Re: [dane] hash truncated to 28 octets

[Viktor Dukhovni <[e-mail]>]

On Tue, Aug 04, 2015 at 03:50:32AM -0400, Paul Wouters wrote:

> >2,since some local-parts are longer than 28 octets, are there some collisions after hash?truncated?to?28?octets??
> 
> I think if you have 100.000 email addresses in one domain, the chance of
> collision would be pretty small. but non-zero.

You'd need 2^112 email addresses for an appreciable chance of
collision.  If every person on the planet (say 10^{10} people some
day) each had 100 email addresses in the same domain, that'd be
10^{12} or ~2^{40} addresses.  The collision probability would be
around 2^{80}/2^{112} = 2^{-32} ~ 10^{-6}.  With "just" 10^{10}
addresses, it drops by a factor of 10^4 to 10^{-10}.

So we'd need around 10^10 Gmail sized domains before seeing a
collision in one of them.

-- 
	Viktor.