Google v. Sonos — Federal Circuit Rejects Broad “Private Key” Infringement Theories

Background

Google accused Sonos smart-speaker systems of infringing patents covering access to protected digital content within a domain of devices. The claims required a private key based on domain information and “utilized by all devices” in the domain. Sonos households can group speakers so they play in sync, but only one player receives and decrypts an encrypted music stream before distributing content to the others.

Google advanced two infringement theories. Under its strong-encryption theory, every speaker indirectly “utilized” the private key because one speaker decrypted content for the group. Under its authentication theory, an authorization token shared among players qualified as a private key even though the token was not used as the key input to a cryptographic algorithm. The district court construed the disputed terms against those theories and granted summary judgment to Sonos.

The Court’s Holding

The Federal Circuit affirmed. On “utilized,” the panel rejected Google’s theory that indirect benefit from another device’s cryptographic operation was enough. Google offered no workable limit separating claimed use from an attenuated connection. The court also favored a construction that avoided injecting uncertainty into the claim’s boundary. Because the other speakers did not themselves use the private key, the strong-encryption theory could not create a triable infringement issue.

The authentication theory failed as well. Read in context, a “private key” was not just any data supplied to a cryptographic algorithm. It had to function as the key input controlling the operation. The claim language and specification consistently distinguished the key from the data on which the algorithm acts, describing the private key as decrypting data or generating signatures. Sonos’s authorization token was never used in that key role.

The panel therefore held that the intrinsic record supported Sonos’s constructions and that the undisputed operation of the accused products entitled Sonos to judgment as a matter of law.

Key Takeaways

• A device does not necessarily “utilize” a key merely because it receives content made available by another device’s use of that key.
• Cryptographic claim terms are interpreted by function and context, not simply by whether information enters an algorithm.
• An infringement theory needs a principled boundary; an undefined concept of indirect use can undermine the proposed construction.

Why It Matters

Connected-device patent disputes frequently involve distributed functions, where one component performs security processing for an entire system. This decision cautions patentees against attributing one device’s cryptographic act to every device that benefits from it unless the claims and specification support that reach. It also gives product designers a clearer distinction between authentication data and a true cryptographic key input.