The attack is not as difficult as that. If you can create a valid git object which collides with another git object, signatures for the previous object tree (wh

The attack is not as difficult as that. If you can create a valid git object which collides with another git object, signatures for the previous object tree (which is identified by SHA-1 hash) will be valid for the new object tree (which has the same hash). So a collision in a blob that represents a file (or any other internal git object) will cause in your old signature still being valid for the new file that corresponds to the git collision.