[Cryptography] Explaining PK to grandma (Re: (no subject))

[Nico Williams]

On Sat, Nov 23, 2013 at 09:45:18PM +0100, Ralf Senderek wrote:
> You seem to have identified the three reasons for the epic failure of
> email encryption:
> 
> 1) The concept of asymmetric key is unexplainable to your granny.

Here's two attempts to explain PK to grandma:

 - It's like the postal service: your mail is secure -let's pretend, for
   this analogy- provided you write the correct recipient addresses on
   the envelopes, otherwise someone else might get it delivered to them
   incorrectly.

 - Same analogy, only this time your correspondents' addresses are
   barcoded and you must affix barcode stamps (or print the barcodes) on
   the envelopes.  If someone replaces the barcodes in your addressbook,
   how would you notice?  If you don't, your mail goes to an MITM.

   This one is a better analogy, methinks.  It clearly illustrates the
   difficulty of bootstrapping trust (how to find a peer's address), it
   clearly illustrates MITM attacks, and it's a clear enough analog of
   RSA encryption.

   Postal addresses in many countries just aren't unwieldy enough to
   make this analogy believable, but this isn't universally so.  Maybe
   grandma has many correspondents in the UK and she can't quite
   recognize/comprehend/lookup their postcodes.

Both analogies also describe the security properties of a trusted third
party system (here the postal service).  Postal mail is only as secure
as the mailboxes, the postal buildings, trucks, and so on, ultimately
only as secure as the postal service itself -- paper envelopes by
themselves are not secure (at best tamper-evident), quite clearly, and
even grandma can grasp this.  And surely grandma will understand that
the postal service will do the government's bidding.  So all of the
major PK security issues are covered.

Nico
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