Slashdot Mirror
HDCP Break Proven
zavyman writes: "I just noticed at Cryptome that the flaws in HDCP posted to Slashdot earlier this year, which one person refused to disclose due to possible threats from the DMCA, have been made public by different authors. Scott Crosby of Carnegie Mellon University, Ian Goldberg of Zero Knowledge Systems, and Robert Johnson, Dawn Song, and David Wagner of UC Berkeley have published a formal cryptanalysis of the High-bandwidth Digital Content Protection System that proves its fatal flaws. Interesting reading for those with some background with cryptanalysis."
I guess this means we need to start pooling bail money then, huh?
--nbvb
They belived a salesman. They don't know how get independent verification. They don't do the needed research. They... OOooo! a shiny object.
The DMCA aims not only to protect companies who use crappy encryption from hackers, it aims to hide from the general public the potential dangers of using encryption that could have been deliberately made to be crackable. So the government could release some (easily crackable) encryption standard that gets added to a lot of hardware and software but the people won't know that their privacy could be easily violated because it would be illegal to try to crack the system. This then makes people vulnerable.
Perhaps I just thought of something that everyone knows already, but I wanted to voice it nonetheless.
Just in case the origonal authors' fears are justified, I've mirrored the page here [http://lookingglass.akardam.net/mirrored/hdcp-wea kness/hdcp111901.htm for the link wary].
Mirror early, mirror often.
From a part-time mathematician's perspective (ok, actually a physicist) this was the line that just made my jaw drop. What were they thinking?! If this text is correct, this algorithm may as well have been designed by a high-school student.
As several people have pointed out already, this is really one of the big threats of the DMCA -- that companies will go around using incredibly poor standards like this, and be immune to any pressure to improve their quality because their customers are legally forbidden to ask what they are receiving. It says a great deal about the present legal climate that anyone could get away with a mess like this cryptosystem in a commercial product.
*sigh*
Perhaps they didn't realize it was a linear system. Many cryptosystems are broken when someone figures out "but your incredibly complex system is really mostly just doing X", for some well-known mathematical construct "X". Real cryptographers have made similar mistakes in the dim past, although in 2001, it is perhaps a little late for repeating this particular one.
(This is the author of the slides, BTW)
Intel wanted a scheme that could be implemented in under 10,000 gates. IMHO, the designers were aware of the flaw, though not necessarily of the full impact of the flaw. Some of the attacks are subtle.
There were two versions posted on cryptome, the second (latex2html, much easier to read) omitted this statement the first version had:
h acks.html), and myself (www.cryptome.org/hdcp-weakness.htm). The last two have been available publically for 3 months and 3 weeks prior to Neils Ferguson's declaration. Neils declaration and the skylarov case were an eye-openeer for me and made fully realize what I had done, and what negative consequences I was in danger of experiencing.
`` The attacks on HDCP are neither complicated nor difficult. They are basic linear algebra. Thus, there have been at least 4 independent discoveries of these flaws. The four I know of are my co-authors, Neils Ferguson, Keith Irwin (http://www.angelfire.com/realm/keithirwin/HDCPAt
What wrathful gods one risks angering by a 20 minute straightforward application of 40 year old math. This was an accident, not a habit. Like other researchers, I do not want to be smited and thus do not expect to analyze any more such schemes as long as the DMCA exists in its current form.
(This statement is my own and does not represent the opinions of my co-authors.)''
So, for those of you who watch cryptome, I broke it there about 3 days after it was leaked, 6 months ago. Keith Irwin also put his observations up 3 months ago. All of this predates skylarov and ferguson.
So, this is only the official version of the break, the slides I presented 2 weeks ago.
I broke it over 6 months ago, go look at the cryptome archives, where its been sitting since May 9th.
:)
I know of at least 4 researchers who have independently discovered the flaws. (See my other slashdot post).
After Skylarov and Ferguson, I was reluctant to point out that my work had been sitting around on cryptome since May. I suspect Keith Irwin felt similarily.
Neils wasn't the first to go public or even second, though he did raise a wonderful stink.
This is pretty basic, but for those who don't know, HDCP is the encryption scheme of choice for HDTV video signals. This is fairly huge news that it has been broken since all TV's and broadcasts in the US will supposedly eventually switch to the HDTV standard. Unless they pull a fast one and switch the standard (which would alienate everyone who has already bought expensive HDTV equipment), this means that DMCA or not, people are going to have guaranteed access to plaintext HDTV signals for as long as the standard is in use. Of course, I'm personally hoping that the DMCA is at least re-written, preferrably scuttled altogether.
I'm sure everyone in NSA shares your educated opinion.
Most likely, NSA fully subscribes to this idea and promotes peer review of top-secret work. They have plenty of scientists with security clearances for that. If NSA doesn't send a paper for review to me or to you it doesn't mean that someone else, better qualified, doesn't look at it.
For this purpose, it doesn't need to be mathematically valid, any more than a cash register needs to be fireproof and have a 28-digit combination lock. All that a cash register needs is to have a door that closes and stays closed. This means that you can't have things move from the cash register into your pocket by accident.
If there was a vulnerability in the standard which meant that you could access the signals without trying to, that would be bad news. As it is, the signals are only accessible by those who want to consciously make equipment designed for the purpose of veiwing them, which has no legitimate alternative use. In other words, the "crack" of this standard only refers to an attack which is against the laws relating to theft (in this case the DMCA).
This is not a "bad" or "stupid" encryption system; it's just an example of a company using the laws which protect them to cut a cost corner. After all, if one could trust people to pay for what they watched, they wouldn't need to encrypt the signal at all.
For a bunch of self-styled "engineers", slashdot has a really hard time understanding the basic concept of "fit for purpose".
-- the most controversial site on the Web
There was a story a couple days ago about IBM's crypto box being broken. That was broken by tricking the box to use a weak 3DES key which was equivalent to a 1DES key and brute forcing that.
The bruteforcing took 2 days on a sub $2000 FPGA running their published wiring schema.
Significantly cheaper than the EFF's machine, but then time does march on.