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The first one is something called Digital Rights Management technology, which is
predicated on the idea that you can give someone material and then control how
they use it, and stop them from copying it: that you can deliver it to their
computer but then stop them from using it, and this fails some fairly elementary
logical examination. If you know a little about cryptography, it just all kind
of falls to bits.
The historic model for cryptography involves an attacker, a receiver and a
sender. And the attacker, the receiver and the sender are in this triad where
the sender and the receiver want to get a message to each other without the
attacker receiving it, or decrypting it - knowing what the message is. So
everybody is assumed to know what the message is in its scrambled form. This
dates back to the Bletchley Park era in WWII when we went from delivering
messages on paper, or in the era of the Caesar we deliver the messages by
shaving the head of the messenger and tattooing it on their scalp, and waiting
for their hair to grow back and then sending them off. So the message was a
secret back then. After the advent of radio it was kind of a non-starter to
assume that the message itself was secret. So we presume that everyone is in
possession of the message - the attacker, the sender and the receiver - in its
scrambled form.
We also presume that everybody knows the system by which the message was
scrambled, the 'cypher' - and this again dates back to the Bletchley Park era -
the WWII era of codebreaking where it was discovered that the mathematicians who
developed the German cipher, the 'Enigma' cypher, had made some flaws in their
maths that allowed the Polish and British cryptographers working on this to
uncover those flaws and silently decrypt all of their messages, and chortle as
they read about what Hitler was having for breakfast that morning.
At the end of the war, the cryptographers who figured this stuff out gave
themselves a long hard look, and realised that anyone could design a security
system that was so fiendishly clever that they themselves couldn't break it, but
unless they were the smartest person in the world, all they'd determined was
that they had built a security system that people dumber than them would be
foiled by, and it would do them no good if anyone smarter than them happened to
come along. So they hit on the strategy of disclosing the system by which the
messages were scrambled, the cypher, sending them out to as many mathematicians
and smart people as they could find, in the hopes that those people would
discover the flaws in it, so that they could be fixed.
This is standard operating procedure today. If you use a cypher, chances are
that you use a cypher that everyone else uses, it's publicly known, it's
publicly disclosed. The MI5, the CIA, Bin Laden, Amazon.com, your bank and
child pornographers all use the same cypher, because to use your own cypher that
you haven't subjected to this kind of rigorous, long-term attack by smart
mathematicians is to invite the fate of the axis powers during WWII.
So you assume that the attacker, the sender and the receiver have the scrambled
message and the cypher, so how do you keep the message secret from the attacker?
Well, the way that you keep it secret is by having a secret key - a very short
piece of information that, when combined with the cypher and the cyphertext,
pops out the cleartext. So you have the message in cyphertext, you have the
cypher, and you have the key - and if you have all three of those, you can make
the message pop out, but if you are lacking one of them then the message is kept
a secret. So the key is known to the sender and the receiver and kept a secret
from the attacker.
Well, that works in regular cryptography. It's how you do your online banking,
it's how Al-Qaeda does its online stuff, its how MI5 communicates, its how we
all do our thing.
In DRM, though, the idea is that you can take the attacker (that's you, the
person who owns the DVD, or owns the iPhone app, or owns the iTune download or
owns the Zune song, or owns the game on your Xbox) - you can take the attacker,
and give the attacker the cyphertext (that's the scrambled message on the DVD,
or the game, or the iTune), let that attacker know what the cypher is (because
that's published), and then embed the key for decrypting the message on the
attacker's device. So in your iPhone, in your PC, on your Xbox, is the key
that's used to decrypt the message, and then what you can do is pretend that the
attacker who has the key sat there in his sitting room, where he has access to
every conceivable piece of equipment without any oversight or surveillance, will
never, ever, ever get the key out of the device. That no-one will ever extract
the key from the device and publish it on the Internet, and fifty million other
people will get access to it, and then everyone will sit around decoding your
messages, and you'll be Hitler in a bunker, and they'll be Bletchley Park. This
turns out not to work very well.
There's a reason that giant IT companies and entertainment companies spend a
decade and a billion dollars developing these fiendishly clever DRM schemes that
are then broken by teenagers in a morning for fun. It's not because the people
who work for these companies are stupid, it's because they're trying to keep
something a secret after telling you what it is, and it's very hard to keep
something a secret when you actually tell millions of people this bit of
information in the form of a little hidden bit on their Xbox, or what have you.
So to show you how vulnerable this is, a guy (I assume it's a guy) named
Muesli64 - a person of such fearsome ability that he named himself after a
breakfast cereal - extracted a key from the DVDHD player. And it's worth noting
here, that where you have a DRM that's across multiple devices like a DVD player
where you've got hundreds of DVD vendors, each of which embed the key in their
device, all you need to do is break the weakest of those DVD players - the worst
implemented one - and they all fall down. You can now extract the keys from all
the DVDs. So he found a software DVDHD player, extracted the keys and published
them online. It was hilarious, the entertainment industry argued that this long
number - 128 bit number - was a trade secret and that no-one was allowed to
publish it, and there were like fourteen million copies on the Internet, and
they were still saying no-one's allowed to publish it because it's still secret,
and it was kind of ridiculous and funny for a couple of days.
And then someone sent an email to Muesli64 or on a message board said, "You
know, I don't have a DVDHD player, I've got a Blu-Ray player. Do you think you
could break that?" And he said, "I don't actually have a Blu-Ray player, so I
don't know, but tell you what; if you just send me the contents of RAM while
you're playing a Blu-Ray movie on your computer - just send me the RAM dump, the
two gigabytes out of your computer's RAM - I'll just have a look and see what I
can do." And what he did was he reasoned that somewhere in this two gigabytes
was the 128 bit key that was decrypting the video on the screen, so he started
at position one, and took the first 128 bits and tried to decrypt the rest of
memory to see if a DVD fell out, and none did, so then he moved to position two,
position three... It took him about two hours. He'd never actually seen or
touched a Blu-Ray player and like Mycroft Holmes sitting in his cellar he
managed to undo the workings of half a decade's worth of security research in
the seriousness and gravitas that accompanies a man who names himself after a
breakfast cereal.
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