Difference between revisions of "Uodemo.dat"

Revision as of 11:59, 22 May 2009

This is a custom made archive file for the Ultima Online Gold Demo.

The archive is divided in 2 area's:

 header area (dynamic in size, the size is a multiple of 280 bytes)
 data area (dynamic in size)

The header area consists of minimum 1 header and can contain up to 3000 files. More files are simply not supported by the code. If the filename in the header is equal to "@@@.@@@" then the end of the header area is reached. The end of the header area marks the beginning of the data area.

The file is encrypted using the GOST block cipher. Each header is encrypted separately, the data of each file is encrypted in blocks of 4KB (4096 bytes). The same encryption/decryption key is used for the entire archive.

One header entry is 280 bytes in size.

struct datheader {

 char filename[260];      // 260 is MAX_PATH in Windows
 int32 filepointer;       // this pointer is relative from the beginning of the data area
 int32 maximumsize;       // if set, the file can grow until this size is reached
 int32 isreadyonly;       // 0 = writeable, <> = read-only
 int32 encryptedsize;     // encrypted filesize (not the actual filesize)
 int32 fileposition;      // internally used by uodemo.exe, not relevant for reading from the archive

};

The actual filesize can be obtained by reading the last int32 in the file data after decryption. This means that for a 0 length file, the encrypted size will be atleast be 4 bytes (size of one int32).