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Gamecards: Difference between revisions

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AriA99 (talk | contribs)
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Describe cart cryptography protocol now that it is confirmed the Switch uses a different protocol
AriA99 (talk | contribs)
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Link to where the 0x200 InitialData comes from, I noticed the pattern looking at the Lotus3 page at Switchbrew
 
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The header command has some initial dummy bytes, and eventually responds with a 0x200 byte header. Here's an example for Lego Starwars 3:
The header command has some initial dummy bytes, and eventually responds with the 0x200 byte [[NCSD#InitialData|InitialData]]. Here's an example for Lego Starwars 3:
  0000000: 00 8c 03 00 00 00 04 00 00 00 00 00 00 00 00 00  ................
  0000000: 00 8c 03 00 00 00 04 00 00 00 00 00 00 00 00 00  ................
  0000010: b3 cf fb c6 6a b1 cb 20 32 af ce 35 d4 1c 74 c9  ....j.. 2..5..t.
  0000010: b3 cf fb c6 6a b1 cb 20 32 af ce 35 d4 1c 74 c9  ....j.. 2..5..t.
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After the 0x82 command, cryptography is initialized, which can be reproduced following this algorithm; unless noted otherwise, all operations are in big endian byte order:
After the 0x82 command, cryptography is initialized, which can be reproduced following this algorithm; unless noted otherwise, all operations are in big endian byte order:


1. Set the [[AES_Registers|AES keyslot 0x3b keyY]] to the values at 0x000:0x010. The corresponding keyX is set in [[Bootloader|Boot9]].
# Set the [[AES_Registers|AES keyslot 0x3b keyY]] to the values at 0x000:0x010. The corresponding keyX is set in [[Bootloader|Boot9]].
2. Decrypt the 16 bytes at 0x010:0x020 using AES-128-CCM in keyslot 0x3b using the 12-byte nonce at 0x030:0x03c to obtain the primary seed; if the response to the 0xa0 command AND 0x00000003 equals 3, instead use slot 0x11 and set the normalkey to 0x00000000000000000000000000000000. Verify that the 16-byte tag at 0x020:0x030 is valid.
# Decrypt the 16 bytes at 0x010:0x020 using AES-128-CCM in keyslot 0x3b using the 12-byte nonce at 0x030:0x03c to obtain the primary seed; if the response to the 0xa0 command AND 0x00000003 equals 3, instead use slot 0x11 and set the normalkey to 0x00000000000000000000000000000000. Verify that the 16-byte tag at 0x020:0x030 is valid.
3. Split the primary seed into two halves: left and right.
# Split the primary seed into two halves: left and right.
4. Initialize a context for the SNOW 2.0 stream cipher. The 128-bit key is the primary seed. The 128-bit IV is a 128-bit static value depending on the gamecard ID2.
# Initialize a context for the SNOW 2.0 stream cipher. The 128-bit key is the primary seed. The 128-bit IV is a 128-bit static value depending on the gamecard ID2.
5. Call the SNOW 2.0 stream cipher 32 times to obtain 1024 bits (32 words) of output. Discard them.
# Call the SNOW 2.0 stream cipher 32 times to obtain 1024 bits (32 words) of output. Discard them.
6. Initialize a context for the RC4 stream cipher. 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 stream.
# Initialize a context for the RC4 stream cipher. 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 stream.
7. Call the RC4 stream cipher 256 times to obtain 2048 bits (256 bytes) of output. Discard them.
# Call the RC4 stream cipher 256 times to obtain 2048 bits (256 bytes) of output. Discard them.


All commands and responses are now encrypted using RC4. The gamecard controller and gamecard itself share the RC4 key and advance the state accordingly.
All commands and responses are now encrypted using RC4. The gamecard controller and gamecard itself share the RC4 key and advance the state accordingly.
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If the 0x83 command is sent, the cryptography is re-keyed:
If the 0x83 command is sent, the cryptography is re-keyed:


1. Initialize a new context for the SNOW 2.0 stream cipher. The 128-bit key consists of the left half of the primary seed followed by the lower 64 bytes of the decrypted 0x83 command. The 128-bit IV is the same 128-bit static value depending on the gamecard ID2 as before.
# Initialize a new context for the SNOW 2.0 stream cipher. The 128-bit key consists of the left half of the primary seed followed by the lower 64 bytes of the decrypted 0x83 command. The 128-bit IV is the same 128-bit static value depending on the gamecard ID2 as before.
2. Call the SNOW 2.0 stream cipher 32 times to obtain 1024 bits (32 words) of output. Discard them.
# Call the SNOW 2.0 stream cipher 32 times to obtain 1024 bits (32 words) of output. Discard them.
3. Initialize a new context for the RC4 stream cipher. The 256-bit key consists of the same 128-bit static value depending on the gamecard ID2 as before followed by four outputs of the new SNOW 2.0 stream.
# Initialize a new context for the RC4 stream cipher. The 256-bit key consists of the same 128-bit static value depending on the gamecard ID2 as before followed by four outputs of the new SNOW 2.0 stream.
4. Call the RC4 stream cipher 256 times to obtain 2048 bits (256 bytes) of output. Discard them.
# Call the RC4 stream cipher 256 times to obtain 2048 bits (256 bytes) of output. Discard them.


The above example commands can be decrypted in this manner.
The above example commands can be decrypted in this manner.


The static values are fixed in the gamecard controller and gamecards themselves, they are not obtained from Process9 or anywhere in NATIVE_FIRM.
The static values are fixed in the gamecard controller and gamecards themselves, they are not obtained from Process9 or anywhere in NATIVE_FIRM.
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