I didn't know either. From Wikipedia [1], SHA-1 has been considered insecure to some degree since 2005. Following the citations, apparently it's been known sinc

I didn't know either. From Wikipedia [1], SHA-1 has been considered insecure to some degree since 2005. Following the citations, apparently it's been known since at least August 2004 [2] but maybe not demonstrated in SHA-1 until early 2005. git's first release was in 2005, so I guess technically SHA-1 issues could've been known or suspected during development time. More generously, it could've been somewhat simultaneous. It sounds like it was considered a state-sponsored level attack at the time, if collisions were even going to be possible. Don't know if the git devs knew this and intentionally chose it anyway, or just didn't know. [1] https://en.wikipedia.org/wiki/SHA-1 https://en.wikipedia.org/wiki/SHA-1 [2] https://www.schneier.com/blog/archives/2005/02/cryptanalysis_o.html https://www.schneier.com/blog/archives/2005/02/cryptanalysis... EDIT: sibling comment has evidence that Linus did in fact know about it and considered it an impractical vector at the time https://git.vger.kernel.narkive.com/9lgv36un/zooko-zooko-com-revctrl-colliding-md5-hashes-of-human-meaningful#post2 https://git.vger.kernel.narkive.com/9lgv36un/zooko-zooko-com...