PTAB

IPR2020-00511

Netflix Inc v. DivX CF Investors LLC

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Key Events
Petition

1. Case Identification

2. Patent Overview

  • Title: Digital Rights Management for Streaming Video
  • Brief Description: The ’920 patent relates to methods and devices for decoding encrypted digital content. The core of the claimed invention is a Digital Rights Management (DRM) scheme that uses a three-level key hierarchy (user, content, and frame encryption keys) in combination with the partial encryption of video frames.

3. Grounds for Unpatentability

Ground 1: Obviousness over Chen and Grab-333 - Claims 1 and 10 are obvious over Chen in view of Grab-333.

  • Prior Art Relied Upon: Chen (Application # 2005/0177741) and Grab-333 (Application # 2004/0081333).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Chen teaches a conventional three-level key ladder for a conditional access (CA) system used in video distribution. Chen’s hierarchy of a master key (Km), a work key (Kw), and a scrambling key (Ks) was asserted to map directly to the ’920 patent’s claimed “user encryption key,” “content encryption key,” and “frame encryption key,” respectively. While Chen discloses a complete key hierarchy, it only generally suggests selective scrambling. Grab-333 was argued to supply the missing element of partial encryption, explicitly teaching a method for encrypting only selected portions of video frames and embedding the necessary decryption information (e.g., key pointers, offsets) into a synchronized data stream.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine the teachings of Chen and Grab-333 to create a more computationally efficient DRM system. Petitioner asserted that reducing processing overhead by using partial encryption was a well-known objective in the art. A POSITA would recognize Chen’s key management system and Grab-333’s partial encryption mechanism as complementary, high-level and low-level DRM techniques designed to be used together.
    • Expectation of Success: A POSITA would have a high expectation of success in combining these references, as both address the same field of video DRM and their respective techniques (key ladders and partial encryption) were well-known, compatible, and commonly used to achieve predictable results in securing video content.

Ground 2: Obviousness over Chen, Grab-333, and Candelore - Claims 1-3 and 10-12 are obvious over Chen in view of Grab-333 and Candelore.

  • Prior Art Relied Upon: Chen (Application # 2005/0177741), Grab-333 (Application # 2004/0081333), and Candelore (Application # 2005/0063541).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground builds upon Ground 1 by adding Candelore to provide specific, advantageous implementation details for the Entitlement Management Messages (EMMs) used in Chen's system. Petitioner argued Candelore teaches that EMMs can contain multiple keys, each associated with a unique "key identifier." This directly addresses the limitation in dependent claims 2 and 11, which require encrypted copies of the content encryption key to be "entries in a table." Candelore further teaches content delivery in an interactive network (e.g., Video-on-Demand), where content is sent in response to a request from a subscriber's device, which maps to the limitations of dependent claims 3 and 12.
    • Motivation to Combine: A POSITA implementing the system of Chen and Grab-333 would be motivated to consult a reference like Candelore for established methods of structuring and managing entitlement messages. Candelore provides a compatible and advantageous framework for handling multiple keys within EMMs, a clear improvement for managing keys in a broadcast environment. A POSITA would apply Candelore's teachings to facilitate Chen's goal of secure video distribution in modern streaming and download applications.
    • Expectation of Success: The combination was asserted to be predictable because Candelore provides specific, compatible details for a system component (EMMs) that is already present in Chen. The combination involves applying known data management techniques (key tables) to a known DRM architecture.

Ground 3: Obviousness over Chen, Grab-333, and Kocher - Claims 1, 3, 5-6, 10, 12, and 14-15 are obvious over Chen in view of Grab-333 and Kocher.

  • Prior Art Relied Upon: Chen (Application # 2005/0177741), Grab-333 (Application # 2004/0081333), and Kocher (WO 2005/008385).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground adds Kocher to the base combination of Chen and Grab-333 to teach key management with greater granularity and security. Petitioner contended Kocher discloses a system where media players are initialized with a unique combination of keys, including keys shared among "increasingly large sets of devices within the same group" (e.g., class of device, manufacturer, or player model). This maps to the limitations of claims 5 and 14, which recite a "base encryption key" that is "inherent to the class of devices." Kocher further teaches encrypting digital rights (e.g., rules, licenses) using these shared keys and having the playback device identify and access these rights, satisfying the limitations of claims 6 and 15.
    • Motivation to Combine: A POSITA would be motivated to enhance the security and flexibility of the Chen/Grab-333 system by incorporating Kocher’s more advanced key management scheme. Kocher's system allows content providers to efficiently distribute content and digital rights to specific subsets of devices and to revoke rights for a compromised group without affecting valid users. This provides improved granularity and security over Chen’s system, which relies on a single unique master key per device.
    • Expectation of Success: A POSITA would expect this combination to work successfully, as it involves integrating a known, flexible key management technique (Kocher) with a standard DRM framework (Chen/Grab-333) to yield the predictable result of a more secure and granular system.

4. Arguments Regarding Discretionary Denial

  • Petitioner argued that discretionary denial under §325(d) would be inappropriate. The core reasoning was that none of the primary prior art references (Chen, Candelore, Kocher) or the specific invalidity arguments based upon them were presented to or considered by the Patent Office during the original prosecution of the ’920 patent. While Grab-333 was incorporated by reference in the patent, it was not substantively discussed or applied against the claims.

5. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-3, 5-6, 10-12, and 14-15 of Patent 9,184,920 as unpatentable under 35 U.S.C. §103.