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.
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