Case 1:24-cv-00082-JJM-LDADocument 1Filed 02/26/24Page 12 of 41 PageID #: 12
console uses a cryptographic key to verify that Nintendo in fact signed that game file using a secret key.
33. Second, each game is encrypted. Nintendo uses industry-standard AES-128 encryption for each of its game files, or “ROMs,”[1] which makes the game file useless unless the user possesses the specific cryptographic key to decrypt it, a key created by and known only to Nintendo in the ordinary course of operation. The key that unlocks a particular game’s encryption, sometimes called a title key for a Nintendo eShop game or a content key for a physical cartridge game (title key and content key shall be collectively referred to herein as the “Title Key”), is distributed by Nintendo with the game file in encrypted form. In other words, the key to unlock the game file is itself encrypted with another cryptographic key. In the case of physical cartridge games, the Title Key is stored in a header of the game file and is encrypted twice: the console first decrypts the file header, extracts the still-encrypted Title Key, and then decrypts the Title Key. In the case of Nintendo eShop games, the Title Key is stored outside the game ROM in its own file (a “ticket”); that Title Key too is encrypted twice but the console actually must perform three decryption operations to get it: the console decrypts the file header to get the ID for the ticket, then finds the ticket which contains a double-encrypted Title Key and decrypts it twice using two separate keys available to the console. Keys used by the console to perform these and other decryption steps and to ultimately produce the decrypted Title Key are part of a set of secured keys on a Nintendo Switch commonly referred to as the “prod.keys.”[2] As noted above, the Title Key is the final key needed to decrypt the game and thus to play the game. Together, the encryption unlocked by the Title Key and prod.keys, including the secret and proprietary process by which authorized Nintendo games are unlocked
- ↑ ROM stands for read-only memory.
- ↑ Each act of decryption discussed herein—along with additional decryption operations performed by the console in the ordinary course and by Yuzu to decrypt a given game—relies on a different cryptographic key, each of which is only available to the console, or extracted in a file called the “prod.keys.”
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