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

Rich Felker dalias at aerifal.cx
Tue Aug 2 02:01:35 CEST 2005

On Mon, Aug 01, 2005 at 05:46:23PM -0400, Giacomo Comes wrote:
> > > 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.

No, I was never talking about breaking cryptography. That's totally
unnecessary if you have the key. All I was talking about was getting a
way to read protected discs.

> 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.

I agree totally, but it's not necessary to break the weak algorithm.
That was just done to avoid distributing the salvaged key since some
people hypothesized the DVD people could claim copyright on the key.
FYI, the original DeCSS _DID_ use the salvaged key. Only modern
libdvdcss does the cracking.


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