[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
-- 


More information about the cryptography mailing list