VobDec+ 0.31 (unofficial) - VOB Decryption Utility
-----------------------------------

VobDec is a utility that decrypts VOBs that have been encrypted using CSS.

Unlike DVD rippers, it does not need to get the decryption key from the
DVD drive, but actually derives the key from the encrypted VOB itself using
a cryptographic attack.

This means that once you can read the VOBs (after the drive has been
authenticated) VobDec should work. This may be useful for people who have
problems with DVD rippers, or those who must disable DMA to get them to work.

VobDec can even decrypt a VOB that has been copied encrypted to the hard
drive.

DVDs, Titles and Keys
---------------------

The VOB files on a DVD are of the form VTS_XX_Y.VOB, where XX is the title
number and Y is the file number within the title. So a single DVD can hold
up to 99 different titles.

The important thing to know is that each title can have a different key.
Older DVDs often had all titles encrypted with the same key, so you only
needed to find one key, and that would allow you to decrypt the entire disk.

Newer DVDs have each title encrypted with a different key. With these DVDs,
you must find the key for each title that you wish to decrypt. If you 
decrypt a title with the wrong key, the output file will be scrambled and
unusable.


Example 1 - Determining a title key from an encrypted VOB
---------------------------------------------------------

To determine the title key used to encrypt a VOB, run VobDec with the
filename of an encrypted VOB as the only parameter:

	vobdec d:\video_ts\vts_01_1.vob

VobDec will scan through the VOB and try to determine the decryption key.
When the key is determined it will be displayed:

	key: 41 4B B2 99 C0


Example 2 - Determining a title key and decrypting a VOB
--------------------------------------------------------

To determine the title key and decrypt a VOB, run VobDec as follows:

	vobdec d:\video_ts\vts_01_1.vob output.vob

VobDec will first scan the VOB to find the key, then will use this key to
decrypt the VOB and save it unencrypted as 'output.vob'.


Example 3 - Decrypting a VOB using a known key
----------------------------------------------

If you know the title key, you can skip the scanning part and go straight
to the decrypting part. Run VobDec as:

	vobdec d:\video_ts\vts_01_1.vob output.vob 41 4B B2 99 C0

With the five key bytes on the command line. VobDec will use this key to
decrypt the VOB.

All VOBs in the same title have the same key. So once you scan the first VOB
and get a key, you can use this method to avoid scanning the others.


Possible Problems
-----------------

VobDec may have a problem determining the DVD key in some cases. This is
especially true if the VOB is very small. If VobDec cannot find the key from
one VOB, try another. Remember, once you have a key, you can use it on all
the VOBs that make up that title. If you have an older DVD, the one key may
work on all VOBs on the disk.


Version History
---------------

+0.311 	- ac3 only ripping possible now
	- ac3 stream merged into 1 file
	- multiangle fix for Matrix (region 1)

+0.31	- multiangle detection and ripping (Matrix,Rock,Insider..)
	- fixed bug in AC3 stream output
	- DODs-Rip used for automatic DVD authentication
	- AC3-stream ripping along with DVD-rip possible
	- continue search on next vobs until key is found
	- skip keyscan to next vobfile for faster key retrieving
	- up to 4 parallel audiostreams dump possible
	- any vts files selectable with 'short' commands 
	- key passing to 'short' commands possible

0.3++   - got rid of minor bugs
	- introduced new hidden bugs
	- really fast backward search for CELL-IDs when dumping to file
	- truncation of files by lba
	- AC3 languages detection from DVD
	- AC3 streaminfo from file
	- fast dumping of AC3 streams to file
	- merging any files
	- remove macrovision bytes from vob
	- regionfree patch for Video_ts.ifo Video_ts.bup files
	- option for skipping keysearch for undecrypted DVDs

0.3+	- automatic detection of DVD drive/path
	- detection of region free disks -> ask for key search is skipped because most disks are not encrypted
 	- write multiple/single files with only 1 option
	- merge files [x option]
	- Windows writefile API is now being called - this should enable files > 4GB? - not tested
	- time and percentage info
	- ask for append/overwrite files
	- dumping/truncation of file from given LBA number
	- fast search for CELL-IDs (needed for correct split of VOB)
  	- 'q' for clean process abortion

0.3s	- Now comes with source

0.3	- Fixed a bug that caused the wrong key to be reported on about
	  0.2% of VOBs.
	- Updated documentation to talk about different title keys.

0.2	- Fixed a bug that caused the LFSRs to be initialised improperly
	  if the key was specified on the command line

0.1	- First release