CatSystem2 Key Files

About each Key File

Notes on cs2_gk.dat

Generation

Generation (cs2_gk.dat)

Technical requirements

Code example

GenerateKeyFile

enum KeyFileType {
 Direct, // "direct.dat"
 Key, // "key.dat" (requires volume serial number)
 Cs2DebugKey, // "cs2_debug_key.dat"
 CommonKey, // "key_com.dat"
}
static class Cs2KeyFile {
 // Generate the data of a key file, that can then be saved to a game's installdir
 public static byte[] GenerateKeyFile(KeyFileType keyType, string vcode1) {
 // "open_cs2" encountered with cs2_open.exe Toolset v4.01, not fully understood
 // (Likely used in the absence of /document/APP/v_code in startup.xml)
 // (V_CODE (1) executable resource is ignored... I think)
 if (vcode1 == null)
 vcode1 = "open_cs2";
 //======== GENERATE MERSENNE TWISTER SEED ========
 // Difference for "cs2_debug_key.dat": append "@@--cs2-debug-key--@@"
 if (keyType == KeyFileType.Cs2DebugKey)
 vcode1 += "@@--cs2-debug-key--@@";
 // Difference for "key_com.dat": append "@@--cs2-common-key--@@"
 if (keyType == KeyFileType.CommonKey)
 vcode1 += "@@--cs2-common-key--@@";
 // Use a CRC-32-style checksum (same as in KIF Archives) of vcode for Mersenne Twister seed
 uint vcode1Seed = Util.GenerateTocSeed(vcode1);
 // Difference for "key.dat": add volume serial number (of %WINDOWS% path)
 if (keyType == KeyFileType.Key)
 vcode1Seed += Util.GetVolumeSerialNumber();
 //======== GENERATE BLOWFISH KEY + FILE DATA ========
 // Generate MT PRNG values for the key file's Blowfish key and file data.
 // (I've rarely seen Cs2 generate multiple MT values from one seed)
 uint[] tmpUIntBuffer = uint[32]; // C# workaround without unsafe
 byte[] blowfishKey = new byte[64]; // First 16 MT values
 byte[] fileData = new byte[64]; // Next 16 MT values
 // Generate 32 MT values: Blowfish key (i=0-15), File data (i=16-31)
 MersenneTwister mt = new MersenneTwister();
 mt.SetSeed(vcode1Seed);
 for (int i = 0; i < 32; i++) {
 tmpUIntBuffer[i] = mt.GenRand();
 }
 // C# workaround uint[] -> byte[]: Blowfish key (i=0-63), File data (i=64-127)
 Buffer.BlockCopy(tmpUIntBuffer, 0, blowfishKey, 0, 64); 
 Buffer.BlockCopy(tmpUIntBuffer, 64, fileData, 0, 64);
 //======== ENCRYPT FILE DATA ========
 // Encrypt key file data using generated Blowfish key
 Blowfish bf = new Blowfish();
 blowfish.SetKey(blowfishKey);
 blowfish.Encrypt(fileData, 0, 64); // Encrypt to the same buffer
 return fileData; // Return the now-encrypted data
 }
}

GenerateTocSeed + GetVolumeSerialNumber

static class Util {
 // Same as used in KIFINT archives, (modified CRC-32/BZIP2)
 internal static uint GenerateTocSeed(string vcode) {
 uint crc = 0xffffffff; // Initial value
 for (int i = 0; i < vcode.Length; i++) {
 crc ^= ((uint) vcode[i] << 24);
 for (int j = 0; j < 8; j++) {
 if ((crc & 0x80000000) != 0)
 crc = (crc << 1) ^ 0x04c11db7; // Polynomial
 else
 crc <<= 1;
 }
 crc = ~crc; // Negate very byte instead of at the end
 }
 return crc;
 }
 // Get volume serial number of %Windows% path on the target machine
 internal static uint GetVolumeSerialNumber() {
 // Includes path root, thus is accepted by the WINAPI function
 string rootPathName = Environment.GetFolderPath(Environment.SpecialFolder.Windows);
 // Be aware: there is a difference between hard drive and volume serial numbers
 bool result = NativeMethods.GetVolumeInformation(
 rootPathName,
 null, 0, // (unused parameters)
 out uint volumeSerialNumber,
 out _, out _, null, 0); // (unused parameters)
 if (!result)
 throw new Win32Exception();
 return volumeSerialNumber;
 }
}

NativeMethods

static class NativeMethods {
 // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getvolumeinformationa
 [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
 [return: MarshalAs(UnmanagedType.Bool)]
 internal extern static bool GetVolumeInformation(
 string rootPathName, // only input
 StringBuilder volumeNameBuffer,
 int volumeNameSize,
 out uint volumeSerialNumber,
 out uint maximumComponentLength,
 out uint fileSystemFlags, // flags that we don’t need
 StringBuilder fileSystemNameBuffer,
 int nFileSystemNameSize);
}