full-disclosure - Re: OpenID/Debian PRNG/DNS Cache poisoning advisory

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Date: Tue, 12 Aug 2008 16:44:50 -0500 (   )
From: "Seth Breidbart" <sethb@...ix.com>
To: "Forrest J. Cavalier III" <mibsoft@...software.com>
Cc: Dan Kaminsky <dan@...para.com>, cryptography@...zdowd.com,
	Eric Rescorla <ekr@...workresonance.com>,
	Nicolas Williams <nicolas.williams@....com>,
	Dave Korn <dave.korn@...imi.com>,
	full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com,
	'OpenID List' <general@...nid.net>, security@...nid.net,
	"Leichter, Jerry" <leichter_jerrold@....com>
Subject: Re: OpenID/Debian PRNG/DNS Cache poisoning
	advisory

On Fri, August 8, 2008 8:37 pm, Forrest J. Cavalier III wrote:
> Eric Rescorla wrote:
>>
>> To be concrete, we have 2^15 distinct keys, so, the
>> probability of a false positive becomes (2^15)/(2^b)=2^(b-15).
>> To get that probability below 1 billion, b+15 >= 30, so
>> you need about 45 bits. I chose 64 because it seemed to me
>> that a false positive probability of 2^{-48} or so was better.

> Since it's a known set, I think you can use perfect hashing.
> There will still be false positives,

Since we don't care _which_ bad key it is, wouldn't
as-imperfect-as-possible hashing be better, by minimizing false positives?

Seth


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