Re: Dishonest Forks? | Was - Re: [Namedroppers-honest] Brian Smith asks: ?Who is Dean Anderson?

I guess I missed that in all the noise at the time.

You wrote: 

> OK, I tried to follow your math. But it really doesn't make any sense
> to me.

Well, I hope you figure it out before they give you a PH.D. in... what?  
computer science?

> ..that the first parameter (the random space) would be 64510*65536.  
> The second parameter (number of balls in one urn) can remain 200
> (MAXUDP). The third parameter (number of balls in the other urn) is
> actually the number of packets sent by the attacker.

That is incorrect. The first parameter is the size of the Urn, which is
64510 ports, since the first 1025 can't be used.

Possibly, you should consult the reference I cited. CRC handbook of
Applied Cryptography.

> And p4 is the _probability_ of at least one coincidence. So the 
> formula does not yield the number of expected packets;

That is correct. From the probability, one can calculate the number of
packets necessary to guarentee success.

> you calculate the probability based on a particular number of packets.

???? If you know one, you can calculate the other.

> So you might ask about the number of packets required to make the
> probability 50%.

A question, I suppose.  Not one we care about, now.

> So the number we really want to know is "n", where 0.5 = 
> p4(64510*65536, 200, n).
>
> Which turns out to be around 16 million.

I think your calculation above is meaningless, because 64510 * 65536 is
the wrong number.  The number we are interested in is how many packets 
have to be sent to get a collision. 

		--Dean

On Wed, 10 Mar 2010, Jeff King wrote:

> On Wed, Mar 10, 2010 at 03:25:01PM -0500, Dean Anderson wrote:
> 
> > Well, other people see it differently.  My math worked out; my math had
> > a credible source (the CRC Handbook on Cryptography).  Day's math didn't
> > work out, and he just made it up.  Day and Kaminsky have been outed as
> 
> Your math may have had a credible source, but you applied it
> incorrectly. I already explained that here:
> 
>   http://article.gmane.org/gmane.network.djbdns/13820
> 
> And you never responded.
> 
> -Peff
> 
> 

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