Re: pushing for a new hash, was Re: [PATCH 2/3] rebase: Add tests for console output

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Jun 6, 2017, 22:45 UTC
Message-ID: <20170606224524.GC21733@aiede.mtv.corp.google.com>
In-Reply-To: <alpine.DEB.2.21.1.1706070008440.171564@virtualbox>

Hi,

Johannes Schindelin wrote:

> On Fri, 2 Jun 2017, Jonathan Nieder wrote:
>> Johannes Schindelin wrote:

Show 11 quoted lines

>>> Maybe we should call out a specific month (or even a longer period) during
>>> which we try to push toward that new hash function, and focus more on
>>> those tasks (and on critical bug fixes, if any) than anything else.
>>
>> Thanks for offering. ;-)
>
> Undoubtedly my lack of command of the English language is to blame for
> this misunderstanding.
>
> By no means did I try to indicate that I am ready to accept the
> responsibility of working toward a new hash dumped on me.

It was a joke. More seriously, I do appreciate your questions to get this discussion going.

[...]

> 3) the only person who could make that call is Junio

I strongly disagree with this.

> 4) we still have the problem that there is no cryptography expert among
> those who in the Git project are listened to

*shrug* I still don't know what you are suggesting here. Are you saying we should find a cryptography expert to pay? Or do you have other specific suggestions of how to attract them?

Show 8 quoted lines

>> How did you get the impression that their opinion had no impact? We have
>> been getting feedback about the choice of hash function both on and off
>> list from a variety of people, some indisputably security experts.
>> Sometimes the best one can do is to just listen.
>
> I did get the impression by talking at length to a cryptography expert who
> successfully resisted any suggestions to get involved in the Git mailing
> list.

I know of other potential Git contributors that have resisted getting involved in the Git mailing list, too. I still don't know what you are suggesting here. Forgive me for being dense.

Show 5 quoted lines

> There were also accounts floating around on Twitter that a certain
> cryptography expert who dared to mention already back in 2005 how
> dangerous it would be to hardcode SHA-1 into Git was essentially shown the
> finger, and I cannot fault him for essentially saying "I told you so"
> publicly.

I think there is a concrete suggestion embedded here: when discussions go in an unproductive direction, my usual practice has been to keep away from them. This means that to a casual observer there can appear to be a consensus that doesn't really exist. We need to do better than that: when a prominent contributor like Linus and people newer to the project are emphatically dismissing the security impact of using a broken hash function, others in the project need to speak up to make it clear that those are not the actual opinions of the project.

To put it another way: "The standard you walk past is the standard you accept". I have failed at this.

It is a very hard problem to solve, but it is worth solving.

Show 9 quoted lines

> In my mind, it would have made sense to ask well-respected cryptographers
> about their opinions and then try to figure out a consensus among them (as
> opposed to what I saw so far, a lot of enthusastic talk by developers with
> little standing in the cryptography community, mostly revolving around
> hash size and speed as opposed to security). And then try to implement
> that consensus in Git. Given my recent success rate with SHA-1 related
> concerns, I am unfortunately not the person who can bring that about.
>
> But maybe you are.

I think you are being a bit dismissive of both the work done so far and the value of your own work.

I am happy to solicit more input from security researchers, though, and your suggestion to do so is good advice.

Thanks and hope that helps, Jonathan