SLSK

Location
SLSK files can be found in SLB2 as personalized and in SPKGs as non-personalized.

Trailer
The last 0x340 bytes of each SLSK is not personalized and not used in any way.

Secret debug mode
Before the ENC is loaded, there is a check for some secret mode. Note these two ports are used in regular syscon SPI-like communications. However, usually these two pins are used as part of the SPI-like protocol for signaling. But the bootrom does not use the SPI registers at all. It uses some registers that is never seen outside of bootrom. Even though it is logically separate from the SPI ports, it could be physically connected to the same pins although this is unconfirmed. Note that when the secret handshake passes and we are in secret mode, the MBR is read from the gamecard instead (with gamecard auth not enabled, so a regular SD card would work). Additionally, the personalization removal is done using keyslot 0x207 instead of 0x206 (see below) although it is not currently known if 0x207 is console-unique. All the signature checks and HMAC is still performed, so this secret mode cannot be used for running unsigned code. However, Glitching would still work when in the secret debug mode.

See also: Ernie_Firmware.

Remove personalization
First, personalization layer is removed. It uses AES-128-CBC with a derived key and decrypts data at ENC+0xE0 (or ENC+0xD0 if there's no plaintext version) for size of code_size+0x1E0.

There are two possible paths to derive the key used to remove personalization. Normally, the key is derived using keyslot 0x206. There's however an alternative path, triggered in secret debug mode, when instead the keyslot 0x207 is used with a different seed.

Once personalization is removed, the source keys are locked down. Keyslots 0x9, 0x206, 0x207 are locked down completely (leaving only 0xA0 protection). However, keyslot 0x8 allows encryption, this lets update manager SM add personalization layer during update without having to derive the keys itself.

Header RSA check
A key is derived from keyslot 0x344 and put into keyslot 0x20. This key is then immediately used to calculate HMAC-SHA256 over enc header, excluding the RSA sig (typically 0x00 to 0x1C0).

2 bytes are read from keyring slot 0x603 is read. This is the bitmask of allowed RSA public keys (0xFFFF on 1.692). If the mask is zero, a hardcoded RSA modulus is used. Otherwise, it checks enc rsa revision against the mask and if it's allowed, it gets the modulus from keyring RSA storage starting at keyslot 0x700.

The signature is typically located at 0x1C0 and is 0x100 bytes. After calculating powmod, it checks the padding and compares previously calculated HMAC-SHA256 against the contents.

Finally, it protects keyslots 0x700 to 0x77F to disable reading out the modulus.

Metadata decryption and code verification
Using keyslot 0x208+aes_key_revision and metadata buffer (0xE0 offset for 0x20 bytes) the code decryption key is derived and put into keyslot 10. Then, 5 more keys are derived in the same way, using seed data [0x100; 0x19F]. These 5 keys are put into keyslots 11, 12, 13, 14, 15.

Keyslots 0x208, 0x209, 0x20A, 0x20B, 0x20C, 0x20D (all possible AES key revision keys) are protected.

Data at [0x1A0; 0x1C0) is decrypted using keyslot 10. This is HMAC-SHA256 of the code segment. HMAC-SHA256 is calculated over the code segment using keyslot 0x20, then keyslot 0x20 is protected. Finally, the calculated hmac over the encrypted code is compared to the one decrypted in the header.

Protecting the keys
Some keys are protected, depending on bit flags buffer located right after plaintext version string (so, at offset 0x50). However, on the latest 3.68 enc it is all zeroes so no keys should be protected by this function (?)

Decrypting code
Code is decrypted using key 10 and a hard coded IV. Then, the key is protected.

Clear
The remainder (0x1C000 - code_sz) after the decrypted code is cleared with dmac. Dmac regs are also cleared.