Re: Git and SHA-1 security (again)

On Mon, Jul 18, 2016 at 5:57 PM, Johannes Schindelin
[off-list ref] wrote:

Hi Zsolt,

On Mon, 18 Jul 2016, Herczeg Zsolt wrote:

quoted

quoted

quoted

I think converting is a much better option. Use a single-hash
storage, and convert everything to that on import/clone/pull.

That ignores two very important issues that I already had mentioned:

That's not true. If you double-check the next part of my message, you I
just showed that an automatic two-way mapping could solve these
problems! (I even give briefs explanation how to handle referencing and
signature verification in those cases.)

My point is not to throw out old hashes and break signatures. My point
is to convert the data storage, and use mapping to resolve problems
with those old hashes and signatures.

If you convert the data storage, then the SHA-1s listed in the commit
objects will have to be rewritten, and then the GPG signature will not
match anymore.

But we can recreate SHA-1 from the same content and verify GPG, right?
I know it's super expensive, but it feels safer to not carry SHA-1
around when it's not secure anymore (I recall something about
exploiting the weakest link when you have both sha1 and sha256 in the
object content). Rehashing would be done locally and is better
controlled.
-- 
Duy