Analogien um das Prinzip von PGP zu erklären

Fraser Tweedale frase at
Thu Jul 3 14:56:30 CEST 2014

On Thu, Jul 03, 2014 at 01:46:33PM +0200, Neal H. Walfield wrote:
> At Thu, 03 Jul 2014 12:50:50 +0200,
> Daniel Krebs wrote:
> > da ich das gerade mit Matthias von der FSFE im Rahmen von 
> > #EmailSelfDefense diskutiere, mal eine Frage: Welche Analogien benutzt 
> > ihr, wenn ihr Menschen das Prinzip von PGP/GPG erklärt?
> > Ich verwende ich meistens folgende Version:
> > 
> > Es gibt ein Schloss mit zwei Schlüssellöchern. Jeder Schlüssel
> > funktioniert nur in eine Richtung, also entweder Geöffnetes schließen
> > oder Geschlossenes öffnen. Daran kann man dann auch das signieren
> > erklären, was ja bei der "klassischen Metapher" (öff. Schlüssel =
> > Schloss, priv. Schlüssel = Schlüssel) nicht funktioniert. Also:
> > Verschlüsseln:
> > Jemand verschließt mit meinem öffentlichen Schlüssel, ich öffne mit
> > meinem geheimen.
> > Signieren:
> > Ich signiere mit meinem privaten Schlüssel, jemand anders überprüft mit
> > meinem öffentlichen.
> > 
> > Anregungen, Meinungen?
> You might want to take a look a this:
>   Email encryption, although cryptographically straightforward,
>   appears too complicated for laypeople to understand.  In our
>   project, we aimed to understand why this problem has eluded
>   researchers for well over a decade and expand the design space of
>   possible solutions to this and similar challenges at the
>   intersection of security and usability.
>   ...
>   In PGP’s metaphors, each user posses two items, a private key and a
>   public key.  Have you inferred how the protocol works yet?  Unless
>   you have previous exposure to cryptography, likely not.  Why do I
>   have two keys? What do these keys open? Aren’t all keys private?
>   When you want to send a message to someone, you encrypt it with his
>   public key, which is known to everyone.  The recipient can decrypt
>   it with his private key, which only he possesses.  But can’t anyone
>   use the public key to decrypt the message again?  Nope.  A public
>   key can only encrypt, not decrypt.  Just trust us on that one.
Not so; this analogy might seem useful for explaining message
encryption, but will lead to more confusion when attempting to
understand/explain signing - where indeed the public key is used to
decrypt a digest encrypted by a public key.


>   You’re probably starting to understand why secure email is so hard
>   to use.  Bear with us for one paragraph longer.
>   ...
>   We decided to test whether better metaphors might be able to close
>   this gap between security and usability.  Specifically, we wanted
>   metaphors that represented the cryptographic actions a user performs
>   to send secure email and were evocative enough that users could
>   reason about the security properties of PGP without needing to read
>   a lengthy, technical introduction.  We settled on four objects: a
>   key, lock, seal and imprint.  To send someone a message, secure it
>   with that person’s lock.  Only this recipient has the corresponding
>   key, so only they can open it.  To prove your identity, stamp the
>   message with your seal.  Since everyone knows what your seal’s
>   imprint looks, it’s easy to verify that the message came from you.
> Neal
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