WhatsApp has this scheme. And to my knowledge, never had there been a report of verification failing.
If an adversary was discovered 0.1% of the time. There would be at least one person on a support forum with the text of the error that occurs when it fails...
I get the warning "your contact key has changed.." all the time with various contacts on WhatsApp. What am I supposed to do? there's no clear next steps to debug / report of suspicious activity. In such cases, users get trained to become complacent of such warnings.
