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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. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @halvarflake @rene_mobile and

      Yes, but that only makes sense if you trust the person who provided the source code (because if you don't trust them, there could be a bugdoor). So another way to verify that would be codesigning, or hosting the binary on a https server, right?

      4 replies 0 retweets 3 likes
    9. Spider 🕷️‏ @spidler May 23
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      Replying to @taviso @halvarflake and

      Code signing doesn't solve the issue of knowing "what code was signed" at the moment of signature. The signature can of course cover a claimed checksum of the code, but even then, it's hard to verify. That does not make signatures bad, it only doesn't solve the same issue.

      1 reply 0 retweets 1 like
    10. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @spidler @halvarflake and

      Yes, but the point is you *have* to trust the vendor. It makes no sense to say you trust their code but not their signature, right?

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

      Let's say the vendor is malicious, so they hide a bugdoor in the code and sign it. You don't trust code signatures for some reason though, and demand a reproducible build.... so what? You now have a reproducible bugdoor. If you do catch them, "oops", and there's zero penalty. 🤷🏻‍♂️

      9:25 AM - 23 May 2020
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      • Deirdre Connolly¹ Cem Paya
      2 replies 1 retweet 1 like
        1.  😷 Juliano Rizzo‏ @julianor May 23
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          Replying to @taviso @spidler and

          You can make an update system where independent entities reproduce a build and sign and then you check m of N signatures of m trusted by you instead of trusting SSL/TLS CAs.

          0 replies 0 retweets 1 like
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        1. stephen0x2dfox‏ @stephen0x2dfox May 23
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          Replying to @taviso @spidler and

          I hadn't thought of this in the context of the software supply chain. A "trusted" vendor could include a library or tool in their build process that can add a bugdoor. Even if you have the vendor's source code, it would be an uphill fight to find, and determine intent.

          0 replies 0 retweets 0 likes
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