Key rotation, user experience, and crypto reporting
WhatsApp was the subject of a recent Guardian article making claims of a “backdoor” stemming from a “bug” in the way WhatsApp handles key rotations for users. The problem? WhatsApp will automatically transmit messages after the recipient’s key has changed without first asking the sender to confirm the new key is genuine.
Far from being a “bug” or “backdoor” (a claim so wrong I am sure hoping the original author of the story Samuel Gibbs will issue a retraction), handling key rotation seamlessly is a difficult problem with a long-storied history, along with many attempts to surface such information to the user in order to ask them to make a security decision, such as in the SSH screenshot above.
Clearly an in-person exchange of key fingerprints is the most secure option for establishing a secure channel, but is inconvenient, often impractical, and doesn’t provide a good means for
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