[aidenn0]

Let's say WhatsApp wants to read the next message sent to user X:

1) WhatsApp makes user X appear offline

2) User Y sends user X a message

3) WhatsApp sends user Y an indication that user X's key has changed, along with the public key for which they have the corresponding private key

With these steps, user Y's message will be resent with the new key that WhatsApp knows, and so they can read the message. There is a configuration setting that will display a notification that the key changed, but no way to prevent an undelivered message from automatically being resent with the new key.

[folex]

So the main problem is that on _identity_ key change, the new one isn't required to be signed with previous identity key? If so, that's plain stupid, isn't it?

[aidenn0]

It's a natural consequence of "My phone got run-over/lost/stolen"