Linus' reply on Git and SHA-1 collision

Re:Linus' reply on Git and SHA-1 collision by jwilk on Friday February 24, 2017 @04:33AM (#13722271)

> The length field makes the attack significantly more difficult. In the publish attack, you take 2 fixed input and prepend special data to make the collision.

That's not how the attack works. Not at all.

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Re:Linus' reply on Git and SHA-1 collision by hvidgaard on Friday February 24, 2017 @05:06AM (#13722433)

If you ignore the prepend part, it is in essence taking known input and calculate a collision.

> This is an identical-prefix collision attack, where a given prefix P is extended with two distinct near-collision block pairs such that they collide for any suffix S.

And

> Our example colliding files only differ in two successive random-looking message blocks generated by our attack. We exploit these limited differences to craft two colliding PDF documents containing arbitrary distinct images.

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