Crypto & Archives

DDON packages a majority of its client resources inside .arc (archive) files. The project supports two archive variants, one of which requires Blowfish decryption and zlib decompression.

Archive Formats

Magic	Format	Deserializer	Description
ARCC	Encrypted archive	EncryptedArchiveDeserializer	Resources are individually Blowfish-encrypted and zlib-compressed
ARCS	Reference archive	ReferenceArchiveDeserializer	Resources are referenced via IDs

Both share:

• Version: 7
• Version byte length: 2 (u16)
• Extension: .arc
• Enum: ClientResourceFileExtension.rArchive

They are distinguished by the magic string and registered as two separate entries in addCommonResourceMapping():

new ClientResourceFile<>(rArchive,new

FileHeader("ARCC",7,2), new

EncryptedArchiveDeserializer());
        new ClientResourceFile<>(rArchive,new

FileHeader("ARCS",7,2), new

ReferenceArchiveDeserializer());

Encrypted Archive Pipeline (ARCC)

ResourceInfo Structure

Each resource entry is described by an 80-byte encrypted header:

Field	Offset	Size	Description
Path	0	64 bytes	Null-terminated string, internal archive path
Type	64	4 bytes (u32)	JamCRC hash of the resource type name
DataSize	68	4 bytes (u32)	Size of the compressed+encrypted data blob
Flags	72	4 bytes (u32)	Bitfield: OriginalSize (bits 0-28), Quality (bits 29-31)
Offset	76	4 bytes (u32)	Offset to the data blob (from a base of 0x8000)

File Extension Resolution

The Type field is a JamCRC hash. To determine the file extension:

String typeName = FrameworkResourcesUtil.getFrameworkResourceClassNameByCrc(resourceInfo.getType());
String extension = FrameworkResourcesUtil.getFileExtension(typeName);
// e.g., Type=0x242BB29A → "rGUIMessage" → ".gmd"

Crypto Utilities

Blowfish (BlowFishUtil / BlowFishCompat)

Located in org.sehkah.ddon.tools.extractor.api.crypto:

Class	Purpose
BlowFishUtil	Static decrypt(byte[]) method using a hardcoded key.
BlowFishCompat	BouncyCastle-based Blowfish implementation. Handles padding and ECB mode.

The Blowfish key is compiled into the application (derived from the game client's known encryption key).

Zlib (ZipUtil)

public class ZipUtil {
    public static byte[] decompress(byte[] data, int originalSize) { ...}
}

Uses java.util.zip.Inflater to decompress zlib-compressed data. The originalSize parameter is used to allocate the output buffer and verify the decompressed result.

JamCRC (CrcUtil)

public class CrcUtil {
    public static long jamCrc(String input) { ...}
}

Computes the JamCRC hash (a variant of CRC32 with inverted final XOR) used by the MT Framework engine to identify resource types. This is used by:

• FrameworkResourcesUtil to build the JamCRC → class name lookup table at startup.
• ClientResourceFileExtension to map enum values to their JamCRC identifiers.

Archive Entity Structure

The deserialized Archive object contains:

1. resourceInfos — metadata about each packed file.
2. resourceFileMap — the actual decompressed/decrypted file contents keyed by their full path (including resolved extension).

Archive Unpacking (CLI)

The CLI's ArchiveUnpacker utility handles writing the archive contents to disk:

1. Deserializes the .arc file using the appropriate archive deserializer.
2. Iterates over resourceFileMap entries.
3. Creates the directory structure mirroring the archive's internal paths.
4. Writes each file's raw bytes to disk.
5. Generates a descriptive metadata file for the archive.

This is triggered by the -u (--unpack-archives) flag. When combined with -x (--unpack-archives-exclusively), only .arc files are processed and all other file types are skipped.