Re: [PATCH] Implement fast hash-collision detection

On Thu, Dec 1, 2011 at 1:05 AM, Junio C Hamano [off-list ref] wrote:

Nguyen Thai Ngoc Duy [off-list ref] writes:

quoted

What I'm thinking is whether it's possible to decouple two sha-1 roles
in git, as object identifier and digest, separately.

Why it would be a good thing? If you have a collided identifier, somebody
has to choose which blob a particular tree wants to have at the path, and
because the tree would not record anything but the identifier, you cannot.

Accidental collision likelihood is small enough we don't have to care about.

quoted

...
The day sha-1 is broken, a project can generate new digests from its
old good repo and enforce developers to use new digests for
verification instead of sha-1. sha-1 is still used by git as
identifier after that day.

And an old blob that is identified with a SHA-1 now has a new blob that
has different contents but happens to have the same SHA-1. How does Git
decide which blob to use when a particular object is named by the SHA-1?

Again, I assume the likelihood that a content happens to have the same
sha-1 with another one is too low to care about. If they are, it's
must be an attack. We do not allow malicious objects to enter in the
first place using other digests. Once objects are in, they are safe to
use.
-- 
Duy