[MPlayer-users] [OT] AC3 vs. DTS

[Ivan Kalvachev]

On 8/2/05, Giacomo Comes <comes at naic.edu> wrote:
> On Mon, Aug 01, 2005 at 05:14:33PM -0400, Rich Felker wrote:
> > On Mon, Aug 01, 2005 at 03:58:11PM -0400, Giacomo Comes wrote:
> > > On Mon, Aug 01, 2005 at 02:12:36PM -0400, Rich Felker wrote:
> > > > On Mon, Aug 01, 2005 at 11:43:00AM -0400, Giacomo Comes wrote:
> > > > > > > For the future I'm still waiting for the next big thing, since I'm not
> > > > > > > that happy with the heavily protected new HD formats. I still want to be
> > > > > >
> > > > > > Heavily protected? Any cryptography where the attacker has the key is
> > > > > > not heavily protected, it's just basic obscuring/obfuscation and will
> > > > > > be cracked in no time, just like CSS.
> > > > >
> > > > > That's completly false. You are talking only about weak encription
> > > > > algorithms like CSS. CSS was a "secret" algorithm. Once people understood
> > > > > how it was working (knowing some keys) they found how weak it was
> > > > > and how to guess the keys analizing the encrypted data (what libdvdcss does).
> > > >
> > > > You fucking didn't read what I wrote. If you can play the movie, YOU
> > > > HAVE THE KEY. DRM/"content protection" is always obfuscation, not
> > > > cryptography.
> > >
> > > It seems that I make you angry, because you start insulting people.
> >
> > Not insulting, just yelling. And it's because you called my statements
> > false when you apparently have no clue about crypto.
> 
> I was thinking the same about you :-)
> 
> > > Anyway I read what you wrote. I just want to remember you that CSS
> > > was not cracked in no time. It took some years after the introduction of
> > > the DVD technology, and the crackers succeed because they found a key not
> > > obfuscated in a software player.
> >
> > DVD was cracked way before DVD drives were common in computers. Before
> > that, there was really very little motivation:
> >
> > 1. Compression software and bandwidth for distributing movies over the
> >    net were severely lacking at the time, so the warez scene had
> >    little motive. Most people were sharing analog-captured .asf and
> >    .rm files if anything at all.. :)
> >
> > 2. Since few computers had DVD drives, no one cared if they could play
> >    their DVDs on their non-windows computer.
> >
> > The digital media scene on the net is much more developed now, and I'm
> > confident that competent people will attack whatever new crap they
> > throw at us quickly and liberate it as well.
> >
> > > In your statement you say that knowing a key "will make the cryptography
> > > be cracked in no time"
> > > That's only valid if the encryption algorithm is weak.
> >
> > No, this statement is blatently false. Assuming you know the key (or
> > have it somewhere and just haven't found it), the only factors making
> > it difficult to crack the 'protection' are the level of obfuscation of
> > the key and the level of obfuscation of the encryption (i.e. using an
> > encryption method that's not well-known). Both of these are matters of
> > security through obscurity. The weakness or strength of the encryption
> > itself is always irrelevant when the only security comes from
> > obscurity.
> 
> Looks like you were thinking about circumventing a protection,
> but you were talking about breaking cryptography.
> Circumventing a 'protection' is one thing, it can be easy.
> Breaking a cryptograph algorithm is another thing.
> libdvdcss does not circumvent CSS, it breaks the weak algorithm.
> 

Well take a look here
 http://www-2.cs.cmu.edu/~dst/DeCSS/Gallery/
 http://www.cs.cmu.edu/~dst/DeCSS/FrankStevenson/analysis.html

CSS is weak algo (40bit) because USA doesn't allowed export of
stronger encryptions at the time .

Anyway the point here is that CSS itself is not bruteforced. The weak
point of DVD is the way keys are stored. As you can read in the
annalys, it requares only 2^17 tries to find matching key (18 second
bruteforce on P2-450MHz).
Not only that, once a key is found we could get all available keys, as
they are stored on the DVD too.

Well an chain is as strong as it weakest branch. 
>From this point of view, no cryptography algorithm could be used as
DRM scheme because the attacker and the reciver are same person.
The reciver need the key to legetimely use the content . Once it have
it, he could become attacker and copy the content.
Even unsymetric key systems ( e.g. RSA ) could not help because
attacker will have the decoding key (in order to use the content
legetimely).

The only protection is obfiscation of the key.
Encrypting the key just bring the question "What to do with the key
for the key?"

Wish You Good Luck
  Ivan Kalvachev
 iive

P.S.
About DTS vs DD, I had read few articles (from both sides) it looks
like the main difference is the LFE, on encoder side. DTS seem to be
louder and this perceived as better.