What puzzles me in all this long and rather arcane discussion is
why isn't the solution of using a double hash - MD5 *and* SHA
whatever. The odds of find a double collision go way up.
Some open source software people are already doing this. I've
played around with the sample files that are out there and find
an easy way to do this but I don't have either the horsepower or
skill to be at all definitive.
My gut tells me that using two processes that use different
algorithms, even though compromised, will raise the bar so high
that it would be secure for a long time.
At my skill level and horsepower I can't find even a single way
to do this with CRC32 and MD5. Granted, that certainly doesn't
mean a whole lot.
But to take a real world example, a safety deposit box, the two
keys have to work together to open the box. It really does not
matter is one is a Yale and the other a combination, either one
of which are easily compromised by themselves, but together you
would have to find both at the same time to open the box, a lot
tougher problem.
Best,
Allen
Francois Grieu wrote:
[EMAIL PROTECTED] wrote:
Dp := any electronic document submitted by some person, converted to its
canonical form
Cp := a electronic certificate irrefutably identifying the other person
submitting the document
Cn := certificate of the notary
Tn := timestamp of the notary
S() := signature of the notary
S( MD5(Tn || Dp || Cp || Cn) ).
In this context, the only thing that guards agains an attack by
"some person" is the faint hope that she can't predict the Tn
that the notary will use for a Dp that she submits.
That's because if Tn is known (including chosen) to "some person",
then (due to the weakness in MD5 we are talking about), she can
generate Dp and Dp' such that
S( MD5(Tn || Dp || Cp || Cn) ) = S( MD5(Tn || Dp' || Cp || Cn) )
whatever Cp, Cn and S() are.
If Tn was hashed after Dp rather than before, poof goes security.
Francois Grieu
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