Re: Git and SHA-1 security (again)

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Brian,

On Sat, 16 Jul 2016, brian m. carlson wrote:

> My current plan is not to implement side-by-side data, for a couple
> reasons.

I am as guilty as the next person to have use the "deafbee(This is my
commit, 2007-08-21)" format to refer to older commits. So I do have
concerns about rewriting history when switching to a new hash.

I understand the technical challenges, of course.

Out of curiosity: have you considered something like padding the SHA-1s
with, say 0xa1, to the size of the new hash and using that padding to
distinguish between old vs new hash?

I guess that it would also possible to introduce an opt-in "legacy mapper"
which would generate a mapping locally of all objects' SHA-1 to whatever
new hash you choose. Generating it locally would side-step the security
issues of the SHA-1 algorithm. We would need to teach Git to pick that
mapping up if available and use it, of course.

However, that latter solution would do nothing to address the problem of
existing GPG-signed commits.

Ciao,
Dscho