Re: SHA1 collisions found

[ankostis <ankostis@gmail.com>]

On 24 February 2017 at 20:20, Junio C Hamano <gitster@pobox.com> wrote:
> Stefan Beller <sbeller@google.com> writes:
>
>> On Fri, Feb 24, 2017 at 10:14 AM, Junio C Hamano <gitster@pobox.com> wrote:
>>
>>> you are inviting people to start using
>>>
>>>     md5,54ddf8d47340e048166c45f439ce65fd
>>>
>>> as object names.
>>
>> which might even be okay for specific subsets of operations.
>> (e.g. all local work including staging things, making local "fixup" commits)
>>
>> The addressing scheme should not be too hardcoded, we should rather
>> treat it similar to the cipher schemes in pgp. The additional complexity that
>> we have is the longevity of existence of things, though.
>
> The not-so-well-hidden agenda was exactly that we _SHOULD_ not
> mimick PGP.  They do not have a requirement to encourage everybody
> to use the same thing because each message is encrypted/signed
> independently, i.e. they do not have to chain things like we do.

But there is a scenario where supporting more hashes, in parallel, is
beneficial:

Let's assume that git is retroffited to always support the "default"
SHA-3, but support additionally more hash-funcs.
If in the future SHA-3 also gets defeated, it would be highly unlikely
that the same math would also break e.g. Blake.
So certain high-profile repos might choose for extra security 2 or more hashes.

Apologies if I'm misusing the list,
  Kostis