PAK files

PAK files are checksum-verified packages that contain a full filesystem structure inside them - they store all assets for the game. PAK files can be layered on top of each other - the game will first search for res.pak, then res1.pak, then res2.pak (etc.) while loading PAKs - PAKs are incrementally stacked on top of each other during the loading process - conflicts are ignored, and the PAK with the highest priority is used.

Format

tip

If you're a REHex user, you can download a fully commented out example PAK file from here

File

Size (bytes)	Name	Description	Struct
Variable	Header	File magic, version, data sizes, stamp	Header
Variable	Root directory	Main directory entry, contains all data in the PAK	Entry
4	DATA marker	Marks the start of file content data	DATA marker
Variable	File contents	Actual file data for all files in the PAK	Raw binary data

Header

Size (bytes)	Name	Description	Struct	Condition
3	Magic	"PAK"	ASCII-encoded text	None
1	Version	0x00 or 0x01 - v0 doesn't support stamping, v1 does	Unsigned byte	None
4	Header size	Size of the header - at v0, guaranteed to be >16, at v1, guaranteed to be >80	Signed 32-bit int	None
4	Data size	Size of the data	Signed 32-bit int	None
64	Stamp	Signature based on git commit - see here	ASCII-encoded text	Game >=v35, PAK >=v1

Entry

An Entry can either be a directory or a file, determined by its Flags.

Size (bytes)	Name	Description	Struct
1	Name length	The number of characters in the name.	Unsigned byte
Variable	Name	The name of the entry.	ASCII text
1	Flags	Bit flags that determine the entry type.	Unsigned byte

The Flags field is a bitmask that specifies the properties of the entry:

• &0x01: If this bit is set, the entry is a directory.
• &0x02: If this bit is set, the Position of the file data is represented as a 64-bit long integer.

note

The 0x02 flag cannot generally be found in Dead Cells on any platforms - but it exists here for completeness of the format. Dead Cells also does not handle deserialising this flag, but other Heaps games (such as Wartales) generate such PAKs.

---

If the entry is a directory

Size (bytes)	Name	Description	Struct
4	Entry count	The number of entries inside this directory.	Signed 32-bit int
Variable	Entries	A recursive list of Entry structures.	Entry

---

If the entry is a file

Size (bytes)	Name	Description	Struct
4 or 8	Position	The offset of the file data from the start of the data section. It is a 64-bit long if the &0x02 flag is set; otherwise, it is a 32-bit int.	Signed 32-bit int or 64-bit long
4	Size	The size of the file data in bytes.	Signed 32-bit int
4	Checksum	The Adler32 checksum of the file data.	Signed 32-bit int

DATA marker

Size (bytes)	Name	Description	Struct
4	Marker	ASCII "DATA" to mark start of content	ASCII-encoded text

The DATA marker serves as a separator between the header/directory information and the actual file contents. It helps in clearly delineating the structure of the PAK file and can be used as a reference point when reading or writing PAK files.

Stamps

In v35+ of the game (v1 of the PAK format), PAK files now include "stamps". A stamp is a 64-character (ASCII) digest of a SHA256 hash, generated with this formula (written in pseudocode):

ASCII digest(
    SHA256(
        UTF-8 encode("Dc02&0hQC#G0:"),
        UTF-8 encode(Current git commit - short hash)
    )
)

Due to the deterministic nature of SHA256 and the short length of the commit hash, it is possible to easily brute-force the short hash from a given stamp - an implementation of this exists in Alive Cells' main script, as the commitbrute subcommand. You can also calculate or extract a stamp from a PAK file or from a short hash using the online stamp calculator.