PS2 Executables (CORE)

Applies to: GT3, GT4, TT · Extension: .GT4 / .TT · Endian: Little

Main builds of Gran Turismo and Tourist Trophy will have splitted executables - the main executable named by the game code and another file usually starting with CORE.

The main executable is in charge of processing the second file.

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File Layout

Encryption layer (GT4O)

Field	Offset	Type	Description
Decryption IV	0x00	byte[8]	Decryption IV for the encrypted data
Data	0x00	byte[...]	Encrypted data
CRC Checksum	EOF - 4	Int	CRC starting from 0x00

C#

private static readonly byte[] k = new byte[16]
{
    // "PolyphonyDigital"
    0x05, 0x3A, 0x39, 0x2C, 0x25, 0x3D, 0x3A, 0x3B,
    0x2C, 0x11, 0x3C, 0x32, 0x3C, 0x21, 0x34, 0x39,
};

// The key is encrypted, decrypt it
private static byte[] GetKey()
{
    byte[] key = new byte[16];
    for (int i = 0; i < 16; i++)
        key[i] = (byte)(k[i] ^ 0x55);
    return key;
}

// For decryption of the body:
byte[] iv = sr.ReadBytes(8);
byte[] key = GetKey();
var s = new Salsa20(key, key.Length);
s.SetIV(iv);
s.Decrypt(file.AsSpan(8), file.Length - 12);

Compression layer

Field	Offset	Type	Description
Boot Load Flags	0x00	ushort	Boot load flags (boot device priority?)
Decompressed Size	0x02	uint	Size of the decompressed data
Compressed Data	0x06	byte[]	Compressed data until end of file

Main Header

Field	Offset	Type	Description
First SHA-512 Hash Size	0x00	ushort	First SHA-512 hash size
First SHA-512 Hash	N/A	ushort	First SHA-512 hash
Second SHA-512 Hash Size	N/A	ushort	Second SHA-512 hash size
Second SHA-512 Hash	N/A	ushort	Second SHA-512 hash
Section Count	N/A	Int	Executable section count
Entrypoint	N/A	Int	Entrypoint address for the executable
Sections	N/A	SectionInfo[]	Section Infos

Section Info

Field	Offset	Type	Description
Target Offset	0x00	Int	EE Memory Target Offset
Size	0x04	Int	Size of the section
Data	...	byte[]	Section Data