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taviso's profile
Tavis Ormandy
Tavis Ormandy
Tavis Ormandy
Verified account
@taviso

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Tavis OrmandyVerified account

@taviso

Vulnerability researcher at Google. This is a personal stream, opinions expressed are mine.

California
taviso.decsystem.org
Joined April 2008

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    1. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @taviso @jix_

      You now have two bit-for-bit identical binaries, one you trust and one you don't and therefore know they're both safe. I'm saying, who cares about the vendor supplied one? Just use the one you built, and it doesn't matter if it was reproducible or not.

      1 reply 0 retweets 1 like
    2. Jannis Harder‏ @jix_ May 25
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      Replying to @taviso

      Sorry, I don't see how that helps in stopping a compromised build server from distributing compromised binaries undetected. What am I missing?

      1 reply 0 retweets 0 likes
    3. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @jix_

      I don't know, walk me though the attack you're imagining. I think if you used my system, the tainted binary will never execute on your system, so it's irrelevant if it's compromised or not?

      1 reply 0 retweets 0 likes
    4. Jannis Harder‏ @jix_ May 25
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      Replying to @taviso

      Jannis Harder Retweeted Tavis Ormandy

      I'm just trying to follow your argument and I understood https://twitter.com/taviso/status/1265052138071195650 … in that you have an alternative to reproducible builds from stopping a compromised build server from distributing tainted binaries. So you disagree with the premise that that's a worthwhile goal?

      Jannis Harder added,

      Tavis OrmandyVerified account @taviso
      Replying to @6502_ftw @dEnergy_dTime and 9 others
      Nobody claims reproducible builds prevent backdoors, they definitely don't. People do (correctly) claim they prevent compromised build servers from producing tainted binaries. I'm saying you can do that *today*, *without* reproducible builds.
      1 reply 0 retweets 0 likes
    5. Jannis Harder‏ @jix_ May 25
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      Replying to @jix_ @taviso

      If that's the case I'd refer to David A. Wheelers thesis (+ thesis website) for arguments why I think it is a worthwhile goal and better than just compiling locally. If I did misunderstand you, sorry, I'm probably too tired and should sleep instead.

      1 reply 0 retweets 0 likes
    6. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @jix_

      Yes, it's arbitrarily specific? Everything else has to remain trusted. It's also never happened, have there ever been any cases of tainted binaries from compromised build infra? Lots of tainted src repos, src tarballs, signing infra, distribution, etc, though.

      1 reply 0 retweets 0 likes
    7. Jannis Harder‏ @jix_ May 25
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      Replying to @taviso

      There have been, search for XcodeGhost on https://dwheeler.com/trusting-trust/ 

      1 reply 0 retweets 0 likes
    8. Jannis Harder‏ @jix_ May 25
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      Replying to @jix_ @taviso

      Also the thesis describes how diversity and independent compilation on isolated systems can be used to increase trust and avoid a single point of failure.

      2 replies 0 retweets 0 likes
    9. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @jix_

      I'm aware of it, I don't think it really qualifies, it wasn't *build infra* being compromised - they could just have easily modified source code. Dozens of examples of source tarballs or repos being modified though.

      1 reply 0 retweets 1 like
    10. Jannis Harder‏ @jix_ May 25
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      Replying to @taviso

      I guess this is the point of disagreement then (at least for me)

      1 reply 0 retweets 0 likes
      Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @jix_

      Hmm, you don't agree build reprodcucibility *has* to have separate build infra to even be relevant? Otherwise the attacker can just modify source code, for example.

      4:27 PM - 25 May 2020
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Jannis Harder‏ @jix_ May 25
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          Replying to @taviso

          I think reproducibility has to have separate systems running the builds, but not necessarily the project's own infra. For me the focus is on detectability. Modified source will be found because people will eventually look at the source. For modified binaries that's not the case.

          1 reply 0 retweets 0 likes
        3. Jannis Harder‏ @jix_ May 25
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          Replying to @jix_ @taviso

          Again I'm aware that I'm probably not stating things as clear as I'd like to currently. I might try again tomorrow.

          1 reply 0 retweets 1 like
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