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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.


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
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

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