sha1collisiondetection

It is possible; the researchers estimate the likelihood of a false positive at 2^-90 (which puts us back in "Sun engulfs the Earth" territory). There are metrics that will alert GitHub's infrastructure team if a collision is found (to confirm that we aren't seeing any false positives). Those metrics were quietly shipped (without the matching "die") for a week before flipping the final switch. If you want to know more about the patterns, see the sha1collisiondetection project: https://github.com/cr-marcstevens/sha1collisiondetection There's a research paper linked in the README.

The article links to this repo that actually does the work of finding possible collisions: https://github.com/cr-marcstevens/sha1collisiondetection My understanding of it is that it runs a SHA-1 and examines the internal state of the of the digest along the way to see if it matches up with known vectors that could be manipulated to cause a collision.

Correct. He's talking about the automated method used on shattered.io to detect files which use the attack. See: https://github.com/cr-marcstevens/sha1collisiondetection They're basically building that into git so that if this specific collision attack is ever used, git will notice and throw a warning/error.

The git mailing list talked about using ubc_check() from here: https://github.com/cr-marcstevens/sha1collisiondetection/blo...

https://github.com/cr-marcstevens/sha1collisiondetection implements a hash that is compatible with SHA-1 for all non-nefarious purposes, and has no known weakneses. Somebody already submitted patch series to (optionally) use it in git in place of SHA-1: https://www.spinics.net/lists/git/msg296714.html

I love the fact that there is a tool for detecting any collision using this algorithm: https://github.com/cr-marcstevens/sha1collisiondetection and it's super effective: The possibility of false positives can be neglected as the probability is smaller than 2^-90. It's also interesting that this attack is from the same author that detected that Flame (the nation-state virus) was signed using an unknown collision algorithm on MD5 (cited in the shattered paper introduction).