[Cryptography] Explaining PK to grandma

[Nico Williams]

On Mon, Nov 25, 2013 at 01:29:29PM +0100, Ralf Senderek wrote:
> On Mon, 25 Nov 2013, Nico Williams wrote:
> >  [...]
> 
> IMHO the analogy does not explain encryption, because grandma's
> vision will be a box that she locks with a key, that's familiar.

Sealing an envelope and dropping it into a mailbox is an analog for
encryption.  It's a lousy one, I know, but we're not going to get
perfect off-line world analogs for crypto, and what we need are not so
much explanations of low-level details of crypto but high-level aspects
of security.

> But unless you can convince gandma that there is a box that you lock with
> one key and open with another, she hasn't understood anything about RSA.
>
> And the most difficult thing is still left to be explained: how does
> the key she has used to lock the first box get to the recipient?

That's not the right analogy.  The recipient will only get the mail if
she addressed it correctly, and only they will be able to open the
envelope.  This analogy covers even physical security aspects of crypto.

> At that point granny will be crying out for something simpler, and we
> have to tell her that we cannot make it simpler.

The thing that causes complexity is the unwieldiness of cryptographic
keys.  If we could recall keys we'd not have passwords, and we wouldn't
have much need for PKI.

Nico
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