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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...

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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.

You're supposed to meet up with that contact and verify the new key.

If even 0.1% of users did that, it would be 2 million verifications. And yet nobody has ever announced they have found a non-matching key.

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