Re: [PATCH v4] technical doc: add a design doc for hash function transition

From: Jason Cooper <jason@lakedaemon.net>
Date: Oct 2, 2017, 19:41 UTC
Message-ID: <20171002194127.GI31762@io.lakedaemon.net>
In-Reply-To: <20170929173413.GI19555@aiede.mtv.corp.google.com>

On Fri, Sep 29, 2017 at 10:34:13AM -0700, Jonathan Nieder wrote:

> Junio C Hamano wrote:
> > Jonathan Nieder <jrnieder@gmail.com> writes:

...

Show 11 quoted lines

> > If it is a goal to eventually be able to lose SHA-1 compatibility
> > metadata from the objects, then we might want to remove SHA-1 based
> > signature bits (e.g. PGP trailer in signed tag, gpgsig header in the
> > commit object) from NewHash contents, and instead have them stored
> > in a side "metadata" table, only to be used while converting back.
> > I dunno if that is desirable.
> 
> I don't consider that desirable.
> 
> A SHA-1 based signature is still of historical interest even if my
> centuries-newer version of Git is not able to verify it.

Agreed, even a signature made by a now exposed and revoked key still has validity. Especially in a commit or merge. We know it was made prior to the key being compromised / revoked.

This is assuming that the keyholder can definitively say "Don't trust signatures from this key after this date/time+0000". And the signature in question is in the git history prior to that cut off.

Tags are a different animal because they can be added at any time and aren't directly incorporated into the history.

thx,

Jason.