Transparent CSS Decryption

itachi · #1 14th August 2008, 01:47 PM

Hi, i thought about this for quite a long time ( few months) and tried several approaches (in Theory). Is there a good way to write a Kernel-module that helps (on the Kernel Layer) to decrypt DVDs without extra programs.
What im trying is following: Insert my own Kernel-module(better based on an existing Module which i just modify) and dump an encrypted DVD just with dd like:

Code:

dd if=/dev/dvd of=~/dvd.iso bs=2048

Basically, i'd like to do the same thing AnyDVD does in Windows. As far as i'm understanding this is that Anydvd is a "Filter Driver" that filters the Encrypted Data stream, decrypts it and sends it to whatever device.
-> You can just copy a DVD via the File Browser.
My problem is that in Linux/Unix does not exist this Filterdriver concept.
I came up with 3 approaches:
1: insert some of the DeCSS code into the VFS code( .. check if the Filesystem that is to be read UDF .. parse the data through DeCSS etc.).
Problem .. the VFS Code is in the Kernel, not extra as a Module - I'd like to write it in a way that it is reusable for others easily.
2: insert the DeCSS code into the UDF driver.
Problem: The Source is Waaay to complex for me right now (i have no idea where i should insert the DeCSS code) - don't know if it is even possible.
3: A new Device that accesses the /dev/dvd device.
Problem: I need to learn how to write a Kernel module from scratch ( which means, I need to read a decent book about this .. costs me a few months .. don't have so much time to read so much about this topic).
Any good suggestions?
Thx.

itachi · #2 29th August 2008, 12:31 AM

Hmmm, i know it's not nice to doublepost. But those 100 people that read this thread; is there really no one who attempted something like this, or has any hints?

Dies · #3 29th August 2008, 01:39 AM

I'm one of those people that read your post...

And thought to myself

"Why would you.... hmm... maybe I'm just not smart enough to see the point?"

I've just never had to do anything with a DVD ( copy, play, record ) that made me think it would be so much better if it was a part of the kernel instead of a normal program or library.

I guess I'm just not seeing the big picture or the potential benefits, features of that approach. Maybe if you list a few it would help.

itachi · #4 29th August 2008, 11:12 PM

1: I just got the idea that i'd like to implement something like this. To be honest i felt like coding something "cool" over the summer holidays until the new semester starts at the university. I guess it's a little experiment to test my knowledge/programming skills a bit (unfortunately for now, it's an Epic Fail).
2: It would be easier to just dump a DVD via dd / copy the vob files directly.
3: No extra ripping software needed ( you can copy the dvd like it's not copy protected)
4: .. don't know

.
Basically, it's my effort to kill time a bit, by doing something that may be a bit useful for me.

Scott_fakename · #5 9th September 2008, 05:53 PM

I don't know, do you really want to clutter up your kernel with things that really don't need to be in the kernel? Using DD to copy a disk would be kind of nice, but it's no easier than using, say dvd decrypter. (I don't know any linux DVD copying tools)

It just seems like it's a lot more trouble than it needs to be.

--Scott

libit · #6 28th September 2008, 07:15 AM

Hi Itachi,

first of all, I ended up in this forum because I WAS LOOKING for a decss dvd driver, so clearly I think it would be useful.
In my case the motivation is that there are some linux based media players that use a sigmatel cpu and that cannot do decss. In fact there are usually 2 versions of this sigmatel cpu: one with decss and one without. If you get the one without decss you cannot play original dvds.

The best place to implement this, in my opinion, would be the UDF driver but I agree that it might be quite difficult and probably not accepted into official kernels.
Another idea that comes to mind is that it might be possible to do this using the loopback driver (which is sometimes used to implement encrypted filesystems).

itachi · #7 3rd October 2008, 05:55 PM

Well, there is now way that they would put my maybe modified version of the UDF Driver into the official Kernel, not to mention that this is not my intention. I'll give you details as soon as i have free time to tinker around with that topic again.
@Scott_fakename: It's my decision to clutter up my kernel

and as i've already written, i just wanted try this, so i don't care if it will be useful to anybody or not. In libit's case, it may be useful - a good reason to try it anyway.