> At issue is the way WhatsApp behaves when an end user's encryption key > changes. By default, the app will use the new key to encrypt messages > without ever informing the sender of the change.... > > Critics of Friday's Guardian post, and most encryption practitioners, > argue such behavior is common in encryption apps and often a necessary > requirement. Among other things, it lets existing WhatsApp users who > buy a new phone continue an ongoing conversation thread.
Ars Technica agrees: "Reported “backdoor” in WhatsApp is in fact a feature" http://arstechnica.com/security/2017/01/whatsapp-and-friends-take-umbrage-at-report-its-crypto-is-backdoored/
