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A Brief Look at the 3DS Cartridge Protocol
About a week ago, there has been a little addition to the 3dbrew wiki page about... Continue reading on Wave Alpha.
The 256-bit key consists of a 128-bit static value depending on the gamecard ID2 followed by four outputs of the SNOW 2.0 streamCart controllerKey generationCall the RC4 stream cipher 256 times to obtain and discard 2048 bits (256 bytes) of outputConsoleRekeyPull 8 bytes of random data from the cryptographically secure random number generatorConsoleRekeySend the 8 bytes to the cart and controllerCartRekeyPerform the same steps as the console and cart controller below until the end of the rekey stepCart controllerRekeyInitialize a new context for the SNOW 2.0 stream cipher. AES-CCM is also a fairly unusual choice but avoids the need for GHASH/POLYVAL in hardware compared to AES-GCM, which would have been the primary alternative at the time. Assuming a performant, hardware-oriented implementation of AES, AES-OCB could be used as the primary method of communication with one authentication tag per packet.
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