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The application itself (APP), and the title metadata (TMD) is encrypted with a console specific key. This means that Nintendo intended that these files can only be imported back into the same DSi.
The application itself (APP), and the title metadata (TMD) is encrypted with a console specific key. This means that Nintendo intended that these files can only be imported back into the same DSi.
While the banner, the public savegame, and several other metadata blocks are encrypted with a shared key, which means any DSi can inspect these parts of the file.
While the banner, the public savegame, and several other metablocks are encrypted with a shared key, which means any DSi can inspect these parts of the file.
= ES blocks =
An ES block, for lack of a better name, is a commonly used data encryption method on DSi by Nintendo.
It uses AES CCM to encrypt a maximum of 0x20000 bytes of data per time, and extends it with a 32 byte encrypted trail block at the end.
This trail block itself is encrypted with AES CTR, and contains the nonce for decryption and size of the ES block:
0000000: qq qq qq qq qq qq qq qq qq qq qq qq qq qq qq qq
0000010: xx nn nn nn nn nn nn nn nn nn nn nn nn yy yy yy
The counter used for decrypting the trail block is the last 16 bytes of the trailblock, with the first, 12th, 13th and 14th byte set to 0:
00 nn nn nn nn nn nn nn nn nn nn nn nn 00 00 00
After decrypting the trailblock, xx is always 0x3A, and yy is the size of the ES block (excluding the trail block). It is assumed that qq is a MAC (Message Authentication Code), used to verify the contents of the ES block after decryption, but this has not been verified yet.
= B4 block =
= B4 block =