WhatsApp mirroring on multiple devices | heise online

Facebook hat [Link auf Beitrag 3115470] started a closed beta test for a new version of the WhatsApp messaging service. Users should be able to use the new software on their smartphone and at the same time on up to four so-called companion devices. This can also be a desktop computer under Windows or macOS, a Facebook portal or web sessions on any hardware. Accordingly, the new WhatsApp version can also be used to transfer chats and contacts, for example from an iPhone to an Android device, even if the installation of several smartphones based on their SIM cards is apparently not planned.

With a newly developed technology, WhatsApp synchronizes loudly Blogpost All messages – including old ones – as well as metadata and contact data on all devices without end-to-end encryption. Facebook announced the test last month.

So far, the smartphone has always served as the only device that can receive and send, encrypt and decrypt messages, initiate calls and identify the user. Keys for cryptography and user authentication are all derived from a single identity key. Users can set up any number of companion devices, but only use one at a time.

This companion device has to maintain a secure connection to the smartphone and only reflects the display on its user interface. With this architecture, all communication takes place via the smartphone and burdens its transmission contingents, provided it is not connected to the Internet via WLAN. In addition, the smartphone may slow down the transmission if it has a bad connection or weakens with an empty battery.

The developers have expanded the security codes for the new software so that they now take into account all of a user’s device IDs. This means that WhatsApp can also check the authenticity of a companion device for the sender at the recipient. In addition, these security queries should in future take place automatically in the background, unless a user has completely logged out of his account and then logged in again.

As a precaution in the event that an attacker smuggles their own device into the victim’s account as a mole, you can specify that you have to additionally authenticate yourself biometrically before the required QR scan to integrate the device. Users can also see at any time which companion devices are registered for their account and when they were last used.

Current data flow

So far, companion devices on WhatsApp have exclusively communicated via the smartphone as the primary device.
(Image: WhatsApp)

To transmit a message, the sender’s app receives a list with the IDs of all the recipient’s companion devices, encrypts the message content individually for each of these devices and sends the ciphers in parallel to all the recipient’s devices and to the sender’s companion devices for synchronization.

When a user registers a new companion device, the already registered device used for it combines the data from previous chats into one object and sends this encrypted to the new device. With this feature, WhatsApp is said to be the only messenger service that also displays messages from the time before it was registered on a companion device.

iPhone users who want to take part in the WhatsApp beta test need the Testflight app and have to register with it. Then they can theoretically take part in the WhatsApp beta test apply for, but there are currently no places available for beta testers. Android users receive a special page of the Play Store Access to the beta version.

With the beta version you can only communicate with other users of this beta version, users of the current WhatsApp release cannot be reached via it.


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