Prior art — US Patent 6502135

Analysis of Prior Art Cited in US Patent 6,502,135

As a senior US patent analyst, this report details the most relevant prior art cited by US Patent 6,502,135, "Agile network protocol for secure communications with assured system availability." Each reference has been reviewed to determine its potential for anticipating the claims of the '135 patent under 35 U.S.C. § 102.

The '135 patent describes a method for secure network communication using seemingly random and changing IP addresses to create a Virtual Private Network (VPN). A key aspect of the invention is the "agile" nature of the protocol, where communicating nodes use a synchronized, pseudo-random sequence of IP addresses, making it difficult to trace the communication.

The following prior art references were cited by the patent examiner during the prosecution of the '135 patent and are foundational to understanding the landscape of secure networking at the time of the invention.

1. U.S. Patent 5,940,591: "Method and apparatus for secure network communications"

Full Citation: US Patent 5,940,591, "Method and apparatus for secure network communications," issued to Sudia, Frank Z.
Publication/Filing Date:
- Publication Date: August 17, 1999
- Filing Date: October 22, 1996
Brief Description: This patent discloses a system for providing secure communication channels over a public network. It describes the use of "virtual network addresses" that are distinct from the actual physical network addresses of the communicating devices. A secure gateway or "firewall" maps these virtual addresses to the real addresses, and this mapping can be changed to enhance security. The system is designed to protect an internal network from unauthorized external access.
Potential Anticipation of Claims: This patent appears to be highly relevant to the core concepts of the '135 patent.
- Claim 1 and 12: Sudia's disclosure of virtual network addresses that are mapped to real addresses and can be changed anticipates the concept of using a different, non-static address for communication. The firewall in Sudia acts as a proxy, which is a component of the transparent creation of a secure link as described in claim 12 of the '135 patent. The dynamic nature of the address mapping in Sudia could be argued to anticipate the "pseudo-randomly varying" data values of the '135 patent's claims.

2. U.S. Patent 5,826,029: "Method for providing transparent network security"

Full Citation: US Patent 5,826,029, "Method for providing transparent network security," issued to Holloway, John T., et al.
Publication/Filing Date:
- Publication Date: October 20, 1998
- Filing Date: September 19, 1996
Brief Description: This patent describes a method for transparently encrypting data between two network devices without requiring modification to the applications on those devices. It uses a "shim" layer inserted into the network protocol stack (between the network and transport layers) that intercepts outgoing packets, encrypts them, and then sends them to the destination. The destination device has a corresponding shim that decrypts the packets. This process is "transparent" to the user and applications.
Potential Anticipation of Claims: The concept of transparency is a key element in several of the '135 patent's claims.
- Claim 12: Holloway's method for "transparently" inserting a security layer is directly relevant to the limitation of "transparently creating a secure communication link." The interception of network traffic without user or application awareness is a core teaching of this prior art. While Holloway focuses on encryption rather than address hopping, the mechanism for achieving transparency is a key component that could be seen as anticipating this aspect of claim 12.

3. U.S. Patent 5,826,014: "System for providing a secure communications link"

Full Citation: US Patent 5,826,014, "System for providing a secure communications link," issued to Foster, G.A.
Publication/Filing Date:
- Publication Date: October 20, 1998
- Filing Date: December 21, 1995
Brief Description: This patent details a system for creating a secure communication link over a public network by encapsulating private network packets within public network packets. This is a foundational concept of VPNs, often referred to as "tunneling." The system uses a security gateway to perform this encapsulation and de-capsulation, effectively creating a secure channel between two private networks.
Potential Anticipation of Claims: This patent is relevant to the general concept of creating a secure link or VPN.
- Claim 1, 7, and 12: Foster's disclosure of creating a secure communications link via encapsulation or tunneling is a fundamental building block for the VPNs described in these claims. While it may not explicitly teach the pseudo-random variation of addresses, it provides the underlying mechanism for establishing the secure link itself, which is a prerequisite for the '135 invention. An argument could be made that combining Foster's tunneling with a known method of changing addresses would render the '135 claims obvious, though it may not directly anticipate them under § 102.

4. U.S. Patent 5,790,548: "Dynamic address mapping for mobile hosts"

Full Citation: US Patent 5,790,548, "Dynamic address mapping for mobile hosts," issued to Sistanizadeh, Kamran, et al.
Publication/Filing Date:
- Publication Date: August 4, 1998
- Filing Date: August 16, 1996
Brief Description: This patent addresses the problem of maintaining network connections for mobile devices that change their physical point of attachment to a network, and thus their IP address. It describes a system where a "home agent" maintains a mapping between a mobile host's permanent IP address and its current, temporary "care-of" address. This allows for continuous communication with the mobile host even as it moves between different networks.
Potential Anticipation of Claims: The concept of dynamic and changing addresses is central to this patent.
- Claim 1: The dynamic mapping of a permanent address to a changing care-of address in Sistanizadeh is a form of address agility. While the purpose is mobility rather than security, the mechanism of using changing network addresses for a single communication session is present. This could be argued as an anticipation of the "pseudo-randomly varying" data values, if the sequence of care-of addresses could be considered pseudo-random from an external observer's perspective.

5. U.S. Patent 5,761,289: "Secure virtual private network"

Full Citation: US Patent 5,761,289, "Secure virtual private network," issued to Keshav, S.
Publication/Filing Date:
- Publication Date: June 2, 1998
- Filing Date: April 2, 1996
Brief Description: This patent describes a method for creating a secure virtual private network over a public network. It focuses on authenticating users and encrypting data to ensure privacy and integrity. The system involves security gateways at the edge of private networks that manage the secure connections.
Potential Anticipation of Claims: This patent provides further context for the state of the art in VPN technology at the time.
- Claim 1, 7, and 12: Similar to Foster ('014), Keshav describes the fundamental components and methods for establishing a VPN. While it does not appear to describe the specific technique of address hopping, it is part of the body of prior art that establishes the context in which the '135 patent's claims of creating a VPN were examined.

6. U.S. Patent 5,659,616: "Secure network with chameleon-like nodes"

Full Citation: US Patent 5,659,616, "Secure network with chameleon-like nodes," issued to Sudia, Frank Z.
Publication/Filing Date:
- Publication Date: August 19, 1997
- Filing Date: August 11, 1995
Brief Description: This patent is highly relevant. It describes a secure network where the network addresses of the nodes ("chameleon-like nodes") are periodically and randomly changed to prevent unauthorized tracking and interception. The system uses a central administrator to distribute new, random addresses to the nodes in the secure network.
Potential Anticipation of Claims: This reference appears to strongly anticipate the core novelty of the '135 patent.
- Claim 1, 7, and 12: Sudia's teaching of periodically and randomly changing network addresses for security purposes is a direct teaching of the core concept in these claims. The "chameleon-like nodes" directly parallel the "agile" protocol of the '135 patent. The distribution of new addresses by a central administrator is a specific implementation of the synchronized, pseudo-random variation claimed in the '135 patent. This patent is likely the most significant piece of prior art for the '135 patent and was a central reference in the subsequent IPR challenges.

In summary, the prior art cited during the prosecution of the '135 patent, particularly the patents by Sudia ('591 and '616), establish a strong foundation for the concepts of using virtual and dynamically changing network addresses to create secure communication channels. These references were critical in the later PTAB proceedings that led to the invalidation of several of the '135 patent's claims.