On 30 October the US Court of Appeals for the Federal Circuit affirmed summary judgment of non-infringement in Google v. Sonos (No. 2025-1346), an appeal from the Northern District of California. Google said Sonos smart speakers infringed its U.S. Patent No. 7,899,187, but both infringement theories failed on claim construction. The decision is nonprecedential and limited to this patent and this appeal.
## The patent
The '187 patent, titled "Domain-Based Digital-Rights Management System with Easy and Secure Device Enrollment", groups devices on one account into a domain that shares protected content, using a private key to decrypt it.
Asserted independent claims 1 and 10 both require the private key to be "utilized by all devices within the domain of devices".
One speaker decrypting is not all devices utilizing
When Sonos speakers are grouped, only one receives the encrypted stream, decrypts it with its private key and forwards the decrypted content to the others. Google argued the others indirectly utilized the key. The court disagreed: read with the specification, to utilize a private key is to decrypt with it. Google also offered no limiting principle for when indirect use becomes too attenuated, and constructions likely to make a claim indefinite should be avoided.
An authorization token is not a private key
To connect to a streaming service, Sonos obtains an authorization token and shares it among the speakers. Google argued the token satisfied the private-key limitation because it is an input to a cryptographic algorithm. The court upheld the construction that a private key must be the key input, not merely a data input, and it was undisputed that Sonos never uses the token as a key input.
What the court left open
Because both constructions were dispositive, the court did not reach whether Google's expert conceded that the controller app does not utilize the key, or whether the token is "based on" domain information.
J&C recommends that drafters of multi-device patent claims test limitations such as "all devices" or "each device" against real product architectures. Where one device commonly decrypts and forwards content, add a claim set covering one device decrypting and others receiving and playing, and state in the specification whether a "key" is meant as the key input or a data input.
Source: www.cafc.uscourts.gov
