WhatsApp enters beta for cross-device use while retaining encryption

WhatsApp has started a beta that allows users to use the service on multiple devices at the same time without the need for a connection to the smartphone. The end-to-end encryption remains intact, according to parent company Facebook.

WhatsApp is starting a public, but limited beta of the new feature, writes parent company Facebook. The new feature allows users to use WhatsApp on up to four other devices besides the smartphone. They can’t be other phones. WhatsApp can therefore also be used when the original phone is off, something that was not possible until recently. The feature does work as it does now, syncing messages, contacts, and favorite messages or archived chats.

According to WhatsApp, it had to ‘completely rethink WhatsApp architecture’. With this new architecture, the service’s end-to-end encryption is maintained. For this purpose, all devices now receive their own identity key, instead of there being one key that is created on the active device. The WhatsApp server through which the traffic passes keeps track of which identities a user has on his account. This list is requested from the server when a message is sent.

The messages are then synchronized by sending an encrypted blob through WhatsApp’s servers. These can only be opened with the keys on the connected computers, after which they are removed again and the connected device retrieves the data locally again. WhatsApp settings, such as user status or which chats are muted, do require a constant connection to the WhatsApp servers.

A number of new security measures have been implemented to prevent, for example, a man-in-the-middle attack. For example, WhatsApp has expanded the security codes that appear when a user switches devices. From now on, it will show all other users’ devices. WhatsApp is also getting Automatic Device Verification that allows users to re-verify devices only when re-registering their account.