Package2

Present in the firmware package titles (0100000000000819, 010000000000081A, 010000000000081B and 010000000000081C) and installed into eMMC storage's BCPKG2 partitions, "package2" contains the Switch kernel and the built-in system modules.

Format

Package2 is distributed in an already encrypted format. Therefore, it's not additionally encrypted when installed into the flash filesystem.

Offset	Size	Description
0x0	0x100	RSA-2048 signature
0x100	0x100	Encrypted header
0x200	Variable	Encrypted body

Encryption

Package2's contents are AES-CTR encrypted with a key known only by TrustZone.

The encrypted header's CTR is stored as it's first 0x10 bytes (offset 0x100). The encrypted body is divided in up to 4 sections, each one with a CTR stored inside the decrypted header.

Header

When decrypted, package2's header is as follows.

Offset	Size	Description
0x0	0x10	Decrypted header's CTR
0x10	0x10	Section 0 CTR
0x20	0x10	Section 1 CTR
0x30	0x10	Section 2 CTR
0x40	0x10	Section 3 CTR
0x50	0x4	Magic "PK21"
0x54	0x4	Unknown
0x58	0x4	Unknown
0x5C	0x2	Version. HighByte must be <{maxver} and LowByte must be >{minver}, where {maxver} and {minver} are constants used by TZ updated with each package1 update.
0x5E	0x2	?
0x60	0x4	Section 0 size
0x64	0x4	Section 1 size
0x68	0x4	Section 2 size
0x6C	0x4	Section 3 size
0x70	0x4	Unknown
0x74	0x4	Unknown
0x78	0x4	Unknown
0x7C	0x4	Unknown
0x80	0x20	SHA-256 hash over encrypted section 0
0xA0	0x20	SHA-256 hash over encrypted section 1
0xC0	0x20	SHA-256 hash over encrypted section 2
0xE0	0x20	SHA-256 hash over encrypted section 3

Each section follows each other immediately and is encrypted with the same key used for encrypting the header.

Section 0

When decrypted, this section contains the plaintext Switch kernel binary.

Section 1

When decrypted, this section contains the built-in system modules encapsulated in a custom format.

INI1

Offset	Type	Description
0x0	u32	Magic "INI1"
0x4	u32	Size
0x8	u32	NumberProcesses
0xC	u32	Zero

KIP1

Kernel internal process?

Offset	Type	Description
0x0	u32	Magic "KIP1"
0x4	char[12]	Name
0x10	u64	TitleId
0x18	u32
0x1C	u32	Flags / etc. Byte3 bit0-2: compression-enable for each section, when set.
0x20	#SectionHeader[3]	Sections
0x50	char[0x20]	Padding
0x70	u64[0x20]	KernelCaps

SectionHeader

Offset	Type	Description
0x0	u32	OutOffset
0x4	u32	DecompressedSize
0x8	u32	CompressedSize
0xC	u32

Compression

The compression used here is BLZ, with a modified footer since 3ds. The footer is now 0xC bytes instead of 0x8, and has the form u32 compressed_data_len; u32 initial_index; u32 additional_len_when_uncompressed;

Section 2

This section has a valid CTR and SHA-256 hash (over NULL) stored in the package2's header, but it's size is always 0. Likely reserved for future expansion.

Section 3

This section is not present (CTR and SHA-256 hash in package2's header are NULL). Likely reserved for future expansion.

Versions

System version	Package1 maxver constant	Package1 minver constant	Package2 version field
2.0.0	0x3	0x4