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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

Tweets

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    1. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @halvarflake @dEnergy_dTime and

      Yes but *why*? You're already building them and you already trust the developer, why does it matter? It seems like just being open source is enough.

      3 replies 0 retweets 0 likes
    2. halvarflake‏ @halvarflake May 25
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      Replying to @taviso @dEnergy_dTime and

      because in a scenario where the dev may have had his signing keys compromised, and someone has compromised the bin repo, i have a chance of knowing. it goes back to "I want to be able to establish that a given binary was built from a given source snapshot".

      1 reply 1 retweet 11 likes
    3. halvarflake‏ @halvarflake May 25
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      Replying to @halvarflake @taviso and

      key compromise in the absence of universal codesigning transparency has a silent failure mode. deterministic builds can help alleviate that.

      1 reply 2 retweets 7 likes
    4. halvarflake‏ @halvarflake May 25
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      Replying to @halvarflake @taviso and

      the reason i want this is also personal: If I was paid to pwn, gathering the worlds code signing keys would be a rather high item on my todo.

      3 replies 1 retweet 10 likes
    5. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @halvarflake @dEnergy_dTime and

      That doesn't make sense though, the only way you can know is because you also built it - at which point you don't need the signed binaries! The code signing is only useful if you want to know the binaries were produced by a vendor you already trust.

      1 reply 0 retweets 2 likes
    6. halvarflake‏ @halvarflake May 25
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      Replying to @taviso @dEnergy_dTime and

      explain to me again how having built the binaries surfaces the use of compromised keys for the binaries on the repo?

      1 reply 0 retweets 2 likes
    7. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @halvarflake @dEnergy_dTime and

      It doesn't matter - you *have* trusted binaries, you were going to build them anyway. Codesigning is only relevant for people who don't have trusted binaries, but do have a vendor they trust, right?

      1 reply 0 retweets 2 likes
    8. halvarflake‏ @halvarflake May 25
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      Replying to @taviso @dEnergy_dTime and

      I am not sure you are engaging with my argument. To repeat: I like deterministic builds because they may surface use of compromised signing keys. I don't think you get to decide that I should not care because I can build my own (trusted) binaries.

      1 reply 1 retweet 14 likes
    9. Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @halvarflake @dEnergy_dTime and

      We agree that you can check if a build server is compromised or not with reproducible builds. I'm not saying you can't enjoy doing that if you like, but I am saying there's no security benefit over just open source.

      4 replies 0 retweets 1 like
    10. Rich Salz‏ @RichSalz May 25
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      Replying to @taviso @halvarflake and

      Really no benefit? Do you inspect your compiler output? Linker? Build libc, etc., from scratch?

      2 replies 0 retweets 2 likes
      Tavis Ormandy‏Verified account @taviso May 25
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      Replying to @RichSalz @halvarflake and

      Walk me through the attack you're imagining. Someone has backdoored your linker, and your solution to this problem is to do some reproducible builds on a few projects and check if the output matches?

      2:18 PM - 25 May 2020
      • 1 Like
      • Yanai Moyal
      1 reply 0 retweets 1 like
        1. New conversation
        2. Rich Salz‏ @RichSalz May 25
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          Replying to @taviso @halvarflake and

          No. Reproducible builds for your toolchain since you think having the source suffices.

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

          I think having the source suffices to prevent against every attack *that reproducible builds prevents*. I don't think it's sufficient to prevent *every* attack. If your linker has already been compromised, I don't think anyone claims reproducible builds are the answer except you?

          0 replies 0 retweets 0 likes
        4. End of conversation

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