Almost impossible to square that requirement with strong end to end encryption.
You can figure out ways to do it, but it's pretty kludgy (messages addressed to you have to be encrypted with the keys of each device you've authorized) and you can't scroll back prior to when a device was authorized and its key was communicated to other participants, which users might not find convenient.
But it's why I don't use Whatsapp as well, personally. I prefer the cross-device seamlessness of Hangouts (and FB Messenger) to E2E crypto.
> You can figure out ways to do it, but it's pretty kludgy (messages addressed to you have to be encrypted with the keys of each device you've authorized) and you can't scroll back prior to when a device was authorized and its key was communicated to other participants, which users might not find convenient.
Apple seems to do OK with iMessage and it faces the same constraints.
You can figure out ways to do it, but it's pretty kludgy (messages addressed to you have to be encrypted with the keys of each device you've authorized) and you can't scroll back prior to when a device was authorized and its key was communicated to other participants, which users might not find convenient.
But it's why I don't use Whatsapp as well, personally. I prefer the cross-device seamlessness of Hangouts (and FB Messenger) to E2E crypto.