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Debian Working on Reproducible Builds To Make Binaries Trustable
An anonymous reader writes: Debian's Jérémy Bobbio, also known as Lunar, spoke at the Chaos Communication Camp about the distribution's efforts to reassert trustworthiness for open source binaries after it was brought into question by various intelligence agencies. Debian is "working to bring reproducible builds to all of its more than 22,000 software packages," and is pushing the rest of the community to do the same. Lunar said, "The idea is to get reasonable confidence that a given binary was indeed produced by the source. We want anyone to be able to produce identical binaries from a given source (PDF)."
Here is Lunar's overview of how this works: "First you need to get the build to output the same bytes for a given version. But others also must to be able to set up a close enough build environment with similar enough software to perform the build. And for them to set it up, this environment needs to be specified somehow. Finally, you need to think about how rebuilds are performed and how the results are checked."
Here is Lunar's overview of how this works: "First you need to get the build to output the same bytes for a given version. But others also must to be able to set up a close enough build environment with similar enough software to perform the build. And for them to set it up, this environment needs to be specified somehow. Finally, you need to think about how rebuilds are performed and how the results are checked."
But that isn't the point of this. It's how to verify that your binary doesn't have tampered with source code.
I care about this, too. That's one reason I run a source-based distribution. It's not the only reason. It's not even the main reason. But it's one reason.
Anyone who really needs this kind of assurance was probably also building from source. You can do it once on-site, then make your own binary packages and push those to all of your other machines so it's really not bad. I think a much more insidious threat comes from malicious yet innocent-looking source, like what you find in the Underhanded C Contests.
It doesn't do much good to have a reproducible build of a program when it contains an innocent-looking yet malicious piece of code. Just consider Heartbleed. Whether Heartbleed was intentional or not, it proves that people can run vulnerable code for a very long time before it's found out, and that was a program intended to be secure.
I was thinking about this being a problem a while back - how to deal with building something from source and knowing I was getting the same output that the developers wanted me to have. Coincidentally about the same time, this article popped on Slashdot and introduced me to Ken Thompson's article Reflections on Trusting Trust - a great read and something that really opened my eyes (in that wide-open-because-of-terror kind of way).
Also from that thread came this email from one of the Tor developers talking about their deterministic build process to do the same thing.
I think this is a problem that would be really great to solve as soon as possible. I very much hope that once we start seeing more reproducible builds we don't suddenly find out that certain compilers have been compromised long ago.
What about compromised CPUs? If you are the NSA I think it's easier to build a backdoor into the CPU than try to keep up with ever changing software builds. Isn't it? CPUs are totally controlled by three or four U.S. companies, are closed source nobody has ever seen into it...
So long as two or more independently developed, self-hosting compilers for a language exist, with at least one as publicly available source code, a Ken Thompson attack on the public-source one is infeasible. David A. Wheeler proved it; here's the gist: