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The Wii has four basic ways of communicating with the environment -- games on DVDs, savegames on SD card, channels/VCs on SD card and updates downloaded from Internet. All of them need to be protected, for the Wii security model to hold up integrity. Different solutions are in place for all of the ways, even if there are similarities between them.
 
The Wii has four basic ways of communicating with the environment -- games on DVDs, savegames on SD card, channels/VCs on SD card and updates downloaded from Internet. All of them need to be protected, for the Wii security model to hold up integrity. Different solutions are in place for all of the ways, even if there are similarities between them.
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=== DVD discs ===
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=== Game discs ===
The DVDs are encrypted to avoid analysis, and signed to avoid modifications.
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Game discs are encrypted to avoid analysis, and signed to avoid modifications.
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The encryption is a symmetric crypto, 128 bit AES-CBC. Symmetric means that the same key is used for both encryption and decryption.
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The encryption is a symmetric cipher, 128 bit AES-CBC. Symmetric means that the same key is used for both encryption and decryption.
The Wii DVD contains of several partitions. Each partition has its own AES key. This key is stored on the disc, in the partition information, but it is encrypted with the master AES key. So, with the master AES key you can decrypt the partition keys, and with the partition keys you can decrypt the partitions. Lucky for us, the master AES key was extracted by the Tweezer hack.
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Each disc usually contains two or more partitions. Each partition has its own AES key, referred to as a "title key". This key is stored on the disc, inside of a "ticket", but it is encrypted with the master AES key. So, with the master AES key you can decrypt the title keys, and with the title keys you can decrypt the partitions. Lucky for us, the master AES key was extracted by the Tweezer hack.
    
The disc is signed by building SHA-1 hashes of small parts of the disc, then aggregating these hashes into a hierarchical structure, which is finally signed with a asymmetric crypto. This solution is chosen for efficiency, since asymmetric cryptos are extremely slow.
 
The disc is signed by building SHA-1 hashes of small parts of the disc, then aggregating these hashes into a hierarchical structure, which is finally signed with a asymmetric crypto. This solution is chosen for efficiency, since asymmetric cryptos are extremely slow.

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