[Cryptography] Explaining PK to grandma
Nico Williams
nico at cryptonector.com
Mon Nov 25 20:10:21 EST 2013
On Mon, Nov 25, 2013 at 06:02:53PM -0500, Kelly John Rose wrote:
> What is so crazy about this analogy?
I just finished trying this analogy on several teenagers, and the
verdict is that it works. The difficulties of using crypto properly
became most evident when I threw in the need for a 411-type white pages
service.
(It will be difficult to try it on grandma, but only because she's far
away, and hard of hearing.)
Some salient points:
- symmetric crypto is easily understood (decoder rings and all that)
- the padlock analogy works (whether you get open padlocks from your
peers or enter a public code for them into off-the-shelf padlocks, or
"print" them, as you suggest)
- the postal service part works, but
- what really drove the point home was the 411 online white pages
concept.
- the very next question was: "so why not always do the symmetric
thing?", so I explained how pair-wise keying fails to scale.
"oh"
I should note that I've previously been able to explain plain old DH
using a pencil and a napkin. DH is easy to explain, and easy to
understand. It's fun to see the lightbulb go off!
> Public Key encryption works as follows:
>
> Your son-in-law build a little lock factory he gives you that you put on
> your computer, this machine creates padlocks that only his key can open.
> So when you want to send him an package, you just tell the machine to
> print a padlock, you put your package into a box, lock it with the
> padlock and mail it to him. As long as you know the lock factory you
> have is his, no one but him will be able to open it.
>
> What am I missing here?
Signatures. I don't know of a good analogy for signatures. Anyone?
Nico
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