I solved this encrypted BART ad. Can you? | Hacker News Reader

I solved this encrypted BART ad. Can you?

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23 pointsNateLawson23 comments

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

It should. They have awesome fun problems to solve.

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

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+.

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+.

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).

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. :)

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.

There's really no need to publish keys if they're eventually cracked anyway. If your goal was to undercut sales of ripping software, why not just release a keygen for their product? It would directly reduce their revenue instead of doing something that hurts your own sales more than the attackers.

NB: Obviously I'm not advocating this, just trying out a thought experiment.

Indeed, except you're talking about a black market with rather severe penalties for those caught participating. Otherwise, you can be sure that what you describe would happen.

DRM and copyright enforcement law are --- for the most part --- orthogonal issues. The RIAA mass enforcement stuff has nothing to do with circumvention.

Their mass lawsuits do not. But I was referring to the DMCA...a BD+ cracker (or whatever is would be called) is illegal software in the U.S.

Research into the BD+ VM isn't illegal. Publishing research isn't illegal. Releasing an easy-to-use circumvention tool is. I don't agree that this is how it should work, but still, we shouldn't tar everyone with the RIAA brush.

At least Microsoft and Apple produce some useful applications. Macrovision is nothing but a preventer of entertainment consumption and fair-use.

Macrovision makes money for its licensees. Money: useful. All allusions to "fair use" aside, I think we all know the score: most of the value they rescue from protected titles was rescued from illegal BitTorrent sharing.

I don't even care, though. I'm just saying, you could do a lot worse as a hacker than to have the CS problems Macrovision gets to grapple with.

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

Is this Jacques Binet?

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

If so, is it about Fibonacci numbers?

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.

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

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

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

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.. :-/

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/

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