On Tue, Oct 22, 2013 at 4:14 PM, DataPacRat <[email protected]> wrote:
> On Tue, Oct 22, 2013 at 3:32 PM, Brian E Carpenter > <[email protected]> wrote: > > On 23/10/2013 04:55, DataPacRat wrote: > >> On Mon, Oct 21, 2013 at 4:46 PM, DataPacRat <[email protected]> > wrote: > > >>> Eg, if I trust my own vCard at a level of 100 decibans, > >>> I trust Alice's card at 30, and Alice trusts Bob's card at 40, it's > >>> easy to determine that Bob's card should be trusted at somewhere under > >>> 30 decibans. (Real situations would be much more complicated, such as > >>> with multiple assertion paths; but this is still early days.) > > > > Excuse my ignorance, but while I have no difficulty understanding > > Bayes' Theorem and know who invented decibans, I don't understand how > > I can use a trust value that is different from 1 or 0, in practice. > > > > I won't trust somebody with half my PIN code because they rate 47 > decibans. > > I could suggest that the values be interpreted in terms of LaPlace's > Sunrise formula - eg, "there's been 10 reports of the key being used > falsely and 500,000 that it's been used successfully: Do you wish to > continue?". > This is why I would not attempt to use Bayesian logic. You have no way to measure probability reliably. An attacker can simulate any behavior before they defect. The only measure that is useful is the cost of simulating that behavior. If it is prohibitively high then we can decide to trust them. Remember that Bernie Madoff paid out 100% of every redemption request right up to the point where the money ran out. -- Website: http://hallambaker.com/
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