SLSK

Offset	Size	Description
0x0	0x4	0x64B2C8E5 magic
0x4	0x4	Offset to code
0x8	0x4	Size of plaintext version string, 0 on 0.931, 0x10 on other
0xC	0x4	Size of unknown block, only seen as 0
0x10	0x4	Code size
0x14	0x2	AES key revision, possible values 0 to 5
0x16	0x2	Public key revision, possible values 0 to 15
0x18	0x8	Unknown/zero
0x20	0x20	sha256 hash of decrypted body
0x40	0x10	Version in ASCII, not present on 0.931
0x50 (0x40 on 0.931)	0x90	Zero
0xE0 (0xD0 on 0.931)	Until Data	Encrypted Header

Encrypted Header

At offset 0xE0 there is a 0x1E0 sized buffer that is speculated to be an encrypted header. For any given firmware version, secure_kernel.enc/second_loader.enc and secure_kernel.enp/second_loader.enp share the first 0xC0 bytes. For non-retail PUPs, each SLSK share the first 0xC0 bytes as observed in 0.931, 0.995, 1.000.41. Similarly in retail PUPs, each SLSK also share the first 0xC0 bytes as observed in 1.05 and 3.60. However, the bytes differ from retail and non-retail SLSK.

There is likely a 0xC0 sized "common" header that is shared by every firmware and by both secure_kernel and second_loader but different between retail and non-retail builds. Then there is likely a 0x20 byte section that is unique per SLSK (maybe contains version, size, load offset, etc). Then a 0x100 byte RSA-2048 signature of the header.

Signature

The last 0x340 bytes of each SLSK is not personalized. For both secure_kernel and second_loader, both the enc and enp variants share the last 0x340 bytes (although they differ from each other and across firmwares). This is likely the signature and might also contain certificates.

Bootrom enc loading process

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 alternative path, triggered in secret debug mode, when instead the keyslot 0x207 is used with a different plaintext.