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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 22
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      Replying to @fugueish @alexstamos and

      I don't really know what reproducible builds prove, that the build server wasn't compromised? If Signal were malicious, they could just add a bugdoor, so you still have to trust them not to be malicious. 🤷🏻‍♂️

      3 replies 2 retweets 20 likes
    2. Rene Mayrhofer‏ @rene_mobile May 23
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      Replying to @taviso @fugueish and

      Reproducible builds make most sense together with open source, of course. And it's of value even if nobody is constantly verifying the builds. Simply the point that they could mitigates the vector of a malicious builds server. Source level backdoors are certainly not addressed.

      1 reply 0 retweets 8 likes
    3. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @rene_mobile @fugueish and

      You can prove the build server isn't compromised, but you can't prove you're not trying to hide a backdoor, right? So users still have to trust you, and you could get the same benefit from getting a third party to privately repro the build for you...

      3 replies 0 retweets 6 likes
    4. Rene Mayrhofer‏ @rene_mobile May 23
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      Replying to @taviso @fugueish and

      I don't fully agree. It is still easier to hide a backdoor in (obfuscated) binary code than it is in (written-to-be-maintainable) source code. Config should ideally be included. And there are other code quality benefits of reproducible builds besides security (testing, deltas).

      2 replies 1 retweet 11 likes
    5. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @rene_mobile @fugueish and

      Is it easier? The benefit of bugdoors isn't ease, it's that they're plausibly deniable, if you get caught, so what? You might even be able to convince people not to talk about it for months, and you can try again in a new patch, there's zero penalty.

      2 replies 4 retweets 23 likes
    6. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @taviso @rene_mobile and

      There might be non-security benefits of reproducible builds to *vendors*, but I don't see any benefit to users of being able to reproduce them. This is just because promising there's no backdoors make no sense when bugdoors are just so perfect?

      1 reply 0 retweets 6 likes
    7. halvarflake‏ @halvarflake May 23
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      Replying to @taviso @rene_mobile and

      Fwiw I see benefits in reproducible builds to answer the question "is the binary on my machine built from this source"?

      3 replies 0 retweets 33 likes
    8. Matthew Green‏ @matthew_d_green May 23
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      Replying to @halvarflake @taviso and

      Without reproducible builds, source analysis offers zero benefit. With reproducible builds, it offers some benefit. For example, crypto bugdoors that allow mass-scale passive decryption are possible (Dual EC, Fortinet) but are also extremely rare.

      2 replies 1 retweet 27 likes
    9. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @matthew_d_green @halvarflake and

      What benefit does it offer? There's no penalty for making a bugdoor, so if you catch the vendor's bugdoor, they have to make a new one?

      2 replies 0 retweets 4 likes
    10. Rich Felker‏ @RichFelker May 23
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      Replying to @taviso @matthew_d_green and

      There's at least a higher degree of scrutiny after bugdoors and distrust in the "vendor". If the "vendor" is real FOSS and has a number of involved contributors, *they're* going to wonder too if the bugdoor was intentional and be extra vigilant.

      2 replies 0 retweets 1 like
      Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @RichFelker @matthew_d_green and

      Would they wonder? Major vendors ship advisories with dozens of backdoor-equivalent vulnerabilities every month, nobody ever asks if they were bugdoors or not. The reason is people have decided they trust that vendor, so reproducible builds wouldn't change that, right?

      9:28 AM - 23 May 2020
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Rich Felker‏ @RichFelker May 23
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          Replying to @taviso @matthew_d_green and

          I think we're talking about different audiences. You can't help people who are committed to trusting the untrustworthy. Repro builds help audiences who actually don't tolerate bullshit.

          1 reply 0 retweets 3 likes
        3. Rich Felker‏ @RichFelker May 23
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          Replying to @RichFelker @taviso and

          Bugdoors aside (a distraction from the main benefits), repro builds let you know that the vuln is in upstream source and that everyone is affected, important info for safety of larger public and a datapoint about targeting.

          0 replies 0 retweets 0 likes
        4. End of conversation

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