Re: Git and SHA-1 security (again)

[Duy Nguyen <pclouds@gmail.com>]

On Mon, Jul 18, 2016 at 6:51 PM, Duy Nguyen <pclouds@gmail.com> wrote:
> On Sun, Jul 17, 2016 at 4:21 PM, brian m. carlson
> <sandals@crustytoothpaste.net> wrote:
>> I'm going to end up having to do something similar because of the issue
>> of submodules.  Submodules may still be SHA-1, while the main repo may
>> be a newer hash.
>
> Or even the other way around, main repo is one with sha1 while
> submodule is on sha256. I wonder if we should address this separately
> (and even in parallel with sha256 support), making submodules work
> with an any external VCS system (that supports some basic operations
> we define).

Post-shower thoughts. In a tree object, a submodule entry consists of
perm (S_IFGITLINK), hash (which is the external hash) and path. We
could fill the "hash" part with all zero (invalid, signature of new
submodule hash format), then append "/<hashtype>:<external hash>" to
the "path" part. This way we don't have to update tree object or index
format. And I suspect the "path" part is available everywhere we need
to handle submodules already, so extracting the external hash should
be possible...
-- 
Duy