Sichere Verschlüsselung in iMessage?

Im an sich wohlklingenden Statement Apples zur Consumer Privacy wird die Ende-zu-Ende-Verschlüsselung von iMessage (und FaceTime) als unknackbar präsentiert.

For example, conversations which take place over iMessage and FaceTime are protected by end-to-end encryption so no one but the sender and receiver can see or read them. Apple cannot decrypt that data. Similarly, we do not store data related to customers’ location, Map searches or Siri requests in any identifiable form.

Die Sache hat aber einen Haken. Ende-zu-Ende-Verschlüsselung ist eine gute Sache, wenn die hierfür verwendeten Schlüssel sicher und ohne Umweg von Sender zu Empfänger transportiert werden. So funktioniert Apples iMessage aber nicht; hier ist ein Server als Schnittstelle für den iMessage-Service dazwischengeschaltet.

this is a critical point — ‚end-to-end encryption‘ is rapidly becoming the most useless term in the security lexicon. That’s because actually encrypting stuff is not the interesting part. The real challenge turns out to be distributing users‘ encryption keys securely, i.e., without relying on a trusted, central service. […] if I can compromise such a service, then I can convince you to use my encryption key instead of your intended recipient’s. In this scenario — known as a Man in the Middle (MITM) attack — all the encryption in the world won’t help you.

And this is where most ‚end-to-end‘ commercial services (like Skype and iMessage) seem to fall down. Clients depend fundamentally on a central directly server to obtain their encryption keys. This works fine if the server really is trustworthy, but it’s huge problem if the server is ever compromised — or forced to engage in MITM attacks by a nosy government.

Dann doch lieber Threema.