Re: Commit SHA1 == SHA1 checksum?

From: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Date: Feb 7, 2022, 13:32 UTC
Message-ID: <20220207133244.kpyczjsxriepjtdt@meerkat.local>
In-Reply-To: <xmqqee4fix0l.fsf@gitster.g>

On Sun, Feb 06, 2022 at 12:02:34PM -0800, Junio C Hamano wrote:

Show 12 quoted lines

> Philip Oakley <philipoakley@iee.email> writes:
> 
> > I think part of Todd's question was how the tag and uncompressed archive
> > 'checksums' (e.g. hashes) relate to each other and where those
> > guarantees come from.
> 
> There is no such linkage, and there are no guarantees.  The trust
> you may or may not have on the PGP key that signs the tag and the
> checksums of the tarball is the only source of such assurance.
> 
> More importantly, I do not think there can be any such linkage
> between the Git tree and release tarball:

Hmm... I've actually considered writing a tool that would verify whether a tarball corresponds to a signed tag/commit. It should be entirely possible, no?

1. list all the files in the tar archive and calculate their hashes
2. use that info to rebuild blob and tree hashes all the way to the top of
   the archive tree
3. verify the signature on the git tag and obtain the corresponding tree hash
4. compare the in-git tree hash with your calculated archive tree hash

It would be slow, but it would be perfectly workable. I didn't end up writing that tool mostly because if you already have a git tree to run "git verify-tag", then you might as well just run "git archive". :)

The only cases where doing the above would make sense would be specifically for forensic/verification purposes.

-K