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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 @dEnergy_dTime @RichFelker and

      Marcus, you've invented a fantasy threat model and you're upset that I don't agree we should defend against it. You don't need reproducible builds, you need open source. So yes, please stop trying.

      2 replies 0 retweets 1 like
    2. May Dave (seize the means of prod)‏ @6502_ftw May 25
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      Replying to @taviso @dEnergy_dTime and

      But open source in absence of reproducible builds isn’t really a solution, unless you’re going to independently audit the entire source every time. A reproducible build lets you at least verify that you can build the same thing as the official builds from the same source/tools.

      1 reply 0 retweets 1 like
    3. May Dave (seize the means of prod)‏ @6502_ftw May 25
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      Replying to @6502_ftw @taviso and

      Essentially, it allows third parties to verify that e.g. the official builds have not been tampered with wrt the publicly available source code. The model isn’t unlike the PGP Web Of Trust, for better or for worse.

      1 reply 0 retweets 1 like
    4. May Dave (seize the means of prod)‏ @6502_ftw May 25
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      Replying to @6502_ftw @taviso and

      Obviously, without periodic, labor-intensive and expensive audits to ensure that the source hasn’t been compromised, it’s not perfect, but it at least provides for third-party attestation that the official build matches the source that’s publicly available. There’s value there.

      1 reply 0 retweets 0 likes
    5. May Dave (seize the means of prod)‏ @6502_ftw May 25
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      Replying to @6502_ftw @taviso and

      Agreed with your later point that if you’re just building it yourself, it’s not a *lot* more useful, but it guards against the scenario where e.g. backdoored builds are slipped into the main site vs. slipped into the source, because the checksums will diverge.

      2 replies 0 retweets 0 likes
    6. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @6502_ftw @dEnergy_dTime and

      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.

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

      Did you describe how to do that instead? I couldn't find it, but it's hard to navigate these threads and I get the impression that whether there is a good alternative to using reproducible builds for this is a point of contention in this discussion.

      1 reply 0 retweets 1 like
    8. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @jix_

      Well, reproducible builds work like this: I give you a source tarball that you *have* to trust (if you don't there might be bugdoors), and a binary that might be tainted. You rebuild the binary, and verify it's bit-for-bit identical, therefore not tainted.

      1 reply 0 retweets 0 likes
    9. 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
    10. 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
      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?

      4:09 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

          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
        3. 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
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