Re: Security review of tag2upload
Marco d'Itri <md@Linux.IT> writes:
> simon@josefsson.org wrote:
>> Can this be substantiated? Using SHA1CD in Git does not necessarily
>> mean someone cannot manually create a Git repository with a colliding
>> git commit somewhere in the history that gets accepted by git, and
>> allows someone to replace actual file contents. That may be the case,
>> but I haven't seen any detailed analysis answering that.
> This is quite a strong assertion, and it is up to you to prove it. The
> current consensus among cryptography experts is that SHA-1 is still
> resistant to preimage attacks.
The attack that Simon is talking about doesn't require a preimage attack,
only a successful collision attack against Git trees using SHAttered plus
some assumptions about where Git may be lazy about revalidating hashes.
It's an interesting point that I didn't think of, although I'm not sure
that it would work against GitLab and thus against Salsa and I think it's
fairly trivial to protect against regardless. I'm working on a longer
response; I needed to do a bit of research first.
--
Russ Allbery (rra@debian.org) <https://www.eyrie.org/~eagle/>
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