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quickben

I don't user whatsapp, but a general question to these that do:

Can the server change keys twice?

Change once to server keys, ask for the entire history retransmission.

Change again to revert to original receipient keys.

Will the receipient be prompted in that case?

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Change once to server keys, ask for the entire history retransmission.

No. the WhatsApp client will not retransmit messages that have already been acknowledged by the recipient device.

Of course, you'll have to trust that this is the case; but obviously you'd have to trust the the WhatsApp client app isn't backdoored in the first place, so there is no change in security posture.

"The WhatsApp clients have been carefully designed so that they will not re-encrypt messages that have already been delivered. Once the sending client displays a "double check mark," it can no longer be asked to re-send that message. This prevents anyone who compromises the server from being able to selectively target previously delivered messages for re-encryption."

Ah, thanks

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