From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Thu, 21 Jul 2016 12:53:33 GMT
Subject: Re: Git and SHA-1 security (again)
Message-ID: <alpine.DEB.2.20.1607211451060.14111@virtualbox>
In-Reply-To: <xmqq4m7mltbw.fsf@gitster.mtv.corp.google.com>

Hi Junio,

On Mon, 18 Jul 2016, Junio C Hamano wrote:

> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
> 
> > I will say that the pack format will likely require some changes,
> > because it assumes ...  The reason is that we can't have an
> > unambiguous parse of the current objects if two hash algorithms are in
> > use....  So when we look at a new hash, we need to provide an
> > unambiguous way to know what hash is in use.  The two choices are to
> > either require all object use the new hash, or to extend the objects
> > to include the hash.  Until a couple days ago, I had planned to do the
> > former.  I had not even considered using a multihash approach due to
> > the complexity.
> 
> Objects in Git identify themselves, but once you introduce the second
> hash function (as opposed to replacing the hash function to a new one),
> you would allow people to call the same object by two names.  That has
> interesting implications.
> 
> [...]

So essentially you are saying that the multi-hash approach has too many
negative implications, right? At least that is what I understand.

Looks more and more like we do need to convert repositories wholesale, and
keep a two-way mapping for talking to remote repositories.

Would you concur?

Ciao,
Dscho