PlayStation 3 predicts next US president
William Allen Simpson
william.allen.simpson at gmail.com
Mon Dec 10 12:31:43 EST 2007
Francois Grieu wrote:
> 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.
First of all, the weakness in MD5 (computational feasibility over time)
that "we are talking about" is not (yet) a preimage or second preimage
attack. Please don't extrapolate your argument.
Second of all, you need to read my messages more carefully. No good
canonical format allows random hidden fields or images.
Third of all, that's not a weakness of a notary protocol -- it's a trap!
The whole point of a notary is to bind a document to a person. That the
person submitted two or more different documents at different times is
readily observable. After all, the notary has the document(s)!
Remember, the notary is not vouching for the validity of the content of
the document. A notary only certifies that something was submitted by
some person at some time. And that cannot be broken by making multiple
submissions, or submissions that themselves have the same hash.
That's one reason I'm much more interested in the attack on X.509.
> If Tn was hashed after Dp rather than before, poof goes security.
But since it's not, that's a ridiculous strawman. I was remembering PGP
off the top of my head. Fairly certain that Kerberos does, too. Not
everybody is naive!
And since the timestamp is "predictable" (within some range, although
picoseconds really aren't very predictable), the protocols that I've
designed include message identifiers, nonces, and sequence numbers, too.
As you may recall, I mentioned that there were other fields....
He asked for an explanation about how a document is identified, he got
one. Don't expect me to redesign an entire notary (or even a timestamp)
protocol on a Sunday evening for a mailing list.... Really, there are
fairly secure standards already available.
However, the actual topic of this thread is code distribution. In that
case, there is no "other" party certifying the documents. The code
packager is also the certifier. There is (as yet) no weakness in the
MD4 family (including MD5 and SHA1) that allows this attack by another
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