It's 2014. Are we there yet?

[Robert J. Hansen]

> I think this one is easy.  The key pair is a mathematical analog of
> the old spy trick (I'm sure it's in the movies somewhere) of tearing a
> playing card in two, giving one piece to each of two people who do not
> know each other but must be able to recognize one another.  No two
> cards tear *exactly* the same way.  And the math does this *much*
> better.

I prefer an analogy of a mailbox.

Anyone can drop a letter in my mailbox.  You walk up to it, slip the  
letter through the mail slot, and you're done.  However, only I have  
the key to my mailbox: once you've dropped it in my mail slot, you can  
no longer read your own message.  After all, you don't have the key to  
my mailbox.  And my mailbox doesn't have to be secret: it's public  
knowledge where it is.  Anyone can drop a letter through the mail  
slot, and it doesn't affect the secrecy of the messages.  Knowing how  
to leave a message for me doesn't help you read messages that other  
people leave for me, but if I lose the keys to my mailbox then I'm in  
a lot of trouble.

Most of the people I deal with have used mailboxes and mail slots  
before.  The analogy seems to work well with them.  YMMV, of course.  :)