On Tuesday, 15 בNovember 2005 20:55, Lionel Elie Mamane wrote:
> They'd take about 2^60 seconds. That is about 10^18 seconds. There
> are about 3*10^7 s to a year, so they'd take about 3*10^10 years, so
> "merely" 10 billion years.
Sucks to be us ;-)
> Looks like you are confusing collision resistance and second preimage
> resistance (or preimage resistance).
Hmm.. yes I am. sorry about that.
> What has _already_ happened is that
> methods for collision construction in about 2^60 hashings have been
> found, and are likely to be improved upon.
Actually, 2^63 last time I checked (5 minutes ago). So that shaves about
2^17 from our result which brings the total of time down to 200 thusand
years. This is bad for cryptographic applications, but still all things
considered - doesn't mean much to kernel development.
> No. Due to the way SHA-1 works (treating chunks of data in a greedy
> manner, which makes it vulnerable to length-extension attacks), once
> you have created a collision for small blocks A and B, you can:
>
> - choose a prefix M freely (the size must be congruent to a constant
> modulo another constant)
> - concatenate A and B, respectively
> - choose a suffix S freely
>
> And then MAS and MBS have same SHA-1 hash. So as big blocks as you
> want.
That's funky - I didn't know that. For the purpose of fooling kernel
developers, you'd still need to have both A and B at least looking like
C code or maybe even compiling, which I suspect would be quite a
problem.
--
Oded
::..
"Xenix is the pinnacle of modern UNIX design, and will be used for many
years to come."
-- Xenix OS API manual
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