Git 3.0 will make SHA-256 the new default content hashing algorithm and it will be an incomprehensibly expensive and ultimately valueless and avoidable global nightmare.
In a well-fleshed-out post, Scott Chacon shows how unneecessary Git 3.0’s move to replace SHA-1 with SHA-256 is.
There’s people who seriously think commit hashes are there for security purposes? Furthermore, there are git MAINTAINERS that think this?
How absurd. Author is completely right, making SHA-256 the default implementation serves no purpose. SHA-1 is a completely valid algorithm for non-security use cases, which is precisely how git uses it. This is a solution looking for a problem.
I think he’s maybe overblowing the impact of this change. Realistically, the only ones who are going to be impacted are the folks who maintain git-related tools and forges, as he mentions. The rest of us probably won’t even notice. But that’s still a ton of pointless work for those folks.
Wait, they don’t affect security? Wouldn’t a hash collision mean pulling that hash from GitHub would pull wrong code? Or maybe delete code? I’d assume the hash is used as a lookup key in a database somewhere.
You also pin dependencies to specific hashes for security reasons.
The vulnerability of SHA-1 is that it’s possible for an attacker to find colliding hashes. But that’s not really an attack vector, because it’s not like they can find aatching hash for just ANY input. In order to pull off an attack, using a hash collision, an attacker would have to already be trusted within the controlling system, in which case they can do a hell of a lot worse than swapping out a file.
Like you say, the hash is used as a lookup key within the git repo’s database. The requirement for that is uniqueness, which SHA-1 still fulfills just fine. The trust isn’t in the database lookup, the trust is in the systems that controls access to and distribution of that database.
As the article points out, Linus Torvalds himself said as much in 2005, when he first wrote git:
I really think people should not consider the sha1 the “security”. The real security is in distribution.
I think he’s maybe overblowing the impact of this change.
Maybe… But I don’t look forward to working with the dozens of IT folks at my company who all installed git once and have never upgraded. This will be multiple meetings, show up on slide decks, break builds…
There’s people who seriously think commit hashes are there for security purposes? Furthermore, there are git MAINTAINERS that think this?
How absurd. Author is completely right, making SHA-256 the default implementation serves no purpose. SHA-1 is a completely valid algorithm for non-security use cases, which is precisely how git uses it. This is a solution looking for a problem.
I think he’s maybe overblowing the impact of this change. Realistically, the only ones who are going to be impacted are the folks who maintain git-related tools and forges, as he mentions. The rest of us probably won’t even notice. But that’s still a ton of pointless work for those folks.
Wait, they don’t affect security? Wouldn’t a hash collision mean pulling that hash from GitHub would pull wrong code? Or maybe delete code? I’d assume the hash is used as a lookup key in a database somewhere.
You also pin dependencies to specific hashes for security reasons.
If you need security, you must sign the commits.
The blog post lays it out pretty well.
The vulnerability of SHA-1 is that it’s possible for an attacker to find colliding hashes. But that’s not really an attack vector, because it’s not like they can find aatching hash for just ANY input. In order to pull off an attack, using a hash collision, an attacker would have to already be trusted within the controlling system, in which case they can do a hell of a lot worse than swapping out a file.
Like you say, the hash is used as a lookup key within the git repo’s database. The requirement for that is uniqueness, which SHA-1 still fulfills just fine. The trust isn’t in the database lookup, the trust is in the systems that controls access to and distribution of that database.
As the article points out, Linus Torvalds himself said as much in 2005, when he first wrote git:
Maybe… But I don’t look forward to working with the dozens of IT folks at my company who all installed git once and have never upgraded. This will be multiple meetings, show up on slide decks, break builds…
It’s going to be a right pain for nothing.