Use IDA Pro and/or BinDiff to inspect releases
We have some concerning issues with our build processes. It's hard to really know for sure that the build machines are secure and not tampered with. See for example #5689 (closed). The most likely situation there is that AV signature engines fucking suck, and were false positives. However, the real fix is not simply scanning the build machines with more shitty AV software (although it was a fine, rational first step -- I'm not hating on you, Erinn). The real fix is unfortunately much harder: We need to ensure that the same source produces the same binaries everywhere: #3688 (closed).
Other than build reproduction, it's nearly fucking impossible to know that the binaries you get actually come from the source you wrote and audited. A handful of Open Source projects have figured it out (see comments in #3688 (closed)), but it's actually pretty darn hard on Windows, if not impossible.
As a stop-gap solution, it's occurred to me that we might be able to crowdsource hobbyists and people looking to learn reversing (or if we're really lucky, some people who already have these skills) to both help verify previous builds, and give us the input we need to proceed on #3688 (closed).
If you have access to IDA Pro (BinDiff will help, but is an extra $200 extension to IDA Pro and is not required), you can participate as follows:
Download a signed TBB release from https://www.torproject.org/dist/torbrowser/.
Compile your own TBB bundle. This is somewhat tricky. Sebastian has instructions for Mac OS in https://gitweb.torproject.org/torbrowser.git/tree/master:/docs/buildmachine_setups. Windows and Linux instructions should arrive there soon.
Analyze/BinDiff the resulting packaging exe as well as the exes contained therein.
If you lack BinDiff, you should consider focusing your efforts on MacOS and Linux packages, which should produce substantially more similar builds than Windows, especially if you build the Linux TBB on Debian Lenny and the Mac one on MacOS 10.7 with Xcode 4 (which are our build machine setups). Start with using the 'cmp' (and/or hexdump and diff) UNIX commands to find the differing sections of the binaries, and then use IDA Pro to inspect those sections (quickest way: Just use the search tool for a long hex string surrounding the difference).
More advanced tools to find minimal binary edit differences may also be useful if the differences the basic tools find are large. http://jojodiff.sourceforge.net/ is an example of one such tool, but there probably are others.
Be sure to verify the difference that IDA and/or BinDiff decodes is the same as a simple diff tool finds (cmp or jojodiff). The simple diff tool is less likely to be fooled than IDA.
You should be able to use IDA Pro for any platform to analyze binaries for any other platform. You do not need to buy the MacOS copy to analyze MacOS binaries.
Use normal UNIX diff on the non-exe components (for example, conf files, shell scripts, contents of Firefox jars and addon sources).
Write up the significant differences.
We need to make the above a semi-regular part of our development process to periodically verify our build integrity.
Writing up the differences you find will also be useful for us to help us work towards #3688 (closed), especially for Mac and Linux builds (which are likely pretty darn close.. It's probably only some timestamps and symbol names that differ if you use the same platform and compiler).
If you want to be extra-helpful, you can write up a detailed howto (and/or just paste the ones you find that already exist) on the process itself to make it even easier for others to learn and participate.
We'll need to do this often.. Perhaps not for every release, but at least randomly on some builds every once and a while. Also, BinDiffing archived signed TBB copies from https://archive.torproject.org/tor-package-archive/torbrowser/ will be useful, too, so no need to wait for future releases. You can start today. The source tarballs are in that directory as well, with -src.tar.gz instead of a language and arch. However, to get the actual git sources for an old release:
git clone git://git.torproject.org/torbrowser.git cd torbrowser git tag -l git checkout torbrowser-2.2.35-9.1
Git will tell you that you can't commit anything that way, but that shouldn't matter to you.
Note that this whole process is a fantastic exercise in learning basic reverse engineering skills. Diffing vendor patches and malware updates is a common practice in the field. It's a useful skill to learn, if you have the time.