On the (Im)possibility of Obfuscating Programs

sl956 writes: "We all know that anybody using the words 'tamper resistant' to describe a software-based solution is incompetent at best. But some of the big players in the DRM field are believing in software-only protection schemes (see Cloakware, Hitachi, IBM or Intel). A mostly unnoticed paper presented to CRYPTO'01 (Santa Barbara, CA, August 19-23, 2001, LNCS vol.2139) *proved* the impossibility of efficiently obfuscating programs. It is the mathematical proof of the impossibility of a software-only DRM system on an untrusted client such as a PC. There are also a lot of interesting theoretical side-effects. You can read the html abstract here, or the postcript full paper here." The paper is from last year, but that doesn't make its conclusion less interesting. (Of course, even hardware isn't always all that secure, either.)

Comments

Mozart

[rjamestaylor]

In my Music Appreciation (Apprehension?) class I learned that as a young boy Mozart broke a vaulted DRM of his day by simply attending a concert in an Italian church. The mass that day was kept under lock and key and would only be played once a year; all copies of the music were kept secret. What Mozart did is hear the mass (once) and then went home and wrote the entire score as if he was copying the original documents yet only assisted by his memory. His scoring was so good he was accused of stealing the score from the church. (Forgive my poor recollection of Mozart's superb recollection ancedote...)

There will always be a Mozart to break the DRM of publically performed (or distributed) works. DRM is a way of controlling the sharing of some piece of work. In reality, the only way to perfectly safeguard the rights is to not share the work -- or trust people. Hmmm...

Could this proof hamper the DMCA?

[CptnKirk]

Now with this proof being published, software companies now have no expectation that their software only copy protection or DRM system is secure. What does this mean?

If I wrote a copywrited piece and then used a form of copy protection that I knew people could break (similar to what some people were doing to "encrypt" song titles on Napster a while back), do I have the right to sue them under the DMCA (and a while back the judge said no)? Maybe so, maybe not, maybe it's a grey area, maybe there are other loopholes I know nothing about. But one thing I think the courts have upheld is that legally there is no degree of separation.

For instance of a judge rules that breaking someone's "lame encryption" does not violate the DMCA, because they knew ahead of time that a person could break it. Then adding to the complexity shouldn't change anything. If you have a proof that shows that software only DRM on an untrusted client is not secure can you or should you be able to claim damages when someone eventually exploits the hole you knew had to exist.

Of course IANAL, and I'm sure this will not cause the DMCA to crumble, but I think it raises some questions. Similarly are you allowed to advertise that such systems baised on obfuscation are secure or should they be clearly labeled as deterants, and not iron clad security?

I've worked with Intel's DRM

[KNicolson]

And they were always very careful to point out that their software is merely tamper *resistant*, not tamper *proof*. This is not just the sales guys, but the engineers too, and even in meetings if I accidentally said, for example, "*blah* will prevent copying", they were quick to correct my mistake.

This isn't as big as the poster is making out....

[jpmorgan]

There's a paper called Protecting Mobile Agents against Malicious Hosts by Tomas Sander and Christian F. Tschudin, which demonstrates it's possible to write a program which can compute a digital signature or other various functions in such a way that it's impossible for the host to hijack the process, i.e., it's cryptographically hard to reverse engineer the program to extract the public key being used, or the function being computed (This paper has been used for various purposes, including proving that it's theoreticaly possible to write computer viruses which have signatures which are impossible to detect).

These papers aren't contradictory, there are important differences between the results.

Ultimately, one paper demonstrates a certain type or program (which would be usefull in implementing a DRM scheme) is impossible, the other paper demonstrates another similar type program (which would also be usefull in implementing DRM schemes) is possible (and demonstrates how to create such a program, and gives a non-trivial example).

Is this the theoretical end of all DRM as the poster is suggesting? Not yet.

Re:software protection

[CaptainSuperBoy]

Was that before or after you spent some time messing with trojans? Yeah you're not going to live that one down. Don't expect me to buy any of your software any time soon.