On 02/23/2017 03:32 PM, James Hogarth wrote:
On 23 February 2017 at 19:55, Lamar Owen lowen@pari.edu wrote:
Not to stir up a hornets' nest, but how does Google's announcement at https://shattered.it affect this now? (Executive summary: Google has successfully produced two different PDF files that hash to the same SHA-1.) There is a whole paragraph on 'How is GIT affected?'
To stave off another ridiculous thread - short version is simply "it isn't"
Ridiculous? Seriously? I don't think it's time to be in panic mode, but it is time to prepare for the generation-after-next of GPUs which will be able to produce SHA-1 collisions quickly enough to be able to keep up with a git repo.
Dan Goodin disagrees that it's not a problem for git in the long run. See: https://arstechnica.com/security/2017/02/at-deaths-door-for-years-widely-use... (not a bit of hyperbole in that headline, right? ) Maybe it's a bit premature to call it 'dead' but it is definitely in its death rattles.
Google is scheduled to release the source code to produce arbitrary "identical-prefix" collisions of SHA-1 hashes in three months. You need about $110,000 worth of compute time to pull off the attack, and that number will go down. We're basically at the same place now with SHA-1 as we were in 2010 with MD5.
The full paper can be read at https://shattered.io/static/shattered.pdf
And an interesting discussion on git's potential handling of a SHA-1 collision on a blob is at https://stackoverflow.com/questions/9392365/how-would-git-handle-a-sha-1-col...
It may not be urgent, but it's not ridiculous.