SHA1 collisions proven possisble

James DeVincentis james.d at
Thu Mar 2 03:50:32 UTC 2017

I like the footnote they attached specifically for SHA1. 

"[3] Google spent 6500 CPU years and 110 GPU years to convince everyone we need to stop using SHA-1 for security critical applications. Also because it was cool."

It’s also not preimage. This isn’t even a FIRST preimage attack. That table needs an additional field type: “First non-preimage deliberate crafted collision created”. 

However, it proves a theory that maybe with some refining *could* turn into a preimage attack. 

Realistically any hash function *will* have collisions when two items are specifically crafted to collide after expending insane amounts of computing power, money, and… i wonder how much in power they burned for this little stunt.

> On Mar 1, 2017, at 9:42 PM, Nick Hilliard <nick at> wrote:
> James DeVincentis via NANOG wrote:
>> On top of that, the calculations they did were for a stupidly simple
>> document modification in a type of document where hiding extraneous
>> data is easy. This will get exponentially computationally more
>> expensive the more data you want to mask. It took nine quintillion
>> computations in order to mask a background color change in a PDF.
>> And again, the main counter-point is being missed. Both the good and
>> bad documents have to be brute forced which largely defeats the
>> purpose. Tthose numbers of computing hours are a brute force. It may
>> be a simplified brute force, but still a brute force.
>> The hype being generated is causing management at many places to cry
>> exactly what Google wanted, “Wolf! Wolf!”.
> The Reaction state table described in
> appears to be entertainingly accurate.
> Nick

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