Re: SHA1 collisions found
From: Jakub Narębski <hidden>
Date: 2017-02-23 20:49:22
W dniu 23.02.2017 o 18:12, David Lang pisze:
On Thu, 23 Feb 2017, Junio C Hamano wrote:quoted
On Thu, Feb 23, 2017 at 8:43 AM, Joey Hess [off-list ref] wrote:quoted
Since we now have collisions in valid PDF files, collisions in valid git commit and tree objects are probably able to be constructed.That may be true, but https://public-inbox.org/git/Pine.LNX.4.58.0504291221250.18901@ppc970.osdl.org/it doesn't help that the Google page on this explicitly says that this shows that it's possible to create two different git repos that have the same hash but different contents. https://shattered.it/ How is GIT affected? GIT strongly relies on SHA-1 for the identification and integrity checking of all file objects and commits. It is essentially possible to create two GIT repositories with the same head commit hash and different contents, say a benign source code and a backdoored one. An attacker could potentially selectively serve either repository to targeted users. This will require attackers to compute their own collision.
The attack on SHA-1 presented there is "identical-prefix" collision, which is less powerful than "chosen-prefix" collision. It is the latter that is required to defeat SHA-1 used in object identity. Objects in Git _must_ begin with given prefix; the use of zlib compression adds to the difficulty. 'Forged' Git object would simply not validate... https://arstechnica.com/security/2017/02/at-deaths-door-for-years-widely-used-sha1-function-is-now-dead/