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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. 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
    2. 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
    3. 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
    4. 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
    5. 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
    6. 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
    7. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @taviso @matthew_d_green and

      To be clear, source analysis is useful to catch non-malicious vendors who make a mistake. If you're trying to determine if a vendor *is* malicious, src analysis provides no benefit, because there is no penalty for hiding a bugdoor....so how do repro builds help?

      1 reply 0 retweets 6 likes
    8. Matthew Green‏ @matthew_d_green May 23
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      Replying to @taviso @halvarflake and

      There are a lot of people involved in the build process. And a much smaller number of people involved in the development of specific portions of code. If you can isolate your security concerns to those areas (still aspirational) you can reduce your trusted dev base.

      2 replies 0 retweets 11 likes
    9. Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @matthew_d_green @halvarflake and

      The discussion is around publishing reproducible builds for the public though, right? This is a way of verifying your build process isn't compromised, but you don't need to publish them and hope the public checks it for that.

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

      It’s a way for auditors and customers to verify as well. And the general public, if you consider them to be auditors.

      1 reply 0 retweets 3 likes
      Tavis Ormandy‏Verified account @taviso May 23
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      Replying to @matthew_d_green @halvarflake and

      Right, so let's say I trust the vendor, but I think their build might be compromised. You're saying "now you can verify their build isn't compromised, but you still have to trust there are no bugdoors", so why wouldn't you trust them not to promise they checked the build repro'd?

      9:39 AM - 23 May 2020
      3 replies 0 retweets 0 likes
        1. New conversation
        2. Tavis Ormandy‏Verified account @taviso May 23
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          Replying to @taviso @matthew_d_green and

          It makes no sense, right? You either trust the code *and* trust them that they verified the build wasn't compromised, or you don't trust them... and it's meaningless? I really think published reproducible builds are a red herring.

          1 reply 0 retweets 1 like
        3. Jeff McJunkin‏ @jeffmcjunkin May 23
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          Replying to @taviso @matthew_d_green and

          I think reproducible builds are useful for locking down a few classes of attack -- delivering dif builds to dif folk, and knowing that the source you see results in the build you're running. There are other attacks, like bugdoors. But don't let perfect be the enemy of better.

          1 reply 0 retweets 2 likes
        4. 4 more replies
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        2. Matthew Green‏ @matthew_d_green May 23
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          Replying to @taviso @halvarflake and

          In order for them to check the build, they’d have to engineer reproducible builds anyway. So the costs have already been incurred. Might as well make them available to your auditors at no additional cost, so they can eliminate another trust point.

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

          I also think you’re considering a model where there’s a binary choice between absolute trust and no consequences for serious bugs, and zero trust. There’s a spectrum.

          1 reply 0 retweets 3 likes
        4. 32 more replies
        1. Jesse D'Aguanno‏ @0x30n May 23
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          Replying to @taviso @matthew_d_green and

          Another scenario: The sw vendor may not be able to prove that a build matches their source when built / distributed by a 3rd party. E.g. Signal can’t repro the build distributed by the App Store (but some verif can be done) OFC, if you don’t trust your platform vendor…¯\_(ツ)_/¯

          0 replies 0 retweets 0 likes
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