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Linus' reply on Git and SHA-1 collision

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Re: Linus' reply on Git and SHA-1 collision

#31

Post by DiabloD3 »

zkms wrote: post #21
paulddraper wrote: post #16

Linus has toned down a lot from a decade ago. > You are _literally_ arguing for the equivalent of "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected". > That's not engineering. That's five-year-olds discussing building their imaginary forts ("I want gun-turrets and a mechanical horse one mi…

> "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected" I think this is a shockingly good example of how smart people get security questions utterly wrong. The right analogy when it comes to security has to involve some type of adversary, not just random, unmotivated natural phenomena -- as l…

The A-10 isn't a plane, it's a gun with a plane wrapped around it.

And it hunts tanks.

Re: Linus' reply on Git and SHA-1 collision

#32

Post by jessaustin »

zkms wrote: post #21
paulddraper wrote: post #16

Linus has toned down a lot from a decade ago. > You are _literally_ arguing for the equivalent of "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected". > That's not engineering. That's five-year-olds discussing building their imaginary forts ("I want gun-turrets and a mechanical horse one mi…

> "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected" I think this is a shockingly good example of how smart people get security questions utterly wrong. The right analogy when it comes to security has to involve some type of adversary, not just random, unmotivated natural phenomena -- as l…

Haha you reminded me of the old riddle about how British engineers decided where to place armor on their bombers, because, "if they put it everywhere the plane wouldn't get off the ground!"

Re: Linus' reply on Git and SHA-1 collision

#33

Post by jessaustin »

DiabloD3 wrote: post #31
zkms wrote: post #21

Earlier quoted context omitted.

> "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected" I think this is a shockingly good example of how smart people get security questions utterly wrong. The right analogy when it comes to security has to involve some type of adversary, not just random, unmotivated natural phenomena -- as l…

The A-10 isn't a plane, it's a gun with a plane wrapped around it. And it hunts tanks.

We took a couple of minutes off this afternoon to watch some Warthogs pulling some tight maneuvers... to think, USAF wants to sell them all to Poland...

Re: Linus' reply on Git and SHA-1 collision

#34

Post by tanderson92 »

jessaustin wrote: post #32
zkms wrote: post #21

Earlier quoted context omitted.

> "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected" I think this is a shockingly good example of how smart people get security questions utterly wrong. The right analogy when it comes to security has to involve some type of adversary, not just random, unmotivated natural phenomena -- as l…

Haha you reminded me of the old riddle about how British engineers decided where to place armor on their bombers, because, "if they put it everywhere the plane wouldn't get off the ground!"

Specifically, during the war the engineers took a Bayesian approach and put armor on the bombers in locations where bombers which came back did not have damage. Reason being that hits in those sections of the planes were more likely than not resulting in fatalities. Smart thinking.

Re: Linus' reply on Git and SHA-1 collision

#36

Post by cldellow »

Strom wrote: post #26

Downloading the PDFs [1] and comparing their sizes takes less than a minute. They're the exact same size. Yet here we have Linus making one bet after another that size has to be different for this attack. Now to be fair, he also keeps repeating that he hasn't seen the attack yet . Which leads me to question why is this post interesting to HN? Is it to show how Linus aimlessly speculates and gets his guesses wrong? --…

I think you're violently agreeing with Linus here.

He says:

> pdf's don't have that issue, they have a fixed header and you can fairly arbitrarily add silent data to the middle that just doesn't get shown.

In other words, he expects the PDFs to have the same size because silent data has been arbitrarily added to the middle that doesn't get shown.

Re: Linus' reply on Git and SHA-1 collision

#37

Post by nyargh »

lamontcg wrote: post #29
nialv7 wrote: post #22

> but git doesn't actually just hash the data, it does prepend a type/length field to it. To me it feels like this would just be a small hurdle? But I don't really know this stuff that well. Can someone with more knowledge share their thoughts? I think Linus also argued that SHA-1 is not a security feature for git ( https://youtu.be/4XpnKHJAok8?t=57m44s ). Has that been changed?

Yeah what is the attack here? If you don't have permissions to my repo that already limits the scope of attackers to people who already have repo access. At that points there's tons of abuse avenues open that are simpler. If someone could fork a repo, submit a pull request and push a sha for an already existing commit and that would get merged and accepted (but not show up in the PR on github) well that would certain…

If the sha matched an existing one, would it be merged as part of the changeset, or just ignored?

Re: Linus' reply on Git and SHA-1 collision

#38

Post by protomyth »

DiabloD3 wrote: post #31
zkms wrote: post #21

Earlier quoted context omitted.

> "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passengers would be protected" I think this is a shockingly good example of how smart people get security questions utterly wrong. The right analogy when it comes to security has to involve some type of adversary, not just random, unmotivated natural phenomena -- as l…

The A-10 isn't a plane, it's a gun with a plane wrapped around it. And it hunts tanks.

I am told the gun is also quite good at shooting ground troops. A relative of mine had an A-10 stay with his group most of the night. Every time the enemy decided to go after them the A-10 came back and made them rethink their actions.

Re: Linus' reply on Git and SHA-1 collision

#39

Post by loup-vaillant »

ckozlowski wrote: post #30
philsnow wrote: post #28

Earlier quoted context omitted.

> > If we want to have any kind of confidence that the hash is reall yunbreakable, we should make it not just longer than 160 bits, we should make sure that it's two or more hashes, and that they are based on totally different principles. Why is this quoted in support of an argument that Linus used to come across as a lunatic in online correspondence ? This seems to me like an entirely reasonable way to make it very,…

I think Linus' point at the time was that the computational cost added to every transaction to protect against a (at the time) highly infeasible event of questionable impact was a poor cost vs. benefit argument. Adding complexity isn't free, and there needs to be a measurable benefit against a threat. But of course, now is not then. And I think zkms' metaphor "there's angry and armed people shooting at my plane with…

While we're at it, every SHA-3 finalist were deemed "good enough", so we now have more than 2 such hashes. (I personally love Blake2b.)

Re: Linus' reply on Git and SHA-1 collision

#40

Post by edanm »

tanderson92 wrote: post #34
jessaustin wrote: post #32

Earlier quoted context omitted.

Haha you reminded me of the old riddle about how British engineers decided where to place armor on their bombers, because, "if they put it everywhere the plane wouldn't get off the ground!"

Specifically, during the war the engineers took a Bayesian approach and put armor on the bombers in locations where bombers which came back did not have damage. Reason being that hits in those sections of the planes were more likely than not resulting in fatalities. Smart thinking.

Definitely smart thinning, but not sure what makes it Bayesian.
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