Re: Migrating away from SHA-1?

[Leo Gaspard <leo@gaspard.io>]

[-- Attachment #1.1: Type: text/plain, Size: 2409 bytes --]

First, sorry for not having this message threaded: I'm not subscribed to
the list and haven't found a way to get a Message-Id from gmane.

I just wanted to ask, as an end-user highly relying on commit
signatures, a few questions as to the migration away from SHA-1.

SHA-1 already suffers from a freestart collision attack. Based on what I
understand of the object model of git, a chosen-prefix collision attack
(perhaps somewhat improved) is enough to make reviewers accept a patch,
sign it, and then swap the innocuous-looking patch for an evil-doing one
-- which *will be signed*.

As for the issue about code checking being an easier entrypoint
(Theodore Ts'o, 2016-04-14 22:40:51 GMT), in a use case of mine there is
a repo with my dotfiles on an untrusted server. Yet I download them and
am able to execute them without fear because each commit is PGP-signed
with my key. The point being that code checking is not even a possible
entrypoint in some cases, so SHA-1 seems to be(come) the weakest link.

So, I don't think it is possible to disagree with Jeff King when he
wrote his 2016-04-12 23:15:19 GMT email.

Peter Anvin (2016-04-14 17:28:50 GMT) gets a point in that there is no
need to hurry (chosen-prefix collisions may be still quite a long way,
even though there is no guesswork in these matters), and quality is
important. Yet Jeff King's proposal (2016-04-12 23:42:52 GMT), amended
by Junio Hamano (2016-04-13 01:03:02 GMT) and himself (2016-04-13
01:36:32 GMT) seem to have met no opposition.

So, my questions to the git team:
 * Is there a consensus, that git should migrate away from SHA-1 before
it gets a collision attack, because it would mean chosen-prefix
collision isn't far away and people wouldn't have the time to upgrade?
 * Is there a consensus, that Peter Anvin's amended transition plan is
the way to go?
 * If the two conditions above are fulfilled, has work started on it
yet? (I guess as Brian Carlson had started his work 9 weeks ago and he
was speaking about working on it on the week-end he should have finished
it now, so excluding this)
 * If the two first conditions are fulfilled, is there anything I could
do to help this transition? (including helping Brian if his work hasn't
actually ended yet)

Sorry for bringing up again a subject that seems to be quite recurrent,
and for this long block of text,
Leo Gaspard


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 648 bytes --]