

I solved this encrypted BART ad. Can you? - NateLawson
http://sfbart.posterous.com/cryptic-math-ad-explained

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hyperbovine
I guess "Come work for Macrovision!" didn't have the geek appeal they were
seeking.

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tptacek
It should. They have awesome fun problems to solve.

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defen
I'm sure they do, but solving those problems is a means to an end considered
evil (or at least unethical) by many hackers.

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NateLawson
That's kind of like saying you'd never work for MSFT or Apple because both
create DRM. If you're that kind of absolutist, yes, you don't want to work
there. But Rovi is a big company and the Blu-ray content protection system is
quite interesting.

The ultimate equilibrium they will achieve if they do their job properly is
that discs will not be rippable when they first come out, but after a couple
months will get cracked. In that time period, the studio makes 90% of their
lost revenue and you still have the ability to make backups after a delay. BD+
has had its ups and downs, but I think it has the potential to achieve this.
It's more than you can say for most DRM systems.

Disclaimer: I am a co-designer of BD+.

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mmastrac
If studios wanted to preserve that balance, they'd release keys to decrypt the
movies for personal use on a set schedule after release. As it stands right
now, users need to hope that someone will manage to "crack" the next BD+
revision (ie: building up the BD+ emulators to a point where they can pass the
next set of checks) in order to back up or transcode their disks. At times,
the cracking community is further behind than a few months, making these
movies useless outside of the standard player. I can't watch Blu-ray movies on
my MacBook or iPhone at all without ripping them, one of the reasons I haven't
bought a single BR disc to own.

If users knew that a key release is coming on a set date, it would remove a
lot of the motivation for people to work on cracking BD+.

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NateLawson
Where are those libertarian commenters when you need them? This is a classic
example of letting the market decide.

If there is enough demand for cracking a given disc, then users will pay
higher prices for ripping software updates and crackers will put more effort
into it. If no one cares about a given disc, then it may never get ripped (but
no one cares so it doesn't matter).

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mmastrac
Aren't disks cracked in batches though? It seems to my (admittedly not as
familiar as I'd like) eye that there are releases of BD+ reference code pushed
out every few months that make it on to a few dozen titles, big and small.

Maybe publishers should release decryption keys for movies after a few months
out using something akin to the street-performer protocol. :)

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tptacek
We're probably treading close to the line where Nate can't talk about stuff. I
should say that it would seem downright weird to me for them to simply publish
the circumvention to a currently unbroken BD+ VM, or unprotection information
for any protected title.

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tptacek
I am really let down by the answer to this poster.

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kazuya
Is this Jacques Binet?

<http://en.wikipedia.org/wiki/Jacques_Philippe_Marie_Binet>

If so, is it about Fibonacci numbers?

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NateLawson
I know it is solvable because I've done it.

Disclaimer: I did not create it. The source of the ad is one of my customers,
although they gave me no hints to solve it.

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tptacek
You pretty much gave away the answer with the title of the posting, for what
it's worth.

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NateLawson
The most important hint is to realize it is encrypted, not a math equation.

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ahlatimer
That, along with finding out who Binet is (if you weren't already aware),
makes it pretty trivial to solve.

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nabin
Ok so l = map(ord,message) for i in l: a = f(l) And now hat? a is a big
integer, chr(a mod 256)? nothing.. :-/

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ahlatimer
I posted the solution on my blog. If anyone wants to figure it out themselves,
then don't read it.

<http://ahlatimer.wordpress.com/2010/01/12/bart-solution/>

