Re: MD6 withdrawn from SHA-3 competition

2009-07-07 Thread Josh Rubin
Paul Hoffman wrote:
> At 10:39 AM -0700 7/4/09, Hal Finney wrote:
>   
>> But how many other hash function candidates would also be excluded if
>> such a stringent criterion were applied? Or turning it around, if NIST
>> demanded a proof of immunity to differential attacks as Rivest proposed,
>> how many candidates have offered such a proof, in variants fast enough
>> to beat SHA-2?
>> 
>
> The more important question, and one that I hope gets dealt with, is
> what is a sufficient proof. We know what proofs are, but we don't have
> a precise definition. We know what a proof should look like, sort
> of. Ron and his crew have their own definition, and they can't make
> MD6 work within that definition. But that doesn't mean that NIST
> wouldn't have accepted the fast-enough MD6 with a proof from someone
> else. 

Mathematicians have a precise definition of what a proof is, thanks to
logicians like David Hilbert and Kurt Goedel. But people in all
disciplines have a terrible time formulating problems, and remembering
the conditions under which a statement was proved. They also quote
theorems incorrectly, and errors propagate through the less
well-reviewed parts of the literature.

--
Josh Rubin
jlru...@gmail.com

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Re: MD6 withdrawn from SHA-3 competition

2009-07-07 Thread Chen Ke-Fei Lin
At 10:39 AM -0700 7/4/09, Hal Finney wrote:
>But how many other hash function candidates would also be excluded if
>such a stringent criterion were applied? Or turning it around, if NIST
>demanded a proof of immunity to differential attacks as Rivest proposed,
>how many candidates have offered such a proof, in variants fast enough
>to beat SHA-2?

Several hash candidates have proofs against differential attacks but only
four with such proofs are faster than SHA-2 (Edon-R, Shabal, Cheetah and
Keccak).
But according to http://eprint.iacr.org/2008/511.pdf
Keccak and Cheetah in 32-bit mode are not actually faster than SHA-2.

C.K.F. Lin

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