WhatsApp starts formally testing multi-device capability


14, 2021

Facebook has announced that they have started testing the long-rumoured multi-device messaging capability for WhatsApp Messenger.

Currently to use WhatsApp on a second device (e.g WhatsApp Web or WhatsApp Desktop) the other device needs to be linked with your smartphone via an active network connection.

With the new multi-device capability, people can use WhatsApp on other devices without requiring a smartphone connection.

Today, Facebook announced the rollout of a limited public beta test for WhatsApp’s updated multi-device capability.

With this new capability, you can now use WhatsApp on your phone and up to four other nonphone devices simultaneously — even if your phone battery is dead. Each companion device will connect to your WhatsApp independently while maintaining the same level of privacy and security through end-to-end encryption that people who use WhatsApp have come to expect. Importantly, Facebook says they have developed new technologies to maintain end-to-end encryption while still managing to sync your data — such as contact names, chat archives, starred messages, and more — across devices.

The current WhatsApp experience for companion devices on web, macOS, Windows, and Portal uses a smartphone app as the primary device, making the phone the source of truth for all user data and the only device capable of encrypting or decrypting messages, initiating calls, etc. Companion devices maintain a persistent secure connection with the phone and simply mirror its contents on their own UI.

With the new architecture, each device now has its own identity key. The WhatsApp server maintains a mapping between each person’s account and all their device identities. When someone wants to send a message, they get their device list keys from the server.

Facebook has also developed technology to prevent a malicious or compromised server from eavesdropping on someone’s communications by surreptitiously adding devices to someone’s account using extended security codes and Automatic Device Verification. This system allows for devices to automatically establish trust between each other in a way that someone needs to compare another user’s security code only if that user reregisters their entire account, rather than each time they link a new device to their account.

Everyone will continue to be required to link new companion devices by scanning a QR code from their phone and the process will now require biometric authentication before linking.

Facebook plans to initially test the experience with a small group of users from their existing beta program. They will continue to optimizing performance and adding a few additional features before slowly rolling it out more broadly.

For more information about the beta and to sign up, visit the WhatsApp Help Center.

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