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Git 3.0's upcoming SHA-256 default will be a costly mistake

570 points · 536 comments · chmaynard

  1. kpcyrd · · focus · HN ↗
    This article is full of mistakes and misleading claims:

    1) It's claiming SHA1 insecurity is theoretical, while SHAttered from 2017 was specifically a pratical proof of concept. The only reason Git wasn't affected, is because they didn't bother bruteforcing a git-blob prefix.

    2) It's claiming collision attacks don't matter, only second-preimage attacks do. This is incorrect, collision attacks are enough for code-smuggling problems, when two repositories are on the same git commit (verified by the full commit hash), yet contain different code in their git checkout.

    3) The Linus quote "The real security is in distribution" is arguing that "git's content-addressed system should not be used to address content". It's arguing that, in case of curl|sh, you shouldn't use a sha256sum-gate to pin the content to something you've reviewed, you should instead ensure curl is fetching from an https server.

    1. kazinator · · focus · HN ↗
      The problem of a SH1 collision happening by coincidence is vanishingly low and theoretical.

      Nothing else matters.

      Git hashes are not supposed to be a security mechanism. If your basis for trusting that you have the right checkout is the git hash, in a situation where you have legitimate concern about untrusted parties manipulating remote repositories, then you're simply wrong.

      1. zygentoma · · focus · HN ↗
        Sorry, no.

        When I check out code from a git repository in a pipeline using a git hash, I expect the code to be exactly what has been reviewed by me under that hash.

        Everything else would just be a crazy invitation to make supply chain attacks uncircumventable.

        1. 7bit · · focus · HN ↗
          Sorry, no. For trusting code there is code signing. A sha-1 hash is cryptographically the wrong approach for it or we wouldn't have RSA and ECDSA algos.
          1. zygentoma · · focus · HN ↗
            And what do these cryptographic signing algorithms do? They sign a cryptographic hash of the data … Which the SHA-family of hashes are.
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