How strong is Nintendo’s legal case against Switch emulator Yuzu?

Nintendo has filed a lawsuit against Tropic Haze LLC, the makers of the popular Yuzu emulator that the Switch-maker says is “facilitating piracy at a colossal scale.”

The federal lawsuit—filed Monday in the District Court of Rhode Island and first reported by Stephen Totilo—is the company’s most expansive and significant argument yet against emulation technology that it alleges “turns general computing devices into tools for massive intellectual property infringement of Nintendo and others’ copyrighted works.” Nintendo is asking the court to prevent the developers from working on, promoting, or distributing the Yuzu emulator and requesting significant financial damages under the DMCA.

If successful, the arguments in the case could help overturn years of legal precedent that have protected emulator software itself, even as using those emulators for software piracy has remained illegal.

“Nintendo is still basically taking the position that emulation itself is unlawful,” Foundation Law attorney and digital media specialist Jon Loiterman told Ars. “Though that’s not the core legal theory in this case.”

Just follow these (complicated) instructions

The bulk of Nintendo’s legal argument rests on Yuzu’s ability to break the many layers of encryption that protect Switch software from being copied and/or played by unauthorized users. By using so-called “prod.keys” obtained from legitimate Switch hardware, Yuzu can dynamically decrypt an encrypted Switch game ROM at runtime, which Nintendo argues falls afoul of the Digital Millennium Copyright Act’s prohibition against circumvention of software protections.

Crucially, though, the open source Yuzu emulator itself does not contain a copy of those “prod.keys,” which Nintendo’s lawsuit acknowledges that users need to supply themselves. That makes Yuzu different from the Dolphin emulator, which was taken off Steam last year after Nintendo pointed out that the software itself contains a copy of the Wii Common Key used to decrypt game files.

Absent the inherent ability to break DRM, an emulator would generally be covered by decades of legal precedent establishing the right to emulate one piece of hardware on another using reverse-engineering techniques. But Yuzu’s “bring your own decryption” design is not necessarily a foolproof defense, either.

Nintendo’s lawsuit makes extensive reference to the Quickstart Guide that Yuzu provides on its own distribution site. That guide gives detailed instructions on how to “start playing commercial games” with Yuzu by hacking your (older) Switch to dump decryption keys and/or game files. That guide also includes links to a number of external tools that directly break console and/or game encryption techniques.

“Whether Yuzu can get tagged with [circumvention] simply by providing instructions and guidance and all the rest of it is, I think, the core issue in this case.”

Attorney Jon Loiterman

Through these instructions, Nintendo argues, “the Yuzu developers brazenly acknowledge that using Yuzu necessitates hacking or breaking into a Nintendo Switch.” Nintendo also points to a Yuzu Discord server where emulator developers and users discuss how to get copyrighted games running on the emulator, as well as publicly released telemetry data that shows the developers were aware of widespread use of their emulator for piracy (as the Yuzu devs wrote in June 2023, “Tears of the Kingdom is by far the most played game on Yuzu”).

While Loiterman says that “instructions and guidance are not circumvention,” he added that “the more layers of indirection between Yuzu’s software and activity and distribution of the keys the safer they are. The detailed instructions, the Discord server, and the knowledge of what all this is used for are at least problematic.”

“Whether Yuzu can get tagged with [circumvention] simply by providing instructions and guidance and all the rest of it is, I think, the core issue in this case,” he continued.

In a response on the Yuzu Discord, the development team wrote, “We do not know anything other than the public filing, and we are not able to discuss the matter at this time.”