Duke Grabowski LDT

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LDT

The game Duke Grabowski: Mighty Swashbuckler uses the LDT files to store subtitle data. The files are actually just regular text encoded as little-endian UTF-16 (UTF-16-LE) but with no byte order mark (BOM). However, the files are also encrypted with a simple cipher, likely to thwart casual analysis or modification.

Text Structure

The text inside of the file contains a sequence of subtitles with no line breaks but delimited with the marker <!>. Each subtitle is formatted as such:

Timestamp<!>Duration<!>Subtitle 1<!>Subtitle 2<!>

The timestamp and duration fields are floating point numbers representing seconds.

Cipher

The LDT files are encrypted with a simple cipher. The key to decrypt all of the files is hardcoded in the game's C# binary.

To decrypt the file, process each byte by subtracting successive values from the key:

 For i in 0 .. length(encrypted_LDT)
   decrypted_LDT[i] = encrypted_LDT[i] - (key[i MOD length(key)])

Recovering the Key

To recover the encryption key, either:

1. Decompile the C# game binary.
2. Perform cryptanalysis on an LDT file by exploiting the knowledge that many of the odd characters in the plaintext are 0 (since most of the characters are in the ASCII range) and that the delimiter "<!>" occurs frequently in the plaintext.