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Solving for faster SHA-1 collision detectionsam.dev

SHA-1 with collision detection doesn't have to be so slow. How a code generator that moves the checks to SIMD can narrow the gap to plain SHA-1 to ~20–30%.

58 points•srijs•9 days ago•10 comments•
#sha#collision#detection#collision detection#solving#faster#faster sha#code

10 comments

gleenn7 days ago
This seems extremely cool, but man does it also sound complicated. The write up was thorough but the algorithm seems so complicated that the author can't even write good tests for it is concerning. I would be very concerned their algorithm might accidentally skip something important accidentally given they are dealing with dynamically combining large binary expressions. You can make it fast, but if you can't prove it and it's security related that probably needs to be proved out more, even if SHA1 is already compromised.
ted_dunning7 days ago
Fuzz tests with tailored random distributions and good logical property tests are excellent tests.

What would you do better?

Also, the author didn't say that there were no other tests. They just said that they use fuzz + property tests a fair bit.

bawolff7 days ago
Why do you conclude the author cannot write good tests for it?
rurban7 days ago
Does git proper already accepts rust? 2x faster pack checks would be worthwhile, as it affects everybody. I heard since 2.55 they already do
masklinn7 days ago
Git proper has had rust code in it since 2.52, as an opt-in optional. 2.55 makes it opt out. 3.0 might make it required.
someonebaggy7 days ago
This writing almost feels AI, but it's not AI. Why is that?
bawolff7 days ago
This reads like a totally normal article to me. At some point these AI accusations feel like a witch hunt.
entrope7 days ago
I thought it was a really good, clear write-up of a very nice engineering discovery and optimization. If anything, I think an LLM would generate native superscript for the `2^(-r)` expression, so I didn't have an impression of LLM authorship.

Maybe an LLM did the search for what expressions to put in the blocks vs tail of the vectorized collision detection, but that seems like a good place to use an LLM as long as all of the expected bit relations are verified as checked properly.

Obscurity43406 days ago
Its seriously such a cheap, easy, and lazy accusation to make by just accusing it of being slop, I actualky hate the slop-accusing more then any slop. Any bot can just randomly say slop and in at least someones eyes a whole writeup will have been discredited thru tho fault of the author.

It needs to stop, if people have a factual or actual valid criticism of the facts or claims then by all means, go to town. But Im done with the slop screamers, its a downvote and scorn all the way down for those

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