Key Points

  • The Federal Circuit affirmed summary judgment that Sonos's grouped speakers do not infringe claims 1 and 10 of Google's U.S. Patent No. 7,899,187.
  • The panel held that a device "utilizes" a private key only by decrypting with it, so speakers that play content decrypted by one group member do not utilize that member's key.
  • The panel adopted that narrower construction in part because Google offered no limiting principle for indirect use, and constructions likely to make a claim indefinite should be avoided.
  • The panel held that a "private key" must be the key input to a cryptographic algorithm, which defeated Google's theory that Sonos's streaming authorization token met the limitation.
  • The opinion, written by District Judge J. Campbell Barker sitting by designation, is nonprecedential and did not reach the expert-concession or "based on" issues.

A federal appeals court on Oct. 30 upheld a ruling that Sonos Inc.'s grouped smart speakers do not infringe a Google LLC patent on protecting streamed music. The court held that the patent's requirement that a decryption key be "utilized by all devices" in a group is not met when only one speaker actually decrypts the content.

Google sued Sonos for patent infringement in the Northern District of California, where Judge Edward M. Chen granted Sonos summary judgment of non-infringement. A three-judge panel of the U.S. Court of Appeals for the Federal Circuit affirmed. U.S. District Judge J. Campbell Barker of the Eastern District of Texas, sitting by designation, wrote the nonprecedential opinion for a panel that also included Circuit Judges Stoll and Stark.

The appeal turned on the meaning of two terms in Google's patent, "utilized" and "private key." The panel adopted the narrower reading of each. It held that a device utilizes a private key only by decrypting with it, and that a private key must serve as the key input to a cryptographic algorithm rather than as any input at all. Those two readings disposed of both theories of infringement Google had planned to take to trial.

The patent, U.S. Patent No. 7,899,187, is titled "Domain-Based Digital-Rights Management System with Easy and Secure Device Enrollment." It describes a way to keep unlicensed parties from reaching proprietary content, such as streamed music, by managing a domain of devices tied to one account. Devices inside the domain use a private cryptographic key to decrypt the content. Google asserted claims 1 and 10, which each require the key to be "utilized by all devices within the domain of devices."

Sonos makes smart speakers that stream music from its own service or from third-party services like Pandora or Spotify. Through a Sonos mobile app, which the opinion calls the Controller, customers can group several speakers into a "household" that plays music in sync. Once speakers are grouped, only one receives the encrypted stream. That player uses a unique private key to decrypt the content and then sends it to the others for playback.

Under what Google called its Strong-Encryption Theory, every speaker in the household utilized the key because each played content that one speaker had decrypted. In its reply brief, as quoted by the panel, Google framed the question as whether the players "may indirectly use the private key by having [one] player perform the decryption for them and forward the resulting unencrypted data." Google argued that "[i]nfringement requires nothing more."

Judge Barker wrote that the panel agreed with Sonos. The claim describes a method for registering a new device, he wrote, and it "expressly requires" that the key be utilized by all devices. The specification points the same way. It describes a device that "must access DRM private key" and uses it "to decrypt the content encryption key."

"We find only evidence that supports the idea that a person of ordinary skill in the art would understand that to 'utilize' a private key is to decrypt with it," Barker wrote. The panel also rejected Google's argument from claim differentiation. Google had pointed to claim 6, which adds decrypting a second encryption key with the private key. Barker answered that both claims still require use by all devices, so the difference in scope remains under Sonos's reading.

Sonos had tested Google's reading with analogies, asking whether bus passengers are "utilizing" the driver's key or whether a homeowner "utilizes" the turbines at a hydroelectric plant by turning on the lights at home. The panel declined to decide whether the hypotheticals fairly captured Google's position. But it said that, "to the extent that Sonos's argument is against ambiguity itself, we find the argument persuasive."

"Google argues that indirect use is sufficient for infringement, but Google offers no persuasive limiting principle on when indirect use of a private key would be so 'attenuated' as to be too 'far-fetched' for infringement," Barker wrote, citing the oral argument. The panel invoked its rule that "constructions that are more likely to result in an indefinite claim should be avoided." Because the parties agreed that all but one player per household uses the key only indirectly, the panel held that no genuine factual dispute kept the theory alive.

Google's second route, the Authentication Theory, targeted an authorization token that a streaming service issues to the Controller app. The app shares the token with the speakers, and a speaker added later presents it to the streaming service to authenticate itself. Google contended that the token was a "private key" because it is an input to a cryptographic algorithm. It was undisputed that no Sonos player ever uses the token as a cryptographic key input.

The district court had originally construed the term as "[a] non-public key that is used as an input to a cryptographic algorithm," and Google argued on appeal that this construction was "both correct and sufficient." At summary judgment, the district court instead required a key used "as the key input (rather than solely as the data input)" to such an algorithm. Sonos pointed out that cryptographic algorithms generally take at least two inputs: a key input and a data input.

The panel again sided with Sonos. Barker wrote that the intrinsic record "shows the 'private key' is used only in accordance with its telos—its identity as a cryptographic key." The specification, he wrote, "treats the private key as the required key input to control the cryptographic algorithm rather than the data input that is the object of the algorithm." Sonos's outside evidence on the meaning of the term in cryptography supported the same reading, he added.

Because those two constructions were dispositive, the panel did not reach whether Google's expert had conceded that the Controller app never utilizes the key, or whether the token was "based on" the domain information as both claims require. The panel said it had considered Google's remaining arguments and found them unpersuasive.

The affirmance leaves in place Judge Chen's grant of summary judgment of non-infringement to Sonos in Google's suit, No. 3:20-cv-03845-EMC in the Northern District of California.

Nathan Kelley of Ashurst Perkins Coie US LLP argued for Google. Elizabeth Moulton of Orrick, Herrington & Sutcliffe LLP argued for Sonos.