The outcome is not publicly detailed but was likely part of a broader settlement or dismissal, a common pattern in this campaign.
TQP Development, LLC	Intuit Inc.	Texas Eastern District Court	2:12-cv-00180	Mar 30, 2012	The case was subject to transfer orders within the district. The final disposition appears to be a dismissal, likely due to settlement.
TQP Development, LLC	MLB Advanced Media, L.P.	Texas Eastern District Court	2:12-cv-00577	Aug 31, 2012	Dismissed, likely due to settlement, consistent with other cases filed by TQP.
TQP Development, LLC	Chrysler Group LLC	Texas Eastern District Court	2:13-cv-00219	Mar 22, 2013	Settled and dismissed. A notice of appeal was filed and subsequently dismissed by the CAFC.
TQP Development, LLC	Callidus Software, Inc.	Texas Eastern District Court	2:12-cv-00799	Nov 20, 2012	This case is linked to the CBM review proceeding and was dismissed with prejudice following a settlement agreement.
TQP Development, LLC	Chegg Inc.	Texas Eastern District Court	2:14-cv-00442	May 21, 2014	Status records indicate this case was also likely resolved through settlement and dismissal.
TQP Development, LLC	Avis Budget Group, Inc.	Texas Eastern District Court	2:12-cv-00586	Aug 31, 2012	Dismissed.

Post-Grant Proceedings (PTAB)

In addition to district court litigation, the patent was challenged at the Patent Trial and Appeal Board (PTAB).

• Proceeding: Covered Business Method (CBM) Review
• Case Number: CBM2014-00007
• Petitioner: Callidus Software, Inc.
• Patent Owner: TQP Development, LLC
• Filing Date: October 11, 2013
• Outcome: The proceeding was terminated on December 3, 2013, following a joint motion by both parties, indicating they had reached a settlement in their parallel district court litigation. Because the termination occurred before a decision on the merits, no estoppel attached to the petitioner.

Based on a review of the patent's litigation history and available records, here is an analysis of the AIA trial proceedings for US Patent 5,412,730.

Proceedings overview

There has been one AIA trial proceeding filed against US Patent 5,412,730, a Covered Business Method (CBM) review which was terminated due to a settlement between the parties before an institution decision was made. Because the proceeding did not result in a final written decision, no claims have been invalidated or sustained by the PTAB, which provides a defendant with a clean slate to pursue a validity challenge at the PTAB without prior art estoppel from this case.

CBM2014-00007 — Callidus Software, Inc. v. TQP Development, LLC

• Type: Covered Business Method (CBM) Review
• Filed: 2013-10-11
• Status: Terminated. The proceeding was ended at the joint request of the petitioner and patent owner, indicating a settlement was reached.
• Judge panel: The case was terminated before a panel was publicly assigned to render an institution or final decision.
• Petition grounds: The petition challenged claims 1-9 of US Patent 5,412,730. The specific statutory grounds and prior art references are detailed in the petition document filed with the PTAB. CBM petitions typically allege that the challenged claims are directed to a covered business method and are invalid under sections 101, 102, 103, and/or 112.
• Institution decision: None. The proceeding was terminated on 2013-12-03, before an institution decision was rendered. Therefore, the PTAB never determined whether there was a reasonable likelihood that the petitioner would prevail on its challenges.
• Final Written Decision: None. As the case was terminated pre-institution, no trial was conducted and no Final Written Decision (FWD) was issued.
• Settlement / termination: The parties filed a joint motion to terminate the proceeding on 2013-12-02, stating they had resolved the matter pursuant to a settlement agreement. The PTAB granted the motion and terminated the proceeding the following day. The specific terms of the settlement are confidential. This termination also resolved the parallel district court case, TQP Development, LLC v. Callidus Software, Inc., No. 2:12-cv-00799 (E.D. Tex.).
• Appeal: Not applicable. There was no Final Written Decision to appeal to the U.S. Court of Appeals for the Federal Circuit.
• Defensive value: This proceeding provides minimal direct defensive value, as it did not invalidate any claims. However, its history is strategically significant. Because it was terminated without a Final Written Decision, no statutory estoppel under 35 U.S.C. § 325(e) applies to the petitioner (Callidus Software) or any other party. This means that a future defendant is not barred from filing a new IPR or PGR and raising the same invalidity grounds or prior art. The fact that the patent owner settled rather than face a validity challenge could signal a risk tolerance that might be exploited in future negotiations.

Strategic summary

The validity of US Patent 5,412,730 has not been substantively tested before the Patent Trial and Appeal Board. The single CBM review was terminated at the preliminary stage, leaving all claims—independent claims 1, 6, 8, and 9, and their dependents—officially UNTESTED by the PTAB. Consequently, no claims are currently CANCELED or SUSTAINED from an AIA trial.

The estoppel landscape is entirely open for a newly accused infringer. Under 35 U.S.C. § 315(e)(2) (for IPRs) and § 325(e)(2) (for CBMs/PGRs), estoppel only attaches to a petitioner after a Final Written Decision is issued. Since CBM2014-00007 did not result in an FWD, a new defendant can challenge any claim of the '730 patent at the PTAB on any ground that could have been raised. The pattern of a single defendant filing a CBM that quickly results in a global settlement of district court litigation is common; it demonstrates the leverage that AIA trials can provide for resolving disputes efficiently. The absence of further PTAB challenges, especially from defensive aggregators like Unified Patents, is notable given the patent's extensive assertion history, perhaps indicating that many defendants preferred to settle for nuisance value rather than fund a full invalidity challenge.

Recommended next steps

For a defendant currently facing a demand letter citing US Patent 5,412,730:

• Recognize that no claims of this patent have been invalidated or "hardened" by the PTAB. The patent's validity remains an open question for an administrative challenge.
• Given the patent's 1992 priority date, it is only eligible for Inter Partes Review (IPR), not Post-Grant Review (PGR). A new IPR petition would be the appropriate vehicle for a validity challenge at the PTAB.
• The absence of PTAB activity is a significant data point. While hundreds of companies have been sued on this patent, only one appears to have initiated a PTAB challenge, which was quickly settled. A potential defendant should conduct a thorough prior art search to assess the viability of a new IPR, as this path remains fully available and unencumbered by estoppel from prior proceedings.

Inventors

• Michael F. Jones: The sole inventor listed on the patent. The initial assignment on record (Reel 006450/0813), executed on 1992-06-25, shows Jones assigning his interest to Telequip Corporation, indicating he was likely employed by or had a contractual obligation to the company at the time of the invention. There are no unusual patterns discernible from the public record regarding his subsequent employment.

Original assignee

The original assignee of record was Telequip Corp, based in Hollis, New Hampshire. Telequip was an operating company that developed and sold data communications hardware, including modems, which directly aligns with the subject matter of the patent. The company appears to have ceased operations, as its entire interest in the patent was assigned away in 2008 (Reel 021881/0612).

Assignment timeline

Assignment records for US patent 5,412,730 are available from the USPTO Patent Assignment Search database.

• 1992-06-25 (executed) / recorded 1992-06-26 — Reel 006450/0813

  • Conveyance: Assignment of Assignors Interest
  • Assignor: Michael F. Jones
  • Assignee: Telequip Corporation
  • Correspondent: McHugh & Assoc., 175 Federal Street, Boston, MA 02110
  • Context: Standard pre-issuance assignment from an inventor to their employer.

• 2008-10-06 (executed) / recorded 2008-12-15 — Reel 021881/0612

  • Conveyance: Assignment of Assignors Interest
  • Assignor: Telequip Corporation
  • Assignee: Safe Sales Tech, LLC
  • Correspondent: The Pacid Group, LLC, 5001 Spring Valley Road, Suite 400 East, Dallas, TX 75244
  • Context: The patent is transferred from its original operating company owner to a Texas LLC, marking the beginning of its life as an asserted asset.

• 2008-11-03 (executed) / recorded 2008-12-15 — Reel 021881/0615

  • Conveyance: Change of Name
  • Assignor: Safe Sales Tech, LLC
  • Assignee: The Pacid Group, LLC
  • Correspondent: The Pacid Group, LLC, 5001 Spring Valley Road, Suite 400 East, Dallas, TX 75244. This is the same correspondent as the preceding and following entries, linking the entities.
  • Context: A simple change of name for the new patent-holding entity, executed less than a month after the acquisition.

• 2008-11-03 (executed) / recorded 2008-12-15 — Reel 021881/0618

  • Conveyance: Change of Name
  • Assignor: The Pacid Group, LLC
  • Assignee: TQP Development, LLC
  • Correspondent: The Pacid Group, LLC, 5001 Spring Valley Road, Suite 400 East, Dallas, TX 75244. The recurring correspondent confirms this is a chain of related entities.
  • Context: Another change of name, executed on the same day as the previous one, establishing the final identity of the assertion entity that would later file hundreds of lawsuits.

Timeline diagram

timeline
    title Ownership of US 5412730
    1992 : Assigned by inventor to Telequip Corp
    1995 : Patent issued
    2008 : Assigned to Safe Sales Tech LLC
         : Name changed to The Pacid Group LLC
         : Name changed to TQP Development LLC
    2012 : First major wave of litigation filed by TQP
    2013 : CBM review filed and settled

NPE / troll-pattern signals

1. Shell-entity transfer — Present. The assignment from Telequip Corporation, an operating company, to Safe Sales Tech, LLC on 2008-10-06 (Reel 021881/0612) is a clear transfer to a non-practicing entity designed for licensing or assertion.

2. Known asserter in the chain — Present. The current assignee, TQP Development, LLC (Reel 021881/0618), is a widely recognized high-volume patent assertion entity, as confirmed by the extensive litigation history provided and by public records from RPX and Unified Patents.

3. Repeat correspondent across the chain — Present. The three consecutive transfers recorded on 2008-12-15 all list "The Pacid Group, LLC" at a single Dallas, TX address as the correspondent (Reel 021881, frames 0612, 0615, and 0618). This recurrence of the same correspondent handling the rapid-fire transfers between differently named LLCs is a strong signal that the entities are controlled by a single operator.

4. Cascading transfers — Present. The assignment to Safe Sales Tech (executed 2008-10-06) was followed by two name changes (both executed 2008-11-03), with all three transactions recorded on the same day (2008-12-15). This rapid series of transactions over less than 30 days (Reel 021881) is a classic maneuver to structure a patent assertion vehicle.

5. Pre-litigation transfer — Not present. The transfers that moved the patent into TQP Development, LLC's hands were completed in 2008. The first major wave of litigation identified began in 2012, more than six months later. While the transfer was clearly made to enable future assertion, it does not fit the narrow definition of an immediate pre-litigation transfer.

6. Bankruptcy fire-sale — Unclear. There is no explicit evidence in the assignment record that the 2008 transfer from Telequip Corp was part of a formal bankruptcy proceeding. It was a standard "Assignment of Assignors Interest," which could have been part of a quiet wind-down or asset sale.

7. Privateering — Not present. There is no public evidence to suggest that the original assignee, Telequip Corp, is directing or profiting from TQP's assertion campaign against Telequip's former competitors.

8. Defensive aggregator (anti-NPE) — Not present. The ownership chain terminates with a prolific patent assertion entity, not a defensive one.

Verdict

NPE — high confidence

The ownership history of US patent 5,412,730 presents a clear and unambiguous pattern of transfer for the purpose of assertion by a non-practicing entity (NPE). The evidence includes a transfer from the original product company to a series of LLCs (Reel 021881/0612), a rapid cascade of name changes between related entities evidenced by a recurring correspondent (Reel 021881/0615, 021881/0618), and the patent's ultimate ownership by TQP Development, LLC, a known high-volume plaintiff.

Verification of the assignment records can be performed at the USPTO Patent Assignment Search page by searching for patent number 5412730.

Analysis of Prior Art Cited in US Patent 5,412,730

The following is a technical analysis of the prior art references cited by the examiner during the prosecution of US Patent 5,412,730. This analysis focuses on the potential relevance of each reference to the patent's claims under 35 U.S.C. § 102 (Anticipation).

A core concept of US 5,412,730 is the use of synchronized pseudo-random number generators at both the transmitting and receiving stations, initialized by a common "seed," with the sequence of keys being advanced based on a predetermined characteristic of the data being transmitted (e.g., a data block count). This avoids transmitting the keys themselves or separate synchronization signals.

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U.S. Patent 4,205,201

• Full Citation: US Patent 4,205,201, "Digital cipher system"
• Publication Date: May 27, 1980
• Brief Description: This patent describes a digital cipher system where a pseudo-random binary sequence is generated and combined with a plain text signal. The state of the pseudo-random generator can be advanced by a number of steps determined by a portion of the preceding plain text message. This ensures that the encrypting sequence is dependent on the message itself.
• Potential Anticipation Analysis: This reference is highly relevant. It teaches the use of a pseudo-random generator for encryption where the key sequence is altered based on the data being transmitted ("a portion of the...plain text message"). This appears to directly teach the core mechanism of advancing the key sequence based on a "predetermined characteristic of the data," as recited in Claim 1 and Claim 6. The key point of differentiation for '730 would be whether the "seed value" concept in the claims is distinct from the initialization method in '201 and whether the monitoring mechanism is identical.

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U.S. Patent 4,316,055

• Full Citation: US Patent 4,316,055, "Stream cipher cryptographic system"
• Publication Date: February 16, 1982
• Brief Description: This patent details a cryptographic system where a key stream, generated by a non-linear combination of shift register outputs, is used to encrypt data. The system includes a method for self-synchronization after a transmission error by using the cipher text itself to reload the registers at the receiver.
• Potential Anticipation Analysis: The '055 patent's focus is on self-synchronization using the cipher text. While it involves synchronized key stream generation, the mechanism for maintaining synchronization appears different from that in '730. The '730 patent advances its key based on monitoring the clear text data count before encryption (or after decryption), a process independent of the cipher text content. Therefore, '055 likely does not anticipate the key advancement method based on a predetermined data characteristic as claimed in Claim 1 and Claim 6.

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U.S. Patent 4,423,287

• Full Citation: US Patent 4,423,287, "Key notation and management system"
• Publication Date: December 27, 1983
• Brief Description: This patent describes a system for managing cryptographic keys in a network. It focuses on a "key notarizing" scheme where keys are encrypted under a master key and include data identifying the intended users and context, preventing misuse or replay of old keys. It manages the lifecycle and distribution of keys in a secure manner.
• Potential Anticipation Analysis: This reference addresses key management and distribution within a network, which relates to the environment described in Claim 9 of patent '730. '287 teaches a method for a central authority to manage which parties can communicate securely. However, it does not appear to describe the specific method of dynamically and randomly altering keys based on the data stream itself. Its primary contribution is to the secure management of static keys for sessions, not the continuous, data-dependent key alteration central to Claim 1.

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U.S. Patent 4,817,141

• Full Citation: US Patent 4,817,141, "Communication system with cryptosynchronization"
• Publication Date: March 28, 1989
• Brief Description: This patent describes a secure communication system that uses a block chaining method. Each block of cipher text is used as a feedback input to the key stream generator for encrypting the next block of plain text. This makes the key stream dependent on all previous message content, and provides self-synchronization.
• Potential Anticipation Analysis: Similar to '055, this patent uses cipher text feedback for synchronization. This differs from the method claimed in '730, which relies on monitoring the quantity or another characteristic of the data stream, independent of its encrypted value. The '730 patent explicitly notes that "no additional synchronization information needs to be added to the data stream" (Col. 3, lines 5-7), which contrasts with the inherent synchronization-via-data-content taught by '141. Thus, it is unlikely to anticipate Claim 1 or Claim 6.

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U.S. Patent 4,850,017

• Full Citation: US Patent 4,850,017, "Encrypted data communication system with master and remote stations"
• Publication Date: July 18, 1989
• Brief Description: This reference discloses a system where a master station and multiple remote stations share a common, periodically changing encryption key. The key change is triggered after a specific number of data transmissions have occurred. Both the master and remote stations contain counters that are incremented with each transmission to maintain synchronization for the key changes.
• Potential Anticipation Analysis: This patent is also highly relevant prior art. It teaches synchronized key changes at both a transmitter and receiver, triggered by counting a characteristic of the transmission ("a specific number of data transmissions"). This directly maps to the method described in the specification of '730 and recited in Claim 1 ("monitoring said sequence of data blocks for a predetermined characteristic thereof" and "generating a next one of said pseudo-random numbers in response thereto"). The use of counters at both ends is a clear embodiment of the claimed monitoring and advancing steps. The novelty of '730 may depend on the specifics of using a "pseudo-random number seed value" to generate a sequence of keys versus the method of generating new keys in '017.

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U.S. Patent 4,941,175

• Full Citation: US Patent 4,941,175, "Method and apparatus for effecting secure communications"
• Publication Date: July 10, 1990
• Brief Description: This patent describes a secure communication system where a key is changed on a message-by-message basis. A new key is generated for each new message, and this new key is itself encrypted using a "master key" and transmitted to the receiver along with the message.
• Potential Anticipation Analysis: This method is fundamentally different from that in patent '730. The '175 patent explicitly transmits the next session key (albeit in an encrypted form), which '730 is designed to avoid. The abstract of '730 states its system works "without these keys being transmitted in any form over the transmission facility." Therefore, '175 does not anticipate Claim 1, Claim 6, or Claim 8.

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U.S. Patent 5,052,040

• Full Citation: US Patent 5,052,040, "Cryptographic communication system and method with chaining and final-block-dependent key"
• Publication Date: September 24, 1991
• Brief Description: This patent describes a system using a block chaining algorithm where the encryption of each block depends on the previous block. To enhance security, it generates a unique "message key" for each message, which is derived from a master key and a "message sequence number." This message sequence number is incremented for each message, ensuring a unique key for each transmission and preventing replay attacks.
• Potential Anticipation Analysis: This patent discloses synchronized key generation based on a counter (the "message sequence number"). This is conceptually similar to the '730 patent's method of advancing a key sequence based on counting data blocks. Both systems use a shared secret (master key) and a synchronized counter to generate keys. This reference could be seen as anticipating the core process of Claim 1 and Claim 6. The distinction would lie in whether the "pseudo-random number seed value" and the resulting sequence in '730 is patentably distinct from the use of a master key and an incrementing message number in '040.

Based on the provided analysis of prior art cited during prosecution, here is an analysis of the obviousness of US Patent 5,412,730 under 35 U.S.C. § 103.

Definition of a Person Having Ordinary Skill in the Art (PHOSITA)

A person having ordinary skill in the art (PHOSITA) in early 1992 would have possessed a bachelor's degree in electrical engineering or computer science, along with practical experience in the fields of data communications, modem technology, and applied cryptography. Such a person would be familiar with standard encryption algorithms like the Data Encryption Standard (DES), the concept of stream ciphers, and common methods for generating pseudo-random number sequences for cryptographic purposes, such as using linear-feedback shift registers (LFSRs) initialized with a secret seed.

Obviousness Analysis of Independent Claims 1, 6, and 8

The core invention recited in claims 1 (transmitting method), 6 (receiving method), and 8 (modem apparatus) is a system where encryption keys are changed in synchrony at two ends of a communication link. This is achieved by:
a) Pre-sharing a secret "seed value."
b) Using this seed to initialize identical pseudo-random number generators (PRNGs) at both ends.
c) Advancing the PRNGs to the next key in their sequence based on monitoring a predetermined characteristic of the data stream itself (e.g., counting a number of data blocks).

A strong case for obviousness can be made by combining U.S. Patent 4,850,017 ('017) with the general knowledge of a PHOSITA regarding cryptographic key generation.

Primary Reference: U.S. Patent 4,850,017 ('017)

The '017 patent discloses the foundational elements of the '730 patent's method. Specifically, it teaches:

• A secure communication system with a master (transmitter) and remote (receiver) station.
• A shared encryption key that is periodically and synchronously changed.
• The key change is triggered after "a specific number of data transmissions have occurred."
• Both the master and remote stations contain counters that are incremented with each transmission to maintain synchronization for the key change.

This directly teaches the core concept of monitoring a characteristic of the data flow (a count of transmissions) and using that count to trigger a synchronized key change at both ends of a link, without transmitting the new key or a separate synchronization signal.

Motivation to Combine '017 with General Knowledge

The only arguable difference between the disclosure of '017 and the claims of '730 is the specific mechanism for generating the sequence of new keys. Claim 1 of '730 recites using a "pseudo-random number seed value" to generate a sequence of "pseudo-random numbers" which serve as keys.

A PHOSITA in 1992, tasked with implementing the key-changing system described in '017, would have found it obvious to use a standard, seeded PRNG to generate the succession of keys. The use of a PRNG initialized with a secret seed was a fundamental and widely known technique for creating a cryptographic key stream. This was a standard building block in the art of cryptography.

Therefore, the motivation would be to implement the "key changing" function of '017 using a well-known, efficient, and standard component: a seeded PRNG. Doing so would be an obvious design choice, not an inventive step. The system in '017 requires a new key upon the counter reaching a certain value; a PRNG provides an immediate and logical source for that new key. The initial shared secret required by the system would naturally serve as the seed for the PRNG.

Conclusion for Claims 1, 6, and 8

Because '017 teaches synchronized key changes based on counting transmissions, and the use of a seeded PRNG to generate a sequence of keys was a well-known and conventional technique in the art, a PHOSITA would have found it obvious to combine these elements. Thus, claims 1, 6, and 8, which cover the method and apparatus for this process, would be rendered obvious by U.S. Patent 4,850,017 in view of the general knowledge of one of ordinary skill in the art of cryptography.

Alternative Obviousness Combination: U.S. Patent 5,052,040

Similarly, U.S. Patent 5,052,040 ('040) teaches using a shared master key (analogous to a seed) and a synchronized, incrementing "message sequence number" (a counter) to generate a unique key for each message. This also teaches the core concept of synchronized key generation based on a shared secret and a counter. A PHOSITA would find it an obvious design choice to substitute the key derivation method of '040 with a standard PRNG key-stream generator, advanced by the same message sequence number, to achieve a similar result.

Obviousness Analysis of Independent Claim 9

Claim 9 expands the core method to a network environment with a central control station and multiple remote terminals, where the central station provides keys to authorize communications between specific terminals.

A strong case for the obviousness of Claim 9 can be made by combining the teachings of the primary obviousness argument above with U.S. Patent 4,423,287 ('287).

Base Combination: U.S. Patent 4,850,017 (or 5,052,040) in view of general cryptographic knowledge.

Secondary Reference: U.S. Patent 4,423,287 ('287)

The '287 patent explicitly teaches a key management system for a network. Its disclosure includes:

• A network with multiple users or terminals.
• A "key notarizing" scheme that functions as a central authority.
• A system for securely distributing keys to intended users for a specific context, thereby managing which terminals are authorized to communicate securely.

Motivation to Combine

A PHOSITA looking to enhance the security of the network key management system described in '287 would be motivated to incorporate a method for dynamic key alteration. The system in '287 manages the distribution of what are essentially static session keys. A known vulnerability in such systems is that if a session key is compromised, the entire session is compromised.

The method taught in '017 (or '040) of continuously changing the key based on the data flow provides a direct solution to this problem. A PHOSITA would be motivated to combine these teachings to build a more robust network. The central controller from '287 would be used to securely distribute the initial "seed values" (from '730's claims) or shared secrets (from '017), thereby authorizing a communication link. Once the link is established, the keys would begin to change dynamically according to the data-counting method of '017. This combination leverages the network control of '287 with the enhanced link security of '017, an obvious improvement that would have been a predictable design goal for anyone skilled in the art of network security.

Conclusion for Claim 9

Claim 9 is obvious over the combination of U.S. Patent 4,850,017 and U.S. Patent 4,423,287. The former teaches the dynamic, data-dependent key-changing mechanism, while the latter teaches the network architecture and central key management role. Combining them would be a straightforward and logical step to improve the security of the managed network.

Term, Expiration, and Family Details for US Patent 5,412,730

Patent Term and Expiration

• Filing Date: April 23, 1992
• Issue Date: May 2, 1995
• Status: Expired

This patent was filed before the June 8, 1995, transition date for patent term rules in the United States. Consequently, its term is calculated as the later of 17 years from the issue date or 20 years from the earliest non-provisional filing date.

1. 17 years from Issue Date: May 2, 1995 + 17 years = May 2, 2012.
2. 20 years from Filing Date: April 23, 1992 + 20 years = April 23, 2012.

The later of these two dates is May 2, 2012. The patent's term was not shortened by a terminal disclaimer. No maintenance fees were due after the expiration of its full term.

The projected and actual expiration date for US Patent 5,412,730 was May 2, 2012.

Patent Term Adjustments (PTA) and Extensions (PTE)

• Patent Term Adjustment (PTA): There are no Patent Term Adjustments for this patent. The provisions for PTA were established by the American Inventors Protection Act of 1999 (AIPA) and generally apply to applications filed on or after May 29, 2000.
• Patent Term Extension (PTE): There is no record of any Patent Term Extension for this patent under 35 U.S.C. § 156, which is typically granted to compensate for delays in regulatory review (e.g., by the FDA). This type of extension would not be applicable to the modem technology disclosed in the patent.

Related Applications and Family Members

The patent text itself provides the direct continuity data for this application.

• Parent Application: US Patent 5,412,730 is a continuation-in-part of application Serial No. 07/418,178, which was filed on October 6, 1989. This earlier application subsequently issued as US Patent 5,159,634 on October 27, 1992. The '634 patent is the parent in this family.
• Divisional or Continuation Applications: There are no child applications (continuations or divisionals) that claim priority back to US Patent 5,412,730. The chain of prosecution appears to have concluded with this patent.
• Foreign Family Members: There are no foreign patent applications claiming priority to either the '730 patent or its parent application. This appears to be a U.S.-only patent family.

This relationship can be verified in public databases such as the USPTO's Patent Center.

This Defensive Disclosure document provides a series of novel technical variations, applications, and integrations based on the core inventive concepts of US Patent 5,412,730. The disclosures herein are intended to enter the public domain and serve as prior art against future patent applications claiming incremental improvements upon the original invention.

Disclosure on Claims 1 & 6: Method of Synchronized, Data-Driven Key Rotation

The core method involves a transmitter and receiver sharing a secret "seed" to initialize identical pseudo-random number generators (PRNGs). The sequence of keys is advanced in synchrony based on monitoring a predetermined characteristic of the data stream, eliminating the need to transmit keys or synchronization signals.

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Axis 1: Material & Component Substitution

• Derivative 1.1: Hardware-Based PRNG using Physical Unclonable Functions (PUFs)

  • Enabling Description: Instead of a software-based PRNG, this variation employs a dedicated hardware module utilizing a Physical Unclonable Function (PUF). Each communicating device has a unique PUF (e.g., an SRAM PUF or an Arbiter PUF) which, when challenged, produces a device-specific, repeatable random number. The initial "seed" is used as the initial challenge to the PUF. Subsequent challenges are generated by hashing the previous PUF output with the data block count. The block counter (e.g., a 64-bit hardware counter) triggers an "advance" signal, which initiates the next PUF challenge-response cycle to generate the subsequent encryption key. This replaces the software PRNG with a non-algorithmic, hardware-rooted source of randomness, making key prediction computationally infeasible even if the algorithm is known. The encryption/decryption is performed by an AES-256 core implemented in an FPGA or ASIC, directly fed by the PUF-based key generator.

  • graph TD
        subgraph Transmitter
            A[Cleartext Data] --> B{Block Counter};
            B -- Trigger @ N bytes --> C{Challenge Generator};
            D[Initial Seed] --> C;
            C -- Challenge --> E[SRAM PUF];
            E -- Response --> F{Key Derivation Function KDF};
            F -- Encryption Key --> G[AES-256 Encryptor];
            A --> G;
            G --> H[Ciphertext Out];
            F -- Hash --> C;
        end
        subgraph Receiver
            I[Ciphertext In] --> J[AES-256 Decryptor];
            J --> K[Decrypted Cleartext];
            K --> L{Block Counter};
            L -- Trigger @ N bytes --> M{Challenge Generator};
            N[Initial Seed] --> M;
            M -- Challenge --> O[SRAM PUF];
            O -- Response --> P{Key Derivation Function KDF};
            P -- Decryption Key --> J;
            P -- Hash --> M;
        end
        Transmitter --> Receiver;
    

• Derivative 1.2: Quantum Random Number Generator (QRNG) Component

  • Enabling Description: The PRNG is replaced with a true random number generator based on quantum phenomena (QRNG). The initial "seed" is not a number but a set of parameters (e.g., laser intensity, measurement basis) for a shared QRNG process. Both the transmitter and receiver contain identical, calibrated QRNG modules. The "advance" signal from the data block counter triggers the QRNG to generate the next random number by measuring a quantum state (e.g., photon polarization). To ensure synchronization without transmitting the random number, both sides use the shared seed parameters and the block count as an input to a deterministic function that selects the specific quantum measurement to perform. Since the underlying quantum event is truly random but the process to capture it is deterministic and synchronized, both sides generate the identical sequence of true random numbers for use as keys.

  • sequenceDiagram
        participant T as Transmitter
        participant R as Receiver
        T->>T: Initialize QRNG with Seed Parameters
        R->>R: Initialize QRNG with Seed Parameters
        loop Data Transmission
            T->>T: Monitor Cleartext Byte Count
            R->>R: Monitor Decrypted Byte Count
            alt Count reaches N
                T->>T: Trigger QRNG Measurement (based on count)
                T->>T: Generate Key K_i
                R->>R: Trigger QRNG Measurement (based on count)
                R->>R: Generate Key K_i
            end
            T->>T: Encrypt Data with K_i
            T->>R: Transmit Ciphertext
            R->>R: Decrypt Data with K_i
        end
    

---

Axis 2: Operational Parameter Expansion

• Derivative 2.1: Hyperscale Datacenter Fabric Encryption

  • Enabling Description: The method is applied to encrypt east-west traffic between servers in a hyperscale datacenter. The "data block" is a full Ethernet jumbo frame (9000 bytes). The "predetermined characteristic" is the source/destination MAC address pair combined with a frame counter. The "seed" is provisioned to each virtual machine (VM) or container by a central orchestration system (e.g., Kubernetes secret) upon instantiation. Each network interface card (NIC) has an offload engine that implements the PRNG (e.g., a Lehmer PRNG) and encryption (e.g., AES-GCM) in hardware. The key is advanced for every 2^16 frames transmitted between a specific MAC address pair. This operates at line rates of 100/400 Gbps, with key rotation occurring thousands of times per second across the fabric, rendering eavesdropping on any single data flow computationally expensive to break before the key changes.

  • graph TD
        subgraph Orchestrator
            O[Kubernetes] -- Seed --> VM1;
            O -- Seed --> VM2;
        end
        subgraph VM1_NIC
            A[Ethernet Frame] --> B{Frame Counter (src/dst MAC)};
            B -- Trigger --> C{PRNG};
            C -- Key --> D[AES-GCM Encrypt];
            A --> D;
            D --> E[Encrypted Frame Out];
        end
        subgraph VM2_NIC
            F[Encrypted Frame In] --> G[AES-GCM Decrypt];
            G --> H[Ethernet Frame];
            H --> I{Frame Counter (src/dst MAC)};
            I -- Trigger --> J{PRNG};
            J -- Key --> G;
        end
        VM1_NIC -- 400Gbps Fabric --> VM2_NIC;
    

• Derivative 2.2: Deep-Space Probe Communication with High Latency

  • Enabling Description: This variation is designed for communication with a deep-space probe where round-trip latency is measured in hours. The "seed" value and the key advancement algorithm (a T-function based PRNG) are pre-loaded on the probe before launch. The "predetermined characteristic" is the mission-elapsed-time (MET) timestamp embedded in the header of each data packet. The key is advanced based on the integer value of the MET, divided by a pre-agreed constant (e.g., a new key every 60 seconds of MET). Both ground control and the probe maintain a synchronized MET clock. Due to relativistic effects, the clocks are periodically re-synchronized using timekeeping packets, but the key generation between syncs is entirely dependent on the MET counter. This allows the probe to continue using a rotating key even if it is out of contact with Earth for long periods, and for ground control to decrypt stored telemetry received later.

  • stateDiagram-v2
        [*] --> Standby
        state Ground_Control {
            direction LR
            [*] --> Key_N
            Key_N --> Key_N_plus_1 : MET_counter % 60 == 0
            Key_N_plus_1 --> Key_N : MET_counter % 60 != 0
        }
        state Deep_Space_Probe {
            direction LR
            [*] --> Key_N
            Key_N --> Key_N_plus_1 : MET_counter % 60 == 0
            Key_N_plus_1 --> Key_N : MET_counter % 60 != 0
        }
        Standby --> Ground_Control : Start_Transmission
        Standby --> Deep_Space_Probe : Start_Transmission
    

---

Axis 3: Cross-Domain Application

• Derivative 3.1: Aerospace (UAV Swarm Command & Control)

  • Enabling Description: In a swarm of unmanned aerial vehicles (UAVs), a central ground station communicates encrypted command and control (C2) messages. A common "seed" is pre-loaded into all UAVs of a specific swarm before a mission. The key is advanced based on a shared, publicly observable characteristic: the GPS satellite constellation geometry. The PRNG is advanced each time the Dilution of Precision (DOP) value, calculated from the visible GPS satellite positions, crosses an integer threshold. All UAVs and the ground station calculate the same DOP value from the same public GPS signals, allowing them to advance their keys in synchrony without any C2 overhead for key management. This provides robust, anti-jamming, secure communication that cannot be broken by compromising a single UAV, as the key rotation is not dependent on inter-UAV communication.

  • graph TD
        GPS[GPS Constellation] --> |Public Signal| GroundStation;
        GPS --> |Public Signal| UAV1;
        GPS --> |Public Signal| UAV2;
        GPS --> |Public Signal| UAV3;
    
        subgraph GroundStation
            A[DOP Calculator] --> B{DOP Threshold Monitor};
            B -- Advance --> C{PRNG};
            C -- Key --> D[Encrypt C2 Msg];
        end
    
        subgraph UAV1
            E[DOP Calculator] --> F{DOP Threshold Monitor};
            F -- Advance --> G{PRNG};
            G -- Key --> H[Decrypt C2 Msg];
        end
    
        D --> H;
    

• Derivative 3.2: AgTech (Irrigation System Control)

  • Enabling Description: A network of wireless irrigation valves and soil moisture sensors in a large agricultural field is controlled by a central base station. To prevent tampering (e.g., a malicious actor turning off water), commands are encrypted. The "seed" is set during installation. The "predetermined characteristic" is a reading from a designated, physically secure "pacemaker" sensor (e.g., a temperature sensor at the base station). The key for the entire network is advanced every time the pacemaker sensor's reading, rounded to the nearest degree Celsius, changes. All nodes, including the valves and the base station, receive this public temperature broadcast (or have their own calibrated sensors). This provides a low-cost, synchronized key rotation mechanism across a wide area low-power network (LoRaWAN) without requiring complex key distribution protocols.

  • sequenceDiagram
        participant BaseStation
        participant PacemakerSensor
        participant Valve1
        participant Valve2
    
        loop Time
            PacemakerSensor->>BaseStation: Temp = 25.1 C
            BaseStation->>BaseStation: Temp_rounded = 25
            alt Temperature change detected (24 -> 25)
                BaseStation->>BaseStation: Advance PRNG, new key K_new
                Valve1->>Valve1: Advance PRNG, new key K_new
                Valve2->>Valve2: Advance PRNG, new key K_new
            end
            BaseStation->>BaseStation: Encrypt command "Open Valve 1" with K_new
            BaseStation->>Valve1: Transmit encrypted command
            Valve1->>Valve1: Decrypt command with K_new
        end
    

• Derivative 3.3: Consumer Electronics (Secure Wireless Audio)

  • Enabling Description: A pair of high-fidelity wireless headphones and a transmitter (e.g., a smartphone) use this method to secure the audio stream. The "seed" is exchanged during the initial Bluetooth pairing process using the standard Diffie-Hellman key exchange. The "predetermined characteristic" used to advance the key is the audio stream's sample count. For a 48kHz audio stream, the key (generated by a lightweight Speck cipher PRNG) is advanced every 480,000 samples, which corresponds to exactly 10 seconds of audio. Both the phone and the headphones count the audio samples being processed, ensuring their keys remain in sync. This prevents eavesdropping on the wireless audio link with minimal computational overhead suitable for a battery-powered device.

  • flowchart LR
        subgraph Phone
            A[PCM Audio Stream] --> B(Sample Counter);
            B -- Trigger every 10s --> C(Speck PRNG);
            C -- Key --> D{Encryptor};
            A --> D;
        end
        subgraph Headphones
            E[Encrypted Stream] --> F{Decryptor};
            F --> G[PCM Audio Stream];
            G --> H(Sample Counter);
            H -- Trigger every 10s --> I(Speck PRNG);
            I -- Key --> F;
        end
        D --> E;
    

---

Axis 4: Integration with Emerging Tech

• Derivative 4.1: AI-Driven Dynamic Key Advancement

  • Enabling Description: The rule for advancing the key is no longer a fixed counter but is determined by an AI model. A lightweight, pre-trained neural network (e.g., a small LSTM) runs on both the transmitter and receiver. The model's input is a feature vector derived from the cleartext data stream (e.g., character frequency, byte-level entropy, packet inter-arrival time). The model's output is a binary decision: "Advance Key" or "Hold Key". Since both sides run the identical, deterministic model on the same data stream, their key advancement decisions are synchronized. The initial "seed" is used to seed the PRNG, and the AI model's weights and architecture are also part of the shared secret. This makes the key rotation pattern non-linear and data-dependent, thwarting attackers who attempt to predict key changes based on simple traffic analysis.

  • graph TD
        subgraph Sender
            Data[Cleartext] --> FeatureExtraction;
            FeatureExtraction --> AI_Model_1[LSTM Model];
            AI_Model_1 -- Advance/Hold --> PRNG_1[PRNG];
            PRNG_1 -- Key --> Encryptor;
            Data --> Encryptor;
        end
        subgraph Receiver
            Decryptor --> DecryptedData[Cleartext];
            DecryptedData --> FeatureExtraction_2;
            FeatureExtraction_2 --> AI_Model_2[LSTM Model];
            AI_Model_2 -- Advance/Hold --> PRNG_2[PRNG];
            PRNG_2 -- Key --> Decryptor;
        end
        Encryptor --> Ciphertext --> Decryptor;
    

• Derivative 4.2: IoT Sensor Network with Real-Time Environmental Triggers

  • Enabling Description: A distributed network of IoT sensors (e.g., monitoring a smart city's power grid) uses the method for secure telemetry. The "seed" is provisioned at the factory. The key advancement is triggered by a consensus-based environmental state. Each sensor monitors a physical parameter (e.g., ambient temperature). When a predefined percentage of sensors in a geographic cluster (e.g., >75%) report a temperature above a critical threshold (e.g., 40°C), all sensors in that cluster and the central aggregator advance their PRNG to the next key. This "event-driven" key rotation ensures that security is heightened during critical environmental conditions (like a heatwave straining the grid) and provides a synchronization mechanism that is resilient to the failure of any single sensor.

  • erDiagram
        CLUSTER ||--|{ SENSOR : contains
        SENSOR {
            string SensorID
            float Temperature
        }
        CLUSTER {
            string ClusterID
            PRNG_State CurrentPRNG
        }
        AGGREGATOR ||--|{ CLUSTER : monitors
        AGGREGATOR {
            string AggregatorID
        }
    
        stateDiagram-v2
        state "Key N" {
            [*] --> Normal
            Normal --> Critical_Temp_Consensus : ">75% of sensors report T > 40C"
        }
        Critical_Temp_Consensus --> "Key N+1" : Advance Key
        "Key N+1" --> "Key N" : Reset Condition
    

• Derivative 4.3: Blockchain-Verified Seed & Algorithm Updates

  • Enabling Description: The "seed" value and the specific PRNG algorithm identifier are not pre-shared via a secure channel but are recorded on a private, permissioned blockchain (e.g., Hyperledger Fabric). Communicating parties are nodes on this blockchain. To initiate a secure session, the transmitter proposes a new "session seed" by writing it to an immutable smart contract. The receiver reads this seed from the blockchain. All subsequent key advancements are based on the data stream as per the original patent. This provides an auditable, non-repudiable log of session initializations. Furthermore, updates to the key advancement algorithm itself (e.g., changing from a block counter to an AI model) can be pushed to devices via a smart contract update, ensuring the entire network securely and verifiably migrates to a new security protocol in a synchronized manner.

  • sequenceDiagram
        participant DeviceA
        participant Blockchain
        participant DeviceB
    
        DeviceA->>Blockchain: Propose new session seed via Smart Contract
        Blockchain-->>DeviceB: Notified of new seed
        DeviceB->>Blockchain: Read and confirm seed
        DeviceA->>DeviceA: Initialize PRNG with seed
        DeviceB->>DeviceB: Initialize PRNG with seed
        Note over DeviceA,DeviceB: Data-driven key rotation begins
        DeviceA->>DeviceB: Encrypted Data (Key K_i)
        DeviceA->>DeviceB: Encrypted Data (Key K_i+1 after trigger)
    

---

Axis 5: The "Inverse" or Failure Mode

• Derivative 5.1: Graceful Degradation to a Fixed Session Key
  • Enabling Description: The system is designed to fail-safe in the event of synchronization loss. Each device maintains a "sync confidence score," which is decremented every time a decrypted block fails its integrity check (e.g., a GCM tag mismatch). If the score falls below a threshold, the receiver assumes sync is lost. It then sends a special unencrypted control packet to the transmitter requesting a "fallback state." Both devices discard their PRNG state and revert to using the initial seed itself as a fixed session key for the remainder of the session. The system logs a critical error, but communication continues in a less secure, but still encrypted, state. This prevents a total loss of communication due to transient errors that might cause the block counters to de-synchronize.

  • stateDiagram-v2
        [*] --> RotatingKey
        RotatingKey --> SyncLossCheck : Decryption Integrity Fail
        SyncLossCheck --> RotatingKey : Integrity OK
        SyncLossCheck --> FallbackMode : Confidence Score < Threshold
        RotatingKey --> FallbackMode : Control Packet RX
        FallbackMode --> SessionEnd
        RotatingKey --> SessionEnd
        note right of FallbackMode
          Communication continues using
          the initial seed as a static key.
        end note
    

Disclosure on Claim 8: The Modem Implementation

• Derivative 8.1 (Component Substitution): SoC with Trusted Execution Environment (TEE)
  • Enabling Description: The modem's functionality is implemented not on a general-purpose microprocessor but on a System-on-Chip (SoC) that features a Trusted Execution Environment (TEE), such as ARM TrustZone. The PRNG, key storage (for the seed), block counter, and the encryption/decryption logic are all executed within the secure world of the TEE. The "normal world" operating system, which handles the modem AT commands and data framing, can feed data into the TEE for encryption but cannot access the seed, the PRNG state, or the keys. This provides hardware-level isolation, preventing compromise of the encryption process even if the main modem firmware is exploited.

  • classDiagram
        class ModemSoC {
            +NormalWorldOS
            +SecureWorldTEE
        }
        class NormalWorldOS {
            +AT_Command_Parser()
            +Data_Framing()
            +RequestEncryption(data)
        }
        class SecureWorldTEE {
            -seed
            -prng_state
            +Initialize(seed)
            +Encrypt(data)
            +Decrypt(data)
        }
        ModemSoC *-- NormalWorldOS
        ModemSoC *-- SecureWorldTEE
        NormalWorldOS ..> SecureWorldTEE : invokes
    

Disclosure on Claim 9: The Secure Network

• Derivative 9.1 (Cross-Domain Application): Vehicle-to-Everything (V2X) Communication Network
  • Enabling Description: A central traffic management authority acts as the "central control station." It provisions "seeds" to authorized vehicles and roadside infrastructure (RSUs). A vehicle wishing to communicate with an RSU uses a seed specific to that RSU. The "predetermined characteristic" for key advancement is the vehicle's own signed GPS coordinate data, which it broadcasts periodically as part of the V2X safety protocol. Both the vehicle and the RSU use the sequence of GPS coordinates in the public safety messages to synchronize their key changes for their private, encrypted communication channel. The central authority can revoke a vehicle's seeds if it is stolen, preventing it from participating in the secure network.

  • flowchart TD
        subgraph CentralAuthority
            A[Provision Seeds] --> B(Vehicle);
            A --> C(RSU);
        end
        subgraph Vehicle
            D[GPS Position] --> E{PRNG Trigger};
            E -- Advance --> F{PRNG};
            F -- Key --> G[Encrypt Data];
        end
        subgraph RSU
            H[Vehicle's Public GPS Position] --> I{PRNG Trigger};
            I -- Advance --> J{PRNG};
            J -- Key --> K[Decrypt Data];
        end
        G --> K;
    

Combination Prior Art Scenarios with Open-Source Standards

1. Combination with TLS 1.3: The synchronized key rotation method is integrated into the TLS 1.3 handshake. The initial "seed" is derived from the master secret established during the handshake, as defined in RFC 8446. Instead of using the static Application Traffic Keys, the client and server use the derived seed to initialize synchronized PRNGs. The key is advanced based on the 64-bit TLS sequence number. For every 2^16 records, the key is rotated. This enhances the security of a standard TLS session by adding an inner layer of data-driven key rotation, making traffic analysis attacks against long-lived connections more difficult.

2. Combination with Zigbee Pro: In an IoT mesh network running the Zigbee Pro protocol, the method secures application-layer data between two devices. The "seed" is the Link Key shared between the two devices, established during the Zigbee commissioning process. The "predetermined characteristic" is the Zigbee Application Support (APS) sub-layer frame counter, which is already maintained for replay protection. Both devices advance their PRNGs based on this counter. This adds a layer of end-to-end encryption on top of the standard Zigbee network-layer encryption, securing communication against compromised intermediate routing nodes in the mesh network.

3. Combination with WireGuard: The method is used to enhance the security of the WireGuard VPN protocol. The static pre-shared key (preshared_key) available for a given peer is used as the "seed" for the PRNG. The key used for the ChaCha20Poly1305 authenticated encryption is not derived directly from the Diffie-Hellman handshake as standard, but from this PRNG. The PRNG is advanced based on the 64-bit nonce that WireGuard already uses for replay protection. As the nonce increments with each packet, the encryption key is rotated on a per-packet basis in a synchronized, deterministic manner, effectively creating a unique key for every single data packet sent and strengthening protection against cryptographic breakthroughs or implementation flaws.